FIELD GUIDE FOR THE

BIOLOGICAL CONTROL OFWEEDS

IN EASTERN NORTH AMERICA

Rachel L. Winston, Carol B. Randall, Bernd Blossey, 

Philip W. Tipping, Ellen C. Lake, and Judy Hough-Goldstein

US Department 

of Agriculture

TECHNOLOGY

TRANSFER

Forest Health Technology

Enterprise Team

FHTET-2016-04

April 2017
The Forest Health Technology Enterprise Team (FHTET) was created in 1995 by the 

Deputy Chief for State and Private Forestry, USDA, Forest Service, to develop and 

deliver technologies to protect and improve the health of American forests. This book 

was published by FHTET as part of the technology transfer series.

http://www.fs.fed.us/foresthealth/technology/

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Printed on Recycled Paper

How to cite this publication: Winston, R.L., C.B. Randall, B. Blossey, P.W. Tipping, E.C. 

Lake, and J. Hough-Goldstein. 2017. Field Guide for the Biological Control of Weeds in 

Eastern North America. USDA Forest Service, Forest Health Technology Enterprise Team, 

Morgantown, West Virginia. FHTET-2016-04. 

Cover photos: Purple loosestrife (Jennifer Andreas, Washington State University Extension), Galerucella 

calmariensis (David Cappaert, Michigan State University, bugwood.org), tropical soda apple ((J. Jeffrey 

Mullahey, University of Florida, bugwood.org), Gratiana boliviana (Rodrigo Diaz, Louisiana State 

University), waterhyacinth (Chris Evans, University of Illinois, bugwood.org), Megamelus scutellaris 

(Jason D. Stanley, USDA ARS, bugwood.org), mile-a-minute weed (Leslie J. Mehrhoff, University of 

Connecticut, bugwood.org), Rhinoncomimus latipes (Amy Diercks, bugwood.org)
BIOLOGICAL CONTROL OF WEEDS

IN EASTERN NORTH AMERICA

Rachel L. Winston

Environmental Consultant

MIA Consulting, LLC

Sandpoint, ID

rachel@getmia.net

Carol Bell Randall

Entomologist, Forest Health Protection

USDA Forest Service

Coeur d’Alene, ID

crandall@fs.fed.us

Bernd Blossey

Associate Professor for Natural Resources

Cornell University, Department of 

Natural Resources

Ithaca, NY

bb22@cornell.edu

Philip W. Tipping

Research Leader

USDA-ARS Invasive Plant Research Lab

Fort Lauderdale, FL 

philip.tipping@ars.usda.gov

Ellen C. Lake

Research Entomologist

USDA-ARS Invasive Plant Research Lab

Fort Lauderdale, FL 

ellen.lake@ars.usda.gov

Judy Hough-Goldstein

Professor for Entomology 

University of Delaware, Department of 

Entomology & Wildlife Ecology

Newark, DE

jhough@udel.edu

For additional copies of this publication, contact: 

Richard Reardon

FHTET

USDA Forest Service

180 Canfield Street

Morgantown, WV 26505

304.285.1566

rreardon@fs.fed.us

Carol Bell Randall

Forest Health Protection

USDA Forest Service

2502 E. Sherman Ave.

Coeur d’Alene, ID 83814

208.769-3051

crandall@fs.fed.us

Acknowledgments

Significant help in reviewing and compiling select content in this field guide was provided 

by Robert Bourchier (Agriculture and Agri-Food Canada), William L. Bruckart, III (USDA, 

ARS, FDWSRU), Greg Wheeler (USDA ARS), and Donald Davis (The Pennsylvania State 

University). Some of the material in this guide was revised from the sister guide “Biological 

Control of Weeds in the Northwest”. We acknowledge and express our appreciation for the 

additional authors of that guide: Rosemarie De Clerck-Floate, Alec McClay, Jennifer Andreas, 

and Mark Schwarzlaender. The layout of this guide was designed by Rachel Winston. We 

would like to thank all of the photographers who granted permission for the use of photos. 

We also extend our gratitude to Richard Reardon (Forest Service-Forest Health Technology 

Enterprise Team) for producing this guide.
Field Guide Components

Efficacy Quick Reference Guide .....................4

Introduction .............................................................8

About This Field Guide................................................................................ 8

Biological Control of Weeds....................................................................... 10

Selected Plant Features............................................................................... 12

Life Cycle ..........................................................................................................12

Duration............................................................................................................12

Typical Leaf Arrangement and Margination.......................................................13

Flower Heads.....................................................................................................13

Biological Control Agent Life Cycles.......................................................... 14

Insects................................................................................................................14

Mites .................................................................................................................16

Nematodes ........................................................................................................16

Fungi.................................................................................................................16

Scientific Name Changes ........................................................................... 17

Collection Methods ................................................................................... 18

Transport Considerations........................................................................... 20

Releasing Biocontrol Agents....................................................................... 22

Monitoring Biocontrol Agents ................................................................... 24

Additional Considerations ......................................................................... 27

Weed Biocontrol Systems................................ 28

Weed species are arranged first by flower color, then grouped by related species and 

listed alphabetically. All biocontrol agents introduced or established on each weed 

are included in that weed’s section, listed according to efficacy on the target weed. 

To look up a particular biocontrol agent or weed, refer to the index at the back 

of this guide.

Pinkish-Purple Flowers .................................. 28

Knapweeds............................................................................................28 

Diffuse knapweed, Centaurea diffusa.................................................. 30

Spotted knapweed, Centaurea stoebe .................................................. 32

Purple loosestrife, Lythrum salicaria ....................................................... 62

Eurasian watermilfoil, Myriophyllum spicatum........................................ 70

Swallow-worts.....................................................................................74

Black swallow-wort, Vincetoxicum nigrum ......................................... 74

Pale swallow-wort, Vincetoxicum rossicum .......................................... 76

Thistles.................................................................................................80 

Bull thistle, Cirsium vulgare............................................................... 82

Canada thistle, Cirsium arvense ......................................................... 84

Musk thistle, Carduus nutans............................................................. 86

Waterhyacinth, Eichhornia crassipes...................................................... 108

Yellow Flowers .................................................118

Table of Contents
Tansy ragwort, Jacobaea vulgaris........................................................... 118

Common St. Johnswort, Hypericum perforatum ................................... 130

Toadflaxes......................................................................................... 142 

Dalmatian toadflax, Linaria dalmatica............................................. 142

Yellow toadflax, Linaria vulgaris ...................................................... 144

Green Flowers....................................................160

Mile-a-minute weed, Persicaria perfoliata ............................................. 160

Spurges............................................................................................... 164 

Cypress spurge, Euphorbia crassipes .................................................. 164

Leafy spurge, Euphorbia esula .......................................................... 166

Tree-of-heaven, Ailanthus altissima ...................................................... 190

White Flowers....................................................194

Alligatorweed, Alternanthera philoxeroides ............................................ 194

Scentless chamomile, Tripleurospermum inodorum ............................... 202

Poison hemlock, Conium maculatum ................................................... 210

Hydrilla, Hydrilla verticillata................................................................ 214

Knotweeds......................................................................................... 222 

Bohemian knotweed, Fallopia xbohemica......................................... 222

Giant knotweed, Fallopia sachalinensis............................................. 224

Japanese knotweed, Fallopia japonica............................................... 226

Melaleuca, Melaleuca quinquenervia..................................................... 230

Multiflora rose, Rosa multiflora ............................................................ 240

Brazilian peppertree, Schinus terebinthifolius......................................... 244

Tropical soda apple, Solanum viarum................................................... 248

Waterlettuce, Pistia stratiotes ................................................................ 254

Does not or Rarely Flowers .....................260

Air-potato, Dioscorea bulbifera ............................................................. 260

Old World climbing fern, Lygodium microphyllum ............................... 264

Salvinias............................................................................................. 272

Common salvinia, Salvinia minima................................................. 272

Giant salvinia, Salvinia molesta........................................................ 274

Current Studies in Weed Biocontrol.... 278

Glossary.....................................................................282

Selected References ...........................................288

Appendix.....................................................................324

Biocontrol Agent Monitoring Form......................................................... 324

Vegetation Monitoring Form ................................................................... 325

Species Index ...........................................................326

Table of Contents
Efficacy Quick Reference Guide

Quick Reference

4 Biological Control in Eastern North America

In this quick reference, weed species are arranged in the order they appear in this 

guide: first by flower color, grouped by related species, and then listed alphabetically. 

Weeds that do not flower are colored gray. The biocontrol agents presently available 

(as of 2016) for each weed are then arranged according to their individual efficacy. 

Please note that efficacy designations are very broad. Some biocontrol agents thrive 

in certain settings and are ineffective in others.

The following broad categories are used:

? ?

US Can Individual Biocontrol Agent Status

High priority; recommended for release/redistribution

Medium priority, recommended to complement other agents or control methods

Low priority; typically low impact and/or survival

Caution when redistributing; not recommended for use in all areas

Illegal to redistribute

Ongoing releases, but establishment not yet confirmed

Released, but failed to establish

Status Organism Page

Diffuse knapweed

Centaurea diffusa 30

Larinus minutus 36

Sphenoptera jugoslavica 40

Cyphocleonus achates 34

Larinus obtusus 38 

Agapeta zoegana 42

Urophora affinis 44

Urophora quadrifasciata 46

Bangasternus fausti 48

Metzneria paucipunctella 52

Pelochrista medullana 54

Pterolonche inspersa 56

Status Organism Page

Cyphocleonus achates 34

Larinus obtusus 38

Agapeta zoegana 42

Larinus minutus 36

Urophora affinis 44

Urophora quadrifasciata 46

Sphenoptera jugoslavica 40

Bangasternus fausti 48

Chaetorellia acrolophi 50

Metzneria paucipunctella 52

Pelochrista medullana 54

Terellia virens 58

Spotted knapweed

Centaurea stoebe 32
Efficacy Quick Reference Guide

Quick Reference

Biological Control in Eastern North America 5

?

Status Organism Page

Purple loosestrife

Lythrum salicaria 62

Galerucella calmariensis 64

Galerucella pusilla 64

Hylobius transversovittatus 66

Nanophyes marmoratus 68

Eurasian watermilfoil

Myriophyllum spicatum 70

Euhrychiopsis lecontei 72

Pale swallow-wort

Vincetoxicum rossicum 76

Hypena opulenta 78

Bull thistle

Cirsium vulgare 82

Urophora stylata 88

Cheilosia grossa 96

Trichosirocalus horridus 100

Rhinocyllus conicus 98

Larinus carlinae (=L. planus) 106

Canada thistle

Cirsium arvensis 84

Hadroplontus litura 90

Urophora cardui 92

Larinus carlinae (=L. planus) 106

Rhinocyllus conicus 98

Status Organism Page

Musk thistle

Carduus nutans 86

Urophora solstitialis 94

Cheilosia grossa 96

Trichosirocalus horridus 100

Rhinocyllus conicus 98

Larinus carlinae (=L. planus) 106

Waterhyacinth

Eichhornia crassipes 108

Megamelus scutellaris 110

Neochetina bruchi/ N.eichhorniae 112

Niphograpta albiguttalis 114

Tansy ragwort

Jacobaea vulgaris 118

Longitarsus jacobaeae 120

Cochylis atricapitana 122

Botanophila seneciella 124

Tyria jacobaeae 126

Common St. Johnswort

Hypericum perforatum 130

Chrysolina hyperici 132

Chrysolina quadrigemina 132

Agrilus hyperici 134

Aphis chloris 136

Aplocera plagiata 138

Zeuxidiplosis giardi 140
Efficacy Quick Reference Guide

Quick Reference

6 Biological Control in Eastern North America

Status Organism Page

Dalmatian toadflax

Linaria dalmatica 142

Mecinus janthiniformis 146

Brachypterolus pulicarius 150

Rhinusa antirrhini 152

Calophasia lunula 156

Yellow toadflax

Linaria vulgaris 144

Mecinus janthinus 146

Rhinusa pilosa 148

Brachypterolus pulicarius 150

Rhinusa antirrhini 152

Rhinusa linariae 154

Calophasia lunula 156

Mile-a-minute weed

Persicaria perfoliata 160

Rhinoncomimus latipes 162

Cypress spurge

Euphorbia crassipes 164

Aphthona nigriscutis 170

Aphthona flava 172

Aphthona lacertosa 168

Aphthona cyparissiae 176

Aphthona czwalinai 178

Hyles euphorbiae 180

Spurgia capitigena/S. esulae 186

Status Organism Page

Leafy spurge

Euphorbia esula 166

Aphthona lacertosa 168

Aphthona nigriscutis 170

Aphthona flava 172

Lobesia euphorbiana 174

Aphthona cyparissiae 176

Aphthona czwalinai 178

Hyles euphorbiae 180

Oberea erythrocephala 182

Pegomya curticornis/P. euphorbiae 184

Spurgia capitigena/S. esulae 186

Tree-of-heaven

Ailanthus altissima 190

Verticillium nonalfalfae 192

Alligatorweed

Alternanthera philoxeroides 194

Agasicles hygrophila 196

Arcola malloi 198

Amynothrips andersoni 200

Scentless chamomile

Tripleurospermum inodorum 202

Omphalapion hookerorum 204

Rhopalomyia tripleurospermi 206

Microplontus edentulus 208
Efficacy Quick Reference Guide

Quick Reference

Biological Control in Eastern North America 7

?

Status Organism Page

Waterlettuce

Pistia stratiotes 254

Neohydronomus affinis 256

Air potato

Dioscorea bulbifera 260

Lilioceris cheni 262

Old World climbing fern

Lygodium microphyllum 264

Floracarus perrepae 266

Neomusotima conspurcatalis 268

Common salvinia

Salvinia minima 272

Cyrtobagous salviniae 276

Giant salvinia

Salvinia molesta 274

Cyrtobagous salviniae 276

Status Organism Page

Poison hemlock

Conium maculatum 210

Agonopterix alstroemeriana 212

Hydrilla

Hydrilla verticillata 214

Hydrellia pakistanae 216

Hydrellia balciunasi 216

Bagous hydrillae 218

Japanese knotweed

Fallopia japonica 226

Aphalara itadori 228

Melaleuca

Melaleuca quinquenervia 230

Boreioglycaspis melaleucae 232

Lophodiplosis trifida 234

Oxyops vitiosa 236

Multiflora rose

Rosa multiflora 240

Rose Rosette Disease 242

Phyllocoptes fructiphilus 242

Tropical Soda Apple

Solanum viarum 248

Gratiana boliviana 250

Tobacco mild green 

mosaic tobamovirus 252
About This Field Guide

Invasive plants are a major concern worldwide. They displace native species, decrease 

forage/agricultural production, alter soil nutrient and water cycling, and lower the 

aesthetic value of natural areas. With the increase of world trade and travel, exotic 

plant introductions are on the rise. Biological control of weeds (“biocontrol”) is the 

deliberate use of living organisms to limit the abundance of a target weed. In this field 

guide, biological control typically refers to “classical biological control,” which reunites 

host-specific natural enemies from the weed’s native range with the target weed in its 

introduced range. Natural enemies used in weed biocontrol (“biocontrol agents” or 

“agents”) include different organisms, such as insects, mites, nematodes, and fungi. 

This guide focuses on the most problematic weeds in eastern North America for which 

there are at least some biocontrol agents established and/or available. Multiple photos 

and descriptions of each weed included in this guide emphasize key identification 

traits and plant ecology. For each weed included in this guide, all biocontrol agents 

released or currently found in North America are described individually. Photos 

highlighting key identification features and damage are included. The release history, 

current status, and recommended use of each biocontrol agent are described in 

detail. Because current impact and recommendations often vary between the US 

and Canada, information is presented separately. Symbols have been added for each 

biocontrol agent described in this manual to allow for quick recommendations:

? ?

8 Biological Control in Eastern North America Introduction

US Can Individual Biocontrol Agent Status

High priority; recommended for release/redistribution

Medium priority, recommended to complement other agents or control methods

Low priority; typically low impact and/or survival

Caution when redistributing; not recommended for use in all areas

Illegal to redistribute

Ongoing releases, but establishment not yet confirmed

Released, but failed to establish

Many biocontrol agents are already widespread. All target weed infestations should 

be surveyed prior to release to ensure the desired agents are not already present. Keep 

in mind some species are approved for use in only the US or Canada, but not both. 

In addition, some biocontrol agents cause damage to nontarget species. Red text 

indicates the biocontrol agent is not recommended for release in all areas. 

Distribution maps are included for each weed included in this guide; maps can be 

found in the bottom right corner of each weed’s description pages. Plant distribution 
data was collected from the USDA-PLANTS database and EDDMapS. Though 

significant effort is put into keeping both databases current, weed spread can be 

rapid, making distribution information quickly out of date. Please visit plants.usda.

gov/du/DistributionUpdate.html for information on how to help update weed 

distribution information on the PLANTS site. For more information on how to 

utilize or contribute to the EDDMapS tools, visit www.eddmaps.org/about/ and 

apps.bugwood.org/. 

Maps depicting each biocontrol agent’s current establishment are presented in the bottom 

right corner on each species’ respective description page. When a biocontrol agent attacks 

more than one weed species, multiple maps are presented and labeled by weed species. 

Maps were created using EDDMapS, available literature, and numerous personal 

communications with regional land managers. Like weeds, biocontrol agents can spread 

rapidly, making accurate distribution information elusive. Some biocontrol agents are not 

yet established, or are established on their target weeds only in western states and provinces 

not covered in this guide; the maps for these species appear blank for eastern states and 

provinces. The figure 

at right illustrates 

Rhinocyllus conicus is 

established on bull and 

musk thistle in eastern 

North America, but 

its establishment on 

Canada thistle is 

restricted to western 

states and provinces 

not covered in this 

guide.

bull Canada musk

Reported establishment of Rhinocyllus conicus in eastern North 

America on bull (left), Canada (middle), and musk thistle (right).

Biocontrol agents that were released but did not establish, natural enemies that are 

native to North America, and some natural enemies that are not currently approved 

for redistribution in the US and/or Canada (but are already present) are addressed 

separately from approved and established biocontrol agents. The description, 

ecology, and history/status for each of these additional species are described, 

accompanied by a photo. Should you encounter species previously believed to have 

failed establishment, contact your local weed superintendent, land grant university, 

or extension service personnel to confirm and document their establishment, and/

or report the sighting to the EDDMapS database. Caution must be taken during 

field redistribution to ensure that species not approved for use are not inadvertently 

collected and redistributed along with approved biocontrol agents. 

Biological Control in Eastern North America 9Introduction
Biological Control of Weeds

Biocontrol agents may attack a weed’s flowers, seeds, roots, foliage, and/or stems. 

Effective agents may kill the weed outright, reduce its vigor and reproductive 

capability, and/or facilitate secondary infection from pathogens—all of which 

compromise the weed’s ability to compete with other plants. Root- and crownfeeding biocontrol agents are usually more effective on perennial plants that 

primarily spread by root buds. Flower- and seed-feeding biocontrol agents are 

typically more useful on annual or biennial plants that only spread by seeds. 

Regardless of the plant part attacked by biocontrol agents, the aim is always to 

reduce populations of the target weed.

To be approved for release in North America, weed biocontrol agents must be hostspecific, meaning they must develop only on the target weed. Rigorous tests are 

required to confirm biocontrol agents are host specific and effective. Candidates often 

undergo five or more years of testing to ensure that rigid host specificity requirements 

are met, and results are vetted at a number of stages in the approval process.

The Technical Advisory Group (TAG) for Biological Control Agents of Weeds 

is an expert committee with representatives from US federal regulatory, resource 

management, and environmental protection agencies, and regulatory counterparts 

from Canada and Mexico. TAG members review all petitions to import new 

biocontrol agents into the US, and make recommendations to USDA-APHISPPQ regarding the safety and potential impact of candidate biocontrol agents. 

Weed biocontrol researchers work closely with USDA-APHIS-PPQ and TAG to 

accurately assess the environmental safety of candidate weed biocontrol agents and 

programs. In addition, some states and some National Parks in the US have their 

own approval process to permit field release of weed biocontrol agents. In Canada, 

the Biological Control Review Committee (BCRC) draws upon the expertise 

and perspectives of Canadian-based researchers (e.g. entomologists, botanists, 

ecologists, weed biological control scientists) from academic, government, and 

private sectors for scientific review of petitions submitted to the CFIA. The 

BCRC reviews submissions that are in compliance with the North American Plant 

Protection Organization’s Regional Standards for Phytosanitary Measures number 

7. The BCRC also reviews submissions to APHIS. The BCRC conclusions factor 

into the final TAG recommendation to APHIS on whether to allow release of the 

candidate agent in the US. When release of an agent is proposed for both the US 

and Canada, APHIS and the CFIA attempt to coordinate decisions based on the 

assessed safety of each country’s plant resources.

Biocontrol practitioners have adopted the International Code of Best Practices for 

Biological Control of Weeds. The Code was developed in 1999 by delegates and 

10 Biological Control in Eastern North America Introduction
participants of the Tenth International Symposium for Biological Control of Weeds 

to both improve the efficacy of, and reduce the potential for negative impacts from, 

weed biological control. In following the Code, practitioners reduce the potential 

for causing environmental damage through the use of weed biological control by 

voluntarily restricting biocontrol activities to those most likely to result in success 

and least likely to cause harm.

INTERNATIONAL CODE OF BEST PRACTICES 

FOR CLASSICAL BIOLOGICAL CONTROL OF WEEDS1

1. Ensure that the target weed’s potential impact justifies release of nonendemic biocontrol agents

2. Obtain multi-agency approval for target

3. Select biocontrol agents with potential to control target

4. Release safe and approved biocontrol agents

5. Ensure that only the intended biocontrol agent is released

6. Use appropriate protocols for release and documentation

7. Monitor impact on the target

8. Stop releases of ineffective biocontrol agents or when control is achieved

9. Monitor impacts on potential nontargets

10. Encourage assessment of changes in plant and animal communities

11. Monitor interaction among biocontrol agents

12. Communicate results to public

1 Ratified July 9, 1999, by the delegates to the X International Symposium on 

Biological Control of Weeds, Bozeman, MT

As per rule 4 of the Code of Best Practices above, species that have not been 

approved are illegal to introduce to the US and Canada. When non-indigenous 

natural enemies of a target weed arrive accidentally, it is generally illegal to 

redistribute them intentionally within the US. A few cases where this is legal are 

described in this manual. Some species introduced accidentally to Canada are safe to 

utilize, however redistribution of non-indigenous natural enemies should only 

be done under the guidance of Canadian biocontrol experts. 

Although weed biological control is an effective and important weed management 

tool, it does not work in all cases and should not be expected to eradicate the target 

weed. Even in the most successful cases, biocontrol often requires multiple years 

before impacts become noticeable. Ideally, biological control should be integrated 

with chemical, mechanical, and/or cultural methods of weed management to 

improve overall weed control success.

Biological Control in Eastern North America 11Introduction
Selected Plant Features

Weed descriptions utilized in this manual refer to a variety of life stages and 

characteristic features to help readers determine the key traits that set the weed 

apart from other plants. Traits referred to most commonly include:

Life cycle

The first recognizable stage of a plant life cycle is a seedling, when a plant has one to 

a few small leaves. Many perennial plants then grow into rosettes, which are clusters 

of leaves typically of the same height. Annual plants and vining species frequently 

do not have an obvious rosette stage. Plants then grow a flowering stem in a stage 

called bolting. In bud, immature flowers appear on flowering stems and branches. 

These open during flowering and then set seed upon maturation. At senescence, a 

plant has typically released its seeds and dies back for the winter or permanently.

a

b

c

d

Generalized stages of spotted knapweed a. seedling; b. rosette; c. bolting,; d. bud; e. flowering; 

f. senescence (Credits: a, f Ohio State University Weed Lab Archive; b Steve Dewey, Utah State 

University; c K. George Beck & James Sebastian, Colorado State University; d John Cardina, Ohio 

State University; e Michael Shephard, Forest Service (a-f bugwood.org)

e

f

Duration

Annual species complete their life cycle (from germination to production of seed) 

within one year and then die. Summer annuals germinate during spring/early 

summer and mature by fall of the same year. Winter annuals germinate during fall 

and mature during the spring or summer of the following calendar year. Biennial 

12 Biological Control in Eastern North America Introduction
species take two years to complete their life cycle. In the first year, the plant is a 

rosette. During the next spring or summer, the plant bolts, sets seeds, and dies. 

Perennial species live for more than two years.

Typical leaf arrangement and margination

alternate opposite whorled smooth

Leaf a. arrangement (how leaves are arranged along a stem); b. margination (shape of a leaf’s edges) 

(a,b Jacqi Sullivan, MIA Consulting)

lobed toothed

Flower heads

Many of the weeds included in this manual are members of the sunflower family 

(Asteraceae). Members of this family produce flower heads, or capitula, that are an 

aggregation of many individual flowers. These flowers, called florets, are clustered 

together and attached to a receptacle. There are two types of florets: disc and ray. 

Some species produce only one type, while others produce both. The receptacle and 

florets are enclosed by modified leaves called bracts. The type, color, and shape of 

florets and bracts can help in weed species identification. Each floret produces one 

seed (achene) from mid- to late summer. Some species produce seeds with a tuft of 

whitish hairs (pappus) on one end, similar to those on seeds of dandelions.

a

a

b

b c

Flower heads in the sunflower family a. Canada thistle, all disc florets (Richard Old, XID Services, 

Inc, www.xidservices.com); b. rush skeletonweed, all ray florets (Rachel Winston, MIA Consulting); 

c. tansy ragwort, both disc (center) and ray (outer) florets (Strobilomyces)

Biological Control in Eastern North America 13Introduction
Biological Control Agent Life Cycles

Classical biocontrol agents may be found in a number of taxonomic groups. The 

majority of approved biocontrol agents are animals in the phylum Arthropoda. More 

specifically, most biocontrol agents are insects (class Insecta) in the orders Coleoptera 

(beetles), Lepidoptera (butterflies and moths), and Diptera (true flies). In addition 

to insects, there are also mite, nematode, fungi, bacteria and virus biocontrol agents.

Insects

Insects are the largest, most diverse class 

of animals in the phylum Arthropoda. An 

understanding of basic insect biology and 

anatomy will help users recognize and identify 

the insects used as biocontrol agents of weeds. 

Most insects included in this field guide have 

complete metamorphosis, which means they 

exhibit a life cycle with four distinct stages: 

egg, larva, pupa, and adult. All adult insects 

have an exoskeleton (a hard external skeleton), 

a segmented body divided into three regions 

(head, thorax, and abdomen), three pairs of 

segmented legs, and may have one or two pairs 

of wings. The head of an adult insect has one 

pair each of compound eyes and antennae. 

Immature insects have an exoskeleton that 

must be shed in order for them to grow to 

the next stage. This process is called molting, 

and larval stages between molts are called 

instars. The larvae of insects with complete 

metamorphosis (e.g. Lepidoptera, Coleoptera, 

Diptera) generally complete 3-5 instars before 

molting into pupae. During the pupal stage, 

insects change from larvae to adults. Insects do 

not feed or molt during the pupal stage. Adult 

insects emerge from the pupal stage and do not grow or molt.

a

b

a. Complete metamorphosis of an insect 

(L. Wilson); b. body parts of adult 

insects A. head, B. antenna, C. thorax, 

D. abdomen, E. wing (adapted from 

Biological Control of Weeds in the West)

Insects in the Hemiptera and Thysanoptera have incomplete metamorphosis, which 

does not include a pupal stage. Instead, their young are called nymphs and resemble the 

adults to a large degree. The transformation from nymph to adult primarily involves 

the development of wings (only in some species) and functioning reproductive organs. 

14 Biological Control in Eastern North America Introduction
Butterflies and Moths (Order Lepidoptera)

Adult Lepidoptera have two pairs of membranous wings covered with powder-like 

scales, prominent antennae, and coiled mouthparts adapted to siphoning nectar from 

plant flowers. Adult Lepidoptera described in this manual usually feed very little, 

if at all. Lepidoptera larvae (known as caterpillars) have a toughened head capsule, 

chewing mouthparts, and a soft body; they are active feeders. The pupal stage of 

Lepidoptera can be naked or enclosed in a cocoon, depending on the species. 

Beetles (Order Coleoptera)

Adult beetles are hard-bodied with tough exoskeletons and possess two pairs of 

wings. The two front wings (elytra) are thickened and meet in a straight line down 

the abdomen, forming a hard, shell-like, protective covering. The two hind wings 

are membranous, larger, and used for flight; these are folded under the elytra when 

not in use. Beetle larvae are grub- or worm-like, often with three small pairs of legs, 

allowing some to be quite mobile. Many are pale white with a brown or black head 

capsule. All beetles have chewing mouthparts.

Flies (Order Diptera)

Adult true flies are easily distinguished from other orders of insects by their single 

pair of membranous wings and typically soft bodies. Larvae of most true flies, 

called maggots, are legless and wormlike. Many insects have the word “fly” in their 

name, though they may not be true flies. In the common names of true flies, “fly” 

is written as a separate word (e.g., house fly) to distinguish them from other orders 

of insects that use “fly” in their name (e.g., butterfly in the order Lepidoptera). 

Key to differentiate biocontrol insects with complete metamporphosis as a. larvae; b. pupae (L. Wilson)

Biological Control in Eastern North America 15Introduction
Biological Control Agent Life Cycles

Thrips (Order Thysanoptera)

Adult Thysanoptera can be wing-less or have two pairs of stalk-like wings with long 

hair fringing the margins. There are two actively feeding nymphal stages for all 

thrips and 2-3 inactive (non-feeding) stages. Adult and actively-feeding nymphal 

stages feed by piercing plants and sucking out the contents.

True Bugs (Order Hemiptera)

Many adult Hemiptera possess two pairs of wings, though some are wing-less. In 

winged individuals, the hind pair is membranous; the two front wings may be 

entirely membranous or only membranous at their tips and hardened at their base. 

Nymphs and adults feed by piercing plants and and sucking out the cell contents.

Mites

Like insects, mites are in the phylum Arthropoda and have an exoskeleton; however 

they belong to the class Arachnida, whose adult members are usually characterized 

by having 8 legs (compared to the 6 legs of insects). In some mite species, the first 

immature stage is called larva; mites in this stage have only 6 legs. The second 

immature stage is called a nymph and has 8 legs. Nymphs typically resemble adults. 

Some mite species do not have a larval stage, and some mite families have only 4 legs.

Nematodes

Nematodes, or roundworms, are animals in the phylum Nematoda. They are 

cylindrical, unsegmented worms that are typically 0.1-2.5 mm long and 5-100 μm 

thick. They have tubular digestive systems with openings at both ends. Eggs hatch 

into larvae that resemble adults but have underdeveloped reproductive systems.

Fungi

Fungi belong to their own kingdom (Fungi). Most fungi described in this manual 

are rusts, which are in the phylum Basidiomycota. Rust fungi are obligate parasites, 

meaning they require a living host to complete their life cycle. They obtain nutrients 

from living plant cells and can produce up to five spore types during their lifetime. 

Rusts are most commonly seen as colored powder (typically yellow, orange, or brown) 

composed of tiny aeciospores that land on vegetation and produce pustules, or uredia, 

on the lower surfaces. Urediniospores are red/orange and are a characteristic sign of rust 

fungus infection. These spores can re-infect the same host plant. During late spring or 

early summer, hair-like structures called telia grow on the leaves and produce teliospores 

which will germinate into aerial basidiospores to spread the infection to new hosts. 

16 Biological Control in Eastern North America Introduction
Scientific Name Changes

The weeds included in this guide are listed according to their common name, 

beneath which is included their scientific (Latin) name. The biocontrol agents are 

listed by their scientific name. Some species have recently undergone changes in 

their taxonomy. The following tables list weeds and biocontrol agents whose names 

have changed most recently (listed in the order in which they appear in this guide).

Biological Control in Eastern North America 17Introduction

Weed Common Scientific Name Previous names

Spotted knapweed Centaurea stoebe Centaurea biebersteinii, C. stoebe subsp. 

micranthos, C. maculosa

Black swallow-wort Vincetoxicum nigrum Cyanchum louiseae

Pale swallow-wort Vincetoxicum rossicum Cynanchum rossicum

Musk thistle Carduus nutans Carduus thoermeri

Tansy ragwort Jacobaea vulgaris Senecio jacobaea

Dalmatian toadflax Linaria dalmatica Linaria genistifolia, L. genistifolia ssp. dalmatica

Mile-a-minute weed Persicaria perfoliata Polygonum perfoliatum

Alligatorweed Alternanthera philoxeroides Achyranthes philoxeroides

Bohemian knotweed Fallopia xbohemica Polygonum ×bohemicum, Reynoutria 

×bohemica

Giant knotweed Fallopia sachalinensis Polygonum sachalinense, Reynoutria 

sachalinensis

Japanese knotweed Fallopia japonica Polygonum cuspidatum, Reynoutria japonica

Scentless chamomile Tripleurospermum inodorum Matricaria perforata, Tripleurospermum 

maritimum ssp. inodorum, T. perforatum

Agent Current Name Target(s) Previous names

Hadroplontus litura Thistles Ceutorhynchus litura

Cheilosia grossa Thistles Cheilosia corydon

Trichosirocalus horridus Thistles Ceuthorhynchidius horridus

Larinus carlinae Thistles Larinus planus

Niphograpta albiguttalis Waterhyacinth Epipagis albiguttalis, Sameodes albiguttalis 

Bellura densa Waterhyacinth Arzama densa

Cercospora piaropi Waterhyacinth Cercospora rodmanii

Botanophila seneciella Tansy ragwort Hylemyia seneciella, Pegohylemyia seneciella

Rhinusa antirrhini; R. linariae; 

R. neta

Toadflaxes Gymnetron antirrhini; G. linariae; G. netum

Austromusotima camptozonale Lygodium Cataclysta camptozonale

Pegomya curticornis, P. euphorbiae Leafy spurge Pegomya argyrocephala

Spurgia capitigena, S. esulae Leafy spurge Bayeria capitigena

Arcola malloi Alligatorweed Vogtia malloi

Omphalapion hookerorum Scentless chamomile Apion hookeri

Microplontus edentulus Scentless chamomile Ceutorhynchus edentulus

Spodoptera pectinicornis Waterlettuce Namangana pectinicornis, Epipsammea 

pectinicornis
Collection Methods

Some of the most commonly used methods for collecting biocontrol agents are sweep 

netting with or without aspirating, hand-picking/tapping, vacuuming, and light traps. 

The effectiveness of each method depends on the type and abundance of biocontrol 

agents being collected and the habitat. Regardless of the method used, extraneous 

debris (e.g., other insects, weed seeds, etc.) must be sorted and removed. Cooling 

the collected sample for 10 to 15 minutes reduces insect activity and makes sorting 

easier. Any cooling should be done in a refrigerator, not a freezer. 

Sweep netting

Sweep nets are made of cotton or muslin on a hoop 10-15 

in (25-38 cm) diameter attached to a handle 3 ft (0.9 m) 

long. They can be purchased from entomological, forestry, 

and biological supply companies or you can construct them 

yourself. As their name implies, these are heavy duty nets 

used to “sweep” biocontrol agents off weeds. 

A sweep is made by swinging the net through the plant 

canopy. It is best to use no more than 25 sweeps before 

removing hard-bodied insects from the net, or as few as 

five times for fragile adult moths and flies. Removing the 

contents at regular intervals reduces the potential harm that 

could result from knocking biocontrol agents around with 

debris, and reduces the opportunity for predator insects and 

spiders from finding and devouring the biocontrol agents.

Aspirating

Use an aspirator to suck the biocontrol agents (usually 

small species) directly from the weed or the sweep net. 

This provides selective sorting; no unwanted or unknown 

material is inadvertently collected. A variety of aspirators can 

be purchased from entomological, forestry, and biological 

supply companies, or you can construct them yourself. For 

the latter, make sure that tubing reaching your mouth is 

covered by fine-mesh screening, so that insects and small 

particles are not inhaled.

Berlese funnels

Berlese funnels are used to extract biocontrol agents from soil or plant litter by 

using light or a heat source. Place plant or soil material on a wire mesh suspended 

over a collection container (e.g. a jar), and secure the heat/light source (e.g. a heat 

Laura Parsons, 

University of Idaho

Laura Parsons, 

University of Idaho

18 Biological Control in Eastern North America Introduction
lamp) above it all. As the light/heat penetrates the material, insects migrate down 

and fall into the collection container. Rubbing petroleum jelly around the rim of 

the collection container helps prevent insects from climbing back out. When using 

a heat source, place a moist napkin in the collection container and check often to 

ensure water is available to organisms collected.

Hand-picking/tapping

Stationary or slow-moving insects can be picked from foliage by 

hand using forceps. Other species can be tapped onto a tray or 

into a bottle topped with a large funnel using a tool such as a 

racquet. Plant segments infested with galls or fungal spores can 

be hand-picked and moved to new infestations. Take care when 

moving plant material to ensure seeds or other propagules are 

not included as this may introduce new genotypes.

Vacuuming

Either a leaf blower with reverse capability or an industrial 

strength wet-dry vacuum cleaner can be equipped with a nylon 

mesh net on the inside mouth of the blowing tube (held in place 

with a rubber band or bungee cord) to suck up organisms. This 

is particularly useful for collecting small biocontrol agents such 

as flea beetles from weed rosettes. Rocks or debris vacuumed 

up may harm collected organisms, so this method should be 

applied to foliage collections only. Adding rosette leaves to the 

net gives biocontrol agents substrates to crawl and hide on and 

reduces the suction strength. Net contents should be aspirated 

to separate biocontrol agents from unwanted material. 

Light trap

Light traps are used to collect nocturnal biocontrol agents 

(typically moths) that are otherwise difficult to collect during 

the day. Construct a wire or wooden framework to support a 

battery-operated lantern and beneath it a large funnel (with a 

wide enough opening for large insects) that rests inside a widemouth jar with target weed material in the bottom. Place it in 

a sheltered place near a target weed infestation. Start the light 

at dusk, and empty it in the morning. Alternatively, prop up a 

white sheet to serve as a reflecting surface, and place a lantern 

in front of it on a stool. Hand-collect the biocontrol agents 

attracted to the sheet as they land on the surface.

Ray Willard, 

Washington Dept. 

Transportation

Eric Coombs, Oregon 

Dept. Agriculture

Jerry Payne, USDA 

ARS

Biological Control in Eastern North America 19Introduction
Transport Considerations

Containers

Collected biocontrol agents must be transferred to containers to protect and prevent 

them from escaping. Containers should be rigid to resist crushing and ventilated to 

provide adequate air flow and prevent condensation. Unwaxed paperboard cartons 

are ideal for most species. Alternatively, use light-colored, lined containers (e.g. ice 

cream cartons) or plastic containers, providing they are ventilated. Cut or poke 

holes in the container or its lid, and cover the holes with a fine mesh screen. Gall- or 

fungus-infected foliage should be stored in large, breathable bags made of paper or 

gauze. Do not use glass or metal containers for insects or foliage; they are breakable 

and make it difficult to regulate temperature, air flow, and humidity.

For insects, fill containers two-thirds full with crumpled tissue paper to provide a 

substrate for insects to rest on/hide in, and to help regulate humidity. Include a few 

fresh sprigs of the target weed foliage. Sprigs should be free of roots, seeds, flowers, 

dirt, spiders, and other insects. Do not place sprigs in water-filled containers; they 

may crush the biocontrol agents or drown them upon leaking. Seal the container 

lids either with masking tape or rubber bands. Be sure to label each container with 

(at least) the name and number of biocontrol agent(s), the collection date and site, 

and the name of the person(s) who did the collecting.

Transporting biological control agents

When transporting short distances, place the containers in large coolers with sealed 

ice packs wrapped in crumpled newspaper or bubble wrap to prevent direct contact 

with containers. Place extra packing material in the coolers to prevent the ice packs 

from shifting and damaging the insect containers. Always keep coolers out of direct 

sunlight. If you sort and package your biocontrol agents indoors, keep them in a 

refrigerator (no lower than 40°F or 4.4°C) until you transport or ship them.

Shipping long distances

If you will be shipping your biocontrol agents to their final destination, use a 

bonded carrier service with guaranteed overnight delivery (e.g. USPS, FedEx, 

UPS, or DHL). In such cases, the release containers should be placed in insulated 

shipping boxes or coolers with one or more ice packs. The sealed ice packs need to 

be wrapped in crumpled newspaper, wrapping paper, or bubble wrap, and should 

be firmly taped to the inside walls of the shipping box to prevent them from having 

direct contact with the release containers and also to prevent crushing should 

they move about during shipping. Empty spaces in the shipping box should be 

loosely filled with crumpled paper, packing peanuts, etc. Enclose all paperwork 

accompanying the biocontrol agents (including permits and release forms) before 

sealing the shipping box. 

20 Biological Control in Eastern North America Introduction
Other factors to consider

• Make shipping arrangements well before agents are collected and ensure the carrier 

can guarantee overnight delivery and the proper treatment of package contents.

• Plan collection/packaging schedules so that delivery occurs Monday-Thursday. 

• Clearly label packages and specify that they contain perishable material.

• Provide the receiver with a tracking number and verify someone will be there 

to accept the shipment.

• Releases should be made immediately upon receipt. If that is not possible, 

biocontrol agents should be checked for food depletion, excess moisture, and 

overcrowding and then be refrigerated.

• Have the receiver provide feedback to the shipper on the overall condition of the 

shipment. This can provide important guidance on packing/shipping methods.

REGULATIONS FOR THE TRANSFER 

OF BIOLOGICAL CONTROL AGENTS

US, intrastate: Generally, there are few if any restrictions governing the collection and 

shipment of approved biological control agents within the same state; however, 

you should check with your state’s department of agriculture or agriculture 

extension service about regulations of your specific biological control agent. The 

state of California regulates release permits at the county level.

US, interstate: The interstate transportation of biocontrol agents is regulated by the 

U.S. Department of Agriculture (USDA), and a valid permit is required to 

transport living biological control agents across state lines. You should apply 

for a Plant Protection and Quarantine (PPQ) permit from the Animal and 

Plant Health Inspection Service (APHIS) as early as possible—but at least six 

months before actual delivery date of your biological control agent. You can 

check the current status of regulations governing intrastate shipment of weed 

biological control agents, PPQ Form 526 at the USDA-APHIS-PPQ website. 

The ePermit process can be accessed by doing an internet search for “USDA 

APHIS 526 permit application”. This allows the complete online processing of 

biological control agent permit requests.

Canada: Canada requires an import permit for any new biocontrol agent or shipment 

of previously-released biocontrol agents entering the country. Permit requests 

are reviewed and issued by the Plant Health Division of the Canadian Food 

Inspection Agency. Redistribution within a province (or within Canada) of weed 

biocontrol agents that have been officially approved for release in Canada is not 

prohibited; however, you should consult with federal and provincial authorities 

and specialists prior to moving any weed biocontrol agent, especially across 

ecozones (e.g., from the prairies to the interior or coast of British Columbia). 

Similarly, you should consult with appropriate experts when considering the 

movement of adventive biocontrol agents that have become established in a 

region, or native organisms that may feed on a weed targeted for control.

Biological Control in Eastern North America 21Introduction
Releasing Biocontrol Agents

Select release site

Survey prospective release sites early to ensure the targeted biocontrol agent is not 

already present. We recommend release sites be large patches with plenty of host 

plants. Different biocontrol agents will have different habitat preferences, so select sites 

on an individual basis. Avoid transferring agents to areas with high disturbance, other 

control methods (e.g. mowing, insecticide/herbicide use), or with a large number of 

ant mounds or ground dwelling animals which may predate biocontrol agents. Good 

sites should be readily accessible year after year. To reduce mortality or injury, it is 

best to redistribute biocontrol agents the same day they are collected. Releases of most 

biocontrol agents should be made under moderate weather conditions (mornings or 

evenings of hot summer days, mid-day for cold season releases). If you encounter an 

extended period of poor weather, however, it is better to release biocontrol agents 

than wait three or more days for conditions to improve, as the agents’ vitality may 

decline with extended storage. 

Establish permanent location marker 

Place a steel or fiberglass pole as a marker at the release point. Avoid wooden or plastic 

posts; they are vulnerable to weather, decay, and fire. Markers should be colorful 

and conspicuous (e.g. red, orange, white). Where obvious posts may encourage 

vandalism, mark your sites with tent/surveyor’s stakes or steel plates that can be tagged 

with release information and located later with a metal detector and GPS. Where 

a sign is appropriate, include contact information. The landowner and local weed 

management authority should be notified and given a map of the release location.

Record site geographical coordinates 

Map coordinates of the release site marker should be determined 

using a GPS device or a GPS-capable tablet/smartphone and 

should complement but not replace a physical marker. Accurate 

coordinates will help re-locate release points if markers are 

damaged or removed. Along with the coordinates, be sure to 

record what coordinate system and datum you are using, e.g. 

Latitude/Longitude in WGS 84 or UTM in NAD83.

Prepare map 

The map should be detailed and describe access to the release 

site, including roads, trails, and relevant landmarks. The map should complement 

but not replace a physical marker and GPS coordinates. Maps are especially useful 

for long-term biocontrol programs in which more than one person will be involved 

or participants are likely to change. Maps are often necessary to locate release sites 

in remote locations or places physically difficult or confusing to access.

Rachel Winston, 

MIA Consulting

22 Biological Control in Eastern North America Introduction
Complete relevant paperwork at site 

Your local land management agency may have standard biocontrol agent release 

forms for you to complete. Typically, the information you provide includes a 

description of the site’s physical location, including GPS-derived coordinates and 

elevation; a summary of its biological and physical characteristics and land use; the 

name(s) of the target weed and biocontrol agent(s) released; date and time of the 

release; weather conditions during the release; and the name(s) of the person(s) who 

released the agents. The best time to record this information is while you are at the 

field site. Consider using a smartphone and reporting app, such as the iBiocontrol 

map from EDDMapS. Once back in the office, submit the information to your 

local weed control authority/agency. Always keep a copy for your own records.

Set up photo point

A photo point is used to visually document changes in weed infestations and the plant 

community over time following the release of biocontrol agents. Use a permanent 

feature in the background as a reference point (e.g., a mountain, large rocks, trees, or 

a permanent structure) and make sure each photo includes your release point marker. 

Pre- and post-release photographs should be taken from roughly the same place and 

at the same time of year. Label all photos with the year and location.

Photo point with photos spanning three years (Rachel Winston, MIA Consulting)

Release as many biocontrol agents as possible 

As a general rule of thumb, it is better to release many individuals of a biocontrol 

agent species at one infestation than it is to spread those individuals too thinly over 

multiple infestations. Releasing all biocontrol agents within a release container in 

one spot will help ensure that adequate numbers of males and females are present 

for reproduction and reduce the risks of inbreeding and other genetic problems. If 

you have more than one release container, be sure to put some distance between the 

two releases; 2/3 mile (1 km) or more is ideal.

Biological Control in Eastern North America 23Introduction
Monitoring Biocontrol Agents

Documenting outcomes (both successes and failures) of biocontrol release 

programs will help generate a more complete picture of biocontrol impacts, guide 

future management strategies, and serve education and public relations functions. 

Monitoring can provide critical information for other land managers by helping 

them predict where and when biological control might be successful, helping them 

avoid releasing ineffective biocontrol agents or the same agent in an area where it 

is already abundant, and/or helping them avoid land management activities that 

would harm local biocontrol agent populations or worsen the weed problem. 

Monitoring activities utilize standardized procedures to help determine:

• If the biocontrol agents have become established at the release site

• If biocontrol agent populations are increasing or decreasing and how far they 

have spread from the initial release point

• If the biocontrol agents are having an impact on the target weed

• If/how the plant community or site factors have changed over time

Monitoring methods can be simple or complex. A single year of monitoring may 

demonstrate whether or not the biocontrol agents established, while multiple years 

of monitoring may allow you to follow the population of the biocontrol agents, 

changes in the target weed population and plant community, and changes in other 

factors such as climate or soil.

a b c

Monitoring: a. checking biocontrol agent abundance; b. measuring vegetation along a transect; c. 

measuring vegetation in a more systematic grid (a-c Rachel Winston, MIA Consulting)

Assessing biocontrol agent populations

If you wish to determine whether or not biocontrol agents have established after 

initial release, you simply need to find the biocontrol agents in one or more of their 

24 Biological Control in Eastern North America Introduction
life stages, or evidence of their presence. Recommendations for the best stages to 

monitor are given for each biocontrol agent in the following section of this guide. 

Begin looking for biocontrol agents where they were first released, and then expand 

to the area around the release site. 

Populations of some biocontrol agents take two or more years to reach detectable 

levels. Thus if no biocontrol agents are detected a year after release, it does not 

mean that the agents failed to establish. Revisit the site at least once annually for 

three years. If no evidence of biocontrol agents is found, either select another site 

for release or make additional releases at the monitored site. Consult with your 

county extension educator or local weed biological control expert for assistance.

To determine the changing densities of biocontrol agent populations, a systematic 

monitoring approach is required. A generalalized biological control agent monitoring 

form can be found in Appendix I. 

Assessing the target weed & co-occurring plants

The ultimate goal of a weed biocontrol program is to permanently reduce the 

negative impacts of the target weed on ecosystem function; success is frequently 

measured as a reduction in target weed abundance. To determine if biocontrol 

efforts are effective, there must be monitoring of plant community attributes, such 

as target weed distribution and density. Ideally, monitoring begins before biological 

control efforts are started (pre-release) and occurs at regular intervals after release. 

There are many ways to qualitatively (descriptively) or quantitatively (numerically) 

assess weed populations and other plant community attributes at release sites.

Qualitative (descriptive) vegetation monitoring

Qualitative monitoring uses subjective measurements to describe the target weed 

and the rest of the plant community at the management site. Examples include 

listing plant species occurring at the site, rough estimates of density (e.g. low, 

moderate, high), age (e.g. young, old) and distribution classes (e.g. isolated plants, 

small patches, dense infestations), visual infestation mapping (e.g. deliniating 

infestations by hand rather than via GPS), and maintaining a series of photos from 

designated photo points. Qualitative monitoring conducted consistently through 

time may provide insight into the status or change of target weed populations. 

However, its descriptive nature does not generally allow for quantitative statistical 

analyses. Qualitative monitoring may help you recognize what quantitative 

monitoring data/protocol might be most useful for the target weed system, which 

you can apply to new release sites in the future.

Biological Control in Eastern North America 25Introduction
Monitoring Biocontrol Agents

Quantitative vegetation monitoring

Quantitative monitoring measures changes in the target weed population and 

associated vegetation community by precisely measuring specific plant and 

community characteristics. When conducted before and after a biocontrol agent 

release, quantitative data can be analyzed using a variety of statistical tests to 

identify where significant changes have occurred. Quantitative monitoring may 

be as simple as counting the number of target weed stems in a small sample area, 

or as complex as measuring plant height, flower and seed production, biomass, 

species diversity, and species cover. Pre- and post-release monitoring should follow 

the same protocol and be employed at the same time of year to ensure that the data 

is consistent and trends are easily identified. Post-release assessments should be 

planned annually for at least 3-5 years (and ideally longer than that) after the initial 

biocontrol agent release. A generalalized vegetation monitoring form can be found 

in Appendix II; it can be easily modified to meet your personal or agency needs.

Assessing impacts on nontarget plants

To address possible nontarget attacks, you must become familiar with the plant 

communities present at and around your release sites and be aware of species closely 

and distantly related to the target weed. You may have to consult with a local 

botanist or herbarium records for advice on areas where nontarget plants might be 

growing and how you can identify them. Care should be taken in the management 

of your weed biocontrol program to ensure that closely related native species are 

identified and monitored along with the target weed. 

If you observe approved biocontrol agents feeding on and/or developing on 

nontarget species, the vegetation sampling procedures described above and in 

Appendix II can be easily modified to monitor changes in density and/or cover of 

the nontarget species. Concurrently, you may wish to collect additional data, such 

as the number of agents observed on nontarget plants, the amount of foliar feeding 

observed, or the presence of characteristic biocontrol agent damage. Collecting this 

data for subsequent years can help determine if there is a population level impact 

or if the nontarget feeding is temporary or of minor consequence to the nontarget 

species. Please be aware that many “look-alike” native insects feed on related 

native plants.

If you observe approved biocontrol agents feeding on and/or developing on native 

species, take samples to a biocontrol specialist in your area. Alternatively, send the 

specialist the site data so he/she can survey the site for nontarget impacts. Be sure 

not to ascribe any observed damage to any specific bioocntrol agent and thus bias 

the confirmation.

26 Biological Control in Eastern North America Introduction
Additional Considerations

Avoiding parasitism

Some biocontrol agent populations are plagued by parasitoids that reduce their 

numbers and, consequently, their impact. When redistributing such species, it 

is important to ensure that parasitoids are not transferred along with the desired 

biocontrol agent. This can be accomplished by collecting plants infested with the 

desired biocontrol agents in the fall and storing them at 39-46°F (4-8°C) over the 

winter. Two to three weeks prior to their normal emergence time, bring them to 

room temperature in rearing cages or breathable, clear containers. Any parasitoids 

that emerge should be separated and destroyed. Emerging biocontrol agents can be 

safely transferred to new target weed patches during the appropriate plant stage.

Biological Control in Eastern North America 27Introduction
28 Biological Control in Eastern North America KNAPWEEDSKnapweed species comparison (Centaurea)

Diffuse and spotted knapweed are the most common knapweed species in North 

America and the primary targets of knapweed biological control efforts. They are 

most problematic in western states and provinces, but are included in this eastern 

guide because some eastern infestations may benefit from biocontrol agent releases. 

Below is a comparison of these two knapweed species, as well as four others that 

are typically considered less problematic in North America but are occasional 

hosts to knapweed biocontrol agents. Russian knapweed is in a different genus, 

Trait

Diffuse

Centaurea diffusa

Spotted

Centaurea stoebe

Squarrose

Centaurea virgata 

ssp. squarrosa

Life History

Annual to short-lived 

perennial (usually 

biennial)

Short-lived perennial Long-lived perennial 

Preferred

Habitat

Disturbed initially; 

Dry

Disturbed initially; 

Dry to mesic

Disturbed initially; 

Dry 

Average

Height

1.5’

(0.45 m)

2.5’

(0.75 m)

1.5’

(0.45 m)

Basal Leaf

Description

4-8” long 

(10-20 cm);

Deeply divided into 

linear lobes;

Gray-green; Densely 

hairy

4-8” long 

(10-20 cm);

Deeply divided into 

elliptic lobes;

Gray-green; Densely 

hairy

4-8” long 

(10-20 cm);

Deeply divided into 

fine lobes;

Gray-green; Densely 

hairy

Capitulum

Diameter

0.25-0.4” 

(7-10 mm)

0.25 - 0.6”

(6-15 mm) 

0.12-0.25“

(3-6 mm)

Bract

Description

Narrow; Fringed 

by sharp spines; 

Terminal spine longer 

than laterals and not 

curved backward 

Fringe short and 

rigid; 

Dark brown 

triangular tip

Narrow; Fringed by 

sharp spines; Terminal 

spine longer than 

laterals and strongly 

curved backward

Capitulum
Biological Control in Eastern North America 29KNAPWEEDS

Rhaponticum, with a distinct biocontrol program not included in this guide because 

it currently pertains only to western North America.

Credits: Diffuse: Richard Old, XID Services, Inc, www.xidservices.com; Spotted: Michael Shephard, 

USDA Forest Service, bugwood.org; Squarrose: Steve Dewey, Utah State University, bugwood.org; 

Meadow: Eric Coombs, Oregon Department of Agriculture; Black: Mikrolit; Brown: Cindy Roche, 

bugwood.org

Meadow

Centaurea jacea 

nothosubsp. pratensis

Black

Centaurea jacea 

ssp. nigra

Brown

Centaurea jacea 

ssp. jacea

Perennial Perennial Perennial

Moist sites Mesic to moist Disturbed initially; Mesic 

to Moist

2’

(0.6 m)

1.5’

(0.45 m)

2’

(0.6 m)

6” long (15 cm); 

Entire margins (sometimes 

tiny teeth or lobes); 

Tapered both ends, widest 

past middle; Green; Less 

hair

6” long (15 cm); 

Entire margins (sometimes 

tiny teeth or lobes); Wide 

at base then taper near 

stem; Green; Fine hair

6” long (15 cm); 

Entire margins (sometimes 

tiny teeth or lobes); 

Tapered both ends, widest 

past middle; Green; Less 

hair

0.5-0.75”

(12-18 mm)

0.6-1” 

(15-25 mm)

0.5-0.85”

(12-22 mm) 

Bearing papery, deeply 

fringed margins

Tipped with comb-like, 

black teeth

Bearing papery, translucent 

margins
30 Biological Control in Eastern North America KNAPWEEDSDiffuse knapweed

Centaurea diffusa Lam.

SYNONYMS: white knapweed, tumble knapweed 

ORIGIN: First recorded in North America in 1907 in an alfalfa field.

DESCRIPTION: A winter-hardy forb that usually grows as a biennial but may 

at times grow as an annual or short-lived perennial. This plant has a deep and 

fibrous taproot. Stems are 1-3.5 ft tall (0.3-1 m) with numerous, spreading 

branches that give the plant a ball-shaped appearance and tumble-weed mobility 

when broken. Rosette leaves are deeply divided, gray-green, and covered in small 

hairs. Stem leaves are stalkless, getting smaller and less divided higher up the 

stem. Flower heads have white (sometimes pink or lavender) florets that occur 

at the ends of branches and produce numerous bristle-topped seeds. Receptacle 

bracts are edged with a fringe of spines; the terminal spine is distinctly longer. 

a b

Diffuse knapweed a. plant (K. George Beck & James Sebastian); b. infestations (Eric Coombs, 

Oregon Department of Agriculture)(a,b bugwood.org)
Biological Control in Eastern North America 31KNAPWEEDS

Family Asteraceae

c d e

Diffuse knapweed c. leaf (K. George Beck & James Sebastian); d. capitulum with white florets 

(Richard Old, XID Services, Inc, www.xidservices.com); e. capitulum with pink florets (Steve 

Dewey, Utah State University)(c-e bugwood.org)

HABITAT: This plant rapidly colonizes dry and disturbed lands, thriving most in 

shrub-steppe zones and dry, open forests. 

ECOLOGY: Diffuse knapweed spreads only by seeds. Unlike other knapweeds, 

the flower heads of diffuse do not open to shed seeds. Instead, seeds are shed 

as the mature plants tumble in the wind after the stiff central stalk breaks. 

Seeds are also spread by vehicles, animals, and people, and can remain viable 

for many years. Flowering occurs from June through October. Seeds germinate 

throughout the growing season.

BIOLOGICAL CONTROL: The majority of releases on diffuse knapweed have 

been made in western North America, where this weed is most problematic. 

As of 2016, only Bangasternus fausti, Larinus minutus, Sphenoptera jugoslavica, 

Urophora affinis, and U. quadrifasciata, have established 

on diffuse knapweed in the East, and typically only 

with small populations and limited impact. 

In the West, successful diffuse knapweed 

control has been achieved at some sites by 

using a combination of insects attacking 

seeds, foliage, and roots of knapweed plants; 

Larinus spp. and Cyphocleonus achates have 

been the most important.

NOTES: A diploid, fertile hybrid between 

diffuse knapweed and spotted knapweed 

has been identified as C. xpsammogena.
32 Biological Control in Eastern North America KNAPWEEDSSpotted knapweed

Centaurea stoebe L. sensu latu

SYNONYMS: bushy knapweed; Centaurea biebersteinii DC, Centaurea stoebe L. 

ssp. micranthos (Gulger) Hayek, Centaurea maculosa Lam. 

ORIGIN: Introduced in contaminated hay from Europe and Asia as early as 1890. 

DESCRIPTION: A bushy, winter-hardy, biennial or perennial forb. This upright 

plant is often found in dense infestations. Plants grow from 1-3.5 ft (0.3-1 m) 

in height and are supported by a deep taproot. Rosette leaves are gray-green, 

woolly, and deeply divided. Stem leaves are pinnately divided, becoming smaller 

and less divided towards the tips of multiple woolly, hairy stems. Mid-plant 

branches are topped by a few to many pink or lavender flower heads producing 

numerous tiny, bristle-topped seeds. Receptacles are covered by shortly fringed 

bracts with dark brown tips which give the plant its common name of “spotted 

knapweed.” 

a b

Spotted knapweed a. plant (Angelica Velazquez, Cowlitz County Noxious Weed Control Board); b. 

infestation (Leslie J. Mehrhoff, University of Connecticut, bugwood.org)
Biological Control in Eastern North America 33KNAPWEEDS

Family Asteraceae

c d e

Spotted knapweed c. rosettes (Rob Routledge, Sault College); d. leaf (John Cardina, The Ohio State 

University); e. flower head (Michael Shephard USDA Forest Service)(c-e bugwood.org)

HABITAT: This species rapidly colonizes disturbed and often dry sites (including 

rocky roadsides, talus slopes, pastures, sandplain grasslands, and coastal dunes), 

then invades adjacent undisturbed grasslands and open forests. 

ECOLOGY: Spotted knapweed spreads only by seeds that are dispersed by wind, 

water, livestock, wildlife, and human activity and which can remain viable in the 

soil for many years. Flowering occurs from June to October. Seeds germinate 

throughout the growing season. Heads persist on the stiff stems through the winter, 

eventually breaking off when new rosette growth appears the following spring. 

BIOLOGICAL CONTROL: The majority of releases on spotted knapweed have 

been made in western North America, where this weed is most problematic. 

As of 2016, Agapeta zoegana, Bangasternus fausti, Cyphocleonus achates, Larinus 

minutus, L. obtusus, Urophora affinis, and U. quadrifasciata have established on 

spotted knapweed in the East, but typically with small 

populations and limited impact. In the West, successful 

spotted knapweed control has been achieved 

at some sites by using a combination of insects 

attacking seeds, foliage, and roots of knapweed 

plants. Larinus spp. and Cyphocleonus achates 

have been the most important in the West; 

the role of Agapeta zoegana is under study.

NOTES: Centaurea stoebe L. is the appropriate 

name for the diploid form present 

throughout Europe; the nomenclature 

for the tetraploid form invasive in North 

America remains to be resolved.
34 Biological Control in Eastern North America KNAPWEEDSCyphocleonus achates (Fåhraeus)

Knapweed root weevil

DESCRIPTION: Eggs are <2 mm in diameter and white or pale yellow initially, 

but darken during incubation. Larvae are plump, creamy white or yellowish, 

with large, light brown head capsules. They can be up to 13 mm long. Similar to 

most weevils, they are C-shaped. Adults are large, 13–15 mm long, brown-gray 

mottled, and have short, thick snouts. Females have rounded abdomens, while 

the males’ are flattened. 

a b c

Cyphocleonus achates a. larva and root damage (Mark Schwarzländer, University of Idaho, bugwood.

org); b. pupa in root; c. adult (b,c Jennifer Andreas, Washington State University Extension)

LIFE CYCLE: Adults emerge in late summer through early fall and spend most 

of their life on the root crown, just below the surface. On hot, sunny days they 

climb to the tops of plants in search of mates. Females lay their eggs in notches 

they excavate on the root crown, just below the soil surface. A typical female 

may lay over 100 eggs. Larvae hatch in 10-12 days and mine towards the center 

of the roots. They develop through four instars, with third- and fourth-instars 

often causing a gall-like enlargement of the root. Larvae overwinter in the roots, 

and pupation occurs in the root over a two-week period in early summer. New 

adult weevils chew through the root and crawl to the surface. They live for 8-15 

weeks but do not overwinter. There is one generation per year.

DAMAGE: Small plants can be killed by larval feeding. Most damage is done 

when multiple larvae occupy a root, which leads to a reduction in plant biomass 

and density of knapweed populations. Tunneling in the root also exposes the 

plant to bacterial and fungal infection that can cause secondary injury.

PREFERRED HABITAT: This weevil prefers hot and dry sites, with loose, welldrained, coarse soils in temperate areas. It favors bare soil surfaces where grasses 

do not crowd the target plants. It disperses by walking so does best at infestations 

with continuous knapweed plants.
Biological Control in Eastern North America 35KNAPWEEDS

Coleoptera: Curculionidae

RELEASE HISTORY: This weevil was introduced from Austria, Hungary, and 

Romania and released on both spotted and diffuse knapweed in the western US 

in 1988 and in western Canada in 1987. Eastern North American releases were 

made only on spotted knapweed in the US, beginning in 1994 (IN, MI, MN, 

NE, NY, SD, WI) and only on spotted knapweed in ON, Canada in 1993. 

Successful redistributions were made to squarrose knapweed in the western US 

in 1995. Attempted redistributions to meadow knapweed in the western US 

failed to establish.

CURRENT STATUS: Attacks both diffuse and spotted knapweed in North 

America. In the eastern US, C. achates is confirmed established only on spotted 

knapweed and only with limited populations. In the western US, the principal 

host is spotted knapweed, on which its abundance and impact vary. Numerous 

studies claim this biocontrol agent can be effective, but largely in combination 

with Larinus spp., with high plant competition, under dry conditions, and in 

loose soil. Damage to diffuse knapweed in the western US is usually (but not 

always) less extensive compared to spotted knapweed. This weevil is established 

on squarrose knapweed in the western US, but only in limited numbers and 

with unknown impact. This weevil is not established in eastern Canada. In 

western Canada, spotted knapweed is also the preferred host, on which high 

weevil populations can decrease plant density and stature, though evidence 

supporting this is anecdotal. Its impact there is greatest in conjunction with 

other biocontrol agents. Populations are smaller on diffuse knapweed than 

spotted knapweed in western Canada, but the weevil is having increasing impact 

on diffuse knapweed, especially at hot, dry, and open sites with loose soil.

REDISTRIBUTION: Adults can be can be netted in late summer, but are large 

enough to be hand-picked. They are most apparent on sunny days and in the 

afternoon. Releases of 50-100 individuals should be made at large infestations 

with hot climates and loose, well-drained soil. Establishment can be monitored by 

observing adults the following late summer or dissecting roots for feeding larvae 

the following autumn through early summer. 

Note that root damage without larvae 

present can be difficult to distinguish 

from other root-feeding insects.

NOTES: Multiple larvae are often found 

attacking the same root, along with 

other species.

diffuse spotted
36 Biological Control in Eastern North America KNAPWEEDSLarinus minutus Gyllenhal

Lesser knapweed flower weevil

DESCRIPTION: This species is very similar to Larinus obtusus. Eggs are elongate, 

yellow, and often clustered in the flower head between pappus hairs. Larvae are 

white, C-shaped, and have brown head capsules. They are approximately 8 mm 

long. Pupae are 6 mm long and white, turning brown shortly before emergence. 

Adults are 4-5 mm long, a mottled-brown color, and have a large, bent snout.

a b c d

Larinus minutus a. pupa (Gary Brown, USDA APHIS PPQ); b. adult (Laura Parsons & Mark 

Schwarzländer, University of Idaho); c. adult feeding damage to stem and leaves (Rachel Winston, 

MIA Consulting); d. emergence hole (Jennifer Andreas, Washington State University Extension)

LIFE CYCLE: Overwintering adults emerge from plant litter throughout the 

summer. Mating occurs continuously during this long period. Adults feed on 

knapweed leaves, outer stem tissue, and flowers prior to laying eggs. Up to five 

eggs are deposited in a flower head between pappus hairs; females lay 28-130 in 

a lifetime. Larvae hatch in three days and feed on pappus hairs before consuming 

seeds and receptacle tissue. Larvae feed through the entire knapweed flowering 

period of and develop through three instars in four weeks. The number of larvae 

per flower head depends on flower head size and knapweed species. Pupation 

occurs in chambers made of chewed seeds and pappus hairs within the flower 

head. New adults emerge by chewing their way out, leaving behind the now-open 

pupal chamber. They feed on foliage and florets before moving to overwintering 

sites at plant bases. There is one generation per year.

DAMAGE: Defoliation by adults can be severe, which can stunt and even kill 

affected plants. Larval feeding consumes large portions of developing seeds, 

reducing the rate of knapweed spread.

PREFERRED HABITAT: This weevil typically prefers sites more dry and hot 

than those tolerated by L. obtusus. It favors dense knapweed stands with little 

plant competition and requires well-drained, coarse soils. Sites with compacted 
Biological Control in Eastern North America 37KNAPWEEDS

Coleoptera: Curculionidae

soil (especially those grazed with livestock during the bolting stage) or places 

with prolonged rainfall are not suitable for this insect.

RELEASE HISTORY: This weevil was introduced from Greece and Romania and 

released on both diffuse and spotted knapweed in the western US in 1991. Eastern 

US releases began in 1992 on both diffuse knapweed (MN, NE, SD, TX) and 

spotted knapweed (IN, MI, MN, NE, NY). The weevil spread naturally and via 

intentional redistributions to meadow and squarrose in the western US in 1997. A 

redistribution attempted on purple starthistle in the western US failed to establish. 

Individuals from Greece were released on diffuse and spotted knapweed in western 

Canada in 1991. In eastern Canada, it was redistributed only to spotted knapweed 

(ON 2007, MB 2012). 

CURRENT STATUS: Attacks both diffuse and spotted knapweed in North 

America, but populations and impact are greatest in western states and provinces. 

Larval feeding decreases knapweed seed output while adult feeding stunts plant 

growth. In the western US, this weevil causes widespread decreases in density 

of diffuse knapweed. Impact on spotted knapweed is variable; it can reportedly 

be high, but is typically less dramatic than on its preferred diffuse knapweed. 

The weevil’s impact on meadow and squarrose knapweed in the western US 

is typically lower than its impact on diffuse knapweed. In Canada, this weevil 

is only established in western provinces, where it prefers diffuse knapweed; it 

causes extensive damage to diffuse and localized damage to spotted. 

REDISTRIBUTION: Adults can be collected with a sweep net (with or without 

an aspirator) during summer when plants are in early flowering. Releases of at 

least 200 individuals should be made at new (uninfested) patches of knapweed. 

Establishment can be monitored the following summer by checking for adults 

and/or feeding larvae within capitula. Note that feeding larvae can be difficult 

to distinguish from other knapweed weevil species.

NOTES: Larinus minutus reportedly prefers 

diffuse knapweed while L. obtusus prefers 

spotted. Both are difficult to differentiate 

with the naked eye, with some evidence 

pointing to them being variants of the 

same species. Many releases of either 

biocontrol agent likely contained a 

mixture of both. Rodent predation 

can be high at some sites. diffuse spotted
38 Biological Control in Eastern North America KNAPWEEDSLarinus obtusus Gyllenhal

Blunt knapweed flower weevil

DESCRIPTION: This species is very similar to Larinus minutus. Eggs are 

elongate, yellow, and deposited in the flower head between pappus hairs. Larvae 

are white, C-shaped, and have brown head capsules. They are approximately 8 

mm long. Pupae are 6 mm and white, turning brown shortly before emergence. 

Adults are 5-7 mm long, a mottled brownish-black, and have a large, bent snout. 

a b c

Larinus obtusus a. adult (Laura Parsons & Mark Schwarzländer, University of Idaho); b. adult 

feeding damage (Rachel Winston, MIA Consulting); c. larval feeding damage (Montana State 

University Archive, bugwood.org)

LIFE CYCLE: Overwintering adults emerge from plant litter throughout the 

summer. Adults feed on knapweed foliage and flowers prior to laying eggs. Eggs 

are deposited in the flower head between pappus hairs. Larvae hatch in three days 

and feed on pappus hairs and developing seeds. Larvae feed through the entire 

knapweed flowering period, and develop through three instars in 3-4 weeks. The 

number of larvae per flower head depends on on flower head size and knapweed 

species. Pupation occurs in 9 days in pupal chambers made of chewed seeds 

and pappus hairs within the flower head. New adults emerge in late summer by 

chewing their way out, leaving behind the now-open pupal chamber. They feed 

on foliage and senescing florets before moving to overwintering sites at the base 

of plants. There is one generation per year.

DAMAGE: Defoliation by adults can be severe, which can stunt and even kill 

affected plants. Larval feeding consumes large portions of developing seeds, 

reducing the rate of knapweed spread.

PREFERRED HABITAT: This weevil favors more moist sites with cooler 

temperatures than those tolerated by L. minutus. It establishes on south and 

west slopes with well-drained coarse soils, often near water. Excess competing 

vegetation may discourage its establishment.
Biological Control in Eastern North America 39KNAPWEEDS

Coleoptera: Curculionidae

RELEASE HISTORY: This weevil was introduced from Romania and Serbia 

and released on both diffuse and spotted knapweed in the western US in 1992. 

Eastern US releases were made only on spotted knapweed and beginning in 

1995 (MI, MN, NE, NY, SD). The weevil spread naturally and via intentional 

redistributions to meadow, black, and brown knapweed in the western US 

beginning in 1999. The weevil was introduced from Romania and released on 

both diffuse and spotted knapweed in western Canada in 1992; no releases or 

redistributions have been made to eastern Canada to date.

CURRENT STATUS: Attacks both diffuse and spotted knapweed in North 

America. In the eastern US, L. obtusus is confirmed established only on spotted 

knapweed and only with limited populations. Throughout the western US, the 

principal host is spotted knapweed, on which its abundance and impact vary. 

Larval feeding decreases knapweed seed output while adult feeding may stunt 

plant growth. This weevil successfully reduces spotted knapweed abundance at 

some locations in the Pacific Northwest but has little to no impact at some other 

knapweed infestations. Populations are more limited and have less impact on 

diffuse, meadow, black, and brown knapweed in the western US, largely via seed 

reduction. In Canada, the weevil is only established in the western province of 

BC where it prefers spotted knapweed. The weevil prefers more moist conditions, 

so it has a smaller distribution than L. minutus, and its overall impact on spotted 

knapweed is moderate. The weevil’s impact on diffuse knapweed in western 

Canada is unknown. 

REDISTRIBUTION: Adults can be collected with a sweep net (with or without 

an aspirator) during summer when plants are in early flowering. Releases of at 

least 200 individuals should be made at new (uninfested) patches of knapweed. 

Establishment can be monitored the following summer by checking for adults 

and/or feeding larvae within capitula. Note that feeding larvae can be difficult 

to distinguish from other knapweed weevil species.

NOTES: Larinus obtusus reportedly prefers spotted 

knapweed while L. minutus prefers 

diffuse. Both are difficult to differentiate 

with the naked eye, with some evidence 

pointing to them being variants of the 

same species. Many releases of either 

biocontrol agent likely contained a 

mixture of both. Rodent predation 

can be high at some sites. diffuse spotted
40 Biological Control in Eastern North America KNAPWEEDSSphenoptera jugoslavica Obenberger

Bronze knapweed root borer

DESCRIPTION: Eggs are flat and white when first laid, but change to dark 

bluish-purple after five days. Larvae have an enlarged head and a long, thin, 

cylindrical body that tapers to the end. They are whitish with inflated segments 

and dark brown head capsules. Pupae are initially white, but later darken. Adults 

can be up to 10 mm long. They are a metallic bronze color and somewhat 

flattened, with their bodies tapering towards the narrowed abdomen tip.

a b c

Sphenoptera jugoslavica a. eggs; b. larva in root (a,b Eric Coombs, Oregon Department of Agriculture); 

c. adult (Laura Parsons & Mark Schwarzländer, University of Idaho)(a-c bugwood.org)

LIFE CYCLE: Adults emerge in summer as knapweed flowers. They feed on 

knapweed leaves for 2-3 days before mating. During late summer, females lay 

multiple eggs between the bases of rosette leaves. Leaf stems with diameters 

of 3-6 mm are preferred over smaller leaves. Females lay an average of 50 eggs 

during their lifetimes. Larvae hatch after two weeks and feed between leaf stalks. 

As knapweed sets seed, second instars mine into the upper root; their feeding 

creates swollen galls and tunnels often filled with frass. Larvae overwinter in 

roots. Pupation (nine days) occurs within the feeding chamber during early 

summer the following year. There is one generation per year.

DAMAGE: Adults feed on knapweed foliage, leaving characteristic circular and 

oval feeding holes over the entire leaf. Feeding larvae consume roots which, in 

turn, may kill plants outright, prevent rosettes from flowering, or decrease the 

reproductive output of already-flowering stalks. 

PREFERRED HABITAT: This beetle prefers arid environments with a period of 

drought in summer. It thrives in well-drained, coarse soils with southern aspects. 

Exposed soil between plants increases the soil temperature, making sites even 

more suitable.

RELEASE HISTORY: Individuals from Greece were released in the western US 
Biological Control in Eastern North America 41KNAPWEEDS

Coleoptera: Buprestidae

on diffuse knapweed in 1980. The beetle spread naturally and via intentional 

redistributions in the western US to spotted knapweed by 1987 and squarrose 

knapweed by 1996. Redistributions to western meadow knapweed infestations 

failed to establish. Though not intentionally introduced in the eastern US, this 

beetle likely spread naturally from nearby states. Individuals from Greece were 

released in BC, Canada on diffuse knapweed from 1976. It was redistributed 

from diffuse to spotted knapweed in BC in 1987.

CURRENT STATUS: Attacks both diffuse and spotted knapweed in North 

America. In the eastern US, S. jugoslavica is confirmed established only on 

diffuse knapweed and only with limited populations. It is established on diffuse, 

spotted, and squarrose knapweed in the western US, though diffuse is the 

preferred host, on which it reduces plant density and seed output, especially 

among competing vegetation. The overall impact on diffuse is moderate, as 

the agent is largely restricted to hot, dry sites. While spotted knapweed can be 

attacked, agent distribution and impact are typically limited. It is slightly to 

moderately effective on squarrose knapweed in the western US. In Canada, S. 

jugoslavica is established on both diffuse and spotted knapweed, but only in the 

western province of BC where diffuse knapweed is again the preferred host. On 

diffuse, high agent populations can be found throughout the driest part of the 

weed’s range; high beetle numbers in conjunction with other biocontrola gent 

can decrease weed stature, seed production, and rosette density, though most 

impact is only localized. On spotted knapweed, S. jugoslavica can decrease seed 

production and stature of plants growing in hot dry areas, but most spotted 

infestations are too moist to support beetle populations. 

REDISTRIBUTION: Adults can be collected with a sweep net (with or without 

an aspirator) during summer when knapweed plants are in flower. Releases of 

50-200 individuals should be made at large infestations with hot climates and 

loose, well-drained soil. Establishment can be monitored by observing adults the 

following summer or dissecting roots for feeding larvae the following autumn 

through early summer. Note that root damage 

without larvae present can be difficult 

to distinguish from other root-feeding 

insects.

NOTES: Plants rarely support more than 

one larva; if two develop on a single 

root, the larva feeding lowest in the 

root is usually smaller. diffuse spotted
42 Biological Control in Eastern North America KNAPWEEDSAgapeta zoegana (L.)

Sulfur knapweed moth

DESCRIPTION: Larvae are white with brown mouthparts and can be up to 7 

mm long. Adults are usually 11 mm long with a wingspan measuring 15-23 

mm. Forewings are bright yellow with brownish band markings; hind wings are 

dark gray. Females have a larger, more rounded abdomen than males and lay 

white, flattened eggs that turn yellow-red in a few days.

a b c

Agapeta zoegana a. egg (Nez Perce Biological control Center Archive); b. larva and root damage 

(USDA ARS); c. adult (Laura Parsons & Mark Schwarzländer, University of Idaho)(a-c bugwood.org)

LIFE CYCLE: Larvae overwinter in knapweed roots and feed within the roots 

the following spring. Pupation occurs in the roots; adults emerge from summer 

to early fall when knapweeds are in bud and flowering. Adults mate within 24 

hours of emergence and are short-lived. They are most active in early mornings 

or evenings, and rest low on plants or on the soil surface during the day. Females 

deposit eggs on knapweed stem crevices and leaves as early as the following day. 

A single adult female lays 21-78 eggs in her lifetime. Larvae hatch in 7-10 days 

and migrate to the crown area and mine roots, developing through six instars. 

As they mine outer root layers, larvae produce a whitish web tunnel that encloses 

them. They create a spiral trail downward before they turn back towards the top 

of the root. There is usually only one generation per year.

DAMAGE: When larvae feed within roots, root tissue can be completely consumed. 

This reduces knapweed biomass and density and may kill small plants. 

PREFERRED HABITAT: This moth is found mostly in dry, well-drained, open 

sites with loamy soil. It survives in areas characterized by a moderately humid 

climate or in areas with arid, subcontinental climates. It can tolerate cold winter 

temperatures, but requires a long growing season. Suitable host plants have root 

diameters of at least 0.1 in (2.5 mm).
Biological Control in Eastern North America 43KNAPWEEDS

Lepidoptera: Tortricidae

RELEASE HISTORY: This moth was introduced from Austria and Hungary 

and released on spotted and diffuse knapweed in the western US in 1984 and 

subsequently redistributed to MN, SD and WI in the eastern US. It remains 

unclear if attempted redistributions to squarrose knapweed in the western US 

were successful. Austrian and Hungarian populations were also used for releases 

on spotted and diffuse knapweed in western Canada in 1982. Redistributions 

were made from spotted to squarrose knapweed in western Canada in 2006.

CURRENT STATUS: Attacks both diffuse and spotted knapweed in North 

America. In the eastern US, A. zoegana is confirmed established only on spotted 

knapweed. This moth can cause significant reduction of spotted knapweed aboveground biomass and number of capitula per plant, but it has not demonstrated 

any obvious effect on plant density. It is expected to primarily affect large plants. 

Its abundance is believed to be limited, and its overall impact is likewise believed 

to be low throughout the US, though this is currently under study. In Canada, 

this moth is established only in western provinces not covered in this guide, 

where high populations may have a significant impact on diffuse and spotted 

knapweed populations, especially in conjunction with other biocontrol agents. 

Though widely distributed in western Canada, moth abundance is variable. 

REDISTRIBUTION: Because moths are delicate, distribution efforts should 

use larvae. Infested plants can be dug up (including the roots) and transferred 

to new sites in late fall or early spring. Alternatively, roots can be collected in 

fall and stored at 39-46°F (4-8°C). Two to three weeks prior to their normal 

emergence time, bring them to room temperature in rearing cages or breathable, 

clear containers. Once they emerge, adults can be transferred to new knapweed 

infestations. Releases of 100-200 individuals should be made on continuous, 

nonlinear patches of knapweed in loamy soil. Establishment can be monitored 

the following spring by dissecting roots for feeding larvae or observing adults in 

low foliage during late summer. Note that root damage without larvae present 

can be difficult to distinguish from other root-feeding insects.

NOTES: Multiple larvae may attack the 

same root. In one observation, more 

than 50 A. zoegana larvae and 20 

Cyphocleonus achates larvae were found 

attacking one very long segment of 

knapweed root.

diffuse spotted
44 Biological Control in Eastern North America KNAPWEEDSUrophora affinis (Frauenfeld)

Banded knapweed gall fly

DESCRIPTION: Eggs are white and elongate. Larvae are creamy white, barrelshaped, and with heads that retract slightly. Larvae of flies do not have head 

capsules but do develop dark brown anal plates by the end of the feeding period. 

The pupa is brown, barrel-shaped, and 3 mm long. Adults can be up to 4 mm 

long. They have dark bodies and clear wings marked with faint horizontal bars. 

Females have long, pointed, black ovipositors.

a b c

Urophora affinis a. larva in gall (Eric Coombs, Oregon Department of Agriculture); b. multiple galls 

(Jim Story, Montana State University); c. adult (Laura Parsons & Mark Schwarzländer, University of 

Idaho)(a-c bugwood.org)

LIFE CYCLE: There is usually one generation per year, though two may occur 

in warm climates. Overwintering as third instars, flies pupate for ~14 days in 

the spring. Adults emerge when knapweed is in bud. Females lay up to 120 eggs 

in groups of 1-5 among immature florets inside closed flower heads. After 3-4 

days, larvae hatch and tunnel into the base of the capitulum to feed on receptacle 

tissue. Larval feeding triggers the formation of a hard, woody gall that surrounds 

the larva. 2-4 galls per capitulum is common, though the number depends on 

capitulum size and knapweed species. Most larvae require a cold period to induce 

pupation, and thus overwinter in flower heads; 10-25% of larvae may pupate 

early in suitable climates, with second generation adults emerging in early fall.

DAMAGE: Larval feeding directly destroys some seeds, reducing the rate of 

knapweed spread. In addition, galls drain nutrients from other parts of the 

plant, which causes stunting and reduces the number of flower heads produced. 

PREFERRED HABITAT: This species is well adapted to a variety of conditions 

and can be found throughout much of North America. It shows a preference for 

mesic sites and appears to do better on dense knapweed populations.

RELEASE HISTORY: Individuals from Austria, France and Russia (some via 
Biological Control in Eastern North America 45KNAPWEEDS

Diptera: Tephritidae

Canada) were released on diffuse and spotted knapweed in the western US in 

1973. Eastern US releases were made on diffuse knapweed in 1983 (MD) and on 

spotted knapweed beginning in 1983 (IN, MD, MI, MN, NY, PA, VA, WI). This 

fly spread naturally and via intentional redistributions to squarrose knapweed 

in the western US from 1988. Individuals from France and Russia were first 

introduced to western Canada in 1970 and subsequently released in MB, QC, 

and ON on spotted knapweed beginning in 1970 and on diffuse knapweed in 

1980. Many releases contained a mixture of U. affinis and U. quadrifasciata.

CURRENT STATUS: Attacks both diffuse and spotted knapweed in North 

America. Throughout the US, and along with U. quadrifasciata, this fly 

contributes to diffuse and spotted knapweed seed reduction >50% at some sites. 

This may slow the rate at which knapweed spreads, but it has not appreciably 

lowered stand density because sufficient seeds remain. At other sites, the direct 

effect of Urophora galls on seed production is negligible, and it is not considered 

as important or effective as other knapweed agents. It has limited abundance 

and impact on squarrose knapweed in the western US. In Canada, high fly 

populations stunt plant growth and significantly decrease seed production, but 

have not resulted in any apparent decline in knapweed density to date.

REDISTRIBUTION: Sweeping adult flies is possible, though flies are fragile 

and can be damaged during collection. The species is best transferred by placing 

plants with infested capitula into uninfested patches during late fall or early 

spring. Transferring infested capitula may also transfer unwanted parasitoids, 

insects, or knapweed seeds. To avoid this, plants with infested capitula can be 

collected and adults reared out indoors. Refer to Additional Considerations in 

the Introduction for instructions on how to do so. Once they emerge in spring, 

flies can be transferred to uninfested knapweed patches in groups of 50-100. 

Establishment can be monitored by observing adults on knapweed foliage the 

following summer or by dissecting capitula for larvae from summer to spring. 

Note that feeding larvae can be difficult to distinguish from other knapweed fly 

species. Urophora species have dark brown anal 

plates and can be found within galls.

NOTES: This species does not disperse 

as rapidly as U. quadrifasciata, but is 

often the dominant species where both 

flies coexist. Deer mice feed heavily on 

Urophora larvae, and mice populations 

are known to increase as a result. diffuse spotted
46 Biological Control in Eastern North America KNAPWEEDSUrophora quadrifasciata (Meigen)

UV knapweed seedhead fly

DESCRIPTION: Eggs are white and elongate. Larvae are creamy white, barrelshaped, and with heads that retract slightly. Larvae do not have head capsules but 

do develop dark brown anal plates by the end of the feeding period. The pupa 

is brown, barrel-shaped, and 3 mm long. Adults can be up to 4 mm long. They 

have dark bodies and clear wings marked with distinctive dark bands forming a 

“UV” pattern on each wing. Females have long, pointed, black ovipositors.

a b

Urophora quadrifasciata a. larva (USDA ARS); b. adult (Laura Parsons & Mark Schwarzländer, 

University of Idaho)(a,b bugwood.org)

LIFE CYCLE: There are usually two generations per year. Overwintering as third 

instars, flies pupate for 14 days in spring, and adults emerge as knapweed is in 

bud. Females lay up to 120 eggs in groups of 1-5 among immature florets inside 

closed flower heads; females prefer well-developed capitula. After 3-4 days, 

larvae hatch and tunnel into the base of the capitulum and feed on receptacle 

tissue through three instars. Larval feeding induces the formation of a papery 

gall that surrounds the larva. 2-4 galls per capitulum is common, though the 

number depends on capitulum size and knapweed species. Pupation occurs in 

galls in late summer. Second generation adults emerge in early fall, attacking 

late-developing seed heads. Larvae overwinter in capitula.

DAMAGE: Larval feeding directly destroys some seeds, reducing the rate of 

knapweed spread. In addition, galls drain nutrients from other parts of the 

plant, which causes stunting and reduces the number of flower heads produced. 

PREFERRED HABITAT: This species is well adapted to a variety of conditions 

and throughout much of North America. It is tolerant of severe winter conditions 

but requires considerably more protective snow cover than U. affinis.

RELEASE HISTORY: Individuals from Russia were released in western Canada 

on diffuse knapweed in 1972 and subsequently spread naturally to spotted 
Biological Control in Eastern North America 47KNAPWEEDS

Diptera: Tephritidae

knapweed by 1975 and meadow knapweed by 2000. Eastern Canada releases 

began on spotted knapweed in 1979 (MB, ON, QC) and diffuse knapweed 

starting in 1993 (MB, ON). The fly spread naturally from Canada to the western 

US by 1979 (diffuse and spotted knapweed) and subsequently spread naturally 

and via intentional introductions throughout the western US to brown, meadow, 

and squarrose knapweed, yellow starthistle, and bachelor’s button. Eastern US 

redistributions occurred only on spotted knapweed beginning in 1983 (AR, IN, 

MD, MI, MN, NY, VA, WI), often under the assumption it was the approved 

U. affinis. It was officially approved for redistribution in the US in 1989.

CURRENT STATUS: Attacks both diffuse and spotted knapweed in North 

America. Throughout the US, this fly is more widely distributed than U. affinis

but less abundant. Together seed reduction can be >50% at some sites, but 

negligible at others. Seed reduction may slow the rate at which knapweed spreads, 

but has not appreciably lowered stand density as sufficient seeds remain. This 

species is not considered as important or effective as other biocontrol agents. It 

has limited abundance and impact on brown, meadow, and squarrose knapweed, 

yellow starthistle, and bachelor’s button in the western US. In Canada, high fly 

populations decrease diffuse and spotted knapweed growth and seed production 

but result in no apparent decline in knapweed plant density. Impacts on meadow 

knapweed in western Canada are even lower.

REDISTRIBUTION: Sweeping adult flies is often damaging. Instead, transfer 

infested capitula into uninfested patches during fall or early spring. This may also 

transfer unwanted parasitoids, insects, or knapweed seeds. To avoid this, plants 

with infested capitula can be collected and adults reared out indoors. Refer to 

Additional Considerations in the Introduction for instructions. Once they emerge 

in spring, flies can be transferred to new knapweed infestations in groups of 50-

100. Establishment can be monitored by observing adults on knapweed foliage 

the following summer or by dissecting capitula for larvae from summer to spring. 

Note that feeding larvae can be difficult to distinguish from other knapweed flies. 

Urophora species have dark brown anal plates 

and can be found within galls.

NOTES: This species disperses more 

rapidly than U. affinis, but U. affinis is 

often the dominant species where both 

flies coexist. Deer mice feed heavily on 

Urophora larvae, and mice populations 

are known to increase as a result. diffuse spotted
48 Biological Control in Eastern North America KNAPWEEDSBangasternus fausti (Reitter)

Broad-nosed knapweed seedhead weevil

DESCRIPTION: Eggs are yellow ovals covered with dark egg caps. Larvae are 

white with brown head capsules, C-shaped, and and up to 8 mm long. Pupae 

are white and up to 5 mm long. Adults are small and gray to brown/black. They 

can be 4 mm long, and they have shorter, more blunt snouts compared to the 

Larinus weevils.

a b

Bangasternus fausti a. pupa (USDA ARS European Biological Control Laboratory); b. adult (Laura 

Parsons & Mark Schwarzländer, University of Idaho)(a,b bugwood.org)

LIFE CYCLE: Overwintering adults emerge from soil and plant litter in spring 

and feed on knapweed foliage prior to egg laying. Eggs are laid from late spring 

through summer, individually on the underside of leaflets or on stems below the 

developing flower head. Eggs are covered with masticated plant tissue (which 

forms a black egg cap) and hatch in 8-12 days. Depending on egg placement, 

hatching larvae either mine into the midrib of the leaflet or into the stem prior 

to tunneling into the flower head. Larvae develop through four instars and feed 

on developing seed tissue throughout summer. Pupation occurs in the flower 

head within a chamber made of frass and fused seeds. Adults emerge in late 

summer or early fall when knapweeds are senescing. Adults drop to the ground 

to overwinter. There is one generation per year.

DAMAGE: Larval feeding destroys seeds and receptacle tissue. Seed consumption 

does not kill existing plants, but does help reduce the rate of knapweed spread. 

PREFERRED HABITAT: This weevil prefers hot, dry areas and does not do well 

in areas with prolonged rain or at high elevations.
Biological Control in Eastern North America 49KNAPWEEDS

Coleoptera: Curculionidae

RELEASE HISTORY: This weevil was introduced from Greece and originally 

released on diffuse knapweed in the western US in 1990. It was subsequently 

redistributed to spotted knapweed in numerous western states, in MN and NE 

in 1992, and in NY in 2009. It was also successfully redistributed to squarrose 

knapweed in the western US in 1993. Attempted redistributions to meadow 

knapweed and purple starthistle in the western US failed to establish.

CURRENT STATUS: Bangasternus fausti attacks both diffuse and spotted 

knapweed in North America. It currently has limited establishment in the eastern 

US. It is established on diffuse knapweed in NE and on spotted knapweed in NE 

and WI. Larvae can consume up to 100% of seed in attacked capitula, though 

a proportion of seeds often escape attack in large flower heads. Its abundance 

is low throughout the US, but not likely due to interspecific competition. The 

overall impact of this weevil is limited in the US. This weevil has not been 

released and is not established in Canada.

REDISTRIBUTION: Though populations are typically low in the US, some 

populations in OR and WA are reportedly large enough for redistribution. Adults 

can be collected with a sweep net (with or without an aspirator) during summer 

when plants are in early bud to early flowering. Releases of 200 individuals 

should be made on patches of at least 2,000 m2 (0.5 acre). Establishment can be 

monitored the following summer by checking for adults and/or feeding larvae 

within capitula. Note that feeding larvae can be difficult to distinguish from 

other knapweed seed-feeding weevil species.

NOTES: This species is not approved for release in Canada.

diffuse spotted
50 Biological Control in Eastern North America KNAPWEEDSChaetorellia acrolophi White & Marquardt

Knapweed peacock fly

DESCRIPTION: Eggs are shiny white, elongate, and have a long filament 

thickened at one end. First generation larvae and pupae are white and barrelshaped. Second generation larvae and pupae are more yellowish-brown in color. 

Adults are 4-5 mm long and have bright green eyes, orange-yellow colored 

abdomens, and overall spotting on the thorax. Wings are clear with light brown 

bands.

a b

Chaetorellia acrolophi a. larva (Rachel Winston, MIA Consulting); b. adult (USDA APHIS PPQ 

Archive, bugwood.org)

LIFE CYCLE: There are usually two generations per year; however, a rare 

third generation is possible under ideal conditions. Adult flies emerge in early 

summer as knapweed buds form. Mating occurs immediately, and oviposition 

starts within two days. Females lay eggs individually or in small groups of 2-4 

underneath bracts of unopened buds. A single female may lay 70 eggs in her 

lifetime. Larvae hatch in 4-5 days and penetrate buds, feeding on immature 

florets until they reach the developing seeds where they feed through three 

instars. Pupation occurs in the flower head 10-15 days after larvae hatch. First 

generation adults typically emerge throughout July, mate, and lay eggs. New 

larvae of this generation continue to feed on developing seed tissue. Third instars 

overwinter. Pupation occurs within the flower head the following spring.

DAMAGE: Larval feeding destroys some developing seeds. This does not damage 

existing plants, but helps reduce the rate of knapweed spread.

PREFERRED HABITAT: This fly is most effective in areas with low density 

knapweed, which is less preferred by other knapweed seed feeders. It generally 

does better at higher elevations and in regions with high rainfall.
Biological Control in Eastern North America 51KNAPWEEDS

Diptera: Tephritidae

RELEASE HISTORY: This fly was introduced from Austria and Switzerland and 

released on spotted knapweed in the western US in 1992; it was subsequently 

redistributed to MN, NE and SD in the eastern US. Populations from Switzerland 

were released on spotted knapweed in western Canada in 1991. Redistributions 

were made from spotted to diffuse knapweed in western Canada in 2011.

CURRENT STATUS: Chaetorellia acrolophi attacks both diffuse and spotted 

knapweed in North America, but it is established only in western states and 

provinces not included in this guide. In the western US, it is established only on 

spotted knapweed, on which larval feeding reduces seed production; however, 

populations are limited throughout its established range so its overall impact 

is minimal. This fly is established on both diffuse and spotted knapweed in 

Canada, but only in a western province not covered by this guide (BC) where its 

abundance is limited and its impact is currently unknown. 

REDISTRIBUTION: Sweeping adult flies is possible, though this is typically 

not the best stage for collection as flies are fragile and can be damaged during 

collection. This species is best transferred by placing plants with infested capitula 

into uninfested patches during late fall or early spring. Transferring infested 

seed heads may also transfer unwanted parasitoids, other seed head insects, or 

knapweed seeds. To avoid this, plants with infested capitula can be collected 

and adults reared out indoors. Refer to Additional Considerations in the 

Introduction for instructions on how to do so. Once they emerge in spring, flies 

can be transferred to new spotted knapweed infestations in groups of 50-100. 

Establishment can be monitored by observing adults on knapweed foliage the 

following summer during the heat of the day or by dissecting capitula for larvae 

from summer throughout the following spring. Note that feeding larvae can be 

difficult to distinguish from other knapweed fly species. Urophora species can be 

differentiated by their dark brown anal plates and from being enclosed by galls.

NOTES: At some western US infestations of spotted knapweed, populations of 

this fly are limited by interspecific competition.

diffuse spotted
52 Biological Control in Eastern North America KNAPWEEDSMetzneria paucipunctella Zeller

Spotted knapweed seedhead moth

DESCRIPTION: Eggs are elongate, oval, and reddish-brown when first 

deposited, but turn yellowish as they mature. Larvae are 4-5 mm long, white 

with dark brown head capsules, distinct body segments, and several pairs of 

prolegs. Pupae, enclosed in a cocoon, are brown with appendages fused to the 

body. Adult moths are small (8 mm long). Their front wings are slightly fringed 

and light gray with peppery spotting and dark tips. When at rest, the wings are 

folded over their backs, giving them a slender appearance.

a b

Metzneria paucipunctella a. larva and pupa; b. adult (a,b Norman Rees, USDA ARS bugwood.org)

LIFE CYCLE: Adults begin emerging and mating in late spring and early summer 

when knapweeds are in the rosette and bolting stages. They fly at dusk and are 

rarely seen. Female moths may lay 60-100 eggs, beginning in early summer. 

Eggs are placed singly on bracts at the base of young flower heads, or on stems 

just below the capitula. Larvae hatch in 10-12 days as flower heads are opening. 

Larvae enter opened capitula and feed on florets, seeds, and receptacle tissue 

(which reduces the viability of uneaten seeds). There are five instars total. Several 

young larvae can occupy a flower head early in the season, but only one larva 

survives beyond the third instar. Larvae overwinter in flower heads. Pupation 

occurs in the capitulum in spring and lasts 3-4 weeks. There is one generation 

per year.

DAMAGE: Feeding larvae can destroy eight seeds per larva (on average) and 

reduce the viability of other seeds. Older larvae bind seeds together, preventing 

seeds from dispersing over long distances.

PREFERRED HABITAT: This moth does not tolerate severe winter 

temperatures. Favored sites are south slopes in dry climates with mild winters. 

Snow cover during winter enhances larval survival. It appears to do best in areas 

where knapweeds flower early.
Biological Control in Eastern North America 53KNAPWEEDS

Lepidoptera: Gelechiidae

RELEASE HISTORY: This moth was introduced from Switzerland and released 

on spotted knapweed in western Canada from 1973. It was redistributed to diffuse 

knapweed in western Canada from 1981 and redistributed to spotted knapweed 

in ON, Canada in 1993. The moth was redistributed from Canada to spotted 

knapweed in the western US from 1980; it was subsequently redistributed to 

MN and VA in the eastern US from 1986. It spread naturally and via intentional 

redistributions to diffuse and meadow knapweed in the western US from 1980.

CURRENT STATUS: Metzneria paucipunctella attacks both diffuse and spotted 

knapweed in North America, but it is established only in western states and 

provinces not included in this guide. In the western US, spotted knapweed is the 

preferred host, though even on this species moth abundance is rarely high and 

seed reduction is typically insufficient to impact knapweed populations. Attack 

to diffuse and meadow knapweed in the western US is far less common; impact 

is insignificant on these species. This moth is established on both diffuse and 

spotted knapweed in Canada, but only in western provinces. It is moderately 

abundant on spotted knapweed but has only limited impact on plant populations. 

Diffuse knapweed is rarely attacked- largely only when growing amongst spotted 

knapweed infestations. 

REDISTRIBUTION: Sweeping adults is possible though it would be difficult 

to collect many, and this method is not recommended due to the likelihood of 

causing damage during collection. The species is best transferred by placing plants 

with infested capitula into uninfested patches during early spring. Transferring 

infested seed heads may also transfer unwanted parasitoids, other seed head 

insects, or knapweed seeds. To avoid this, plants with infested capitula can be 

collected and adults reared out indoors. Refer to Additional Considerations in 

the Introduction for instructions on how to do so. Once they emerge in spring, 

adults can be transferred to new knapweed infestations in groups of 50-100. 

Establishment can be monitored by dissecting capitula for larvae from late 

summer throughout the following spring.

NOTES: Populations in western states 

and provinces of the US and Canada 

are limited by overwintering mortality, 

parasitism, and predation (frequently 

deer mice). 

diffuse spotted
54 Biological Control in Eastern North America KNAPWEEDSPelochrista medullana (Staudinger)

Brown-winged knapweed root moth

DESCRIPTION: Eggs are oval, somewhat flattened, and have a strong outer 

shell with distinct ribs. Initially they are white, but gradually turn dark yellow 

during incubation. The segmented larvae are whitish-yellow with brown head 

capsules. They are usually less than 10 mm long. Adult moths are tan to gray 

with mottled wings fringed at their tips. They can be up to 10 mm long.

a b

Pelochrista medullana a. larva in root (USDA APHIS PPQ Archive); b. adult (Bob Nowierski, 

Montana State University)(a,b bugwood.org)

LIFE CYCLE: Adults emerge throughout summer when knapweed is bolting and 

flowering. They mate within 24 hours of emergence and lay eggs primarily on 

the lower surface of rosette leaves. Females can lay up to 120 eggs in warm dry 

weather, but this can be greatly reduced by cold, rainy conditions. Larvae hatch 

7-9 days after oviposition, move to the center of the rosette, and mine into the 

root crown. Larvae feed on outer layers of root tissue, similar to Agapeta zoegana. 

Webbed tubes are produced along feeding tracks, which can be irregular, 

downward or spiralling; tunnels are lined with a silken web. There are six larval 

instars. This species seems to prefer rosette plants; larvae that feed on roots 

of flowering plants develop poorly. Larvae overwinter in roots and complete 

development in spring or early summer. Pupation occurs within webbing inside 

the root. There is one generation per year.

DAMAGE: Larval damage to the roots is similar to that caused by A. zoegana. 

Larvae reduce root storage capacity and expose the plant to pathogens, but only 

the third to sixth instars cause measurable damage. Small plants with <0.4 in (10 

mm) root diameter can be completely destroyed. Plants that survive insect attack 

usually grow smaller and produce fewer flower heads than uninfested plants. 
Biological Control in Eastern North America 55KNAPWEEDS

Lepidoptera: Tortricidae

PREFERRED HABITAT: This moth prefers hot, dry areas and dense knapweed 

patches. Knapweed populations growing in poor, coarse, or gravel soils are ideal.

RELEASE HISTORY: This species has only been released in western North 

America. Individuals from Austria and Hungary were released on diffuse and 

spotted knapweed in the western US in 1984. Individuals from Austria were 

released in western Canada on diffuse knapweed (beginning in 1982) and 

spotted knapweed (beginning in 1986 in rearing tents).

CURRENT STATUS: Pelochrista medullana attacks both diffuse and spotted 

knapweed in North America, but it is established only in the western US in 

a state not covered by this guide (MT). In MT, its preferred host is diffuse 

knapweed. Populations remain limited on both knapweed species for unknown 

reasons, causing only minimal damage at localized sites. This moth failed to 

establish on either diffuse or spotted knapweed in Canada.

REDISTRIBUTION: Populations are so small as to likely preclude redistribution. 

Where established, infested plants can be dug up (including the roots) and 

transferred to new sites in late fall or early spring. Alternatively, roots can be 

collected in fall and stored at 39-46°F (4-8°C). Two to three weeks prior to 

their normal emergence time, bring them to room temperature in rearing cages 

or breathable, clear containers. Once they emerge, adults can be transferred to 

new knapweed infestations. Releases of 50-100 individuals should be made on 

continuous, nonlinear patches of knapweed. Establishment can be monitored 

the following spring by dissecting roots for feeding larvae. Note that root 

damage without larvae present can be difficult to distinguish from other rootfeeding insects.

NOTES: Usually only one larva develops per root, likely due to intraspecific 

competition. Very large roots have been observed to contain up to four.

diffuse spotted
56 Biological Control in Eastern North America KNAPWEEDSPterolonche inspersa Staudinger

Grey-winged knapweed root moth

DESCRIPTION: Eggs are black and oval-shaped with a slightly depressed center. 

Larvae are pearly white with inflated segments and have brown head capsules. 

Pupae are enclosed in silken “chimney tubes”. Adult moths can be up to 8 mm 

long. Their wings are light brown, exhibiting a silvery sheen. Wingspans are up 

to 20 mm. When at rest, adults hold their wings close to their sides.

a b c

Pterolonche inspersa a. larva and root damage (Eric Coombs, Oregon Department of Agriculture); 

b). silken chimney tube (USDA ARS European Biological Control Laboratory); c. adult (USDA 

APHIS PPQ Archive)(a-c bugwood.org)

LIFE CYCLE: Adults emerge from late summer through early fall, mate, and 

lay eggs during their short, 15-20 day life span. Eggs are laid singly or in small 

groups on the lower surfaces of rosette leaves. A single female may lay 140+ eggs 

in her lifetime. Larvae hatch within 12 days and mine down the root, feeding on 

the root's woody central portion or soft tissue near the outer edges causes galls to 

form. There are five larval instars; third instars typically overwinter within roots 

and resume feeding the following spring. Larvae construct silken “chimney” 

tubes that extend from the galls upward to 20 mm above the soil surface, where 

they pupate. The chimneys provide easy exits for emerging adults. Pupation 

usually lasts 15 days and occurs in early summer. There is one generation per 

year.

DAMAGE: Larvae feed on roots, which interrupts the vascular flow of nutrients 

plants, thereby decreasing the plant’s biomass and flowering ability. Damaged 

roots become spongy and fragile and easily break apart. Damage attracts other 

predators, which move into the roots and provide secondary attack.

PREFERRED HABITAT: This moth prefers hot, dry sites with low to moderate 

knapweed densities. It requires a period of drought during summer, so it is only 

suited to more arid environments. Preferred soils consist of loosely compacted 

sand or gravel.
Biological Control in Eastern North America 57KNAPWEEDS

Lepidoptera: Pterolonchidae

RELEASE HISTORY: This species has only been released in western North 

America. Individuals from Austria, Hungary and Greece were released on 

diffuse knapweed in the western US in 1986. Individuals from Hungary were 

reintroduced and released on spotted knapweed in the western US in 1988. Eggs 

imported from Greece were distributed on squarrose knapweed in the western 

US in 1990. Individuals from Austria and Hungary were released on diffuse and 

spotted knapweed in western Canada in 1986.

CURRENT STATUS: Pterolonche inspersa attacks both diffuse and spotted 

knapweed in North America, but it is established only in western states and 

provinces not included in this guide. In the western US, this moth is established 

on diffuse knapweed in one region in OR where insect populations are now 

rare and provide no impact because of dramatic control of diffuse knapweed 

by Larinus spp. The moth was believed to have failed establishment on spotted 

knapweed, but it was recently recovered in very limited numbers at one site in 

MT where its impact is unknown but likely insignificant. Releases on squarrose 

knapweed failed. In western Canada, it is confirmed established only on diffuse 

knapweed, even in patches with spotted and diffuse knapweed interspersed. 

Moth populations on diffuse knapweed are moderately abundant and may stunt 

plants, though the impact due to this biocontrol agent alone remains unclear.

REDISTRIBUTION: Populations are so small as to likely preclude redistribution. 

Where established, infested plants can be dug up (including the roots and 

any attached larval chimneys) and transferred to new sites in late fall or early 

spring. Alternatively, roots can be collected in fall and stored at 39-46°F (4-

8°C). Two to three weeks prior to their normal emergence time, bring them to 

room temperature in rearing cages or breathable, clear containers. Once they 

emerge, adults can be transferred to new knapweed infestations. Releases of 50-

100 individuals should be made on continuous, nonlinear patches of knapweed. 

Establishment can be monitored the following spring by dissecting roots for 

feeding larvae. Note that root damage without larvae present can be difficult to 

distinguish from other root-feeding insects.

NOTES: Usually only one larva of this 

species develops per root, due to 

aggressive intraspecific competition. 

However, very large roots may contain 

up to four larvae. The moth can cooccur with Sphenoptera jugoslavica by 

feeding below S. jugoslavica galls. diffuse spotted
58 Biological Control in Eastern North America KNAPWEEDSTerellia virens (Loew)

Green clearwing knapweed fly

DESCRIPTION: Eggs are elongate, about 1 mm long, and shiny white. Larvae 

are plump, barrel-shaped, and white, but turn yellow-brown as they mature. 

Pupae are yellow-brown. Adults are approximately 5 mm long. They have clear 

wings and large, bright green, and iridescent eyes.

a b

Terellia virens a. larva; b. adult (a,b Eric Coombs, Oregon Department of Agriculture)

LIFE CYCLE: Adults emerge in spring when knapweed is still in the rosette or 

bolting stage. Adults feed heavily on nectar when knapweed flower heads bloom. 

Mating begins with the onset of warm weather and continues throughout 

summer. In summer and fall, females lay one to several eggs between florets in 

young flower heads. The female lays an average of 80 eggs in her lifetime and often 

marks the bracts of the flower head with a substance to discourage egg laying 

by other females. Eggs hatch in 3-5 days, and larvae feed on ripening seeds and 

receptacle tissue through three instars. Larvae overwinter within capitula, then 

pupate in chambers made of pappus in spring. Weather conditions determine 

the number of generations (one or two) of Terellia virens; however, only one 

generation has been confirmed at most North American sites. 

DAMAGE: Larvae can consume up to 90% of seed in flower heads. Seed 

consumption does not damage existing plants, but does reduce knapweed’s rate 

of spread.

PREFERRED HABITAT: This fly prefers plants on south-facing slopes and at 

dry locations.

RELEASE HISTORY: Individuals from Austria and Switzerland were released 

on spotted knapweed in the western US in 1992 and in the eastern US (MN) 
Biological Control in Eastern North America 59KNAPWEEDS

Diptera: Tephritidae

in 1994. Redistributions were attempted on purple starthistle and squarrose 

knapweed in the western US but failed to establish. Individuals from Austria and 

Switzerland were released on spotted knapweed in western Canada from 1991.

CURRENT STATUS: Terellia virens attacks and is established only on spotted 

knapweed and only in western states and provinces of the US and Canada not 

covered by this guide. In western North America, populations are limited, likely 

due to competition with Urophora spp. and Larinus spp. This fly causes only 

minor reductions in seed production with minor impact overall. In western 

Canada, T. virens established initially. No recoveries have been made in recent 

years; however, sampling times may not accurately reflect the agent’s life cycle. 

This fly is currently considered rare in BC, and impact is unknown.

REDISTRIBUTION: Sweeping adult flies is possible, though this is not always 

the best stage for collection as flies are fragile and can be damaged during 

collection. The species is best transferred by placing plants with infested capitula 

into uninfested patches during late fall or early spring. Transferring infested 

seed heads may also transfer unwanted parasitoids, other seed head insects, or 

knapweed seeds. To avoid this, plants with infested capitula can be collected 

and adults reared out indoors. Refer to Additional Considerations in the 

Introduction for instructions on how to do so. Once they emerge in spring, 

flies can be transferred to new knapweed infestations in groups of 50-100. 

Establishment can be monitored by observing adults on knapweed foliage the 

following summer during the heat of the day or by dissecting capitula for larvae 

from summer throughout the following spring. Note that feeding larvae can be 

difficult to distinguish from other knapweed fly species. Urophora species can be 

differentiated by their dark brown anal plates and by their presence within galls.

NOTES: This fly may attack diffuse knapweed, but to a much smaller extent than 

spotted knapweed. 

diffuse spotted
60 Biological Control in Eastern North America KNAPWEEDS

Unapproved Non-Indigenous Natural Enemy

Urophora jaceana L.

(Diptera: Tephritidae)

DESCRIPTION AND LIFE CYCLE: 

Adults emerge in spring to early summer, 

are up to 4 mm long, and have dark 

bodies. Wings are clear with two 

distinctly separate black bands followed 

by a “V” pattern. Females have long, 

black ovipositors. Eggs are laid in flower 

buds just starting to open. Larvae feed on 

receptacle tissue, forming woody galls. 

They are creamy white, barrel-shaped with retracting heads, and have dark anal 

plates. Larvae overwinter in galls inside the capitula; pupation occurs in spring. 

HISTORY AND CURRENT STATUS: This fly was accidentally introduced to 

Canada, likely as a contaminant of ship’s ballast. It was discovered on brown and 

black knapweed in Newfoundland and Nova Scotia by 1937 where up to 75% 

of seed heads are attacked. High fly populations decrease knapweed growth and 

seed production but result in no apparent decline in knapweed plant density. It 

was subsequently redistributed to BC in western Canada, but failed to establish. 

This species is not approved for redistribution in the US.

Urophora jaceana adult (AfroBrazilian)
Biological Control in Eastern North America 61KNAPWEEDS
62 Biological Control in Eastern North America loosestrifePurple loosestrife

Lythrum salicaria L.

SYNONYMS: purple lythrum, spiked loosestrife

ORIGIN: Native to Europe, northern Africa, Asia; introduced to North America 

in the early 1800s in ship ballast, wool, and as an ornamental or medicinal herb.

DESCRIPTION: Herbaceous, upright perennial typically growing numerous 

stems 2-9 ft tall (0.5-2.75 m) from a spreading, robust, woody root. Stems 

are squarish in cross-section with 4-6 sides. Leaves are lance-shaped, smoothmargined, stalk-less, and are 2-5 in long (5-12 cm). Leaves are usually opposite 

but may be whorled near the base. Flowers are less than 1 in across (2.5 cm) 

with 5-7 pink to purple (sometimes crumpled-looking) petals. Flowers occur in 

spiked clusters; each flower can produce well over 100 small, light-colored seeds. 

HABITAT: An invader of sunny or partially shaded wetlands, this plant can be 

found along lakes, ponds, moist roadsides, streams, rivers, and irrigation ditches/

a b

Purple loosestrife a. plant (Jennifer Andreas, Washington State University Extension); b. infestation 

(Eric Coombs, Oregon Department of Agriculture, bugwood.org)
Biological Control in Eastern North America 63loosestrife

Family Lythraceae

c d e

Purple loosestrife c. leaves and stem (Jennifer Andreas, Washington State University Extension); 

d. flowers (Richard Old, XID Services, Inc, www.xidservices.com); e. fruit and seeds stem (Gary L. 

Piper, Washington State University)(d,e bugwood.org)

canals and in swamps and freshwater tidal flats. It can tolerate a wide range of 

water levels, pH, soil, climatic conditions, and vegetation types. Consequently it 

can be problematic in seasonally wet meadows and wet prairies, and infestations 

can expand from moist locations into neighboring areas with drier conditions.

ECOLOGY: Purple loosestrife spreads primarily by seeds that are easily carried by 

water, people, and animals, but can also reproduce from buds on root fragments 

and cut stems. Seeds may remain viable for more than three years following 

dissemination, but potentially much longer. Seedlings germinate in late spring 

or early summer, and plants may flower the first year. Flowers occur in spiked 

clusters from summer to early fall. Plants die back in winter temperatures, and 

the standing dead vegetation is persistent for many years. 

BIOLOGICAL CONTROL: Since 1992, four beetles 

have been introduced and established in the US and 

Canada. Galerucella calmariensis and G. pusilla 

are the most abundant and effective; they 

defoliate plants, reduce seed production, and 

stunt plant growth. Root-feeding by Hylobius 

transversovittatus can result in plant death. 

Populations of H. transversovittatus are 

believed to be limited, but its cryptic nature 

makes assessments difficult. The flowerfeeding Nanophyes marmoratus reduces 

loosestrife seed output, which reduces 

spread. Galerucella spp. have the highest 

priority for redistribution.
64 Biological Control in Eastern North America loosestrifeGalerucella calmariensis (L.) & G. pusilla (Duftschmidt)

Black-margined loosestrife beetle & Golden loosestrife beetle

DESCRIPTION: Galerucella species cannot be distinguished in the egg or larval 

stage. Larvae are up to 5 mm long. They are greenish-yellow with darkened head 

capsules and black spots down their backs. Adults of both species are typically 5 

mm long. Adult G. calmariensis are orange-brown and typically have darkened 

edges to their hard, outer wings and a dark triangle behind their heads. Adult G. 

pusilla are light gold to orange-brown with dark antenna from the middle to the 

tips. Coloration differences develop fully only in overwintered beetles. 

a b

Adult a. Galerucella calmariensis (David Cappaert, Michigan State University, bugwood.org); b. G. 

pusilla (Eric Coombs, Oregon Department of Agriculture)

LIFE CYCLE: Overwintering adults feed on leaves and young shoot buds in early 

spring when purple loosestrife shoots emerge. Females lay up to 400 eggs in 

groups of 2-10 on stems and leaves from late spring through summer. Hatching 

larvae feed on shoot tips and then developing leaves and flowers. There are three 

larval instars. Pupation occurs in plant litter or in stem tissue if stems are in 

standing water. Adults emerge in summer, resume feeding, then overwinter in 

plant litter. There is usually one generation per year (two at some locations).

DAMAGE: Larval feeding strips photosynthetic tissue off leaves, creating a 

“window-pane” effect. Adult feeding causes a characteristic “shot-hole” defoliation 

pattern. Larval and adult feeding stunt plant growth, reduce seed production, 

and may kill plants outright over several years and at high insect densities.

PREFERRED HABITAT: Both species are established in a wide variety of climatic 

conditions. Both prefer sites without shade or dramatic water fluctuations (such 

as dam reservoirs or tidal flats). 

RELEASE HISTORY: Both species were introduced from Germany and released 

(often as a mix) throughout the US and Canada in 1992. 
Biological Control in Eastern North America 65loosestrife

Coleoptera: Chrysomelidae

c d e

Galerucella spp. c. eggs and larva; d. larval window-pane feeding (c,d Bernd Blossey, Cornell 

University); e. adult shot-hole feeding (Eric Coombs, Oregon Department of Agriculture)(c-e 

bugwood.org)

CURRENT STATUS: Throughout the US, both species are well established in 

some states but infrequent in others. Galerucella calmariensis is generally more 

abundant than G. pusilla, but the reverse is true at some sites for unknown 

reasons. High densities have heavy impact on purple loosestrife by reducing seed 

production and stunting growth. At some sites, purple loosestrife density has 

decreased up to 90%; at others purple loosestrife density remains unchanged. 

Fluctuations in purple loosestrife abundance are common for this system: as 

Galerucella populations build, greater dispersal results in increases in the weed, 

followed by increases in biocontrol agent populations. Impact is greatest in 

mixed plant communities that provide competition to recovering loosestrife. 

In Canada, both Galerucella species again often appear in a mix. Together they 

have provided excellent control throughout the majority of purple loosestrife’s 

range. Both species were initially widespread, but more recent surveys indicate 

populations at many sites now consist primarily or wholly of G. calmariensis.

REDISTRIBUTION: Adults can be collected in spring using a funnel or sweep 

nets and aspirators; new generation adults can be collected in mid-summer. 

Adults should be transferred to uninfested sites in groups of 100-200 in spring 

or groups of 2,000 in mid-summer. Establishment can be monitored the 

following year by observing shot-hole or window-pane feeding characteristic 

of adults and larvae, respectively. Eggs, larvae, and adults are also 

readily observed on foliage throughout the growing season. 

NOTES: Following mass outbreaks of Galerucella spp., 

limited spillover feeding has been observed on a few 

nontarget species. Predation and parasitism may limit 

some populations.
66 Biological Control in Eastern North America loosestrifeHylobius transversovittatus (Goeze)

Loosestrife root weevil

DESCRIPTION: Eggs are white and oval-shaped. Larvae are C-shaped, offwhite, and have brown head capsules. They can be up to 10 mm long. Adults are 

reddish-brown and have two rows of dots on their backs that are comprised of 

white hairs. They are thick insects and up to 12 mm long.

a b c

Hylobius transversovittatus a. eggs; b. larva and root damage (a,b Gary Piper, Washington State 

University, bugwood.org); c. adult (Jennifer Andreas, Washington State University Extension)

LIFE CYCLE: This species often requires two years to complete one generation. 

Overwintering larvae become more active in early spring, feeding on roots and 

filling feeding tunnels with frass. They develop through three instars. Pupation 

occurs in the root crown mainly in early summer. Emerging adults feed on 

purple loosestrife leaves and stems. Females lay eggs singly (though up to 100 

annually) in the soil or loosestrife stems. Larvae emerge in late summer, mine 

into purple loosestrife roots as they feed, and overwinter in roots. Larvae may 

feed within roots for one to two years. Adults often overwinter, and can live up 

to three years. Overwintering adults emerge after purple loosestrife sprouts in 

spring. They are most active at night, and during warm, sunny days adults hide 

in plant litter at the base of purple loosestrife plants.

DAMAGE: Adult feeding is typically not significant. Roots attacked by larvae have 

reduced reserve capacity leading to reduced plant size, lower seed production, 

and even death, especially for small root systems. Large roots can withstand 

substantial feeding pressure, however, and several larval generations will be 

necessary before significant impacts are observed.

PREFERRED HABITAT: This weevil tolerates a wide range of environmental 

conditions. Though adults and larvae can survive extended submersion, 

permanently flooded sites will prevent adult access to plants and will eventually 

kill developing larvae.
Biological Control in Eastern North America 67loosestrife

Coleoptera: Curculionidae

d e

Hylobius transversovittatus feeding damage to a purple loosestrife d. root (Bernd Blossey, Cornell 

University, bugwood.org); e. leaf (Eric Coombs, Oregon Department of Agriculture)

RELEASE HISTORY: Individuals from Germany, Finland, Austria, France, 

Sweden, and Switzerland (though largely from Germany and Finland) were 

released beginning in 1992 in the eastern US (IL, IN, IA, KS, ME, MD, MA, 

MI, MN, NE, NH, NJ, NY, ND, OH, PA, RI, SD, TN, VA, VT, WI) and 

eastern Canada (MB, NS, ON). 

CURRENT STATUS: In the eastern US this weevil is slower to disperse and 

reproduce than the other established biocontrol agents. It is believed to have 

well-established populations in NY and MN, but information is largely limited 

elsewhere. It may be well established throughout the range of purple loosestrife 

in North America. Extensive root feeding by this weevil can complement 

defoliation by Galerucella spp., often resulting in plant death. However, its 

establishment and impact are both difficult to fully assess as larvae are hidden 

feeders, and adults are active at night. In Canada, its limited populations and 

cryptic nature make this species difficult to study so its current status in Canada 

is largely unknown.

REDISTRIBUTION: Where populations are sufficiently large, adults can be 

tapped or hand-picked from purple loosestrife foliage or plant litter in mid- to 

late summer. Adults are nocturnal, so should be collected at night with the aid 

of flashlights. Because of the difficulty in this method, and because this species is 

not widely established at present, it will often be necessary to obtain 

weevils from laboratory rearing operations. Establishment 

can be confirmed the following growing season by observing 

adults on foliage at night, or (more easily) by dissecting 

roots to find larval damage over the course of the next few 

growing seasons.

NOTES: Up to 40 larvae have been found per root system.
68 Biological Control in Eastern North America loosestrifeNanophyes marmoratus (Goeze)

Loosestrife flower-feeding weevil

DESCRIPTION: Eggs are tiny, spherical, and white. Larvae are C-shaped, creamy 

white, and have brown head capsules. They can be up to 2 mm long. Adults are 

dark brown with orange legs and large, whitish-yellow shoulder patches. Adults 

are very small (up to 2.5 mm long) and have a long snout and wide body.

a b c

Nanophyes marmoratus a. egg in purple loosestrife flower; b. larva in flower bud (a,b Gary Piper, 

Washington State University); c. adult (Laura Parsons & Mark Schwarzländer, University of Idaho)

(a-c bugwood.org)

LIFE CYCLE: Overwintering adults emerge in late spring and feed on purple 

loosestrife shoot tips and young leaves. Adults then feed on developing flowering 

buds. Females lay 60-100 eggs singly inside immature flower buds throughout 

summer as purple loosestrife flowers. Hatching larvae feed on flower petals and 

ovaries through three instars. Pupation occurs in the base of attacked buds. New 

adults emerge in late summer and feed on remaining green leaves of purple 

loosestrife before overwintering in plant litter. There is one generation per year.

DAMAGE: Adult and larval feeding cause flower bud abortion which reduces 

the seed output of purple loosestrife. At high loosestrife flower weevil densities, 

larval feeding can reduce seed output of a purple loosestrife plant by up to 60%. 

This does not kill existing plants, but helps reduce the rate of spread.

PREFERRED HABITAT: This flower weevil is well adapted to a variety of 

environmental conditions throughout the range of purple loosestrife in North 

America. It does not do as well at sites with high populations of Galerucella spp. 

which often reduce the availability of Nanophyes feeding and oviposition sites.

RELEASE HISTORY: Individuals from France and Germany were released in 

the eastern US beginning in 1994 (CT, IA, IN, MN, NE, NJ, NY, PA, SD, WI). 

Weevils from Germany were released in eastern Canada (MB) in 1997. 
Biological Control in Eastern North America 69loosestrife

Coleoptera: Nanophyidae

d e

Nanophyes marmoratus d. adult exit hole in a dead purple loosestrife bud (Gary Piper, Washington 

State University); e. (right) damage resulting in 100% abortion of buds on an attacked inflorescence 

next to (left) inflorescences not attacked (S. Schooler, Oregon State University)(d,e bugwood.org)

CURRENT STATUS: In the US, N. marmoratus feeding on floral buds often 

results in bud abortion, which helps reduce purple loosestrife spread. However, 

flower weevil populations are sometimes limited due to interspecific competition 

with Galerucella spp. (defoliated purple loosestrife plants often do not flower, 

removing N. marmoratus’ food supply and oviposition sites). Though the flower 

weevil should not be released at sites with high populations of Galerucella

spp., N. marmoratus is often complementary to the leaf beetles by attacking 

flowers on purple loosestrife plants that escape defoliation. The flower weevil 

is an important biocontrol agent at sites with decreasing loosestrife and smaller 

populations of other biocontrol agents. In Canada, though the flower weevil is 

established, it only occurs in MB, and its abundance and impact are not known.

REDISTRIBUTION: During the heat of the day in summer, bend and shake 

developing purple loosestrife inflorescences over a sweep net or tray, dislodging 

adult beetles into the net or tray. Adults can be transferred to uninfested sites in 

groups of 100-200. Establishment can be monitored the following spring and 

summer by observing adults on foliage and flowers or dissecting flower buds 

during the growing season for signs of larval feeding.

NOTES: This weevil has successfully overwintered on exposed 

islands in an estuary with high tidal exchange where multiple 

releases of Galerucella spp. have failed. It can also persist 

where purple loosestrife plants are scattered at low densities. 

A related species, Nanophyes brevis, was tested and approved 

for importation but was never released in North America 

because of problems with a parasitic nematode.
70 Biological Control in Eastern North America MILFOILEurasian watermilfoil

Myriophyllum spicatum L.

SYNONYMS: spiked watermilfoil

ORIGIN: Native to Europe, northern Africa, and Asia, Eurasian watermilfoil 

was introduced possibly unintentionally in ship ballast by the 1880s or possibly 

intentionally by US federal authorities in the 1940s.

DESCRIPTION: Submersed, aquatic perennial with roots typically buried in 

the hydrosoil. Roots are slender and white and stoloniferous in the hydrosoil or 

may grow from stem nodes. Stems are slender but thicken significantly further 

away from the inflorescence. Stems are reddish-brown to light green, typically 

6-20 ft (2-6 m) long, and become more branched at the surface, forming dense 

intertwined mats. Submersed leaves occur in whorls of 4 all along the stem. Leaves 

are 0.6-1.6 in (1.5-4 cm) long and feather-like with 14-24 pairs of filamentous 

divisions. Tiny pink flowers occur on red emergent spikes 1.5-8 in (4-20 cm) long. 

Fruits are 4-chambered; each fruit produces a single seed.

a b

Eurasian watermilfoil a. plant (Chris Evans, University of Illinois); b. infestation (Graves Lovell, 

Alabama DCNR)(a,b bugwood.org)
Biological Control in Eastern North America 71MILFOIL

Family Haloragaceae

c d e

Eurasian watermilfoil c. leaves (Graves Lovell, Alabama DCNR); d. fragment (Rob Routledge, Sault 

College); e. flowers on center spike (Leslie J. Mehrhoff, University of Connecticut)(c-e bugwood.org)

HABITAT: This species grows in freshwater lakes, ditches, springs, marshes, and 

rivers with slow-moving water. It can grow in water depths from a few inches 

(7.5 cm) to 33 ft (10 m). It can tolerate a wide variety of temperatures and 

brackish water and capitalizes on disturbance and nutrient runoff.

ECOLOGY: Eurasian watermilfoil produces seeds, though seedlings are rare in 

the field. It primarily reproduces vegetatively. New stems grow from stolons and 

roots in spring. Throughout the growing season and especially after flowering, the 

plant auto-fragments. Stem fragments containing a single node (whorl of leaves) 

can sprout new plants; segments grow roots prior to separating from the parent 

plant. Flowering typically occurs in summer. At some locations, plants flower 

both in late spring and early fall. In warm climates, the plant continues to grow 

over the winter. At extremly cold sites, stems die back to the stolons, lower stem 

segments, and roots, and new stems re-sprout the following spring. 

BIOLOGICAL CONTROL: Despite extensive 

foreign exploration, as of 2016, there are no 

classical biocontrol agents approved for use in 

North America. The native weevil Euhrychiopsis 

lecontei has been redistributed extensively, 

suppressing Eurasian watermilfoil in some lakes 

but not others. It feeds on native Myriophyllum

spp. when densities are high; caution should 

be used in redistribution. The accidentally 

introduced Acentria ephemerella is widely 

distributed in NE North America, but with 

variable impacts. It feeds on many native 

species and isnot approved for redistribution. 
72 Biological Control in Eastern North America MILFOIL

Native Natural Enemy

Euhrychiopsis lecontei (Dietz)

(Coleoptera: Curculionidae)

DESCRIPTION AND LIFE CYCLE: 

Adults are 3 mm long and dark with 

black and yellowish mottled stripes. 

Adults feed on leaves and stems. 

Females lay hundreds of eggs singly on 

milfoil stems. Larvae are whitish tan 

turning purplish gray. They feed on 

stem tips and mine plant stems before 

pupating in chambers within stems. 

There are up to 5 generations per year, 

though 3 is more common in the field. In late summer, adults move to shore to 

overwinter in leaf litter.

HISTORY AND CURRENT STATUS: The original host of this weevil is the 

native northern milfoil Myriophyllum sibiricum. After it was found feeding on 

and suppressing Eurasian watermilfoil, the weevil was redistributed to Eurasian 

watermilfoil in multiple states in the US (previously commercially available). 

While E. lecontei occurs naturally in Canada on northern watermilfoil, it has not 

been redistributed there for Eurasian watermilfoil control. The weevil is widely 

distributed throughout North America and is associated with weed declines in 

some lakes in the Northeast but not in others. High weevil densities can suppress 

Eurasian watermilfoil populations; however, most infestations can potentially 

recover when weevils move to shore for overwintering. Augmentation with larvae 

and/or eggs has proven ineffective, but augmentation with adults increases weevil 

densities the year following release. Although this weevil does best on Eurasian 

watermilfoil, it feeds on native Myriophyllum spp. when densities are high. 

Redistributions are recommended only for water bodies where native milfoil 

species are limited or absent. Caution should be used in redistribution, and 

an APHIS 526 permit is required for transporting E. lecontei interstate.

Euhrychiopsis lecontei adult (Robert L. 

Johnson, Cornell University, bugwood.org)
Biological Control in Eastern North America 73MILFOIL

Unapproved Non-Indigenous Natural Enemy

Acentria ephemerella (Denis & Schiffermüller)

(Lepidoptera: Crambidae)

DESCRIPTION AND LIFE CYCLE: 

Adults are 5-9 mm long and white to 

tan. Females are typically wingless and 

lay 100-300 eggs on host plants in early 

summer. Larvae are up to 12 mm long 

and greenish-transparent. Larvae mine 

plant leaflets until large enough to build 

shelters of plant material. 4th-5th instars 

feed on stem tips before pupating within 

cocoons attached to plant stems. There 

are two generations per year; new adults emerge in late summer and hatching 

larvae overwinter in various instars.

HISTORY AND CURRENT STATUS: This aquatic European moth was 

first found in QC, CAN in 1927 and MA, US in 1949. It was intentionally 

redistributed in NY, US from 1999-2002. Though now widely distributed, its 

abundance varies. High populations control Eurasian watermilfoil in some lakes 

by preventing weed canopy growth, but not in others; augmentative releases 

do not improve populations or control. Although testing indicated it prefers 

and does better on Eurasian watermilfoil, it feeds on other aquatic species, 

including many native, and is not approved for redistribution in the US. 

Acentria ephemerella winged female (Robert L. 

Johnson, Cornell University, bugwood.org)
74 Biological Control in Eastern North America swallow-wortsBlack swallow-wort

Vincetoxicum nigrum (L.) Moench

SYNONYMS: black dog-strangling vine, Cynanchum louiseae Kartesz & Gandhi

ORIGIN: Native to France, Spain, Portugal and Italy, it was intentionally introduced 

to North America in the late 1800s as an ornamental and subsequently naturalized.

DESCRIPTION: Herbaceous, perennial, twining vine with single or multiple 

stems growing from an extensive fleshy, fibrous root system with rhizomes. 

Stems are erect initially, but as plants mature they twine around adjacent 

vegetation or each other for support, often forming impenetrable thickets. Vines 

are typically 2-6.5 ft long (60-200 cm), though in shaded understories, plants 

often grow longer. Stems have hairs in longitudinal bands and are green but turn 

brown with age. Leaves are opposite, up to 4.8 in long (12 cm), elliptical with 

a pointed tip, and rounded or heart-shaped at their base. Leaves on some plants 

may appear glossy. Flowers are up to 0.25 in across (7 mm), star-shaped, and 

have 5 fleshy petals. Petals are purplish-black with white hairs and are wide at 

their base. Flowers appear in clusters of 6-10 at leaf axils. Fruits are thin pods up 

a b

Black swallow-wort a. climbing plants; b. infestation (Leslie J. Mehrhoff, University of Connecticut, 

bugwood.org)
Biological Control in Eastern North America 75swallow-worts

Family Apocynaceae

c d e

Black swallow-wort c. leaves and stems; d. flowers; e. mature fruit and splitting fruit (c-e Leslie J. 

Mehrhoff, University of Connecticut, bugwood.org)

to 2.7 in long (7 cm) that often occur in pairs and at maturity split open along 

one side to release multiple tufted, wind-borne seeds.

HABITAT: Black swallow-wort has a temperate distribution, and germination rates 

are highest where seeds are subjected to cold winter temperatures. It tolerates a wide 

range of light and moisture conditions from sunny and dry to moist and wooded. 

It capitalizes on disturbance but can invade undisturbed plant communities. It is 

often found at upland sites such as rocky hillsides or forested slopes or in/along 

roads, fields, alluvial woods, forest understories, and riverbanks.

ECOLOGY: Black swallow-wort reproduces by seed and rhizomes. Seed 

production is greatly reduced under low light conditions. A single seed may yield 

up to 4 seedlings. In North America, seeds germinate throughout the growing 

season. Flowers appear from June to August, and fruits are produced from July 

through October. Seeds are transported by wind, and 

seed longevity is unknown. Plants die back in the fall 

and re-sprout from the root system in spring.

BIOLOGICAL CONTROL: As of 2016, 

Hypena opulenta has been approved by TAG 

for release on both black and pale swallowwort, but a release permit has not yet been 

issued in the US. Releases in Canada to 

date have occurred only on pale swallowwort. Additional species are being tested for 

potential future release in North America.
76 Biological Control in Eastern North America swallow-wortsPale swallow-wort

Vincetoxicum rossicum (Kleopow) Barbar.

SYNONYMS: dog-strangling vine, European swallow-wort, Cynanchum rossicum 

Kleopow

ORIGIN: Native to Ukraine and Russia, it was intentionally introduced to North 

America in the late 1800s as an ornamental and subsequently naturalized.

DESCRIPTION: Herbaceous, perennial, twining vine with single or multiple 

stems growing from an extensive fleshy and fibrous root system. Some plants 

produce short, horizontal, woody rhizomes. Stems are erect initially, but as plants 

mature they twine around adjacent vegetation or each other for support, often 

forming impenetrable thickets. Vines are typically 2-6.5 ft long (60-200 cm), 

though in shaded understories, plants often grow longer. Stems have hairs in 

longitudinal bands and are green but turn brown with age. Leaves are opposite, 

up to 4.8 in long (12 cm), elliptical with a pointed tip, and rounded or heartshaped at their base. Leaves on some plants may appear glossy. Flowers are up 

to 0.25 in across (7 mm) and star-shaped with 5 narrow petals that are maroon, 

a b

Pale swallow-wort a. climbing plant (David Nisbet, Invasive Species Centre); b. infestation (John 

M. Randall, The Nature Conservancy)(a,b bugwood.org)
Biological Control in Eastern North America 77swallow-worts

Family Apocynaceae

c d e

Pale swallow-wort c. leaves and stems; d. flowers (John M. Randall, The Nature Conservancy); e. 

mature, splitting fruit (c,e Leslie J. Mehrhoff, University of Connecticut)(c-e bugwood.org)

purple, or pinkish. They appear in clusters of 4-6 at leaf axils. Fruits are thin 

pods up to 2.7 in long (7 cm) that often occur in pairs and at maturity split open 

along one side to release approximately 20 tufted, wind-borne seeds.

HABITAT: Pale swallow-wort has a temperate distribution, and germination rates 

are highest where seeds are subjected to cold winter temperatures. It tolerates a 

wide range of light and moisture conditions, but does best in partial to full sun. 

It capitalizes on disturbance but can invade undisturbed plant communities. 

It is found in or along fields, fencerows, talus slopes, alluvial woods, forest 

understories, forest openings, and riverbanks.

ECOLOGY: Pale swallow-wort’s short rhizomes do not significantly contribute to 

population spread. This species reproduces primarily by seed, and a single seed 

may yield up to 4 seedlings. Seed production is greatly reduced under low light. In 

North America, seeds germinate throughout the growing 

season. Flowers appear from May to June, and fruits are 

produced from June through August. Seeds 

are transported by wind, and seed longevity is 

unknown. Plants die back in the fall and resprout from the root system in spring.

BIOLOGICAL CONTROL: As of 2016, 

Hypena opulenta has been approved by TAG, 

but a release permit has not been issued in 

the US. It was released in Canada in 2013; 

evidence for establishment is encouraging. 

Additional species are being tested for 

potential future release in North America.
78 Biological Control in Eastern North America swallow-wortsHypena opulenta (Christoph)

Ukranian swallow-wort moth

DESCRIPTION: Eggs are small and pale yellow. Larvae are white initially but 

gradually turn green. At maturity, larvae are up to 2 cm long and have a yellow 

head capsule as well as black spots on their green bodies. Pupae are dark brown 

and up to 2 cm long. Adults are up to 1 cm long with a 3 cm wide wingspan. 

The forewings are light brown with dark brown centers while the hindwings are 

pale yellow with brown edges.

a b

Hypena opulenta a. larva (Rob Bourchier, Agriculture and AgriFood Canada); b. adult (Jeem 123, 

voucher speciment provided by Naomi Cappuccino, Carleton University)

LIFE CYCLE: Pupae overwinter in soil and plant litter. Adults emerge in spring 

and lay an average of 400 eggs in small groups on swallow-wort leaf petioles or 

the undersides of leaves. Hatching larvae feed on swallow-wort leaves through 

five instars. Early instars skeletonize leaves while later instars feed on all leaf 

tissue between veins. Fifth instars prepare pupation sites in the soil either by 

tying leaves together or by constructing a silk chamber at the base of plants. 

Adults emerge in late summer, resume feeding, then overwinter in plant litter. 

In the native range, there are at least two generations per year, with generations 

overlapping.

DAMAGE: Defoliation by larvae reduces plant biomass and reproductive output. 

Repeated defoliation may lead to reductions in root biomass.

PREFERRED HABITAT: In its native range, Hypena opulenta is restricted to 

shady, forested habitats.

RELEASE HISTORY: Individuals from Ukraine were released on pale swallowwort in Ontario, Canada in 2013 and 2014.
Biological Control in Eastern North America 79swallow-worts

Lepidoptera: Erebidae ?

CURRENT STATUS: While this moth attacks both black and pale swallowwort, it has thus far only been released on pale swallow-wort in North America. 

The 2013 release failed to result in establishment; however, following releases 

made in 2014-2016, subsequent generations were observed in the field. Though 

it is too early to confirm the field establishment of this species, initial observations 

are encouraging.

REDISTRIBUTION: Because populations are not currently confirmed to be 

established in the field, further releases are recommended. Any releases made 

should be done using laboratory colonies and under the guidance of appropriate 

authorities. In the future, should this biocontrol agent become established, field 

redistributions can be done by collecting larvae from foliage. Any instar can be 

collected, though larger, mature larvae are most conspicuous and easy to find. 

Gently remove larvae by hand or with soft forceps, and place them directly in 

a release container. Alternatively, clip vine sections infested with larvae. This 

species can be transferred in groups of 50-100 to uninfested swallow-wort 

patches. Establishment can be monitored by observing adults or larvae on 

swallow-wort foliage throughout the following growing season.

NOTES: Although Hypena opulenta is a biological control agent of both black 

and pale swallow-wort, releases in Canada to date have occurred only on pale 

swallow-wort. As of 2016, TAG has approved release of this insect on both pale 

and black swallow-wort in the US, but it is still within the US regulatory process 

and a release permit has not yet been issued.

pale
80 Biological Control in Eastern North America thistlesThistle species comparison

Bull, Canada and musk thistle are the primary targets of North American thistle 

biocontrol efforts. Weed descriptions and biocontrol agent distribution maps are 

given only for these three species. Below is a comparison of bull, Canada, and musk 

thistle, as well as six other exotic thistles that are occasional hosts to biocontrol agents. 

Trait

Bull

Cirsium vulgare

Canada

Cirsium arvense

Musk

Carduus nutans

Marsh

Cirsium palustre

Life

History

Biennial Perennial Biennial Biennial 

Preferred

Habitat

Various light/

soil conditions; 

Mesic

Disturbed 

initially; Moist

Disturbed 

initially; Fertile 

soil; Mesic

Acidic soil; 

Moist

Avg Height 3’ (0.9 m) 3’ (0.9 m) 5’ (1.5 m) 4’ (1.2 m) 

Basal

Leaves

3-12” long (7.6-

30 cm); Lobed; 

Coarsely hairy; 

Yellow spines 

from midrib and 

lobes

≤5” long (13 

cm); Slightly 

downy lower 

surface; Lobed; 

Prickly, ruffled 

margins 

≤20” long (51 

cm); Hairless, 

waxy, white 

margins; 

Coarsely lobed; 

White spines on 

margins and lobe 

tips

≤8” long (20 

cm);

Deeply lobed, 

strong midvein;

Prominent 

spines on 

margins but not 

leaf surfaces

Stems Spiny along 

entire length Not spiny

Spiny wings 

along lower 

sections, not 

upper

Spiny wings 

along entire 

length

Capitulum

Diameter 1.5” (3.75 cm) 0.5” (1.25 cm) 3” (7 cm) 0.5” (1.25 cm) 

Bracts Spiny; Tipped in 

yellow Not spiny

End in small 

spines; Wide, 

triangular; 

Purple at 

maturity

Not spiny; 

Purplish

Capitulum
Biological Control in Eastern North America 81thistles

Credits: Bull: Jennifer Andreas, Washington State University Extension; Canada: Richard Old, 

XID Services, Inc, www.xidservices.com; Musk & Italian: Mary Ellen (Mel) Harte, bugwood.org; 

Marsh: © Malcolm Storey, www.bioimages.org.uk; Plumeless: Becca VanKampen, MIA Consulting; 

Slenderflower: Washington State Noxious Weed Control Board; Milk: Eric Coombs, Oregon 

Department of Agriculture; Scotch: Rachel Winston, MIA Consulting

Italian

Carduus 

pycnocephalus

Plumeless

Carduus 

acanthoides

Slenderflower

Carduus 

tenuiflorus

Milk

Silybum 

marianum

Scotch

Onopordum 

acanthium

Annual Annual Annual Annual Biennial

Disturbed, 

open; High 

pH soil; Dry

Disturbed; 

Well-drained 

soil; Mesic

Open areas; 

Fertile soil; Dry

Disturbed 

initially; Fertile 

soil; Mesic

Disturbed; 

Well-drained 

soil; Dry

4’ (1.2 m) 3.5’ (1 m) 3.5’ (1 m) 5’ (1.5 m) 7’ (2 m)

≤5” long (13 

cm); Deeply 

lobed; Short 

matted hairs 

on undersides; 

Spines on 

lobe tips and 

margins

≤8” long (20 cm);

Deeply lobed 

to midvein; 

Hairy 

underside;

1-3 spines on 

margins of 

each lobe

≤5” long (13 

cm); Deeply 

lobed; Short 

matted hairs on 

undersides; Spines 

on lobe tips and 

margins

≤20” long (51 

cm); Waxy, 

white marbling 

along veins; 

Lobed; Prickly, 

ruffled margins 

≤24” long (61 

cm); Woolly 

above and 

below; Graygreen; Yellow 

spines along 

wavy toothed 

margins

Slightly 

winged and 

spiny along 

entire length

Leaf-like spines 

covering stems 

entire length

Triangular-shaped 

stem wings tipped 

with spines along 

entire length

Not spiny

Spiny wings 

along entire 

length

≤ 1” (2.5 cm) ≤ 1” (2.5 cm) <1” (2.5 cm) 2’ (5 cm) 2’ (5 cm)

Triangular; 

Long; Have 

stiff, forwardpointing hairs; 

Cobwebby

Spiny; NeedlelikeSpiny; Triangular 

but narrow

Tipped in 

very long 

stiff spines; 

Leathery

Spiny; Needlelike; Tipped in 

yellow
82 Biological Control in Eastern North America thistlesBull thistle

Cirsium vulgare (Savi) Ten.

SYNONYMS: spear thistle 

ORIGIN: Native to Europe, Asia, and northern Africa; introduced to North 

America in the mid 1800s. 

DESCRIPTION: An upright forb typically growing as a biennial, but can also 

behave as an annual or very short-lived perennial. Plants grow from 3-4 ft (1-

1.2 m) tall on average. Leaves are long (3-12 in or 8-30 cm), lance-shaped, and 

lobed, with coarse hairs covering both surfaces. Long, yellow spines extend from 

the midrib and at each leaf lobe. Stems are stout, hairy, and have spiny wings. 

Capitula are 1.5-2 in (4-5 cm) in diameter, have rows of narrow, spiny bracts 

tipped in yellow, purplish pink florets, and are solitary at the ends of branches.

HABITAT: Bull thistle grows best on neutral soils rich in nitrogen and with moderate 

moisture. It is not typically found in sand, pure clay, or in soils with high humus 

a b

Bull thistle a. plant (Marianna Szucs, Colorado State University); b. infestation (Forest and Kim 

Starr, Starr Environmental, bugwood.org)
Biological Control in Eastern North America 83thistles

Family Asteraceae

c d e

Bull thistle c. leaf (Dan Tenaglia, Missouriplants.com, bugwood.org); d. stem; e. flower head (d,e 

Jennifer Andreas, Washington State University Extension)

content, nor does it grow well in shade and drought. It can be found in almost 

any type of disturbed area including forest clear cuts, riparian areas, and pastures.

ECOLOGY: This species reproduces only by seed. Seeds are readily transported 

by water, wildlife, and human activity and may remain viable in the soil for 

many years. Seeds germinate and form rosettes whenever moisture is sufficient, 

but the majority of rosettes form during spring. Bolting occurs in late spring, 

and plants flower in early to mid-summer (typically June to July).

BIOLOGICAL CONTROL: While five species of thistle biocontrol agents are 

established on bull thistle in North America, Urophora stylata is the most effective. 

This fly reduces seed production which helps reduce bull thistle populations, 

especially where the plant is stressed by competition and other control methods. 

Cheilosia grossa, Larinus carlinae, Rhinocyllus conicus, and Trichosirocalus horridus

preferentially attack other species, and their impact on 

bull thistle is minor. Cheilosia grossa and L. carlinae are 

established on bull thistle only in western 

North America. Larinus carlinae, R. conicus, 

and T. horridus are no longer permitted for 

interstate redistribution in the US, and 

C. grossa is not approved for release in 

Canada.

NOTES: Phenolic acids produced by this 

thistle have allelopathic effects against 

competing plants and (along with spines) 

serve as a defense against herbivory.
84 Biological Control in Eastern North America thistlesCanada thistle

Cirsium arvense (L.) Scop.

SYNONYMS: creeping thistle, field thistle 

ORIGIN: Introduced from Eurasia in the 1600s. 

DESCRIPTION: An upright perennial forb often found in dense infestations. 

Plants grow from 1-4 ft tall (0.3-1.2 m) from a rhizomatous root system. Leaves 

are irregularly lobed and have very prickly and ruffled margins. They are green 

on both sides with a slightly downy lower surface. Basal leaves are less than 5 in 

long (12.5 cm). Leaves grow alternately along the slender, grooved stems which 

can be finely haired but are not spiny. Upper branches are topped by clusters 

of small, compact (0.5 in or 1.25 cm diameter) capitula producing numerous 

tufted seeds. Receptacle bracts are not spiny. Florets vary in color from white to 

deep lavender.

HABITAT: This species rapidly colonizes disturbed moist sites including prairies, 

meadows, ditches, stream banks, lawns, and agricultural fields. 

a b

Canada thistle a. plants (Steve Dewey, Utah State University); b. infestation (Jan Samanak, 

Phytosanitary Administration)(a,b bugwood.org)
Biological Control in Eastern North America 85thistles

Family Asteraceae

c d e

Canada thistle c. leaf (Jennifer Andreas, Washington State University Extension); d. stem (Rob 

Routledge, Sault College); e. flower head (Richard Old, XID Services, Inc, www.xidservices.com)

(d,e bugwood.org)

ECOLOGY: Canada thistle reproduces both vegetatively through its roots and 

by seed. Seeds are readily transported by water, wildlife, and human activity 

and may remain viable in the soil for many years. Seeds germinate whenever 

moisture is sufficient, though the majority of rosettes are formed in spring. 

Stems bolt in late spring with flowering occurring from June to September.

BIOLOGICAL CONTROL: Four species successfully established on this 

weed. Of these, Hadroplontus litura, Urophora cardui, and Larinus carlinae 

attack Canada thistle in eastern North America. While both H. litura and U. 

cardui can reduce Canada thistle density and stature under favorable conditions, 

the impact of both is typically limited overall. The impact of L. carlinae is 

often greater on native thistles than Canada thistle; it is not approved for 

redistribution in the US. Rhinocyllus conicus is established on Canada thistle 

only in western states and provinces not included in this 

guide; it preferentially attacks other thistle species 

and is not approved for redistribution in 

the US. Altica carduorum and Lema cyanella 

both failed to establish in North America. 

NOTES: This species is dioecious; the florets 

on all flowering shoots of a single clonal 

plant are either male or female. This trait 

is unique among North American exotic 

thistles. At some sites, infestations consist of 

plants of only one sex.
86 Biological Control in Eastern North America thistlesMusk thistle

Carduus nutans L.

SYNONYMS: nodding thistle, nodding plumeless thistle; Carduus thoermeri

(Weinman)

ORIGIN: Native to Europe, Asia, and northern Africa; introduced to North 

America in the mid 1800s. 

DESCRIPTION: Upright, herbaceous biennial typically growing 5-6 ft tall (1.5 

to 1.8 m) from a fleshy taproot. Leaves are dark green, hairless, waxy and have 

characteristic white margins. Leaves are also coarsely lobed with white spines 

along margins and at lobe tips. Basal leaves are up to 20 in long (50 cm); stem 

leaves are smaller, grow alternately, and lightly clasp the stem. Stems are stout, 

highly branched, and have spiny wings along their lower sections but not their 

upper portions. Flower heads are up to 3 in (7 cm) in diameter, are solitary at 

stem tips, and produce numerous tufted seeds. They droop or “nod” when fully 

developed and have rows of wide, triangular bracts that end in small spines and 

are purple at maturity. Florets are magenta.

a b

Musk thistle a. plant (Stefan Lefnaer); b. infestation (Marianna Szucs, Colorado State University)
Biological Control in Eastern North America 87thistles

Family Asteraceae

c d e

Musk thistle c. leaf (Rachel Winston, MIA Consulting); d. stem; e. flower head (d,e Mary Ellen 

(Mel) Harte, bugwood.org)

HABITAT: This species readily invades pastures, roadsides, ditches, and meadows. 

It grows best in disturbed, neutral to acidic soils with moist conditions. 

ECOLOGY: Musk thistle spreads only by seed. Seeds are readily transported by 

water, wildlife, and human activity and may remain viable in the soil for many 

years. Rosettes usually form in spring, with plants bolting by early summer. 

Flowering occurs throughout summer.

BIOLOGICAL CONTROL: Urophora solstitialis is established on musk thistle 

in eastern Canada, but only with low populations/impact. Rhinocyllus conicus and 

Trichosirocalus horridus are effective at some sites when used in combination and 

in conjunction with plant competition. Both species are no longer approved 

for interstate transport in the US. Cheilosia grossa and L. carlinae are established 

on musk thistle, but only with low populations/impact and only in western 

North America. Cheilosia grossa is not approved for 

release in Canada, and L. carlinae is not approved for 

redistribution in the US. The beetle Psylliodes 

chalcomera failed to establish in the US and was 

not released in Canada.

NOTES: Carduus nutans is part of a variable 

complex that has been treated as one to several 

species or, more recently, as a single species 

with several subspecies. Various intermediates 

are evident, and many specimens cannot be 

reliably assigned. In the US, subspecies 

include nutans, leiophyllus (= Carduus 

thoermeri), and macrocephalus.
88 Biological Control in Eastern North America thistlesUrophora stylata (L.)

Bull thistle seedhead gall fly

DESCRIPTION: Larvae are barrel-shaped, off-white, and have dark anal plates. 

They can reach lengths of 5 mm at maturity. Adults are brownish gray with a 

yellow head and brownish legs. Wings are clear and with a gray-brown “IV” 

marking, the “V” being near the tip of the wing. Adult males can be up to 5 mm 

long while females can be 7 mm.

a b

Urophora stylata a. larvae in seed head; b. adult (a,b Peter Harris Agriculture and Agri-Food Canada, 

bugwood.org)

LIFE CYCLE: Overwintering larvae pupate in galls in spring when bull thistle 

plants are bolting. Adults emerge in early summer and deposit eggs on maturing 

bull thistle buds. Hatching larvae burrow into seed heads and feed on seedproducing tissue, inducing the formation of galls. There may be multiple 

larvae per seed head. Third (final) instars overwinter within galls. There is one 

generation per year.

DAMAGE: Larval feeding reduces seed production which can help reduce the 

rate of bull thistle spread. Seeds in infested seed heads are physically stuck to 

gall tissue, thereby reducing dispersal further. Galls from larval feeding act as 

metabolic sinks, diverting resources away from normal plant development.

PREFERRED HABITAT: Urophora stylata does best in open meadows with 

scattered plants. It does not do as well in dense stands of thistle or at sites with 

flooding and high winds. 

RELEASE HISTORY: Individuals from Germany and Switzerland were released 

on bull thistle in Canada beginning in 1973 (NS, ON, QC). A second shipment 

from Austria and France was released in QC in 1976, but it failed to establish. 
Biological Control in Eastern North America 89thistles

Diptera: Tephritidae

Individuals established in Canada were redistributed to bull thistle throughout 

the western US and MD, US beginning in 1983.

CURRENT STATUS: Urophora stylata attacks only bull thistle in North America. 

In the US, it is established only in western states where its abundance and impact 

on bull thistle vary. Most populations are cyclical or limited. From 60-90% of 

seed heads are attacked in some areas, which has reduced seed production by up 

to 60%. However, in general, it is difficult to maintain high fly populations on 

the short-lived bull thistle. In Canada, this fly naturally dispersed from all release 

sites and is now abundant on bull thistle. The weed has decreased at most sites, 

likely due to a combination of land use and attack by U. stylata and Rhinocyllus 

conicus.

REDISTRIBUTION: Sweeping adult flies is possible, though may be damaging. 

Instead, place capitula infested with galls into uninfested patches during fall 

or early spring. Transferring infested seed heads may also transfer unwanted 

parasitoids, insects, or bull thistle seeds. To avoid this, plants with infested 

capitula can be collected and adults reared out indoors. Refer to Additional 

Considerations in the Introduction for instructions on how to do so. Once they 

emerge in spring, adult flies can be transferred to uninfested bull thistle patches in 

groups of 50-100. Establishment can be monitored by observing adults on thistle 

foliage the following summer or by dissecting capitula for larvae from summer 

throughout the following spring. Alternatively, squeezing capitula between the 

thumb and forefinger from late fall through spring can quickly indicate larval 

presence. Those infested with galls will feel very firm, while uninfested capitula 

readily give when pressure is applied, and they easily fall apart.

NOTES: Bull thistle is short-lived and populations follow disturbance patterns, 

typically not lasting long in the same location. Consequently, it is difficult to 

maintain large populations of U. stylata. Very small numbers are occasionally 

reared from Canada thistle in western Canada.

bull
90 Biological Control in Eastern North America thistlesHadroplontus litura (Fabricius)

Canada thistle stem weevil

SYNONYMS: Ceutorhynchus litura (Fabricius)

DESCRIPTION: Larvae are white, C-shaped, and may be pointed in the front 

end. They grow up to 3 mm long and have brown head capsules. Adults are 

mottled black and white with a “T”-shaped marking on their backs. The adults 

have long snouts and can be up 4 mm long.

a b c

Hadroplontus litura a. larvae in stem; b. adult (Laura Parsons, University of Idaho); c. stem-mining 

damage (a,c Norman E. Rees, USDA ARS)(a-c bugwood.org)

LIFE CYCLE: Overwintering adults emerge from plant litter and feed on Canada 

thistle leaf and stem tissue in early spring. Eggs are laid in spring in the midvein on the underside of new rosette leaves. Emerging larvae mine leaf veins, 

stems, and root crowns of target plants throughout spring and summer. They 

develop through three larval instars before pupating in the soil. Emerging adults 

overwinter in plant litter. There is one generation per year.

DAMAGE: Larval mining and adult feeding do not significantly impact weed 

populations directly as only non-essential tissues are typically consumed. Feeding 

does cause secondary damage, however, as pathogens and other organisms enter 

stems of targeted plants via holes made by exiting larvae.

PREFERRED HABITAT: This stem weevil does well in moist, disturbed areas 

where target thistles are dense and not stressed by drought, grazing, or other 

control methods. 

RELEASE HISTORY: Populations from Germany were released on Canada 

thistle in the eastern US from 1971 (MD, NJ, NY, SD). Populations from 

France, Germany, Italy and Switzerland were released in eastern Canada from 

1965 (MB, NB, NS, ON, PEI, SK).
Biological Control in Eastern North America 91thistles

Coleoptera: Curculionidae

CURRENT STATUS: Attacks only Canada thistle in North America. In the US, 

some reports indicate this beetle is very effective due to reduced overwintering 

survival of the weed; however, most studies show a lack of impact, likely due 

to only non-essential parenchyma tissue being consumed by larvae, leaving 

vascular tissues untouched. Though this weevil is established at most release 

sites on Canada thistle in Canada, the weevil has low reproductive and dispersal 

ability so populations are typically small. Mining over multiple years decreases 

root biomass, when in conjunction with other stresses. Even in combination 

with other biocontrol agents, overall impact is limited.

REDISTRIBUTION: Adults can be collected with a sweep net and aspirator 

during spring when host plants are bolting. Releases of 200 adults should 

be made on on uninfested patches of Canada thistle. Establishment can be 

monitored the following spring by observing adults on thistle foliage, or during 

summer by checking for larvae feeding within plant stems. 

NOTES: Some populations are infected with Nosema pathogens. Infected 

populations should not be used in redistribution efforts.

Canada
92 Biological Control in Eastern North America thistlesUrophora cardui (L.)

Canada thistle stem gall fly

DESCRIPTION: Larvae are barrel-shaped, white, and have dark brown anal 

plates. They can be up to 5 mm long at maturity. Adults have dark bodies and 

dark bands on their white wings that form a ‘W’. Adults can be up to 8 mm 

long.

a b c

Urophora cardui a. larvae in gall (Eric Coombs, Oregon Department of Agriculture); b. adult (Laura 

Parsons, University of Idaho); c. gall (Jennifer Andreas, Washington State University Extension)

LIFE CYCLE: Larvae overwintering inside galls pupate in early spring. Adults 

emerge in late spring and early summer when new plants are flowering. Eggs are 

deposited on plant shoots in axillary buds throughout summer. Hatching larvae 

burrow into stems and cause galls to form. There are often multiple larvae in 

one gall. Larvae overwinter in the third (final) instar, with pupation occurring in 

early spring as plants start bolting. There is one generation per year.

DAMAGE: Larval feeding causes gall formation. Galls act as metabolic sinks, 

diverting resources away from normal plant development. Attacked plants 

produce fewer seeds, are less competitive, and may be more susceptible to 

pathogens and other insects.

PREFERRED HABITAT: This fly does well in moist, open and partially shaded 

areas where its host plant is scattered, especially areas with high grass competition. 

Areas subject to other means of control (grazing, mowing, chemical treatment, 

etc.) are not suitable for this fly’s survival. 

RELEASE HISTORY: Individuals from Austria and France were released on 

Canada thistle in the US beginning in 1977 (IA, MD, SD from 1981). Flies 

from Austria, France, and Germany were released on Canada thistle in Canada 

in 1974 (NB, NS, ON, PEI, QC beginning in 1975). An additional strain from 

Finland was released in western Canada in 1987.
Biological Control in Eastern North America 93thistles

Diptera: Tephritidae

CURRENT STATUS: Urophora cardui attacks only Canada thistle in North 

America. It is moderately abundant in the US, through primarily in western 

states not covered in this guide. Attacked plants may be stunted and produce 

fewer seeds, especially when galls occur at terminal growing tips; however, the 

overall impact is largely limited. The fly is often restricted to shaded infestations, 

close to riparian areas. In Canada, populations vary by location and year but 

are highest in areas with sheltering canopy, near water, and in climates with 

mild winter temperatures. Under favorable conditions this fly can reduce 

Canada thistle density and stature. In other areas, even in combination with 

Hadroplontus litura, this fly has no measurable impact.

REDISTRIBUTION: Sweeping adult flies is possible, though may be damaging. 

Instead, place gall-infested plants into uninfested patches during fall or early 

spring. Transferring infested plants may also transfer unwanted parasitoids, 

insects, or Canada thistle seeds. To avoid this, gall-infested plants can be 

collected and adults reared out indoors. Refer to Additional Considerations in 

the Introduction for instructions on how to do so. Once they emerge in spring, 

adult flies can be transferred to new Canada thistle infestations in groups of 50-

100. Establishment can be monitored by observing adults on thistle foliage the 

following spring or by finding the characteristic large, swollen galls created by 

larval feeding throughout summer and fall. 

NOTES: Galls and/or larvae within them are often preyed upon by rodents, birds, 

and an unidentified mite. Though Urophora larvae can be difficult to distinguish, 

the characteristic swollen galls help to easily differentiate U. cardui from other 

thistle-attacking Urophora species.

Canada
94 Biological Control in Eastern North America thistlesUrophora solstitialis (L.)

Musk thistle seedhead fly

DESCRIPTION: Larvae are barrel-shaped, off-white, and have dark anal plates. 

They can reach lengths of 4 mm at maturity. Adults are brownish-black with a 

yellow head and legs. Wings are clear and with two black “VII” markings, the 

“V” being near the tip of the wing. Adults are 3-5 mm long, and females have 

long, pointed, black ovipositors..

a b

Urophora solstitialis a. larvae in seed head (Peter Harris Agriculture and Agri-Food Canada); b. adult 

(Eric Coombs, Oregon Department of Agriculture)(a,b bugwood.org)

LIFE CYCLE: Overwintering larvae pupate in galls in spring when their thistle 

host plants are bolting. Adults emerge throughout late spring and early summer 

and deposit eggs in developing thistle capitula. Hatching larvae burrow into seed 

heads and feed on seed-producing tissue, inducing the formation of hardened 

galls. There may be multiple larvae per seed head. Most larvae overwinter in galls 

during the third (final) instar, but early maturing larvae may pupate in early 

summer as a second generation. There are up to two generations per year.

DAMAGE: Larval feeding reduces seed production which can help reduce the rate 

of thistle spread. Seeds in infested seed heads are physically stuck to gall tissue, 

thereby reducing dispersal further. Galls from larval feeding act as metabolic 

sinks, diverting resources away from normal plant development.

PREFERRED HABITAT: Specific habitat requirements of U. solstitialis in 

North America are unknown. 

RELEASE HISTORY: Individuals from Italy were released on plumeless thistle 

in the eastern US (MD) in 1993 and on musk thistle in MD and the western 

US beginning in 1993. Flies from Germany were released on plumeless thistle in 
Biological Control in Eastern North America 95thistles

Diptera: Tephritidae

ON and western Canada in 1990. A second shipment from Austria was released 

on musk thistle in western Canada in 1991.

CURRENT STATUS: Urophora solstitialis attacks primarily musk thistle in 

North America. It failed to establish in the US. The fly is established on both 

plumeless and musk thistle in ON, Canada. Populations are limited on plumeless 

thistle, and its impact is considered low overall. The abundance and impact of U. 

solstitialis on musk thistle in ON are unknown. 

REDISTRIBUTION: Where populations are sufficiently large, sweeping adult 

flies is possible, though may be damaging. Instead, place capitula infested with 

galls into uninfested patches during fall or early spring. Transferring infested 

seed heads may also transfer unwanted parasitoids, insects, or thistle seeds. To 

avoid this, plants with infested capitula can be collected and adults reared out 

indoors. Refer to Additional Considerations in the Introduction for instructions 

on how to do so. Once they emerge in spring, flies can be transferred to new 

thistle infestations in groups of 50-100. Establishment can be monitored 

by observing adults on thistle foliage the following summer or by dissecting 

capitula for larvae from summer throughout the following spring. Alternatively, 

squeezing capitula between the thumb and forefinger from late fall through 

spring can quickly indicate larval presence. Those infested with galls will feel 

very firm, while uninfested capitula readily give when pressure is applied, and 

they easily fall apart.

NOTES: In Canada, there is believed to be no conflict between U. solstitialis and 

Rhinocyllus conicus.

musk
96 Biological Control in Eastern North America thistlesCheilosia grossa (Fallén)

Thistle stem hover fly

SYNONYMS: Cheilosia corydon (Harris)

DESCRIPTION: Larvae are tan maggots growing up to 19 mm long. Adults are 

fuzzy with orange-tan hairs, large black eyes, and clearish wings. Adults can be 

up to 15 mm long, including their wings.

a b c

Cheilosia grossa a. adult; b. larval mining damage; c. capitula death due to mining (a-c Eric Coombs, 

Oregon Department of Agriculture, bugwood.org)

LIFE CYCLE: Adults emerge in very early spring and deposit eggs on young 

leaves as host plants bolt. Larvae soon emerge and mine into shoots and stems. 

As the season progresses, larvae mine into roots and continue feeding. They 

develop through three instars. Pupae overwinter in roots or in plant litter. There 

is one generation per year.

DAMAGE: Larval mining interferes with water and nutrient transport and 

ultimately results in a decrease of seed production, sometimes even plant death.

PREFERRED HABITAT: This fly survives a wide array of climatic conditions 

throughout the range of its host thistles. It tends to do better in areas where host 

plants flower early.

RELEASE HISTORY: Cheilosia grossa was introduced from Italy and released on 

musk and slenderflower thistle in the eastern US beginning in 1990 (MD, NJ, 

TX) and Italian thistle in the western US in 1993. This fly was found feeding on 

bull thistle in the western US by 2001.

CURRENT STATUS: Attacks bull, musk, Italian, slenderflower, and (rarely) 

plumeless thistle in North America. In the eastern US, C. grossa is established 

only on slenderflower thistle in MD, though its abundance and impact are 

unknown. In the western US, C. grossa is established on bull, musk, Italian, and 
Biological Control in Eastern North America 97thistles

Diptera: Syrphidae

slenderflower thistle, though it is not very abundant on any of these species. 

Carduus species are preferred over Cirsium, but it is rarely found on plumeless 

thistle. Where established on any of the above species in the West, plants 

with large stem diameters (>10 mm) are most often attacked, reducing seed 

production and (infrequently) causing plant death. The overall impact of this 

biocontrol agent is typically minor. 

REDISTRIBUTION: Sweeping adult flies is possible in spring when host plants 

are beginning to bolt, though this may be damaging. Alternatively, pupae can be 

collected by digging roots in late summer and early fall as host plants die back 

with lower temperatures. Infested roots can then be transferred to uninfested 

thistle patches. Or they may be stored overwinter at 39-46°F (4-8°C). Two to 

three weeks prior to normal emergence times, bring them to room temperature 

in rearing cages or breathable, clear containers. Once adults emerge, flies can be 

transferred to new thistle infestations in groups of 50-100. Damage similar to 

that caused by this insect has been observed in several native thistles species 

(Cirsium edule group), thus caution should be used when considering 

introduction of this fly into new areas. Establishment can be monitored the 

following summer through spring by dissecting stems and looking for larval 

damage. Note that feeding damage can be difficult to distinguish from other 

mining species if larvae are no longer present.

NOTES: This species is not approved for release in Canada.

bull musk
98 Biological Control in Eastern North America thistlesRhinocyllus conicus (Frölich)

Thistle seedhead weevil

DESCRIPTION: Eggs, laid on buds and stems, are covered with chewed plant 

material that becomes tan with age, appearing as part of the plant. Larvae are 

white with brown head capsules, C-shaped, and reach up to 4 mm long. Adults 

are dark brown or black with yellowish tufts of hair, giving them a mottled 

appearance in spring. As they age, adults lose some of these hairs and turn 

brownish-black. They can be up to 6 mm long.

a b c

Rhinocyllus conicus a. eggs (Whitney Cranshaw, Colorado State University); b. larvae and damage in 

capitula (Mark Schwarzländer, University of Idaho); c. adult (Eric Coombs, Oregon Department of 

Agriculture)(a-c bugwood.org)

LIFE CYCLE: Overwintering adults emerge in early spring and deposit eggs on 

bracts of thistle capitula and stems. Larvae hatch in late spring and early summer 

and develop through four instars. They burrow into seed heads and feed on 

receptacle tissue and developing seeds. Pupation occurs within seed heads in late 

summer as seeds mature. Adults emerge for a brief time before overwintering in 

sheltered areas. There is one generation per year.

DAMAGE: Adults feed on foliage and leave signature rounded feed holes over the 

entire leaf surface, though this damage is typically minor. Larval feeding destroys 

some seeds. Seed consumption does not kill existing plants, but does help reduce 

the rate of thistle spread. 

PREFERRED HABITAT: This seed weevil does best in meadows and moist areas 

with moderate temperatures. In areas where summer arrives quickly, weevils are 

unable to utilize later-developing capitula. 

RELEASE HISTORY: Three strains have been collected for use against exotic 

thistles in the US, originating from three host species in France and Italy; releases 

began in 1969 on musk, plumeless, Scotch (failed), Italian, slenderflower, and 

milk thistle. Releases on Scotch and slenderflower thistle occurred only in the 
Biological Control in Eastern North America 99thistles

Coleoptera: Curculionidae

western US. The weevil spread naturally to bull and Canada thistle in the western 

US. Weevils from France were released on plumeless and musk thistle in eastern 

Canada beginning in 1968 (MB, ON, QC). The weevil spread naturally and via 

intentional redistributions to bull, Canada, and marsh thistle in western Canada 

and bull thistle in eastern Canada (ON). Redistributions to Canada thistle in NS 

(1991) and Scotch thistle in western Canada (1998) failed to establish.

CURRENT STATUS: Attacks bull, Canada, musk, Italian, marsh, milk, 

plumeless, and slenderflower thistle in North America. This weevil typically 

prefers Carduus spp. (musk, plumeless, Italian, slenderflower) over other thistles. 

In the eastern US, it is abundant on musk thistle on which it is effective when 

combined with Trichosirocalus horridus and plant competition. It is established 

on plumeless thistle, though impact is typically low as only early capitula are 

attacked. In the US, the weevil is abundant on Italian and slenderflower thistle, 

but only in western states, where it can be effective on early-blooming plants, but 

only in combination with plant competition. It is established on Canada, bull, 

and milk thistle only in western states. On Canada thistle, it is largely ineffective 

because seed reduction doesn’t hinder the plant’s spread via roots. Its impact on 

bull and milk thistle in the western US is minimal. This weevil attacks 22 of 

90 Cirsium spp. native to the US, and redistribution permits were revoked 

in 2000. In Canada, it attacks over 90% of musk thistle capitula, reducing seed 

production by ~50%. It has been credited with controlling this species especially 

when plant competition is present. It has limited impact on plumeless thistle in 

ON, as only the early capitula are attacked; populations and impact are believed 

to be higher in western Canada, especially in conjuction with other agents. Attack 

to bull, marsh, and Canada thistle throughout Canada is more minor.

REDISTRIBUTION: This weevil is no longer approved for redistribution in 

the US. In Canada, adults can be collected in spring with nets and aspirators 

and transferred in groups of 200 to new thistle infestations. Establishment 

can be monitored the following summer by dissecting capitula for larvae, or 

observing adults on foliage 

in late summer. 

NOTES: Adults have 

shorter snouts than 

Larinus carlinae. 

Multiple larvae 

typically occur in 

the same capitula. bull Canada musk
100 Biological Control in Eastern North America thistlesTrichosirocalus horridus (Panzer)

Musk thistle crown weevil

SYNONYMS: Ceuthorhynchidius horridus (Panzer)

DESCRIPTION: Eggs are opaque, white, and small. Larvae are creamy white 

with dark brown head capsules and can be up to 3 mm long. Adults are small 

(approximately 4 mm long), round, and brown with white mottling. They have 

obvious spines on their thorax and long snouts.

a b c

Trichosirocalus horridus a. larva and root crown damage; b. adult (Laura Parsons, University of 

Idaho); c. adult feeding damage (a,c Eric Coombs, Oregon Department of Agriculture)

LIFE CYCLE: Overwintering adults emerge in spring and feed on rosettes of host 

plants. Eggs are deposited on leaf undersides, along midrib and primary veins 

of young plants. Hatching larvae move down and feed on the tissue at the rootstem junction, developing through three instars. Pupation occurs in the soil in 

early summer. Adults emerge over the summer but are inactive until fall, when 

they feed superficially on host plant foliage. Adults overwinter in plant litter, 

emerging again in spring and often living until the next generation of adults 

begins to emerge. There is only one generation per year.

DAMAGE: Adult feeding in spring has minimal impacts, though larval feeding 

can weaken, reduce the seed production, and alter the growth of attacked plants.

PREFERRED HABITAT: This crown weevil does best in open infestations of its 

target weed and on the perimeter of infestations where stems do not grow as tall. 

It is widely distributed throughout portions of North America, but does not do 

as well at high elevations or under marshy conditions. 

RELEASE HISTORY: Individuals from Italy were released in the eastern US 

onto plumeless and musk thistle beginning in 1974. The weevil spread naturally 

and via intentional redistributions to bull thistle. In the western US, the weevil 
Biological Control in Eastern North America 101thistles

Coleoptera: Curculionidae

spread naturally and via intentional redistributions to Italian, Scotch (failed), 

and slenderflower thistle. In Canada, weevils from Germany were released on 

musk thistle beginning in 1975 (MB 1980) and plumeless thistle in 1975 (ON 

and QC beginning in 1977). It was later redistributed to marsh and Scotch 

thistle (failed) in western Canada (2007). 

CURRENT STATUS: Attacks bull, musk, Italian, marsh, plumeless, and 

slenderflower thistle in North America. In the US, T. horridus prefers musk over 

plumeless thistle (established on the latter in KS, MD, MO, NJ, VA, WV). On 

both it can be effective when in combination with plant competition and other 

biocontrol agents, but it is ineffective at many sites. Its impact on bull thistle is 

minimal. The weevil is established on Italian and slenderflower thistle only in 

the western US, where it is moderately effective. In eastern Canada, T. horridus is 

established on musk and plumeless thistle on which damage is limited; attacked 

rosettes frequently survive to produce seed later in the season. It is established 

on marsh thistle in western Canada with unknown impact.

REDISTRIBUTION: Adults can be hand collected in spring from thistle 

rosettes. Alternatively, the summer generation can be collected in the adult stage 

using a sweep net and aspirator when host plants are flowering. Groups of 100-

200 adult weevils can be released at uninfested thistle patches. Establishment can 

be monitored the following spring by observing adults on foliage or dissecting 

root crowns in summer in search of feeding larvae. Due to observed nontarget 

attack, interstate transport is not permitted in the US, and some states have 

prohibited its redistribution within their borders. Where this biocontrol 

agent is approved for redistribution, it is imperative to refrain from making 

releases at sites where known related or susceptible species co-occur. Contact 

your local county extension or land management agency for more information.

NOTES: In 2002, it was determined that T. horridus was in fact a complex of three 

species, each with distinct host plant preferences. A 2015 analysis concluded 

there are only two species in this complex, of 

which only T. horridus is established in 

North America. 

bull musk
102 Biological Control in Eastern North America thistles

Non-Established Biocontrol Agents

Altica carduorum Guérin-Méneville

(Coleoptera: Chrysomelidae)

DESCRIPTION AND LIFE CYCLE: 

Adults are metallic blue-black and 4 mm 

long. They emerge in late spring and 

feed on young thistle leaves. Oviposition 

occurs on the underside of thistle leaves. 

Larvae emerge in mid to late summer, 

and feed on thistle leaves. When mature, 

they drop to the soil for overwintering.

RELEASE HISTORY: Altica carduorum from France and Switzerland were 

released on Canada thistle in eastern Canada beginning in 1963 (NS, ON) and 

the eastern US starting in 1966 (DE, IN, MD, MN, NJ, SD, WI). Establishment 

failed at all sites. An additional strain from Italy released in MD, US also failed 

to establish, possibly influenced by predation. 

Lema cyanella (L.)

(Coleoptera: Chrysomelidae)

DESCRIPTION AND LIFE CYCLE: 

Overwintering adults emerge in spring 

and oviposit on leaf undersurfaces and 

stems of Canada thistle. Larvae feed 

on the undersides of leaves, leaving the 

upper epidermis intact which forms a 

characteristic feeding window. Mature 

larvae drop to the soil in mid-summer, 

pupating within cocoons made of foam they secrete. Adults emerge in late summer 

and feed on foliage prior to overwintering in soil. 

RELEASE HISTORY: Lema cyanella introduced from Switzerland was released 

on Canada thistle in NB and SK from 1983. After establishment failed, a 

population sourced from Switzerland and France obtained via New Zealand was 

released in western Canada from 1993. One population initially established, 

but concerns over nontarget attack led to its eradication. It is no longer 

considered established. Not approved for release in the US.

André Gassmann, CABI-Switzerland

Alec McClay, McClay Ecoscience
Biological Control in Eastern North America 103thistles

Non-Established Biocontrol Agents

Psylliodes chalcomera (Illiger)

(Coleoptera: Chrysomelidae)

DESCRIPTION AND LIFE CYCLE: 

Overwintering adults emerge in spring 

and oviposit on musk thistle plant 

bases. Adults are shiny and dark with 

a metallic blue-green sheen. Larvae are 

slender and white with brown head 

plates. Adults and larvae can be up to 

3 mm long. Larvae feed through three 

instars on leaves, buds, and flowers of 

musk thistle throughout the growing season. Pupation occurs in plant litter. 

There is one generation per year.

RELEASE HISTORY: Psylliodes chalcomera introduced from Italy was released 

on musk thistle in the US in 1997 (KS, TX) but failed to establish. It is not 

widespread in its native range; as a result, it has been difficult to collect large 

enough numbers for re-release and establishment in North America. Not 

approved for release in Canada.

USDA ARS European Biological Control 

Laboratory (bugwood.org)
104 Biological Control in Eastern North America thistles

Unapproved Non-Indigenous Natural Enemies

Six accidentally introduced species are established on exotic thistles in North 

America. Though some have been intentionally redistributed at different times, all 

six species are not approved for use. It is illegal to intentionally move these species 

to new areas in the US. Care should be taken when transferring approved agents to 

ensure that these unapproved species are not also included in transferred material.

Aceria: Eric Erbe, USDA ARS, bugwood.org, Cassida: Laura Parsons, University of Idaho, Cleonis: 

Ivo Tosevski, CABI-Switzerland, Larinus: Alec McClay, McClay Ecoscience, Puccinia: USDA ARS, 

bugwood.org, Terellia: Peter Harris, Agriculture and Agri-Food Canada

Aceria 

anthocoptes

Cassida 

rubiginosa

Cleonis 

pigra

Larinus 

carlinae

Puccinia 

carduorum

Terellia 

ruficauda

In addition to the above species, the rust Puccinia punctiformis is also widespread on 

Canada thistle in North America. Though believed to be present inadvertently, it is 

established throughout much of the world, and questions remain about its native range. 

While not officially approved for general use in the US, there is recent interest in 

gaining authorization within states to intentionally utilize state-specific US isolates.

Puccinia punctiformis (F. Strauss) Röhl.

(Pucciniomycetes: Pucciniales)

DESCRIPTION AND LIFE CYCLE: 

Teliospores germinate in spring and 

produce basidiospores. Aeociospores are 

then produced in a sweet, sticky nectar 

that attracts flies to disperse spores. 

Resulting urediniospores form dense 

yellow-brown pustules on upper leaf surfaces that are easily blown to uninfected 

plants to repeat the cycle. Teliospores form on senescing plants and drop onto 

rosettes in fall, overwintering and producing systemically-infected stems in spring. 

HISTORY AND CURRENT STATUS: Likely introduced into North America 

by 1890 in diseased Canada thistle roots, this rust is now widespread throughout 

the US and Canada wherever its host occurs. Systemic infections can be lethal 

but are dependent on suitable conditions. Superficial foliar infections are more 

common; these have less impact on the plant by stunting growth and flowering but 

not reducing populations. Not approved for general redistribution in the US.

© Malcolm Storey, www.bioimages.org.uk
Biological Control in Eastern North America 105thistles

Unapproved Non-Indigenous Natural Enemies

Aceria anthocoptes (Nalepa)

(Acari: Eriophyidae)

DESCRIPTION AND LIFE CYCLE: 

Mites appear on foliage in spring as 

Canada thistle plants bolt. Larvae, 

nymphs and adults are white, tan, pink, or 

yellow, depending on the developmental 

stage. All are tiny (0.15-0.20 mm long). Females exist in reproductive (summer) 

and overwintering forms. Feeding mites suck out the contents of leaf cells. There 

are multiple generations per year; overwintering is likely on roots or root buds.

HISTORY AND CURRENT STATUS: This mite was discovered on Canada 

thistle in the US in 1998 (MD). It is now established in DE, KS, MD, MN, 

NE, ND, PA, SD, VA, WV in the eastern US and in AB, Canada. It can cause 

thinning and leaf deformation in the lab, but has not been properly evaluated in 

the field where it appears impact is minimal. It has been collected from numerous 

thistles native to North America. Not approved for redistribution in the US.

Cassida rubiginosa O.F. Müller

(Coleoptera: Chrysomelidae)

DESCRIPTION AND LIFE CYCLE: 

Adults emerge in early spring and feed 

on new foliage. They are oval, have 

black undersides and a hard, green 

protective covering, and can be up to 

7.5 mm long. Eggs are laid in spring and 

summer; emerging larvae feed on leaves. Larvae are green with spined margins, 

on which they accumulate molted skins and waste. They grow to 6 mm and 

pupate in late summer. Adults emerge and feed on young foliage until late fall 

and overwinter in plant litter. There is one generation per year.

HISTORY AND CURRENT STATUS: This beetle was recorded on Canada 

thistle in North America in 1901 and was intentionally redistributed in the US 

in the 1970s. It is currently established in DE, MD, MI, NH, NJ, NY, OH, 

SD, VA, WV (US) and MB, NB, ON, QC, SK (Canada). In some areas, it 

can significantly reduce biomass and survival, but its overall impact is typically 

minimal, likely hindered by predation and parasitism. It feeds on numerous 

native thistle species. Not approved for redistribution in the US.

Eric Erbe, USDA ARS, bugwood.org

Laura Parsons, University of Idaho
106 Biological Control in Eastern North America thistles

Unapproved Non-Indigenous Natural Enemies

Cleonis pigra (Scopoli) 

(Coleoptera: Curculionidae)

DESCRIPTION AND LIFE CYCLE: 

Adults emerge in spring and feed on 

young leaves. They are up to 7 mm long 

and mottled brown with many shiny 

black lumps. Their wide snouts appear 

grooved. Larvae hatch in summer and bore to the stem base where they feed 

internally. They are white with brown head capsules and up to 3 mm long. 

Pupation occurs in plant litter. Adults emerge throughout fall and overwinter in 

plant litter. There is one generation per year.

HISTORY AND CURRENT STATUS: Cleonis pigra was recorded on Canada 

thistle in the US by 1919 and in Canada by 1933. It is established in IN, MI, 

NY, PA (US) and NB, ON, QC (CAN). Larval root mining may kill plants, but 

regeneration is typical. It feeds on several important species, but its overall impact 

to exotic thistles is minimal. Not approved for redistribution in the US.

Larinus carlinae (Olivier)(=L. planus)

(Coleoptera: Curculionidae)

DESCRIPTION AND LIFE CYCLE: 

Adults emerge in early spring and feed 

on young foliage, resulting in leaf holes 

and deformed bracts/seed heads. Adults 

are elongate (≤8 mm long), have black 

bodies with mottled tan-yellow hairs, and long snouts. Eggs are laid inside 

developing capitula. Larvae feed on developing seeds and receptacle tissue 

throughout summer. Larvae are white with brown head capsules and are up to 

5 mm long. Pupation occurs within capitula; adults emerge in late summer and 

early fall and overwinter in plant litter. There is one generation per year.

HISTORY AND CURRENT STATUS: Larinus carlinae was recorded in the US 

by 1968 and Canada by 1988 and intentionally redistributed in both countries. It 

is established on Canada thistle in the eastern US (IN, MD, NY, OH, PA, WV) 

and in NS, CAN and on bull, Canada, musk, and plumeless thistle in western 

Canada. It attacks numerous native thistle species; damage to natives often exceeds 

damage to exotics. Not approved for redistribution in the US.

Ivo Tosevski, CABI-Switzerland

Alec McClay, McClay Ecoscience
Biological Control in Eastern North America 107thistles

Unapproved Non-Indigenous Natural Enemies

Puccinia carduorum Jacky

(Pucciniomycetes: Pucciniales)

DESCRIPTION AND LIFE CYCLE: 

Overwintering teliospores germinate in 

spring. Basidiospores infect rosettes and 

bolting plants. Urediniospores are the 

most characteristic, being gold brown, 

covered in short spines, round and tiny (25 μm). Spores occur in dense pustules on 

infected leaves. Pustules are reddish brown and powdery. Urediniospores are easily 

blown long distances to uninfected plants to repeat the entire cycle within two weeks. 

HISTORY AND CURRENT STATUS: One strain was found present 

(inadvertently) on slenderflower thistle in CA, US by 1951. It is specific to that 

species and established in the western US, though its overall impact is unknown. 

A new strain was introduced on musk thistle in VA in 1987 for experimental 

field release. It spread naturally and now occurs as far west as CA (US) including 

the eastern states of DE, GA, IN, KY, MD, MO, OH, SC, TN, and VA. It is 

specific to C. nutans ssp. leiophyllus on which it reduces seed set and quality. 

Neither strain is approved for redistribution in the US.

Terellia ruficauda (Fabricius)

(Diptera: Tephritidae)

DESCRIPTION AND LIFE CYCLE: 

Adults emerge in early spring, are up to 

5 mm long, and yellow-orange with dark 

spotted abdomens. Wings have 3 black 

marks along leading margins and fainter 

marks on hind margins. Eggs are laid in 

immature female capitula. Larvae feed 

on seeds and receptacle tissue. They are white maggots up to 6 mm long. Pupa 

overwinter in capitula; there is one generation per year. 

HISTORY AND CURRENT STATUS: Terellia ruficauda was discovered on 

Canada thistle in the US and Canada by 1873. Populations are widely distributed 

in eastern North America; the fly is abundant in Canada but generally limited 

in the US. Larvae destroy some seeds, but its overall impact on Canada thistle is 

minimal. Not approved for redistribution in the US.

USDA ARS, bugwood.org

Peter Harris, Agriculture and Agri-Food Canada
108 Biological Control in Eastern North America waterhyacinthWaterhyacinth

Eichhornia crassipes (Mart.) Solms

SYNONYMS: water hyacinth, common water hyacinth, lilac devil, river raft

ORIGIN: Native to the Amazon basin of South America; believed to have been 

introduced to Louisiana, US by 1884.

DESCRIPTION: Upright, herbaceous, free-floating, and stoloniferous perennial 

typically growing 2 in to 3.2 ft tall (5 cm-1 m). Plants often form thick mats 

growing on open water, though seedlings and individual plants may also root in 

moist soil. In uncrowded situations, plants have short, spreading petioles with 

pronounced, buoyant swelling 1-2 in thick (2-5 cm). In dense stands, plants are 

taller and more erect with little or no swelling of petioles. Leaves are arranged in 

whorls of 6-10. Leaf blades are rounded or kidney-shaped, leathery, and up to 6 

in across (15 cm). Flowers usually occur in clusters of 8-15 at the end of a single 

spike. Flowers are 1.5-2.5 in across (4-6 cm) and have 6 violet or bluish-purple 

petals. The top petal has a bright yellow spot. Flowers may have short, medium, 

or long styles, but only the short- and long-style forms occur in North America. 

Fruits are 3-celled capsules that contain up to 50 small, ribbed seeds.

a b

Waterhyacinth a. plant (Chris Evans, University of Illinois); b. infestation (Karen Brown, University 

of Florida)(a,b bugwood.org)
Biological Control in Eastern North America 109waterhyacinth

Family Ponteridaceae

c d e

Waterhyacinth c. leaves (Barry Rice, sarracenia.com); d. leaves and swollen petioles (Leslie J. 

Mehrhoff, University of Connecticut); e. flowers (Wing1990hk)(c,d bugwood.org)

HABITAT: Waterhyacinth grows best in still or slow-moving water bodies including 

lakes, rivers, marshes, and canals. It prefers full sun, warm temperatures, and 

high nutrient water. Cold and salt water limit growth of this weed.

ECOLOGY: Waterhyacinth spreads by seed and (primarily) by stolons. At 

maturity, flowering stalks bend and release seeds below the water surface. Seeds 

may remain viable for 15-20 years. Seedlings germinate in moist soil or shallow 

water. Once seedlings become buoyant, they separate from their roots and float 

to the surface. New roots form under each leaf and create a dense mass. Stems 

periodically produce stolons that grow horizontally for 4-20 in (10-50 cm) before 

establishing daughter plants. Huge, interconnected mats can develop rapidly, 

though connecting stolons eventually die. Flowering occurs year-round at warm 

locations and from late summer through autumn in cold climates. At cold sites, 

plants cease growth and stem bases overwinter, resuming growth in spring.

BIOLOGICAL CONTROL: Four species have been 

released in the US since 1972. Megamelus 

scutellaris is still increasing; heavily attacked 

plants produce fewer leaves, wilt, and die. 

Neochetina bruchi and N. eichhorniae have 

reduced waterhyacinth 50-66%. Niphograpta 

albiguttalis may have had high impact initially, 

but is now rarely seen in the field. No species 

are approved for release in Canada.

NOTES: "Establishment" at many northern 

sites is due to annual reintroductions. 

Plants do not survive heavy freezes.
110 Biological Control in Eastern North America waterhyacinthMegamelus scutellaris Berg

Waterhyacinth planthopper

DESCRIPTION: Eggs are elliptical and milky white when laid but turn yellowish 

with reddish eye spots before hatching. Nymphs are similar to wing-less adults 

but are smaller (up to 2.5 mm long). Nymphs have yellowish bodies with 

mottled brown markings; their coloration darkens through each instar. Adults 

can be either wing-less or winged (with clear wings). Adults are 2.5-3.7 mm long 

and are mottled brown, gray, and yellowish. 

a b c

Megamelus scutellaris a. adult (Jason D. Stanley, USDA ARS, bugwood.org); b. adults and nymphs; 

c. adults and damage to waterhyacinth (b,c Philip Tipping, USDA ARS)

LIFE CYCLE: At warm locations, both M. scutellaris and waterhyacinth develop 

throughout the year. At cold sites, immature stages overwinter in decaying 

mats of waterhyacinth. Adults lay eggs within leaves of waterhyacinth in 

spring; oviposition scars can be recognized by three parallel marks. Nymphs 

develop through five instars. Nymphs and adults feed on leaves and stems of 

waterhyacinth. Environmental cues determine whether adults will be winged or 

wing-less. When planthoppers are overcrowded or waterhyacinth plants are of 

poor quality, adults develop wings that enable them to disperse to more suitable 

waterhyacinth plants/infestations. There are multiple overlapping generations 

per year.

DAMAGE: Nymphs and adults pierce waterhyacinth lleaves and stems and feed 

on sap. Plants with heavy feeding produce fewer leaves and eventually wilt and 

die. 

PREFERRED HABITAT: This planthopper appears to do best at sites with some 

cover or shading. Though the reasons for this are not currently known, shading 

may promote increased humidity which increases survival of the planthopper.

RELEASE HISTORY: The waterhyacinth planthopper was initially released 

in FL, LA, and TX in 2010 using populations from Argentina (releases were 
Biological Control in Eastern North America 111waterhyacinth

Hemiptera: Delphacidae

also made in CA from 2011). The first releases were believed to have failed 

establishment, though establishment was subsequently confirmed at FL release 

sites. A second release sourced from northern Argentina/Paraguay was released 

in FL beginning in 2012. 

CURRENT STATUS: Both releases successfully established in FL and are 

no longer differentiated. Though it is too early to determine their overall 

impact, populations are spreading and slowly increasing. Parasitism may limit 

populations at some FL locations.

REDISTRIBUTION: Plants infested with planthoppers can be transferred to 

new waterhyacinth sites and placed against uninfested plants when waterhyacinth 

is actively growing, taking care not to also transfer unwanted parasitoids, other 

insects, or waterhyacinth seeds. Alternatively, late-instar nymphs and adults 

can be aspirated from plants and released at new waterhyacinth populations. 

Establishment can be confirmed the following year by observing nymphs, adults, 

or their piercing/sucking feeding damage on waterhyacinth leaves and stems.

NOTES: This species is not approved for release in Canada. Adult Megamelus 

scutellaris can be difficult to differentiate from other species of Megamelus.
112 Biological Control in Eastern North America waterhyacinthNeochetina bruchi Hustache & N. eichhorniae Warner

Waterhyacinth weevils

DESCRIPTION: Both species are morphologically very similar. Eggs are white 

and oval. Larvae are C-shaped, white with yellow-orange heads, and up to 9 mm 

long. Pupae are white and enclosed in cocoons. Adults are somewhat rounded 

and have long snouts. Adult Neochetina bruchi are tan or brown and often 

have a lighter-colored v-shaped band on the lower parts of the elytra. Adult 

N. eichhorniae is usually a darker mottled gray and brown. Both species have 

two dark markings on their elytra. The markings are shorter for N. bruchi and 

located midway down the elytra while the markings for N. eichhorniae are longer 

and situated closer to the weevil’s head (Figure b).

a b c

Neochetina spp. a. larva; b. adults: N. bruchi (left), N. eichhorniae (right)(a,b Willey Durden, USDA 

ARS); c. adult feeding scars on waterhyacinth (Katherine Parys, USDA ARS)(a-c bugwood.org)

LIFE CYCLE: Both species are continuously brooded, creating frequent overlap 

of generations. In warm areas where waterhyacinth remains present and does 

not freeze, all stages can overwinter. Adults may live longer than a year and can 

be found year-round. Adults feed on waterhyacinth leaves and stems, producing 

feeding scars 2-3 mm wide. Adults lay eggs (300-400 in a lifetime) embedded 

in waterhyacinth leaf and petiole tissue. Neochetina bruchi may deposit several 

eggs in the same site while N. eichhorniae deposits eggs singly. Larvae feed on 

plant tissue through three instars and mine the petioles towards the root crown. 

Neochetina bruchi larvae develop somewhat faster than N. eichhorniae larvae. 

Pupation occurs in cocoons attached to waterhyacinth roots below the water 

surface. Emerging adults climb on waterhyacinth tissue above the water surface 

to feed and mate. 

DAMAGE: Adult feeding causes characteristic feeding scars on leaves and petioles. 

Larval feeding leaves mining tunnels in leaf petioles. Damage from adults and 

larvae stunts plant growth and reduces floral and vegetative reproduction. Heavy 

feeding and mining causes leaf petioles to become thin and brittle, and plants 

become waterlogged and gradually sink. 
Biological Control in Eastern North America 113waterhyacinth

Coleoptera: Erirhinidae

PREFERRED HABITAT: The specific habitat requirements of both species are 

unknown, though both appear to thrive wherever waterhyacinth populations 

remain persistent throughout the year. 

RELEASE HISTORY: Neochetina eichhornia from Argentina was released in FL 

in 1972 and then redistributed to TX and LA beginning in 1974 and to CA in 

the western US in 2002. Neochetina bruchi was also introduced from Argentina 

and then released in FL, LA, and TX starting in 1974. It was redistributed to CA 

in the western US in 1982 and 2002.

CURRENT STATUS: In the southeastern US, both weevil species are well 

established in FL, LA, and TX. Neochetina bruchi is usually dominated by N. 

eichhorniae. Separating the two species based on their feeding damage is difficult, 

but they likely complement each other. Both weevils have had heavy impact on 

the weed and are credited with reducing waterhyacinth abundance from 1/2 to 

1/3 of its original levels in Gulf Coast states. In managed systems, significantly 

less chemical controls are now needed much less frequently to manage the weed. 

Waterhyacinth still remains a problem in some parts of this region. 

REDISTRIBUTION: Adults are most easily collected by aspirating or handpicking individuals from within unfurled leaves and leaf sheaths and transferring 

them to new waterhyacinth infestations in groups of 200-300. When weevil 

populations are high, infested plants can be transferred to new waterhyacinth 

sites and placed against uninfested plants when waterhyacinth is actively 

growing, taking care not to also transfer unwanted parasitoids, other insects, 

or waterhyacinth seeds. Establishment can be confirmed the following year by 

observing adults feeding on waterhyacinth leaves, observing adult feeding scars 

on leaves, or by dissecting leaf petioles for evidence of larval mining. 

NOTES: Neither species is approved for release in Canada. Spillover attack 

by Neochetina eichhornia adults (and possibly N. bruchi) was observed on the 

native Pontederia cordata L. and other native 

species intermixed with waterhyacinth, 

including Canna spp., though this 

attack was insignificant and temporary. 

More recently, no nontarget attack has 

been observed.

N. bruchi N. eichhorniae
114 Biological Control in Eastern North America waterhyacinthNiphograpta albiguttalis (Warren)

Waterhyacinth moth

SYNONYMS: Epipagis albiguttalis (Warren), Sameodes albiguttalis (Warren)

DESCRIPTION: Eggs are small, spherical, and creamy-white. First instars have 

a brown body with darker spots and a dark brown head. Later instars are creamcolored with scattered dark brown spots and a dark orange head and can be up 

to 2 cm long. Adults are variable in coloration, and females are often darker than 

males. Adult forewings range from golden to brown, while the hindwings are 

more consistently golden. Light-colored segments make their abdomens appear 

ringed. There is typically a distinct white spot midway along the leading edge of 

the forewing, and a distinct dark spot near the center of the hindwing. Adults 

are typically 6-10 mm long with wingspans of 17-25mm.

a b c

Niphograpta albiguttalis a. larva and damage (Willey Durden, USDA ARS, www.bugwood.org); b. 

pupae with larval damage (US Army Corps of Engineers, ERDC); c. adult (© Monica)

LIFE CYCLE: This species is continuously brooded, creating frequent overlap of 

generations. In warm areas where waterhyacinth remains present and does not 

freeze, all stages can overwinter. Adults lay eggs (350-600 in a lifetime) singly 

or in small groups in leaf and petiole tissue, usually in existing leaf injuries or 

feeding scars left by the Neochetina weevils. Larvae feed on leaf tissue through 

five instars, mining in petioles towards the root crown. Pupation occurs in 

cocoons within waterhyacinth petioles. Emerging adults are short-lived (up to 

10 days), typically nocturnal, and can often be found resting on the undersides of 

waterhyacinth leaves. When adults emerge from leaf petioles, a glassy “window” 

is left covering the emergence tunnel.

DAMAGE: Larval tunneling in leaf petioles causes a characteristic curling and 

browning of the affected leaf. Tunneling destroys shoot tips, preventing future 

growth. Attacked waterhyacinth stems often die or lose buoyancy and sink.

PREFERRED HABITAT: The specific habitat requirements are unknown, 
Biological Control in Eastern North America 115waterhyacinth

Lepidoptera: Crambidae

d e

Niphograpta albiguttalis damage to waterhyacinth a. leaves; b. close-up (d,e US Army Corps of 

Engineers, ERDC)

though this species thrives wherever waterhyacinth populations remain 

persistent throughout the year. It appears to prefer young waterhyacinth plants 

with bulbous petioles, as are typically found in more open infestations with less 

dense populations of waterhyacinth.

RELEASE HISTORY: Individuals from Argentina were released in FL, LA, and 

TX beginning in 1977 and then redistributed to CA in the western US in 1983. 

CURRENT STATUS: The waterhyacinth moth is supposedly established in the 

Gulf Coast states of FL, LA, and TX. It at times establishes quickly and causes 

significant damage to bulbous waterhyacinth stems locally before disappearing; 

however, is has rarely been observed in the most recent field surveys.

REDISTRIBUTION: Larvae may be collected by hand, but populations dense 

enough to make this worthwhile are hard to locate. Nonetheless, the best method 

for collection is typically the transfer of waterhyacinth plants infested with larvae 

and pupae. These can be placed against uninfested plants when waterhyacinth 

is actively growing, taking care not to also transfer unwanted parasitoids, other 

insects, or waterhyacinth seeds. Establishment can be confirmed the following 

year by observing adults resting on waterhyacinth leaves, 

observing windows covering adult emergence holes, or by 

dissecting leaf petioles for evidence of larval mining. 

NOTES: This species is not approved for release in 

Canada.
116 Biological Control in Eastern North America waterhyacinth

Native Natural Enemies

Bellura densa (Walker)(=Arzama densa)

(Lepidoptera: Noctuidae)

DESCRIPTION AND LIFE CYCLE: 

Adults are mottled tan, up to 17 mm 

long, and have a wingspan of 35 mm. 

Females lay eggs in spring in masses on 

waterhyacinth leaves. Larvae feed on 

waterhyacinth leaves and bore into stems. Late instars are olive green with dark 

horizontal bands and are up to 5 cm long. Pupation occurs in cocoons in plant 

stems. Adults emerge in summer and lay eggs; there are two generations per year 

in southern regions. Larvae overwinter in waterhyacinth stems.

HISTORY AND CURRENT STATUS: Bellura densa is native to SE North 

America. It was redistributed in southern states in the 1970s-80s. High populations 

significantly reduce waterhyacinth cover and biomass in some ponds, but have 

little impact in others. Populations are greatly hindered by parasitism, predation 

and disease. This moth feeds on native and economically important species, 

so it is not safe for redistribution.

Cercospora piaropiTharp (=C. rodmanii)

(Dothideomycetes: Capnodiales)

DESCRIPTION: This pathogen causes 

necrotic spots on waterhyacinth leaves. 

Infection kills leaf tissue from the tip to 

the stem. New leaves are often produced 

to combat leaf loss. Under severe disease 

conditions, new leaves are killed faster 

than they can be replaced, and the 

entire plant dies. Disease symptoms can be found year-round in warm climates. 

HISTORY AND CURRENT STATUS: This pathogen was intentionally 

redistributed in FL and LA, US in the 1970s. Extensive research was conducted 

on economical applications of this fungus, though it was never formally registered 

as a bioherbicide. It is capable of decreasing waterhyacinth biomass, and in some 

instances has caused substantial decline of weed populations. Long-term success 

of this pathogen with only a single application is unlikely when waterhyacinth 

growth is rapid. Combined feeding by the Neochetina weevils and infection with 

this fungus has additive effects.

Willey Durden, USDA ARS, bugwood.org

Infected leaves (Forest and Kim Starr, Starr 

Environmental, bugwood.org)
Biological Control in Eastern North America 117waterhyacinth

Unapproved Non-Indigenous Natural Enemy

Orthogalumna terebrantis Wallwork

(Acari: Galumnidae)

DESCRIPTION AND LIFE CYCLE: 

This species is continuously brooded, 

creating frequent overlap of generations. 

In warm areas where waterhyacinth 

remains present and does not freeze, 

all stages can overwinter. Adults lay 

tiny yellow eggs in damaged areas of 

waterhyacinth leaves. Nymphs and 

adults are brown, becoming shiny and 

nearly black with maturity. Adults are teardrop-shaped and less than 1 mm long, 

appearing as small black dots on waterhyacinth leaves. Feeding mites produce 

characteristic feeding tunnels that are long (5-10 mm) and thin, extending 

towards the tip of the leaf between leaf veins. There may be three generations 

per year.

HISTORY AND CURRENT STATUS: Orthogalumna terebrantis was 

recorded in FL and LA in the US by 1968. It is widespread in these states, but its 

populations are sporadic, and it provides no substantial control. In combination 

with Neochetina eichhorniae, the mite can significantly reduce size and density 

of waterhyacinth in natural situations locally. Not approved for redistribution 

in the US or release in Canada.

Adult Orthogalumna terebrantis (Willey 

Durden, USDA ARS, bugwood.org)
118 Biological Control in Eastern North America ragwortTansy ragwort

Jacobaea vulgaris Gaertn.

SYNONYMS: ragwort, tansy, stinking Willy; Senecio jacobaea L. 

ORIGIN: Native to Europe, Siberia, and Asia. Likely introduced to North 

America in contaminated ship’s ballast; recorded as early as 1850s.

DESCRIPTION: Upright, herbaceous biennial (winter annual or short-lived 

perennial under certain conditions). Typically grows 1-3 ft tall (0.3-1 m) from 

one to several soft, fleshy roots. Leaves are deeply lobed to pinnately toothed, 

alternate, and 3-8 in long (7.5-20 cm). Stems arise singly or in clumps and 

branch near the top with multiple inflorescences. Flower heads consist of yellow 

disc (center) and ray (outer) florets. Ray flowers (usually 13) resemble petals and 

grow 0.3-0.75 in long (8-20 mm) long. Seeds are topped by a fine pappus.

HABITAT: Tansy ragwort is especially problematic in pastures, grasslands, and 

open forests, generally with moist soils.

a b

Tansy ragwort a. plant (Jennifer Andreas, Washington State University Extension); b. infestation 

(Leslie J. Mehrhoff, University of Connecticut, bugwood.org)
Biological Control in Eastern North America 119ragwort

Family Asteraceae

c d e

Tansy ragwort c. rosette (Jennifer Andreas, Washington State University Extension); d. stem leaf 

(Marianna Szucs, Colorado State University); e. flower head (Strobilomyces)

ECOLOGY: This species spreads only by seed, which are dispersed short distances 

by wind and longer distances by humans, other animals, and water. Seeds may 

remain viable in the soil for up to eight years. The life history varies depending on 

climatic conditions. Where winters are mild, the plant typically acts as a biennial. 

Rosettes grow during the winter, and bolting occurs early the following spring. 

Flowering occurs from July to September; it may occasionally occur the first 

year, but is usually delayed until the second. At locations with harsh winters and 

shorter growing seasons, the plant may behave as a short-lived perennial. Seeds 

typically germinate in spring. Seedlings increase in size throughout the summer, 

and only the largest successfully overwinter. Bolting typically occurs early the 

following summer, and flowers appear from July to October. Cutting or mowing 

the plant in either climate may cause it to grow as a perennial.

BIOLOGICAL CONTROL: The majority of releases on tansy ragwort have 

been made in western North America, where this 

weed is most problematic. Large Longitarsus jacobaeae 

populations effectively control tansy ragwort 

at many sites, especially those with cool, moist 

coastal climates. Cochylis atricapitana is 

only approved in Canada, where it stunts 

plant growth and reproductive output 

at some locations. Botanophila seneciella 

is established only in the West and has 

only limited impact. Defoliation by Tyria 

jacobaeae may kill ragwort in cold climates, 

but plants typically recover at mild coastal 

sites; it is no longer permitted for 

interstate transport in the US.
120 Biological Control in Eastern North America ragwortLongitarsus jacobaeae (Waterhouse)

Tansy ragwort flea beetle

DESCRIPTION: Three L. jacobaeae strains are presently established in North 

America; all are morphologically identical. Eggs are small (<1 mm diameter) and 

whitish-yellow, turning orange with maturity. Larvae are white and may be 1-4 

mm long. Last instars have brown head capsules. Pupae are white and 2-4 mm 

long. Adults are golden brown, 2-4 mm long, and have enlarged hind legs.

a b c

Longitarsus jacobaeae a. eggs and hatching larva (Ken Puliafico, Montana State University); b. late instar 

(Eric Coombs, Oregon Department of Agriculture); c. pupa (Laura Parsons, University of Idaho)

LIFE CYCLE: The three strains established in North America differ genetically 

and in their life cycle timing. Only one strain (Italian CPNW) is established 

in eastern North America. Adults of this strain emerge in late spring and feed 

briefly on tansy ragwort rosettes before becoming dormant for the summer. 

They become active again and continue feeding in fall, causing a "shot-hole" 

pattern in attacked leaves. Adults mate and lay eggs around the bases of ragwort 

rosettes, sometimes laying eggs until early spring. Larvae mine leaf petioles and 

then root crowns of rosettes throughout winter and early spring, developing 

through three instars. In spring, larvae leave root crowns to pupate in the soil. 

There is one generation per year.

DAMAGE: Adult feeding may decrease plant size and even cause death in waterstressed plants. Larval mining of the root crown is generally the most destructive, 

reducing seed production and causing plant death.

PREFERRED HABITAT: The Italian CPNW strain thrives in dense, unshaded 

tansy ragwort infestations. Flooding interferes with the larval and pupal stages. 

This strain is best suited for low elevation sites (at or below 400 m or 1,300 ft) 

with climates characterized by warm summers and mild, moist winters. 

RELEASE HISTORY: The Italian CPNW strain was introduced from Italy and 

released in the western US in 1968 and redistributed to BC in western Canada 
Biological Control in Eastern North America 121ragwort

Coleoptera: Chrysomelidae

d e f

Longitarsus jacobaeae d. adult (Marianna Szucs, Colorado State University); e. adult feeding damage; 

f. larvae in roots (e,f Jeff Littlefield, Montana State University)

Italian CPNW strain

in 1971. A small shipment from England was also released in BC in 1972. The 

different populations in BC were later not differentiated and then redistributed 

(likely as a mix) to NB, NS, ON, and PEI from 1978. 

CURRENT STATUS: All three strains are established in western states and 

provinces not covered in this guide. In eastern North America, only the Italian 

CPNW strain is established, and only in Canada where it is abundant at cool 

coastal climates. Establishment failed or is very limited at interior sites. Where 

populations are large, the beetle controls tansy ragwort well in conjunction with 

other biocontrol agents. 

REDISTRIBUTION: Adults can be collected via sweep net (with or without an 

aspirator) or with an insect-collecting vacuum in the fall and then transferred 

to uninfested tansy ragwort patches in groups of 200. Establishment can be 

monitored the following year by observing adults on ragwort foliage along with 

the characteristic shot-hole feeding. Alternatively, plants can be dissected fall 

through spring for evidence of larval feeding. Note that larvae feeding within 

root crowns may be confused with early instars of Cochylis atricapitana. 

NOTES: This beetle works well in conjunction with Tyria 

jacobaeae. For further information on the life cycles, 

habitat, release history, and current status of the strains 

established in western North America, refer to the sister 

guide "Field Guide for the Biological Control of Weeds in 

the Northwest."
122 Biological Control in Eastern North America ragwortCochylis atricapitana (Stephens)

Ragwort stem and crown boring moth

DESCRIPTION: Larvae are creamy white to tan with small black heads and can 

be up to 8 mm long. Pupae are yellowish-brown, 7-8 mm long, and enclosed 

in a white cocoon. Adults are small and tent-winged with a wingspan of 7-16 

mm. The forewings have irregular brown marks flecked with black and grey on a 

white or yellowish-white background. Females are more pink than males. A tuft 

of dark-colored scales extends from behind the head.

a b c

Cochylis atricapitana a. larva in rosette; b. adult (© Geoff Riley); c. feeding damage (a,c © Province 

of British Columbia. All rights reserved. Reproduced with permission of the Province of British 

Columbia)

LIFE CYCLE: There are 2-3 generations per year. Overwintering larvae resume 

activity in spring, feeding on tansy ragwort stems and root crowns through five 

instars. Pupation occurs either in the stem or in surrounding plant litter. Adults 

emerge in late spring as tansy ragwort is bolting and lay eggs on tansy ragwort 

crowns or undersides of leaves. Hatching larvae mine leaves and petioles while 

older larvae mine stems and root crowns. Mature larvae pupate within the plant. 

Emerging adults lay eggs in similar locations in mid- to late summer. Newly 

hatching larvae may overwinter, or a third generation may emerge from eggs laid 

in autumn and overwinter in plant stems. 

DAMAGE: Larval mining suppresses flower formation, stunts plant growth, and 

may kill plants outright.

PREFERRED HABITAT: This moth is adapted to a wide variety of habitats 

where tansy ragwort grows, including high elevations and sites with early winters. 

To date, it is best established in mild coastal zones. 

RELEASE HISTORY: Individuals from Spain were obtained via Australia and 

released in Canada in 1990 (NB, NS). 
Biological Control in Eastern North America 123ragwort

Lepidoptera: Tortricidae

CURRENT STATUS: Cochylis atricapitana established readily in NS where it 

dispersed widely and contributed to control of the plant within five years at some 

locations. The moth did not fare as well in western Canada, where populations 

are small and restricted to coastal regions; introductions into interior climates 

failed. 

REDISTRIBUTION: Adults can be collected at night with the use of a black 

light; however, sufficient numbers can be difficult to find. Consequently, it is 

easier to redistribute larvae. Infested plants can be dug up and transferred to new 

sites in groups of 50 during spring, prior to flower maturation. Transplanting in 

fall is typically less successful for this biocontrol agent, and also creates the risk 

of spreading tansy ragwort seeds (from potentially different genotypes) which 

may make the tansy ragwort problem worse. Establishment can be monitored 

throughout the following season by dissecting stems and root crowns to find 

larvae. Note that early instars feeding in the root crown may be easily confused 

with Longitarsus jacobaeae larvae.

NOTES: This species is not approved for release in the US.
124 Biological Control in Eastern North America ragwortBotanophila seneciella (Meade)

Ragwort seedhead fly

SYNONYMS: Hylemyia seneciella (Hardy), Pegohylemyia seneciella (Meade)

DESCRIPTION: Eggs are small, oval in shape, and off -white in color. Larvae 

(maggots) are creamy white and narrowed at one end. Late instars can be up 

to 6 mm long. Pupal chambers are barrel-shaped and brown. Adults resemble 

house flies with reddish eyes, dark bodies, and slightly clouded wings that extend 

beyond their body. They are up to 6 mm long. 

a b c

Botanophila seneciella a. larva; b. pupae; c. adult (a-c © Malcolm Storey, www.bioimages.org.uk)

LIFE CYCLE: Pupae overwinter in loose soil or litter. Adults emerge in spring 

when tansy ragwort is in the rosette to late bolting stage. Adults lay eggs in 

young flower buds in late spring and early summer. Hatching larvae burrow into 

capitula and feed on developing seeds (one larva per seed head). Attacked seed 

heads are easily identified—initially by a brown discoloration as florets die and 

later by the presence of frothy spittle. Final (third) instars exit seed heads in late 

summer, leaving behind characteristic exit holes, and pupate in the soil where 

they overwinter in puparia. There is one generation per year.

DAMAGE: Larval feeding destroys some or all seeds within attacked seed heads. 

Seed consumption does not kill existing plants, but does help reduce the rate of 

ragwort spread.

PREFERRED HABITAT: This fly does well in meadows and forest clearings. 

Where it is established alongside the cinnabar moth, the ragwort seedhead fly is 

often restricted to scattered tansy ragwort plants growing in habitats less suitable 

to the moth (e.g. shaded forests or narrow mountain valleys).

RELEASE HISTORY: Individuals from France were released in the western US 

in 1966 and redistributed from there to BC and PEI (CAN) starting in 1968. 
Biological Control in Eastern North America 125ragwort

Diptera: Anthomyiidae

d e f

Botanophila seneciella d. infested seed head; e. spittle on infested seed heads (d,e Jennifer Andreas, 

Washington State University Extension); f. exit hole (Marianna Szücs, Colorado State University)

CURRENT STATUS: Botanophila seneciella is established only in western 

states and provinces not covered in this guide. In the western US, the fly is 

moderately abundant. Infestation rates of up to 40% of available capitula have 

been documented in small, isolated tansy ragwort populations, though 5-10% 

attack rates are more typical. Only early seed heads are utilized; later-developing 

capitula generally escape attack. This agent is susceptible to resource competition 

from Tyria jacobaeae, which also consumes tansy ragwort seed heads, as well as 

tansy ragwort mortality caused by Longitarsus jacobaeae. Consequently, though 

the ragwort seedhead fly is the most widely distributed, it is usually the least 

abundant and least effective of the three agents established in the US. This fly 

is widely distributed in western Canada though abundance is low. Populations 

are often restricted to small relic populations of ragwort that are less desired by 

other biocontrol agents. It is unable to control the weed alone, but it contributes 

to partial control in combination with Longitarsus spp. and Cochylis atricapitana. 

REDISTRIBUTION: Sweeping adult flies is often damaging. Moving fly-infested 

seed heads to uninfested patches is effective, but may inadvertently spread new 

tansy ragwort seeds (and from potentially different genotypes). The safest method 

is to collect pupae. Bouquets of infested plants can be placed in flasks of water 

(small-mouth jars prevent emerging maggots from falling in the water and 

drowning). Flasks are placed in open buckets amid a thick layer 

of fine sand or loose peat moss during late summer. Maggots 

exiting seed heads will burrow into the sand to pupate. Sand 

can be stored at 4-8 °C (39-46 °F) to overwinter and then 

be placed into uninfested patches of tansy ragwort in early 

spring. Establishment can be monitored the following 

season by dissecting capitula to find feeding larvae or 

observing frothy spittle on infested seed heads.
126 Biological Control in Eastern North America ragwortTyria jacobaeae (L.)

Cinnabar moth

DESCRIPTION: Eggs are small (1 mm) and bright yellow when new, but turn 

black with age. First instars are light brown or orange; instars 3-6 are banded 

orange and black. Mature larvae are up to 25 mm long. Adults have black 

forewings with two red dots and red-lined borders. Hind wings are bright red. 

Wingspans may be up to 40 mm, and their coloring often fades with moth age.

a b c

Tyria jacobaeae a. eggs (Jeff Littlefield, Montana State University); b. early instars (George Markin, 

USDA Forest Service); c. late instar (Mark Schwarzländer, University of Idaho)

LIFE CYCLE: Pupae overwinter in loose soil or plant litter. Adults emerge in late 

spring, mate, and lay eggs in clusters on the undersides of tansy ragwort rosette 

leaves. Hatching larvae feed on the undersides of rosette leaves. As plants bolt, 

later instars feed on stem leaves and developing buds, often in groups of 10-30. 

Final (sixth) instars leave plants in late summer and pupate in suitable locations 

before overwintering. There is one generation per year.

DAMAGE: Larvae may completely defoliate tansy ragwort plants, leaving behind 

only bare stems. In milder climates plants can recover. In colder, harsher climates, 

frost kills ragwort regrowth before plants can fully recover.

PREFERRED HABITAT: This species does best in warm, sunny areas with dense 

tansy ragwort infestations. It is less successful in shady habitats, narrow canyons, 

saturated soils, locations with harsh winters and little protective snow cover, or 

over-grazed areas. Because pupae overwinter in shallow soil or plant litter, they 

are highly susceptible to trampling or predation by rodents or other insects.

RELEASE HISTORY: Individuals from France were released in the western US 

in 1959. In Canada, moths from Sweden were released in NS in 1961, and moths 

established in the US were redistributed to PEI in 1966; both introductions 

failed to establish. Moths from Switzerland were released in NB, NS, ON, PEI 

released beginning in 1963. 
Biological Control in Eastern North America 127ragwort

Lepidoptera: Erebidae

d e f

Tyria jacobaeae d. pupa (George Markin, USDA Forest Service); e. adult (Mark Schwarzländer, 

University of Idaho); f. larvae feeding gregariously (Jeff Littlefield, Montana State University)

CURRENT STATUS: In the US, this moth is only established in western states 

not covered in this guide. In the West, populations fluctuate. High densities 

often completely defoliate plants. In mild regions, the weed often re-grows and 

recovers sufficiently to successfully overwinter and reproduce. In the colder, 

harsher Intermountain West, frosts usually kills regrowth before plants fully 

recover, so the moth is more effective at reducing weed populations. In Canada, 

the moth’s overall impact is typically minimal. Its complete defoliation of tansy 

ragwort can lead to decreased winter survivorship and decreased seed production 

in some locations at some times; however, ragwort populations persist in all 

major infested areas despite even high cases of defoliation. Weather-induced 

fluctuations of the weed tend to control insect populations rather than the insect 

controlling the weed.

REDISTRIBUTION: This species is best collected in the larval stage by tapping 

or shaking plants over an open pan throughout the growing season. Larvae can 

be transferred to new sites in groups of 50-100. Establishment can be monitored 

the following year by observing feeding larvae throughout the growing season. 

Due to observed nontarget attack, interstate transport is not permitted in the 

US, and some states have prohibited its redistribution within their borders. 

Where this species is approved for redistribution in the western US, it is 

imperative to refrain from making releases at sites where 

known related or susceptible species co-occur.

NOTES: Tyria jacobaeae complements the effect of Longitarsus 

jacobaeae. The conspicuous colors of Tyria larvae serve 

as warnings to potential predators. Larvae are capable of 

sequestering alkaloids from their host for use as toxic 

defenses against birds and other animals.
128 Biological Control in Eastern North America ragwort

Unapproved Non-Indigenous Natural Enemies

Longitarsus spp.

(Coleoptera: Chrysomelidae)

DESCRIPTION AND LIFE CYCLE: 

The four accidental or adventive tansy 

ragwort flea beetles (L. flavicornis, L. 

ganglbaueri, L. gracilis, and L. succineus) 

very closely resemble and are frequently 

mistaken for L. jacobaeae, especially L. 

flavicornis which differs only in the size of 

the male genitalia. Though less is known 

about the biology of the latter three flea 

beetles, L. flavicornis is a highly studied and successful tansy ragwort biological 

control agent in Australia. It has one generation per year. Larvae mine the petioles, 

lower leaves, and then root crowns of tansy ragwort where they overwinter. Larvae 

develop through three instars. They are white with brown head capsules, and may 

be 1.5-4 mm long. Pupation occurs in the soil in late spring or early summer. 

Pupae are white and 2-4 mm long. Adults emerge in early summer, feed on tansy 

ragwort leaves, and lay small yellowish eggs (<1 mm diameter) at the base of 

ragwort rosettes in late summer. Adults are coppery brown and 2.5-3.5 mm long. 

They have fully developed wings and are capable of flight, though they more often 

utilize their enlarged hind legs to jump. Newly hatching larvae feed on ragwort 

stems, root crowns, and roots where they overwinter; occasionally the egg stage 

overwinters in Canada. 

HISTORY AND CURRENT STATUS: Since the 1970s, four species 

of Longitarsus have been observed in Canada as either adventive species 

or as successfully established populations after accidental introductions in 

contaminated releases of L. jacobaeae, likely from Europe. Longitarsus flavicornis 

was initially reported as established only on Vancouver Island in western Canada 

in mixed populations with L. jacobaeae where it reportedly had limited impact 

on the weed. Additional evaluation is needed to confirm its continued presence. 

Longitarsus ganglbaueri is only present in limited numbers in MB and NS, but 

it has reportedly been documented at some point in the western US. Its current 

status remains unknown. Longitarsus gracilis was identified in NS, most likely 

inadvertently introduced in mixed shipments of L. jacobaeae from Europe. 

What was believed to be a population of L. jacobaeae was redistributed from 

NS to BC in 2005. Subsequent monitoring of the BC release site yielded only 

L. gracilis. Longitarsus succineus is established only in NL. The current impact 

of L. gracilis and L. succineus in Canada is unknown. These four flea beetles 

Adult Longitarsus flavicornis (Mark 

Schwarzländer, University of Idaho)
Biological Control in Eastern North America 129ragwort

are not recommended for redistribution in Canada or the US due to their 

broad host range. Care should be taken to ensure adults or eggs of these 

unapproved species are not accidentally collected. Check with your local 

biological control experts for help with identifying flea beetle species.
130 Biological Control in Eastern North America St. JohnswortCommon St. Johnswort

Hypericum perforatum L.

SYNONYMS: St. Johnswort, klamath weed, goatweed

ORIGIN: Native to Asia, Europe, northern Africa. Introduced to the United States 

on multiple occasions by European settlers interested in the plant’s medicinal 

properties. First escaped cultivation in 1793.

DESCRIPTION: Perennial, upright forb typically growing 1-3 ft tall (0.3-1 

m) with numerous stems that are somewhat woody at their base. Stems turn 

rust-colored later in the growing season. Roots produce short runners. Leaves 

are opposite, without stems or lobes, and are up to 1 in long (2.5 cm). Leaves 

have numerous transparent dots as well as tiny black glands along their margins. 

Flowers are numerous, bright yellow, 0.75 in (1.5 cm) in diameter, have many 

stamens, and have petals with additional black glands along margins. Seed pods 

are sticky, 3-celled, 0.25 in (0.6 cm) long, and filled with numerous seeds.

a b

Common St. Johnswort a. plant (Catherine Herms, Ohio State University); b. infestation (John M. 

Randall, The Nature Conservancy)(a,b bugwood.org)
Biological Control in Eastern North America 131St. Johnswort

Family Hypericaceae

c d e

Common St. Johnswort c. leaves (Steve Dewey, Utah State University); d. mature plant in the fall 

(Norman Rees, USDA ARS); e. flowers (Rob Routledge, Sault College)(c,d bugwood.org)

HABITAT: This species prefers open sunlight and disturbance, such as in forest clear 

cuts, along roadsides, and in abandoned fields. It frequents sandy or gravelly soil.

ECOLOGY: Common St. Johnswort spreads by seed and root runners. Sticky 

seed capsules can be dispersed short distances by wind and longer distances 

by water and adhering to humans and other animals. First year plants do not 

produce flowers or seeds, and it may take two to several years to reach maturity. 

Flowering occurs from late spring through autumn. Seeds germinate throughout 

spring and summer or following autumn rains. Seeds may remain viable in the 

soil for several years. Vegetative reproduction is responsible for much of the 

growth in a common St. Johnswort population.

BIOLOGICAL CONTROL: This weed is most problematic in western states 

and provinces, though biocontrol has also proven beneficial on some infestations 

in the East. Chrysolina hyperici and C. quadrigemina are 

the most effective biocontrol agents, especially at open, 

sunny sites. Agrilus hyperici is established 

only in the West, where it is effective at some 

locations but has been displaced by Chrysolina

spp. at others. Aphis chloris provides significant 

control in NS (Canada), though populations 

fluctuate due to weather and competition 

with Chrysolina spp.; it is not approved 

for release in the US. The low abundance 

and impact of Aplocera plagiata make it 

a low priority. High parasitism hinders 

Zeuxidiplosis giardi; redistributions are 

not warranted. 
132 Biological Control in Eastern North America St. JohnswortChrysolina hyperici (Forster) & C. quadrigemina (Suffrian)

Klamathweed beetles

DESCRIPTION: Two species of klamathweed beetles are established in North 

America, both morphologically very similar. C. quadrigemina is slightly larger 

than C. hyperici. Eggs are orange and cylindrical. Larvae are initially orange and 

later gray and up to 6 mm in length. Adults are oval-shaped, robust, and are up 

to 6 mm long. They are shiny metallic with green, bronze, or blue undertones.

a b

c

d

Chrysolina spp. a. eggs (Norman Rees, USDA ARS, bugwood.org); b. larva; c. C. hyperici adult 

(Laura Parsons & Mark Schwarzländer, University of Idaho); d. C. quadrigemina adult (b,d Eric 

Coombs, Oregon Department of Agriculture, bugwood.org)

LIFE CYCLE: Larvae emerge in early spring and feed on young foliage when the 

plant is bolting. Ingesting common St. Johnswort makes larvae photosensitive, 

so most feeding occurs before sunrise. They develop through four instars, and 

pupation occurs in the soil in late spring. Adults emerge in early summer as 

common St. Johnswort begins flowering. They feed and then often rest in the 

soil over summer. If fall rains are sufficient, adults return to plants and resume 

feeding on foliage in the fall, laying eggs on leaves as common St. Johnswort 

is senescing. Both species primarily overwinter as eggs. When fall rains are 

not significant, adults overwinter and lay eggs in spring. In mild climates, fallhatched larvae can survive the winter. There is one generation per year.

DAMAGE: Larval feeding can decimate populations of common St. Johnswort. 

Summer defoliation by adults is also striking, but not as effective as larval feeding.

PREFERRED HABITAT: Both beetles do poorly in shaded, barren, or rocky areas. 

They prefer warm, sunny regions with wet winters. C. quadrigemina prefers more 

maritime conditions than C. hyperici, which is more cold and moisture tolerant.

RELEASE HISTORY: Chrysolina hyperici and C. quadrigemina were introduced 

from England and France (respectively) via Australia and released on St. 

Johnswort in the western US in 1945 and 1946, respectively. US-established 
Biological Control in Eastern North America 133St. Johnswort

Coleoptera: Chrysomelidae

e f

Chrysolina spp. e,f. adults and damage (e,f Jennifer Andreas, Washington State University Extension)

beetles were redistributed to eastern Canada beginning in 1969 (C. hyperici MB, 

NB, NS, ON, PEI, spread naturally to QC; C. quadrigemina NB, NS, ON). 

CURRENT STATUS: In the US, both beetles are established primarily in 

western states where they can help reduce the weed by more than 97% at most 

open, sunny sites. In Canada, the beetles are also abundant and effective in the 

East. Both species are ineffective in shady habitats. Populations of both the weed 

and the beetles often follow a boom/bust cycle; when St. Johnswort control 

is high, beetle populations crash, leading to a St. Johnswort increase, but at 

lower than historical levels. Without improvement of land use, St. Johnswort 

will continue being a cyclical problem. C. hyperici and C. quadrigemina are often 

mixed in both the US and Canada, though C. quadrigemina is now typically 

considered to be more abundant and effective, especially at drier, warmer sites. 

REDISTRIBUTION: Adults can be collected with a sweep net in summer and 

transferred to uninfested St. Johnswort patches in groups of 200 (adults often rest 

in the soil in late summer). Establishment can be monitored by observing larvae 

on St. Johnswort foliage the following spring (at night). Adults can be observed 

the following summer (daytime). Attacked plants appear stripped and wilty.

NOTES: In the US, C. quadrigemina attacks the 

native Hypericum concinnum and H. 

punctatum and the exotic H. calycinum.

A third Chrysolina species, C. varians 

(Schaller), was introduced from Europe 

and released on common St. Johnswort 

in the western US from 1950 and 

western Canada from 1957, but failed 

to establish in either country. C. hyperici C. quadrigemina
134 Biological Control in Eastern North America St. JohnswortAgrilus hyperici (Creutzer)

St. Johnswort root borer

DESCRIPTION: Larvae are white with brown mouthparts, have inflated 

segments, and reach 11 mm in length. Adults are a metallic brown color; females 

are all one color while males’ heads are slighter greener than the rest of their 

bodies. Adults are flattened and tapered toward the rear and reach 5 mm in 

length.

a b c

Agrilus hyperici a. larva in root (Eric Coombs, Oregon Department of Agriculture); b. pupa in root 

(Norman Rees, USDA ARS); c. adult (Laura Parsons & Mark Schwarzländer, University of Idaho)

LIFE CYCLE: Larvae overwinter within common St. Johnswort roots, feeding 

again within roots the following spring as plants bolt. Pupation occurs in the 

roots after the fourth instar. Adults emerge through early summer as common 

St. Johnswort flowers. Adults are most active in the heat of the day. Oviposition 

occurs near the base of common St. Johnswort plants in late summer. Newly 

emerging larvae burrow into the roots to feed and then overwinter. There is one 

generation per year.

DAMAGE: When larvae feed within roots of common St. Johnswort, root tissue 

can be completely consumed. Stems arising from attacked roots and root crowns 

are stunted and produce fewer flowers; the attacked plant dies outright in some 

instances.

PREFERRED HABITAT: Common St. Johnswort is found mostly in 

mountainous regions in North America and drier, more southern portions of 

Europe. Damp sites are less suitable as larvae are often susceptible to fungal 

attack. This beetle prefers large plants with multiple stems. It will attack plants 

in shade, unlike some other common St. Johnswort biological control agents. 

RELEASE HISTORY: This beetle was introduced from France and released on 

common St. Johnswort in the western US in 1950. Beetles established in CA, 
Biological Control in Eastern North America 135St. Johnswort

Coleoptera: Buprestidae

US were redistributed to BC in western Canada multiple times between 1955 

and 1987. 

CURRENT STATUS: Agrilus hyperici is established only in western states and 

provinces not covered by this guide. In the western US, its abundance and 

impact vary. It disperses widely, but populations are typically low until occasional 

explosions. This beetle initially displayed the ability to destroy common St. 

Johnswort at many locations, but was displaced by Chrysolina quadrigemina 

and persisted only in some areas. It contributed significantly to common St. 

Johnswort suppression in ID where it is still abundant. In western Canada, the 

beetle is typically less common. Its overall impact is unknown due to the lack 

of initial baseline data and the prolific occurrence of the Chrysolina beetles at A. 

hyperici release sites.

REDISTRIBUTION: Adults can be collected with a sweep net (with or without 

an aspirator) during summer when common St. Johnswort is in flower and can be 

transferred to uninfested St. Johnswort patches in groups of 50-100. Preference 

should be placed on new sites with no to minimal Chrysolina populations. 

Establishment can be monitored by observing adults on St. Johnswort foliage 

the following spring and summer during the heat of the day or by dissecting 

roots for evidence of larval mining from autumn through the following spring.

NOTES: This beetle has been observed attacking Hypericum concinnum, a forb/

small shrub endemic to California.
136 Biological Control in Eastern North America St. JohnswortAphis chloris Koch

St. Johnswort aphid

DESCRIPTION: Eggs are yellowish at first, turning black with time. Nymphs 

and adults are lime green, tending to dark green in cooler climates. They are 

typically 1-2 mm long. Winged females have transparent wings.

a b

Aphis chloris a. eggs (Peter Harris, Agriculture and Agri-Food Canada); b. adults and nymphs (© 

Province of British Columbia. All rights reserved. Reproduced with permission of the Province of 

British Columbia)

LIFE CYCLE: Eggs overwinter. Self-fertile females hatch in late spring and 

produce live young. 6-11 days are required for these immatures to reach the 

reproductive stage. Live young births continue until temperatures cool in the 

fall, though in warm areas, self-fertile females continue to be produced. Under 

crowded conditions from summer through fall, winged females disperse to 

start new colonies. Adults and nymphs congregate on common St. Johnswort 

stems, root collars, leaf axils, flowers and leaves. The onset of cool, short days in 

northern regions initiates the production of males and egg-producing females. 

Each female produces four eggs on average, depositing them onto basal winter 

foliage.

DAMAGE: Nymphs and adults attack common St. Johnswort stems and leaves, 

feeding on plant fluids. Under high aphid densities this feeding can cause 

individual plants to wither and die. In field studies, healthy potted plants were 

killed in one month when attacked by this species.

PREFERRED HABITAT: This aphid does best where summers are humid 

and temperatures are cool. Sufficient cold winter temperatures are required for 

egg development. It does not do well in hot, dry locations where common St. 

Johnswort plants wither and burn from heat. 
Biological Control in Eastern North America 137St. Johnswort

Hemiptera: Aphididae

RELEASE HISTORY: Aphis chloris was introduced from Austria, Germany, and 

Hungary and released in MB, NB, and NS, Canada beginning in 1990 (released 

in western Canada in 1979).

CURRENT STATUS: This biocontrol agent provides significant control at 

some sites in NS, Canada, though populations fluctuate due to weather and 

abundance/impact of Chrysolina spp. Low numbers of the beetles provide more 

suitable habitat for the aphid.

REDISTRIBUTION: Plant material infested with adults and nymphs can 

be transferred to uninfested common St. Johnswort patches throughout the 

growing season. Alternatively, foliage with eggs attached can be collected from 

fall through spring and transferred to new sites prior to egg hatch. In either case, 

infested plant material should be placed in direct contact with uninfested stems 

at new sites (taking care not to spread common St. Johnswort seeds to new sites). 

Establishment can be monitored throughout the same or following growing 

season by observing adults or nymphs on foliage of common St. Johnswort. 

NOTES: This species is not approved for release in the US.
138 Biological Control in Eastern North America St. JohnswortAplocera plagiata (L.)

St. Johnswort inchworm

DESCRIPTION: Eggs are small, pearly-white ovals. Larvae resemble twigs and 

are reddish brown with weak gray stripes. They are up to 2.5 cm long. Pupae are 

greenish-golden and slender. Adults are triangular in shape and have gray wings 

with dark gray bands. Wingspans reach 3.75 cm (1.5 in).

a b

Aplocera plagiata a. eggs (Norman Rees, USDA ARS, bugwood.org); b. larva (Eric Coombs, Oregon 

Department of Agriculture)

LIFE CYCLE: Overwintering larvae emerge in early spring and feed on common 

St. Johnswort foliage (typically at night) when the plant is bolting. They develop 

through four instars. Pupation occurs in the soil. Adults emerge in late spring 

and early summer and lay eggs on St. Johnswort foliage. Larvae of the first new 

generation emerge in midsummer as common St. Johnswort flowers, repeating 

the life cycle. Second generation larvae hatch in late summer, coinciding with the 

late flowering stage of common St. Johnswort, and feed on foliage and flowers. 

This generation overwinters in the larval stage within the soil. There are up to 

two generations per year, depending on winter temperatures.

DAMAGE: Larval defoliatily weakens but typically does not kill common St. 

Johnswort. Attack by large populations of this biological control agent can lead 

to a reduction of flower and seed formation.

PREFERRED HABITAT: This species prefers dry areas to those with high 

rainfall. It does well on rocky ground, open sandy places, and in limestone 

regions. 

RELEASE HISTORY: Moths from Germany were introduced to western Canada 

in 1967. Eastern releases were made with individuals from Switzerland (NB 1977) 

and France (NS, ON beginning in 1984). Only the moths from France established 
Biological Control in Eastern North America 139St. Johnswort

Lepidoptera: Geometridae

c d

Aplocera plagiata c. adult (Eric Coombs, Oregon Department of Agriculture); d. defoliation 

(Norman Rees, USDA ARS, bugwood.org)

in eastern Canada. All three releases were successful in western Canada, from 

where the moths were redistributed (as a mix) to the western US in 1989. 

CURRENT STATUS: In the US, A. plagiata is established only in western states 

not covered by this guide. Where it is locally abundant, defoliation hinders and 

may kill plants outright. However, its overall abundance is typically limited. It is 

most effective in warm, dry areas where the insect can complete two generations. 

In Canada, the moth's abundance and impact in ON are unknown. In western 

Canada, the moth disperses readily throughout southern interior BC. However, 

populations remain low and do minimal damage.

REDISTRIBUTION: Collecting adults is typically very damaging. The species 

is best collected in the larval stage using sweep nets. First generation larvae are 

available in midsummer as common St. Johnswort flowers. Second generation 

larvae hatch in late summer or early fall, coinciding with the late flowering stage 

of common St. Johnswort. Groups of 50-100 can be transferred to uninfested St. 

Johnswort patches immediately after collection. Establishment can be monitored 

by observing adults on St. Johnswort foliage the following spring/summer or 

larvae feeding on foliage (typically at night) in midsummer or 

early fall. Attacked plants appear stripped and wilty. 

NOTES: Adults are usually fewer in number in the first 

generation compared to the second generation. Warm, 

dry, and long summers are needed to complete both 

generations. When cold temperatures arrive too soon, 

second generation larvae do not survive winter.
140 Biological Control in Eastern North America St. JohnswortZeuxidiplosis giardi (Kieffer)

St. Johnswort gall midge

DESCRIPTION: Eggs are elongated and pale red in color. Larvae are orange and 

can be up to 2 mm long. Pupae are a yellowish-red, becoming darker red as they 

mature. Adults are very small (3 mm long) and have dark red bodies with gray 

heads, wings, and legs. They have fine, delicate legs and antennae.

a b

Zeuxidiplosis giardi a. adult; b. gall damage (a,b Norman Rees, USDA ARS, bugwood.org)

LIFE CYCLE: Larvae emerge in early spring and feed on common St. Johnswort 

leaf buds, causing leaves to grow into a spherical gall that is green with reddish 

markings. Larvae feed inside at the base of the gall through three instars; several 

larvae are often found within one gall. Pupation also occurs inside the gall. 

Adults are sexually mature upon emergence and live for up to five days. There 

may be up to seven generations per year, though there are usually fewer than five. 

Larvae and pupae overwinter inside galls.

DAMAGE: In suitable habitats, this insect can cause a loss of vigor and reduction 

of both root and foliage development. Heavily attacked plants are unable to 

obtain moisture and frequently die during drier seasons.

PREFERRED HABITAT: This midge does best with moderate to high humidity, 

thriving in damp locations and at high elevations. It does poorly in areas with 

dry summers and constant wind. It also does poorly with heavy livestock grazing. 

RELEASE HISTORY: Midges collected in France were released in the western 

US in 1950. A second release attempt was made in the western US in 1992 

utilizing individuals from Hawaii that were reportedly doing much better than 

individuals in the US. This second introduction failed to establish. Populations 

in the western US were redistributed to western Canada in 1955. 
Biological Control in Eastern North America 141St. Johnswort

Diptera: Cecidomyiidae

CURRENT STATUS: In North America, Z. giardi has established only in 

western US states not covered by this guide. In the West, the fly can reduce 

growth in heavily infested common St. Johnswort plants. However, Z. giardi is 

heavily parasitized, so populations are very limited. This midge did not establish 

in Canada. Populations thrived the first summer of release but were subsequently 

annihilated due to sudden sub-zero temperatures in mid-November.

REDISTRIBUTION: Sweeping adult midges is possible, though may be 

damaging. Instead, place plants infested with galls into uninfested patches 

throughout the growing season. Alternatively, galls infested with larvae may be 

hand-picked and transferred to uninfested patches of common St. Johnswort. 

When transferring galls, it is important to keep the galls moist to prevent 

dessication. Transferring infested galls may also transfer unwanted parasitoids, 

other seed head insects, or common St. Johnswort seed. To avoid this, galls can 

be collected and adults reared out indoors. Refer to Additional Considerations 

in the Introduction for instructions on how to do so. Once they emerge in 

spring, flies can be transferred to new common St. Johnswort infestations in 

groups of 50-100. Establishment can be monitored throughout the following 

season by observing galls on new common St. Johnswort foliage.

NOTES: This biocontrol agent is capable of forming galls on Hypericum 

concinnum, a forb/small shrub endemic to California. However, damage to this 

plant is insignificant.
142 Biological Control in Eastern North America toadflaxesDalmatian toadflax

Linaria dalmatica (L.) Mill.

SYNONYMS: broad-leaved toadflax; Linaria genistifolia (L.) Mill., Linaria 

genistifolia (L.) Mill. ssp. dalmatica (L.) Maire & Petitm.

ORIGIN: Likely introduced from Eurasia by 1900 in horticultural trials.

DESCRIPTION: Upright, herbaceous perennial typically growing numerous 

upright and prostrate stems 1-4 ft tall (0.3-1.2 m) from a deep taproot with 

lateral branches. Leaves are alternate, thick (succulent to leathery), green to 

blue-green, and often with a waxy surface. Leaves are heart-shaped at the base, 

clasp the stem, and are typically 1-2 inches long (2.5-5.0 cm) and nearly as 

wide. Flowers are bright yellow and snapdragon-like with an obvious upper and 

lower lip and a long spur pointing downward. Each has a fuzzy, yellowish-orange 

throat. Flowers occur in spiked clusters emerging from leaf axils. Each flower 

produces a round capsule holding 60-300 small, somewhat triangular seeds.

HABITAT: Dalmatian toadflax is often found in or along disturbed areas such as 

railroads, roadsides, riversides, abandoned pastures and fields, and open forest 

slash piles. It does well in cool, semiarid climates and on coarse-textured soils. 

a b

Dalmatian toadflax a. plant (K. George Beck & James Sebastian, Colorado State University, 

bugwood.org); b. infestation (Jennifer Andreas, Washington State University Extension)
Biological Control in Eastern North America 143toadflaxes

Family Plantaginaceae

c d e

Dalmatian toadflax c. leaves; d. flower (c,d Bonnie Million, National Park Service); e. seeds (Steve 

Hurst, USDA NRCS PLANTS database)(c-e bugwood.org)

ECOLOGY: This species reproduces both by seed and root fragments. Severed root 

segments as small as 0.4 in (1 cm) can sprout new plants. Seedlings germinate 

in fall or (more often) in spring; bolting occurs in spring. Flowering occurs 

throughout the summer. Seeds may remain viable in the soil for up to 10 years. 

BIOLOGICAL CONTROL: This weed is most problematic in midwestern and 

western states and provinces, though biocontrol may also prove beneficial on 

some infestations in the East. While both Mecinus janthinus and M. janthiniformis

established, M. janthiniformis is highly effective on Dalmatian toadflax and 

redistributions of this species are warranted. Brachypterolus pulicarius and Rhinusa 

antirrhini were accidentally introduced, but later intentionally redistributed in 

both the US and Canada. Both prefer yellow toadflax; their abundance/impact 

on Dalmatian is minor. Populations of Calophasia lunula are typically low; 

in eastern North America, they are restricted to Canada. High densities can 

defoliate toadflax, though plants usually recover, and 

overall impact is limited. Eteobalea intermediella, E. 

serratella, and R. linariae failed to establish on 

Dalmatian toadflax in North America.

NOTES: Dalmatian and yellow toadflax are 

highly variable in North America and can 

hybridize. This manual uses the interpretation 

that Linaria genistifolia (L.) Mill. is distinct 

from L. dalmatica (L.) Mill. and that L. 

dalmatica consists of two subspecies, of 

which only L. dalmatica ssp. dalmatica is 

invasive and weedy in North America. The 

taxonomy of this group is under review. 
144 Biological Control in Eastern North America toadflaxesYellow toadflax

Linaria vulgaris Mill.

SYNONYMS: common toadflax, butter-and-eggs

ORIGIN: Possibly introduced from Eurasia as early as 1600s as an ornamental 

and medicinal plant, and as a source of textile dye.

DESCRIPTION: Upright, herbaceous perennial typically growing numerous 

stems 1-3 ft tall (0.3-1 m) from a taproot with spreading lateral roots. Leaves are 

alternate, green, pointed at both ends, and may have small stalks. Older leaves 

are narrow and typically 1-2 in long (2.5-5 cm) with a large central vein on the 

underside. Flowers are pale yellow and snapdragon-like with an obvious upper 

and lower lip and a spur pointing downward. Each has a fuzzy, bright orange 

throat. Flowers occur in spiked clusters at the top of the stem. Each flower 

produces an oval capsule fruit holding 10-40 viable, flat, disc-shaped seeds.

HABITAT: This species is often found along roadsides and railroads and in cultivated 

fields and pastures, but it can also invade undisturbed, healthy ecosystems. It is 

frequently found in more fertile and moist soil than Dalmatian toadflax.

a b

Yellow toadflax a. plant (Tiffany Wax, Washington State University Extension); b. infestation (L.L. 

Berry, bugwood.org)
Biological Control in Eastern North America 145toadflaxes

Family Plantaginaceae

c d e

Yellow toadflax c. leaves; d. flowers (c,d Michael Shephard, USDA Forest Service); e. seeds (Steve 

Hurst, USDA NRCS PLANTS database)(c-e bugwood.org)

ECOLOGY: Yellow toadflax reproduces by seeds, creeping root systems, and root 

fragments. Seedlings typically germinate and bolt in spring. Lateral roots are 

capable of vegetative reproduction within three weeks of germination. Severed 

root segments as short as 4 in (10 cm) can form new plants. Flowering occurs 

throughout summer and fall, depending on location. Seeds generally have low 

viability (<50%), but some may remain viable in the soil for 8 years or more. 

BIOLOGICAL CONTROL: This weed is most problematic in midwestern and 

western states and provinces, though biocontrol may also prove beneficial on 

some infestations in the East. While both Mecinus janthinus and M. janthiniformis

established, M. janthinus prefers yellow toadflax; densities and impact can be high 

locally. It is too early to know if Rhinusa pilosa is established, though early results are 

encouraging. Brachypterolus pulicarius and R. antirrhini were accidentally introduced, 

but later intentionally redistributed. Both are widespread on yellow toadflax but 

have only minor impact. Rhinusa linariae is established only 

in the West and at such low densities impacts are limited. 

Populations of Calophasia lunula are typically 

low; in eastern North America, they are restricted 

to Canada. High densities can defoliate toadflax, 

though plants usually recover, and overall 

impact is limited. Eteobalea intermediella

and E. serratella failed to establish on yellow 

toadflax in North America.

NOTES: Dalmatian and yellow toadflax are 

highly variable in North America and can 

hybridize. The taxonomy of this group is 

under review.
146 Biological Control in Eastern North America toadflaxesMecinus janthiniformis Toševski & Caldara & M. janthinus Germar

Toadflax stem weevils

DESCRIPTION: Both species are morphologically very similar. Eggs are white 

and oval. Larvae are C-shaped, white with brown head capsules, and up to 5 mm 

long. Adults are bluish-black, elongate with long snouts, and up to 5 mm long. 

Mecinus janthinus is smaller than M. janthiniformis.

a b c

Mecinus spp. a. larva (Rosemarie De Clerck-Floate, Agriculture and Agri-Food Canada); b. pupa, c. 

adult (b,c Bob Richard, USDA APHIS PPQ)(a-c bugwood.org)

LIFE CYCLE: Overwintering adults emerge in early spring and feed on toadflax 

shoot tips, producing a shot-hole pattern in upper leaves (most obvious on 

Dalmatian toadflax). M. janthinus emerges a few weeks earlier on yellow toadflax 

than M. janthiniformis does on Dalmatian. Females chew holes into toadflax 

stems and lay eggs singly (up to 45 in a lifetime), covering eggs with chewed plant 

tissue. Larvae feed through three instars in short tunnels chewed into toadflax 

stems. M. janthinus tends to mine lower in toadflax stems than M. janthiniformis. 

Pupation occurs in mid-summer within chambers inside feeding tunnels. Adults 

overwinter inside pupal chambers. There is one generation per year.

DAMAGE: Adult feeding stunts shoots and roots and suppresses flowering. Larval 

mining severs water/nutrient conducting tissues, causing desiccation and death. 

PREFERRED HABITAT: Mecinus janthiniformis is well adapted to a variety of 

conditions. Because overwintering sites are often above snow cover, populations 

do better in less fluctuating winter temperatures and above -18.5°F (-28° C). The 

optimal conditions for M. janthinus in North America are still being determined.

RELEASE HISTORY: What was originally released in the US and Canada as 

Mecinus janthinus was recently discovered to be a mixture of M. janthinus and the 

closely related M. janthiniformis. The true M. janthinus was sourced from France 

and Germany and released in 1991 on Dalmatian and yellow toadflax in western 

Canada and in 1995 on yellow toadflax in NS, Canada. Established individuals 
Biological Control in Eastern North America 147toadflaxes

Coleoptera: Curculionidae

d e f

Mecinus spp. damage d. (Jennifer Andreas, Washington State University Extension); e. (Gary Piper, 

Washington State University, bugwood.org); f. (Laura Parsons, University of Idaho)

were redistributed to Dalmatian and yellow toadflax in the western US in 1996. 

Eastern US releases occurred only on Dalmatian toadflax and began in 2010 

(KS, ND, SD, WV). Mecinus janthiniformis was reportedly introduced from the 

Republic of Macedonia and released in western Canada on Dalmatian toadflax 

(1992) and yellow toadflax (2000). Redistributions of M. janthiniformis were 

made from Canada to both Dalmatian and yellow toadflax in the US post 1996 

in mixes with the true M. janthinus. Most of these redistributions were made in 

western states; eastern releases started in 2000 (NE, ND, SD).

CURRENT STATUS: Mecinus janthiniformis prefers Dalmatian toadflax; M. 

janthinus prefers yellow. M. janthiniformis is established on Dalmatian primarily 

in northwestern US and Canada where it has reduced the weed dramatically at 

some locations. M. janthinus is established primarily in northwestern North 

America and NS (CAN). While currently not widely distributed, M. janthinus

densities and impact on yellow toadflax can be high locally, and it appears to 

establish well in new areas. 

REDISTRIBUTION: Adults can be tapped from toadflax foliage from spring 

through mid-summer when plants are bolting to flowering and transferred to 

uninfested toadflax patches in groups of 200. Establishment can be monitored by 

observing adults on toadflax foliage the following 

spring or by dissecting stems for larvae 

from late spring through late summer.

NOTES: As the identification of M. 

janthiniformis has only recently been 

made, sorting the release history and 

establishment status of Mecinus spp. 

on both toadflaxes is a work in progress. Dalmatian yellow
148 Biological Control in Eastern North America toadflaxesRhinusa pilosa (Gyllenhal)

Yellow toadflax stem-galling weevil

DESCRIPTION: Eggs are pale yellow and oval-shaped. Larvae are C-shaped, 

creamy white with brown head capsules and up to 5 mm long. Adults are black, 

up to 4 mm long, and covered in upright hairs. They have a distinctive curved 

profile, and the snout gives this weevil a distinctive hook-nosed appearance.

a b

Rhinusa pilosa a. adult; b. galls on yellow toadflax stems (a,b Ivo Toševski, CABI)

LIFE CYCLE: Overwintering adults emerge in early spring. Females lay eggs 

in actively growing tips of yellow toadflax stems, triggering the formation of 

large, obvious galls. Larvae feed on nutrient-rich inner gall tissues through three 

instars before pupating, also within the gall. New adults remain in the gall for a 

period of time in early summer-mid fall and feed on remnant gall tissues before 

chewing their way through the gall wall to exit. Feeding continues on host shoots 

for a brief period before adults move to the soil where they become inactive. 

Once temperatures cool consistently in late autumn, adults feed extensively 

on toadflax re-growth before overwintering in soil or plant litter. There is one 

generation per year.

DAMAGE: Stem galls reduce yellow toadflax height, number of stems, and 

biomass. Adult and larval feeding reduces nutrient reserves and photosynthetic 

tissue which may stunt plants and reduce reproductive output.

PREFERRED HABITAT: The habitat preferences of R. pilosa in North America 

are unknown because confirmed established populations are restricted to limited 

sites in AB and BC in western Canada. In its native Europe, R. pilosa does well in 

a variety of habitats throughout the range of yellow toadflax.

RELEASE HISTORY: Individuals from Serbia were released on yellow toadflax 

in western Canada beginning in 2014 and in MB, NS, ON, and PE in 2016. 
Biological Control in Eastern North America 149toadflaxes

Coleoptera: Curculionidae

CURRENT STATUS: This weevil attacks only yellow toadflax in North America 

and has thus far been released only in Canada. Following several releases of R. 

pilosa, successful galling of yellow toadflax was confirmed in multiple provinces. 

There also was successful overwintering survival of first generation adults 

produced from many releases. It is still too early to confirm establishment, 

especially in eastern Canada. Continued monitoring of new weevil populations 

is planned to determine population changes, spread, and impact.

REDISTRIBUTION: Any releases made should be done using laboratory 

colonies and under the guidance of appropriate authorities. In the future, 

should this biocontrol agent be further established, field redistributions can be 

done by collecting adults from toadflax stems in early spring using a sweep 

net and aspirator. They can be transferred in groups of 100-200 to uninfested 

yellow toadflax patches. Establishment can be monitored by observing adults 

on toadflax stems the following spring or by observing the obvious galls in stem 

tissue. 

NOTES: As of 2016, TAG approval of this insect has led to its release in Canada, 

but in the US it is still within the regulatory process. Approval for release is 

expected in the near future. 

Four species of Rhinusa are currently established on toadflaxes in North America. 

Adult R. pilosa are longer (4 mm) than R. linariae (2.5 mm), R. antirrhini (3 

mm) and R. neta (3 mm). Rhinusa pilosa is black while R. neta is gray to brown, 

and R. pilosa is covered with longer, upright hairs while the hairs on R. linariae, 

R. antirrhini, and R. neta are short and more flattened. Rhinusa pilosa also differs 

from the other Rhinusa species by its location of attack; R. pilosa adults and 

larvae can be found on/in stems, while R. linariae adults can be found on stems 

and larvae on/in roots, and R. antirrhini/R. neta adults attack flowers and larvae 

attack seeds. 

yellow
150 Biological Control in Eastern North America toadflaxesBrachypterolus pulicarius (L.)

Toadflax flower-feeding beetle

DESCRIPTION: Eggs appear milky white at first, becoming yellow just before 

hatching. Larvae are yellow with brown head capsules and are up to 7 mm long. 

Adults are shiny, dark brown to black, or sometimes black with brown mottling. 

They are 2-3 mm long and somewhat oval.

a b c

Brachypterolus pulicarius a. larva; b. adult (a,b Daniel K. MacKinnon, Colorado State University); c. 

adults (Susan Turner, British Columbia Ministry of Forests)(a-c bugwood.org)

LIFE CYCLE: Adults emerge in late spring and feed on young toadflax shoot 

tips. Females lay eggs singly into unopened toadflax buds, just beneath the 

folded petals. Larvae feed on pollen, anthers, ovaries, and immature seeds. They 

develop through three instars and drop to the soil in fall to overwinter as pupae 

in soil or plant litter. There is one generation per year.

DAMAGE: Adult feeding can delay flowering and reduce the number of healthy 

flowers (and thus seeds). Larval feeding is generally more significant, reducing 

seed output by more than 75% in attacked flowers. Decreasing seed output does 

not kill existing plants but can help reduce the rate of toadflax spread.

PREFERRED HABITAT: This flower beetle is well adapted to a variety of 

environmental conditions and can be found throughout the majority of toadflax 

infestations in North America. 

RELEASE HISTORY: This species was initially an unintentional introduction 

documented on yellow toadflax in NY (US) in 1919. It spread naturally 

and via intentional redistributions throughout the US on both yellow and 

Dalmatian toadflax. It was first recorded on Dalmatian and yellow toadflax as 

an accidental introduction in western Canada in 1950. One population found 

feeding exclusively on Dalmatian in Canada was subsequently redistributed to 

the western US on Dalmatian toadflax (1992) and yellow toadflax (1997). The 

different groups of B. pulicarius in the US now overlap. Because they are not 
Biological Control in Eastern North America 151toadflaxes

Coleoptera: Kateretidae

genetically different and are likely moving between the two weed species on 

their own, they can no longer be differentiated.

CURRENT STATUS: Attacks both Dalmatian and yellow toadflax in North 

America. It was initially believed different “strains” of B. pulicarius had evolved 

sufficiently to be suited differently to yellow and Dalmatian toadflax. Recent genetic 

studies have since found no evidence to support this. Brachypterolus pulicarius

prefers and performs better on yellow toadflax, even for individuals collected from 

Dalmatian toadflax. Its use of Dalmatian toadflax remains incidental in both the 

US and Canada. Though it is established throughout the US, most information 

has been recorded from western states not covered in this guide. On Dalmatian 

in the western US, abundance is variable. High densities can stunt plant height, 

though its overall impact to flowering and seed production is minimal at most sites. 

The beetle is abundant on yellow toadflax in the western US on which it can delay 

flowering and reduce seed production by 80-90% at some locations. However, 

its overall impact is minimal. It is abundant on yellow toadflax in Canada, but its 

overall impact is limited. It delays flowering and seed production but has not truly 

changed the scope or prevalence of problems associated with yellow toadflax. It is 

found sporadically on Dalmatian toadflax in Canada but appears to be too rare to 

have any major impact on seed production. 

REDISTRIBUTION: This beetle is already widespread throughout much of 

North America. Where necessary, adults can be collected by aspirating, tapping, 

or sweeping individuals from toadflax flowers. Adults should be collecting 

during spring when plants are in bud or flowering and transferred to uninfested 

toadflax patches in groups of 200. Establishment can be monitored by observing 

adults on toadflax stem tips the following spring. Alternatively, flowers can be 

dissected to reveal larvae feeding within during late spring and early summer.

NOTES: Competition between Rhinusa antirrhini and B. pulicarius prevents 

additive impact in many locations. Though B. pulicarius was first an accidental 

introduction in the US, it is approved for 

redistribution. It has been redistributed 

intentionally in both the US and Canada. 

It is likely present in many more 

eastern states in the US than what 

have been officially documented. 

Dalmatian yellow
152 Biological Control in Eastern North America toadflaxesRhinusa antirrhini (Paykull)

Toadflax seed capsule weevil

SYNONYMS: Gymnetron antirrhini (Paykull)

DESCRIPTION: Eggs are oval and flattened. Larvae are C-shaped, creamy white 

with dark brown head capsules, and up to 4 mm long. Adults are gray to black 

and covered in dense, short hairs. They have a long, curved, and pointed snout 

and a wide body. Adults collected from yellow toadflax are typically 2.5-3 mm 

long while those developing on Dalmatian are up to 5 mm long.

a b c

Rhinusa antirrhini a. larva in seed capsule; b. adult (a,b Ivo Toševski, CABI); c. adults on flowers 

(Eric Coombs, Oregon Department of Agriculture, bugwood.org)

LIFE CYCLE: Overwintering adults emerge in late spring and feed on toadflax 

shoot tips, leaf buds, and young leaves. As toadflax flowers open, adults feed on 

pollen and flower tissue. Females lay 40-50 eggs singly inside flower ovaries; this 

oviposition triggers the development of galls of enlarged seed tissue. Larvae feed 

on seed tissue through three instars. Pupation occurs within seed capsules, with 

adults emerging in late summer or early fall to overwinter in plant litter. There 

is one generation per year.

DAMAGE: Adult feeding is typically insignificant. Galls and larval feeding destroy 

the viability of affected seeds. 

PREFERRED HABITAT: The habitat preferences of R. antirrhini are unknown. 

It is distributed throughout most yellow toadflax infestations in North America, 

indicating it is well adapted to a variety of conditions.

RELEASE HISTORY: This species was initially an unintentional introduction 

documented on yellow toadflax in the US (MA) in 1909 and in Canada (QC, 

ON) by 1917. It spread naturally and via intentional redistributions throughout 

the US and Canada on both yellow and Dalmatian toadflax. An additional 
Biological Control in Eastern North America 153toadflaxes

Coleoptera: Curculionidae

strain was intentionally introduced from the former Yugoslavia and released on 

Dalmatian toadflax in western Canada in 1993 and the western US in 1996.

CURRENT STATUS: Attacks both Dalmatian and yellow toadflax in North 

America. On Dalmatian, R. antirrhini is established largely in western states and 

provinces not covered in this guide, and its impact on Dalmatian has not been 

studied. This beetle is well established on yellow toadflax throughout the US. 

Larval feeding destroys some seeds in attacked capsules, and seed reductions of 

85-90% have been reported at some western sites; however, seed reduction is 

typically much lower and has minimal impacts on plant density. In Canada, the 

widespread distribution of R. antirrhini has yet to lead to satisfactory control 

of yellow toadflax. It is believed the overall impact of R. antirrhini on yellow 

toadflax is limited, and likely also limited on Dalmatian toadflax. 

REDISTRIBUTION: This beetle is already widespread throughout much of 

North America. Where necessary, adults can be tapped from toadflax foliage 

during late spring when plants are bolting to flowering and can be transferred to 

uninfested toadflax patches in groups of 200. Establishment can be monitored 

by observing adults on toadflax flowers the following spring. Alternatively, seed 

capsules can be dissected to reveal larvae within them throughout the summer.

NOTES: Competition between R. antirrhini and Brachypterolus pulicarius prevents 

additive impact in many locations. Though R. antirrhini was first an accidental 

introduction in the US, it is approved for redistribution within North America. 

It has been redistributed intentionally in both the US and Canada and is likely 

present in many more eastern states in the US than what have been officially 

documented.

Four species of Rhinusa are currently established on toadflaxes in North America. 

Adult R. antirrhini have more pointed and curved snouts than R. neta and are 

dark grayish-black while R. neta are lighter gray to brown. Rhinusa antirrhini, R. 

neta, and R. linariae all have short hairs on their 

bodies while the hairs of R. linariae are 

longer and upright. Rhinusa antirrhini

and R. neta adults attack flowers and 

shoot tips and larvae attack seeds, R. 

linariae adults attack stems and larvae 

attack roots, and R. pilosa adults and 

larvae attack stems.

Dalmatian yellow
154 Biological Control in Eastern North America toadflaxesRhinusa linariae (Panzer)

Toadflax root-galling weevil

SYNONYMS: Gymnetron linariae Panzer

DESCRIPTION: Eggs are pale yellow, smooth surfaced, and pear-shaped. Larvae 

are C-shaped, creamy white with brown head capsules and up to 4 mm long. 

Adults are small and black with pronounced, curved snouts. They are covered in 

dense, short hairs and up to 2.5 mm long.

a b

Rhinusa linariae a. adult (Bob Richard, USDA APHIS PPQ, bugwood.org); b. galls on yellow 

toadflax roots (Ivo Toševski, CABI)

LIFE CYCLE: Overwintering adults emerge in spring and feed on new toadflax 

shoots. Females lay eggs singly into pockets chewed into toadflax roots and root 

crowns, triggering gall formation. Larvae feed on galled root tissue through 

three instars. Pupation occurs in galls with new adults emerging in mid- to late 

summer. Adults often feed briefly on toadflax stems and then overwinter in soil 

or plant litter. There is one generation per year.

DAMAGE: Root galls disrupt nutrient and water transport and may act as a 

metabolic sink. Adult and larval feeding reduces nutrient reserves which may 

stunt plants and reduce reproductive output.

PREFERRED HABITAT: The habitat preferences of R. linariae in North 

America are unknown because confirmed established populations are restricted 

to limited sites in BC in western Canada. In Europe, R. linariae does well in 

grassland habitats, is rarely found in subalpine habitats, and is absent from 

alpine zones.

RELEASE HISTORY: Individuals from Germany were released on Dalmatian 

and yellow toadflax in the western US in 1996. Populations from central and 
Biological Control in Eastern North America 155toadflaxes

Coleoptera: Curculionidae

southern Europe and southern Russia were released on both Dalmatian and 

yellow toadflax in western Canada in 1996. After US introductions failed to 

establish, weevils established in BC in western Canada were redistributed to the 

western US in 2008 and again in 2015. The 2008 releases failed to establish.

CURRENT STATUS: This weevil attacks only yellow toadflax in North America. 

It has only been released in western North America, and is currently confirmed 

established only in CO (US) and BC (Canada). Adult foliage feeding and larval 

galling are known to reduce plant nutrient reserves. At some locations in BC, 

populations are reportedly having significant impacts; however, populations 

in CO and BC are generally limited. Because populations are slow to build, 

redistributions are made whenever possible. 

REDISTRIBUTION: Populations are restricted to CO (US) and BC (CAN) 

where they are generally too small to redistribute. Where appropriate, adults 

could be collected from toadflax stems and flowers in spring using a sweep 

net and aspirator. They can be transferred in groups of 100-200 to uninfested 

yellow toadflax patches. Establishment can be monitored by observing adults 

on toadflax foliage the following spring or by digging up roots in summer to 

observe galls on root tissue. 

NOTES: Four species of Rhinusa are currently established on toadflaxes in North 

America. Adult R. linariae have a more pointed and curved snout than R. neta

and are black while R. neta are gray to brown. Adult R. linariae have short, dense 

hair on their bodies while R. pilosa have longer, upright hairs. Rhinusa linariae

differs from R. antirrhini in its location of attack (adults on stems and larvae on 

roots compared to R. antirrhini adults attacking flowers and larvae attacking 

seeds).

yellow
156 Biological Control in Eastern North America toadflaxesCalophasia lunula (Hufnagel)

Toadflax moth

DESCRIPTION: Eggs are pale yellow, strongly ribbed, and slightly conical. 

Larvae are gray initially but have vivid black and yellow stripes with white spots 

at the final instar. They can be up 4.6 cm long. Pupae are reddish-brown or 

golden within green cocoons. Adults are mottled gray-brown with light and dark 

markings on the wings. They are 1-1.5 cm long with a wingspan of 2.5-3 cm.

a b c

Calophasia lunula a. larva, b. cocoon (Gary Piper, Washington State University, bugwood.org); c. 

adult (a,c Laura Parsons & Mark Schwarzländer, University of Idaho)

LIFE CYCLE: Adults emerge in late spring and feed on nectar of toadflaxes and 

other plants. Females lay up to 100 eggs singly on toadflax foliage. Larvae feed 

on young leaves, but will consume older, tougher lower stem leaves as plants 

become increasingly defoliated. Larvae nearing the end of the fifth and final 

instar move to the base of toadflax plants and spin cocoons of silk, chewed leaves, 

and soil that they attach to stem bases, plant litter, or soil. Adults emerge in midsummer and repeat the process. There are 1-3 generations per year, depending 

on climate. The final generation overwinters as pupae within cocoons.

DAMAGE: Severe defoliation of seedlings and one-year-old plants can be fatal; 

older, larger plants can usually rebound from defoliation, although defoliated 

plants are less vigorous and may produce fewer flowers. Complete defoliation of 

an entire patch of toadflax by this moth has not been documented.

PREFERRED HABITAT: This species prefers warm, dry sites with coarsetextured soils and sparse toadflax populations. Establishment can be limited in 

cold climates, at northern latitudes, and at high elevations. 

RELEASE HISTORY: Individuals from Switzerland were released in Canada 

beginning in 1962 on both Dalmatian toadflax (MB, NS, ON, SK) and 

yellow toadflax (MB, NB, NS, ON). After limited establishment only in ON, 

individuals from the former Yugoslavia were released in Canada in 1989 (NB, 
Biological Control in Eastern North America 157toadflaxes

Lepidoptera: Noctuidae

d e

Calophasia lunula d. larvae and damage (Laura Parsons & Mark Schwarzländer, University of 

Idaho); e. larval damage (Susan Turner, British Columbia Ministry of Forests)(d,e bugwood.org)

NS). Moths that established from the Swiss release were redistributed from ON 

to the US in 1968 and released on both Dalmatian and yellow toadflax, but only 

in western states.

CURRENT STATUS: Attacks both Dalmatian and yellow toadflax in North 

America. In the US, C. lunula is established only in western states not covered 

in this guide where its populations are limited on both Dalmatian and yellow 

toadflax (though some localized population explosions occur). At high densities 

it can lead to patch defoliation, but this does not have a significant impact on 

attacked plants. In Canada, both source populations established but are only 

moderately abundant, and the moth’s impact is limited. Cold climates and 

parasitism may also limit populations in some parts of Canada.

REDISTRIBUTION: Adults are easily damaged by sweep netting and difficult 

to find so this species is best transferred in the larval stage. Larvae can be gently 

picked from toadflax foliage using flexible forceps in summer through fall 

and transferred to new sites in groups of 100. Later instars may regurgitate 

a dark liquid when handled; this is not harmful to the insect or collector. 

Establishment can be monitored by observing 

larvae on toadflax foliage throughout 

the following growing season. 

NOTES: There are reportedly some 

concerns regarding this species’ host 

specificity; caution should be taken 

during redistributing to areas with 

desirable snapdragon species present. Dalmatian yellow
158 Biological Control in Eastern North America toadflaxes

Non-Established Biocontrol Agent

Eteobalea intermediella Riedl &

E. serratella Treitschke

(Lepidoptera: Cosmopterigidae)

DESCRIPTION AND LIFE CYCLE: 

Both species are very similar, differing 

mainly in their egg appearance, egglaying behavior, and number of 

generations per year. Adults are slender, 

8-10 mm long, and are black with 

white and yellow spots. Adults emerge 

in late spring, and females lay up to 180 eggs in loose strings of 3-8. Eteobalea 

intermediella lays eggs in the lower leaf axils or on the base of yellow toadflax and 

non-flowering Dalmatian toadflax stems. Eteobalea serratella lays eggs at the base 

of yellow toadflax stems or on the soil surface. at the base of toadflax stems. The 

pattern on the surface of E. intermediella eggs is net-like while the surface of E. 

serratella eggs has a ridged appearance, marked by fine parallel lines or furrows. 

Larvae bore into the root crown where they feed on tissue inside tunnels they 

carve and line with silk. Larvae are cream-colored with brown head capsules. 

They develop through five instars and are up to 12 mm long. E. serratella has 

one generation per year while E. intermediella has two; second generation adults 

emerge in mid-summer. Mature larvae of both species overwinter in roots then 

pupate in spring inside cocoons within the root crown.

RELEASE HISTORY: Eteobalea intermediella from former Yugoslavia and E. 

serratella from Italy were introduced against both Dalmatian and yellow toadflax 

in the western US in 1996. Eteobalea intermediella from Serbia was released on 

Dalmatian toadflax in western Canada in 1991. Eteobalea serratella from Italy 

was released on yellow toadflax in western Canada and NS beginning in 1992. 

All introductions are believed to have failed establishment in both the US and 

Canada.

Eteobalea intermediella (Ivo Toševski, CABI)
Biological Control in Eastern North America 159toadflaxes

Unapproved Non-Indigenous Natural Enemy

Rhinusa neta (Germar)

(=Gymnetron netum)

(Coleoptera: Curculionidae)

DESCRIPTION AND LIFE CYCLE: 

Overwintering adults emerge in late 

spring and feed on toadflax shoot tips, 

leaf buds, and young leaves. Adults 

are gray or brown with a snout that 

is somewhat blunt and only slightly 

curved and not tapered or pointed. 

Adults are covered in dense, short hairs 

and are typically 3 mm long. As toadflax flowers open, adults feed on pollen and 

flower tissue. Females lay 40-50 eggs singly inside flower ovaries. Larvae feed on 

seed tissue through three instars. Larvae are C-shaped, creamy-white with light 

brown head capsules, and are up to 4 mm long. Pupation occurs within seed 

capsules, with adults emerging in late summer or early fall to overwinter in soil 

or plant litter. There is one generation per year. 

HISTORY AND CURRENT STATUS: This beetle was unintentionally 

introduced and discovered on both Dalmatian and yellow toadflax in the eastern 

US in 1937 and in Canada by 1957. It has not been intentionally redistributed 

in either country. In the US, R. neta now occurs on both toadflaxes in several 

eastern states and at least WA in the Northwest, but only in scattered populations. 

In Canada, it is more widespread on yellow toadflax, but only found sporadically 

on Dalmatian toadflax. In both countries, R. neta prefers yellow toadflax over 

Dalmatian toadflax. Larval feeding destroys a high proportion of seeds in 

attacked capsules, though overall attack rates on yellow toadflax are typically 

limited in the US. Even in Canada, where yellow toadflax attack rates are higher, 

satisfactory control has yet to be achieved. Not approved for redistribution in 

the US.

Rhinusa neta (Ivo Toševski, CABI)
160 Biological Control in Eastern North America mile-a-minuteMile-a-minute weed

Persicaria perfoliata (L.) H. Gross

SYNONYMS: Devil's tearthumb, Asiatic tearthumb, devil’s-tail tearthumb, giant 

climbing tearthumb, minuteweed Polygonum perfoliatum L.

ORIGIN: Native to Asia, it was introduced to North America in the 1930s, likely 

unintentionally mixed in with holly seeds. 

DESCRIPTION: Herbaceous, annual climbing vine growing from a shallow 

and fibrous root system. The vines grow up to 20 ft long (6 m) in a single 

growing season, blanketing trees and surrounding vegetation. Stems are green 

but turn red with age. Stems, petioles, and the undersides of major leaf veins all 

have sharp, hook-like barbs that are distinctively curved backwards. Leaves are 

alternate, triangular, and 1.2-2.8 in long by 0.8-2 in wide (3-7 cm long and 2-5 

cm wide). An ocrea (saucer-shaped sheath) up to 0.8 in across (2 cm) surrounds 

the stem at each leaf node. Flowers are tiny, greenish-white, and inconspicuous. 

They appear in clusters of 10-15 at vine tips or at the axils of upper leaves. 

a b

Mile-a-minute weed a. vines; b. infestation (a,b Leslie J. Mehrhoff, University of Connecticut, 

bugwood.org)
Biological Control in Eastern North America 161mile-a-minute

Family Polygonaceae

c d e

Mile-a-minute weed c. leaves, barbs, and ocreae; d. flowers (Dalgial); e. fruit and ocrea (c,e Leslie J. 

Mehrhoff, University of Connecticut, bugwood.org)

Fruits are green and berry-like, turning a deep purple-blue at maturity. Each 

fruit contains a single shiny black seed (achene).

HABITAT: Mile-a-minute weed prefers low, wet ground and full sun, but it can 

tolerate partial shade. In North America it is restricted to regions with cold 

winter temperatures and can be found in flood plains, parks, conservation areas, 

and orchards and along ditches, forest edges, roadsides, and rights-of-way.

ECOLOGY: This species reproduces by seed only. In North America, most 

germination is in early spring from March through April. Flowers appear from 

June to July and fruits are generally produced from June through the first frost, 

depending on site conditions. Seeds are readily transported by water, humans, 

birds, deer, and other animals. Seeds may remain viable in the soil for up to 6 years.

BIOLOGICAL CONTROL:Rhinoncomimus latipes has been released throughout 

the northeastern and mid-Atlantic US since 2004 and 

has significantly impacted this weed by reducing weed 

density, cover, and seed production. Impacts 

are greatest under warm, dry conditions and 

with high plant competition. Additional 

species are being tested for potential future 

release into North America. No species are 

approved in Canada; the weed has not been 

recorded in Canada.

NOTES: Mile-a-minute weed is used 

in traditional Chinese medicine for 

its supposedly diuretic and antiinflammatory properties.
162 Biological Control in Eastern North America mile-a-minuteRhinoncomimus latipes Korotyaev

Mile-a-minute weevil

DESCRIPTION: Eggs are tan-colored, cylindrical, and covered with thin strips 

of frass. Larvae are up to 3 mm long and have a creamy-yellow body and brown 

head capsule. Adults are 2 mm long with longitudinal ridges in their elytra. They 

are black when they first emerge from pupation, but after a few days of feeding 

are covered in a rust-colored layer derived from plant sap.

a b c d

Rhinoncomimus latipes a. egg on leaf tip; b. larva; c. black adult (Kelsey Paras, University of 

Delaware); d. rust-colored adult (a,b,d Amy Diercks)(a-d bugwood.org)

LIFE CYCLE: Overwintering adults feed on young leaves in early spring, leaving 

a characteristic “shot-hole” feeding pattern. Eggs are laid singly (40-130 per 

female) on buds, stems, and the undersides of leaves. Hatching larvae burrow 

into plant nodes to feed within mile-a-minute stems, developing through three 

instars. At maturity, larvae drop to the soil to pupate. Total development time 

from egg to adult is 3-4 weeks. There are 3-4 generations per year. Last generation 

adults overwinter in the soil or plant litter.

DAMAGE: Larvae mining in stems weakens the plant and stunts growth. Adult 

feeding at stem tips reduces growth and seed production while defoliation causes 

leaves and stems to curl and wither. At high densities, the combination of larval 

and adult feeding kills impacted vines.

PREFERRED HABITAT: This beetle prefers sunny habitats. While it survives in 

dry and moist conditions, its impact on mile-a-minute weed is highest at warm, 

dry locations. 

RELEASE HISTORY: Populations sourced from China were released in the 

northeastern and mid-Atlantic US from 2004 onward (CT, DE, MD, MA, NJ, 

NY, NC, PA, RI, WV, VA).
Biological Control in Eastern North America 163mile-a-minute

Coleoptera: Curculionidae

e f

Rhinoncomimus latipes e. larva and damage (Amy Diercks); f. adult feeding damage (Ellen C. Lake, 

USDA ARS Invasive Plant Research Laboratory)

CURRENT STATUS: The overall impact has been substantial, but varies from 

year to year. Populations have increased considerably and rapidly dispersed from 

most sites. In NJ, R. latipes has already spread to all known weed infestations. 

This species decreases mile-a-minute weed density, cover, and seed production. 

The greatest reduction in plant density and biomass occurs in communities with 

competing vegetation. Impact is highest in warm, dry years and lower in cool, 

moist years, especially when those conditions occur in spring. 

REDISTRIBUTION: This species is best collected in the adult stage from midMay through August. Adults can be tapped from mile-a-minute vines into 

collection containers. They can be transferred to new sites in groups of 250-

500. Establishment can be monitored by observing adults or their distinctive 

shot-hole feeding pattern on mile-a-minute foliage the following summer. 

Alternatively, stems can be dissected throughout the growing season for evidence 

of larval mining. 

NOTES: This beetle was initially misidentified as Homorosoma chinensis (Wagner) 

in the native range of China.
164 Biological Control in Eastern North America spurgesCypress spurge

Euphorbia crassipes L.

ORIGIN: Native to Eurasia. Likely introduced to North America as an ornamental; 

recorded present by the late 1850s.

DESCRIPTION: Herbaceous perennial with thickly clustered stems typically 

growing no higher than 16 in (40 cm) tall. The root system is rhizomatous. Roots 

are brown, have pinkish buds, and can be 10 ft deep (3 m). Leaves are green, 

alternate, stalkless, narrow (0.06 to 0.125 in or 1-2 mm wide), and 0.5-1.5 in 

(1-3 cm) long. They have smooth margins and are clustered tightly on plant 

stems. Flowers are tiny, lime green, and enclosed by showy, yellow-green bracts. 

They are arranged in clusters at stem tips. Seed pods contain three smooth, 

elongated, gray-brown seeds. 

HABITAT: Cypress spurge capitalizes on disturbance and can be found in dry to 

moderately moist meadows, pastures, cemeteries, and gardens and along forest 

edges, roadsides, and rights-of-way.

ECOLOGY: This species reproduces both by seed and by its spreading root 

a b

Cypress spurge a. plant (Danny Steven S.); b. infestation (Leslie J. Mehrhoff, University of 

Connecticut, bugwood.org)
Biological Control in Eastern North America 165spurges

Family Euphorbiaceae

c d

Cypress spurge c. leaves (Sander van der Molen); d. flowers (Leslie J. Mehrhoff, University of 

Connecticut, bugwood.org)

system. Root pieces as small as 0.5 in (1 cm) can develop into new plants under 

the right circumstances. Peak germination is in early spring from March through 

May with new seedlings usually not flowering the first year. Flowers appear from 

May to June. A second flowering often occurs in late summer or early fall. Seed 

pods shatter upon maturation, scattering seeds great distances. Seeds are also 

readily transported by water, humans, and other animals. Seeds may remain 

viable in soil for up to 20 years.

BIOLOGICAL CONTROL: Of the five Aphthona spp. established on cypress 

spurge, A. nigriscutis is most effective at reducing plant density. Aphthona flava

is moderately abundanct, and its impact may be significant in combination with 

other species. Aphthona lacertosa, A. cyparissiae and A. czwalinai are believed to 

have limited abundance and impact. Populations of Hyles euphorbiae, Spurgia 

capitigena, and S. esulae are limited and have only minor impact, even at high 

densities. Lobesia euphorbiana, Oberea erythrocephala, and 

Pegomya euphorbiae failed to establish on cypress spurge 

in eastern North America. Chamaesphecia 

empiformis may have established, but additional 

confirmation is needed.

NOTES: North American cypress spurge is 

considered a complex of subspecies from 

multiple introductions. Cypress spurge is 

very similar to leafy spurge, but it grows 

shorter and less robust, has much smaller 

bracts, and narrower and denser leaves 

than leafy spurge. A toxic, milky latex 

oozes from damaged stems and leaves. 
166 Biological Control in Eastern North America spurgesLeafy spurge

Euphorbia esula L.

ORIGIN: Native to Eurasia. Likely introduced to eastern North America in 

contaminated ship’s ballast and as a seed contaminant in the prairie states and 

provicnes; recorded as early as 1827.

DESCRIPTION: Herbaceous perennial with thickly clustered stems up to 3 ft tall 

(90 cm) and roots 9-21 ft deep (3-7 m). The root system is rhizomatous; roots are 

brown and have pinkish buds. Leaves are alternate, narrow, and 1-3 in long (2.5-

7.5 cm). They have smooth margins and a deep midvein. Flowers are tiny, lime 

green, and enclosed by showy, yellow-green bracts. They are arranged in clusters 

at stem tips. Seed pods contain three smooth, elongated, gray-brown seeds. 

HABITAT: This weed occupies many different habitats and soil types and can be 

found from grasslands to forests to riparian areas. It is dominant in pastures and 

abandoned fields, and along roadsides.

ECOLOGY: Leafy spurge reproduces both by seed and by its spreading root 

system. Root pieces as small as 0.5 in (1 cm) can develop into new plants. Peak 

a b

Leafy spurge a. plant (John M. Randall, The Nature Conservancy); b. infestation (Leslie J. 

Mehrhoff, University of Connecticut)(a,b bugwood.org)
Biological Control in Eastern North America 167spurges

Family Euphorbiaceae

c d e

Leafy spurge c. milky latex; d. leaves and stem (K. George Beck & James Sebastian, Colorado State 

University); e. flowers (c,e Norman E. Rees, USDA ARS)(c-e bugwood.org)

germination is from April through May with new seedlings usually not flowering 

the first year. Flowers appear from June to July. A second flowering often occurs 

in late summer or early fall. Seed pods shatter upon maturation, scattering seeds 

great distances. Seeds are also readily transported by water, humans, and other 

animals. Seeds may remain viable in the soil for up to eight years.

BIOLOGICAL CONTROL: This weed is most problematic in the Midwest and 

West, but biocontrol has also proven beneficial on some infestations in the East. 

Of the five Aphthona spp. established on leafy spurge, A. lacertosa and A. nigriscutis

are effective at reducing plant density. Aphthona flava is moderately abundant, 

and its impact may be significant in combination with other species. Aphthona 

cyparissiae and A. czwalinai are believed to have limited abundance and impact. 

Lobesia euphorbiana has a moderate impact locally in Canada. Populations of 

Hyles euphorbiae, Oberea erythrocephala, P. euphorbiae, Spurgia capitigena, and 

S. esulae are typically limited, but even at high densities 

they have only minor impact. Aphthona abdominalis, 

Minoa murinata, and Pegomya curticornis failed 

to establish on leafy spurge in eastern North 

America. Chamaesphecia spp. also likely failed. 

NOTES: Leafy spurge is a morphologically 

variable species believed to represent a 

complex of forms, species, and hybrids. It 

is very similar to cypress spurge, but grows 

taller and more robust, has larger bracts, and 

much wider leaves that are more sparsely 

spaced than cypress spurge. A toxic, milky 

latex oozes from damaged stems and leaves.
168 Biological Control in Eastern North America spurgesAphthona lacertosa Rosenhauer

Brown-legged leafy spurge flea beetle

DESCRIPTION: Larvae are up to 5 mm long, slender, whitish and with a brown 

head capsule. Adults are shiny black and 3 mm long. Legs are largely reddishbrown in color. The top of the hind femurs sometimes have dark patches.

a b

Aphthona lacertosa a. adult (Laura Parsons & Mark Schwarzländer, University of Idaho); b. adults 

and damage (Todd Pfeiffer, Klamath County Weed Control)(a,b bugwood.org)

LIFE CYCLE: Overwintering larvae resume feeding on young roots in early 

spring as cypress and leafy spurge are resuming growth. Pupation occurs in the 

soil. Adults are active from early to late summer as spurges bolt, flower, and 

mature. Each female lays 200-300 eggs into the soil throughout the growing 

season. Hatching larvae burrow into spurge roots to feed, developing through 

three instars. There is one generation per year.

DAMAGE: Larvae feed on root hairs and young roots, inhibiting root function 

and stunting spurge stem growth. Adults feed on leaves and flowers, decreasing 

photosynthesis and plants’ sugar-making ability for root reserves.

PREFERRED HABITAT: This species does best in moderately-dense infestations 

of cypress and leafy spurge found growing in loamy soils. It can adapt locally to 

both dry and wet habitats in the US but does better at mesic to moist sites in 

Canada. It does poorly in soils with too much sand or clay.

RELEASE HISTORY: Individuals from Austria, Hungary, and the former 

Yugoslavia were released on leafy spurge in the US beginning in 1993 (IA, 

MI, MN, NE, NH, NY, ND, RI, SD, WI) and redistributed to cypress spurge 

starting in 1995 (NH, RI). Many US releases contained a mixture of Aphthona

species. In Canada, individuals from Hungary and the former Yugoslavia were 

released on leafy spurge in western provinces in 1987; eastern releases began on 
Biological Control in Eastern North America 169spurges

Coleoptera: Chrysomelidae

leafy spurge in MB in 1991. Beetles initially from Hungary were redistributed 

from the US and released in MB and western Canada beginning in 1995.

CURRENT STATUS: Aphthona lacertosa attacks both cypress and leafy spurge 

in North America. Its abundance is limited on cypress spurge in RI, US where 

it and A. czwalinai are being replaced by A. flava and A. nigriscutis. Its density 

and impact in NH are unknown. This beetle is widespread and abundant on 

leafy spurge in the US. Along with A. nigriscutis, it is significantly reducing leafy 

spurge density at the local level in most regions, though it is not effective at all 

sites. In Canada, this beetle is established only on leafy spurge, on which it is 

reducing plant density at most sites. Aphthona lacertosa appears to be displacing 

A. czwalinai at many locations. Resampling efforts are currently underway at 

initially pure A. czwalinai release sites and pure A. lacertosa sites throughout 

Canada for molecular analysis.

REDISTRIBUTION: This species is best collected in the adult stage using a net 

and aspirator in early summer when plants are bolting. They can be transferred 

to new sites in groups of 200-300. Establishment can be monitored by observing 

adults on spurge foliage the following summer during the heat of the day. Keep 

in mind flea beetles quickly jump away when disturbed. Alternatively, roots can 

be dissected for evidence of larval feeding from autumn through the following 

spring. Note that feeding larvae can be extremely difficult to distinguish from 

other leafy spurge Aphthona species. 

NOTES: Five species of Aphthona are established on cypress and leafy spurge in 

North America. Aphthona lacertosa has lighter colored hind femurs than the 

other black spurge flea beetle, A. czwalinai. Aphthona cyparissiae, A. flava, and A. 

nigriscutis are all brown spurge flea beetles.

cypress leafy
170 Biological Control in Eastern North America spurgesAphthona nigriscutis Foudras

Black dot leafy spurge flea beetle

DESCRIPTION: Larvae are 1-6 mm long, slender, whitish (more translucent 

when young) and with a brown head capsule. Adults are usually just over 3 mm 

long. They are orangish-brown and typically have a black dot on the back near 

the leading edge of the wings.

a b

Aphthona nigriscutis a. larva (Neal Spencer, USDA ARS, bugwood.org); b. adult (R. Richard, USDA 

APHIS)

LIFE CYCLE: Overwintering larvae resume feeding on root hairs in early spring 

as cypress and leafy spurge are resuming growth. Pupation occurs in the soil. 

Adults are active from early to late summer as spurges bolt, flower, and mature. 

Females lay numerous eggs in groups on spurge stems at or just below the soil 

surface. Hatching larvae burrow into spurge roots to feed, developing through 

three instars. There is one generation per year.

DAMAGE: Larvae feed on root hairs and young roots, inhibiting root function 

and stunting spurge stem growth. Adults feed on leaves and flowers, decreasing 

photosynthesis and plants’ sugar-making ability for root reserves.

PREFERRED HABITAT: This species prefers relatively sparse cypress and leafy 

spurge patches at dry sites with sandier soil. It does poorly in soils with too much 

clay.

RELEASE HISTORY: In Canada, individuals from Hungary were released on 

leafy spurge beginning in 1983 (MB, NS, ON) and on cypress spurge in ON 

starting in 1986. After establishment in Canada, beetles were redistributed to 

leafy spurge in the US beginning in 1989 (IA, MI, MN, NE, NH, NY, ND, 

RI, SD, WI) and redistributed to cypress spurge in 1995 (NH, RI). Many US 

releases contained a mixture of Aphthona species.
Biological Control in Eastern North America 171spurges

Coleoptera: Chrysomelidae

CURRENT STATUS: Aphthona nigriscutis attacks both cypress and leafy spurge 

in North America. This species is considered abundant on cypress spurge in RI, 

US where, along with A. flava, it is replacing A. lacertosa and A. czwalinai. Under 

ideal conditions, stem density may decrease quickly, but unattacked roots help 

plants recover; numerous years are typically required for this biocontrol agent to 

decrease cypress spurge populations permanently. Its density and impact in NH 

are unknown. Aphthona nigriscutis is widespread and abundant on leafy spurge 

in the US. Along with A. lacertosa, it is significantly reducing plant density at 

the local level in most regions, though it is not effective at all sites. Impact may 

be hindered by a bacterium which causes high mortality in males, resulting in 

female-biased populations. In Canada, A. nigriscutis abundance and impact are 

variable. It helps control cypress spurge in the immediate vicinity of release sites 

at dry, open locations. It is extremely effective at reducing or removing leafy 

spurge in open, warm, very dry habitats with lighter soils. Populations are low 

or absent at moist, sheltered sites on heavy soil.

REDISTRIBUTION: This species is best collected in the adult stage using a net 

and aspirator in mid-summer when plants flower. They can be transferred to 

new sites in groups of 200-300. Establishment can be monitored by observing 

adults on spurge foliage the following summer during the heat of the day. Keep 

in mind flea beetles quickly jump away when disturbed. Alternatively, roots can 

be dissected for evidence of larval feeding from autumn through the following 

spring. Note that feeding larvae can be very difficult to distinguish from other 

spurge Aphthona species. 

NOTES: Five species of Aphthona are established on cypress and leafy spurge in 

North America. The other brown spurge flea beetles (A. cyparissiae and A. flava)

typically do not have the black spot on the back as does A. nigriscutis. Aphthona 

flava is also usually more orange in color than A. nigriscutis, though coloration 

differences among brown spurge flea beetles are often unreliable. Aphthona 

czwalinai and A. lacertosa are black spurge flea beetles. Spillover feeding by A. 

nigriscutis was observed on the native Euphorbia 

robusta; as leafy spurge density declined, 

so did feeding on E. robusta, and E. 

robusta populations increased.

cypress leafy
172 Biological Control in Eastern North America spurgesAphthona flava Guillebeau

Copper leafy spurge flea beetle

DESCRIPTION: Larvae are 1-6 mm long, slender, whitish (more translucent 

when young) and with a brown head capsule. Adults are orangish-copper in 

color and 3.5 mm long. Females are slightly larger than males.

a b c

Aphthona flava a. larva (Neal Spencer, USDA ARS); b. adult (USDA APHIS PPQ); c. adults and 

damage (Norman E. Rees, USDA ARS)(a-c bugwood.org)

LIFE CYCLE: Overwintering larvae resume feeding on root hairs in early spring 

as cypress and leafy spurge are resuming growth. Pupation occurs in the soil. 

Adults are active from early summer to early fall as spurges bolt, flower, and 

mature. Females lay numerous eggs in groups on spurge stems at or just below 

the soil surface. Hatching larvae burrow into spurge roots to feed, developing 

through three instars. There is one generation per year.

DAMAGE: Larvae feed on root hairs and young roots, inhibiting root function 

and stunting spurge stem growth. Adults feed on leaves and flowers, decreasing 

photosynthesis and plants’ sugar-making ability for root reserves.

PREFERRED HABITAT: This species does best in moderately-dense infestations 

of leafy spurge found on more mesic, dry sites in alluvial soils above flood lines 

and light shade (US) and at mesic, dry sites with warm temperatures (CAN). 

It does poorly in soils with too much sand or clay. It is probably less likely to 

survive low temperatures than other Aphthona spp. 

RELEASE HISTORY: Beetles from Hungary and Italy were released on leafy 

spurge in the western US beginning in 1985; eastern US releases began in 

1986 (IA, MI, MN, NE, NH, NY, ND, RI, SD, WI). Established beetles were 

redistributed to cypress spurge in 1995 (NH, RI). Many US releases contained 

a mixture of Aphthona species. In Canada, indiviuals from Hungary and Italy 

were released on leafy spurge starting in 1982 (MB, NS, ON) and on cypress 
Biological Control in Eastern North America 173spurges

Coleoptera: Chrysomelidae

spurge in 1982 (NS, ON). Beetles established on leafy spurge were redistributed 

to cypress spurge within BC in western Canada in 2011.

CURRENT STATUS: Aphthona flava attacks both cypress and leafy spurge in 

North America. This species is considered abundant on cypress spurge in RI, US 

where, along with A. nigriscutis, it is replacing A. lacertosa and A. czwalinai. Under 

ideal conditions, stem density may decrease quickly, but unattacked roots help 

plants recover; numerous years are typically required for this biocontrol agent to 

decrease cypress spurge populations permanently. Its density and impact in NH 

are unknown. Aphthona flava is considered widespread on leafy spurge in the US, 

but overall it is much less abundant than other Aphthona spp. It persists at fairly 

low levels with little noticeable impact on infestations. In Canada, this beetle is 

only established on cypress spurge in western Canada where its abundance and 

impact are unknown. On leafy spurge, this species is moderately abundant in ON 

and western Canada. Leafy spurge density has declined where populations of A. 

flava are high; however, this is typically at sites that have been grazed by sheep and 

where A. nigriscutis is also present. 

REDISTRIBUTION: This beetle is best collected in the adult stage using a net 

and aspirator in late summer when plants are flowering and beginning to mature. 

They can be transferred to new sites in groups of 200-300. Establishment can be 

monitored by observing adults on spurge foliage the following summer during 

the heat of the day. Keep in mind flea beetles quickly jump away when disturbed. 

Alternatively, roots can be dissected for evidence of larval feeding from autumn 

through the following spring. Note that feeding larvae can be extremely difficult 

to distinguish from other spurge Aphthona species. 

NOTES: Five species of Aphthona are established on cypress and leafy spurge in 

North America. Aphthona flava is typically more orange than the other two brown 

spurge flea beetles, A. cyparissiae and A. nigriscutis. Aphthona flava also does not 

have the black spot on the back that A. nigriscutis has. However, coloration 

differences among brown spurge flea beetles are 

often unreliable. Aphthona czwalinai and 

A. lacertosa are black spurge flea beetles.

cypress leafy
174 Biological Control in Eastern North America spurgesLobesia euphorbiana (Freyer)

Spurge leaf tying moth

DESCRIPTION: Eggs are translucent yellow and round. Larvae have brown 

head capsules and segmented bodies up to 12 mm long. Young larvae are 

pale yellowish-green, turning nearly black with maturity. Pupae are pale green 

initially, turning brown with time. Adults are mottled with yellow, brown, and 

rust tones and light-colored legs and antennae. Adults can be 9-11 mm long 

with wingspans up to 14 mm.

a b c

Lobesia euphorbiana a. larva; b. cocoon; c. pupa (a-c Laura Parsons, University of Idaho, bugwood.org)

LIFE CYCLE: Adults emerge in spring as spurge is bolting and flowering. Females 

lay eggs immediately (an average of 55 eggs each) and singly on the undersides 

of leaves. Hatching larvae move towards terminal leaf tips and tightly tie leaves 

with silky webbing. They feed on buds within ties, developing through four 

instars typically, but occasionally five when food is scarce. Prior to pupation, 

larvae move to leaf tips where they spin thick webs. Second generation adults 

emerge from mid- to late summer and repeat the process. Second generation 

pupae overwinter in plant litter within folded leaves. There are two generations 

per year, with three possible in suitable climates.

DAMAGE: Larval feeding of buds prevents flowering, and repeated heavy attack 

may eventually kill plants. When larvae vacate leaf ties, the sites often receive 

secondary attack from thrips and aphids.

PREFERRED HABITAT: This species does best at mesic sites where plants have 

high nutrient quality. Complete development requires high temperatures so 

sites that are warm to hot over summer are preferred. This moth often inhabits 

riparian areas as well as fringe forested areas, so shade is tolerated. 

RELEASE HISTORY: Moths from Italy were released in Canada on leafy spurge 

in western provinces beginning in 1983; eastern releases began in 1987 (MB, 
Biological Control in Eastern North America 175spurges

Lepidoptera: Tortricidae

d e

Lobesia euphorbiana d. adult (CABI, previously IIBC); e. damage (Laura Parsons, University of 

Idaho, bugwood.org)

NS, ON). Established individuals were redistributed to cypress spurge in ON in 

1991, though this redistribution failed.

CURRENT STATUS: Lobesia euphorbiana is established only on leafy spurge 

and only in Canada where populations are dispersing well from release sites. Its 

impact is moderate and fluctuates with leafy spurge density and vigor. Repeated 

heavy attack kills target plants at some locations.

REDISTRIBUTION: The best stage for redistribution is larvae in leaf ties. In 

early to mid-summer, clip below infested leaves. Transfer material to new sites as 

soon as possible and ensure infested leaves touch the foliage of plants at the new 

sites. Establishment can be monitored the following season by observing leaf ties 

on new spurge foliage throughout the growing season.

NOTES: Gall terminals made by Spurgia esulae will occasionally be used by L. 

euphorbiana. This species is not approved for release in the US.

leafy
176 Biological Control in Eastern North America spurgesAphthona cyparissiae (Koch)

Brown dot leafy spurge flea beetle

DESCRIPTION: Larvae are 1-5 mm long and have a white body and yellow 

head with a thick head capsule. Adults are usually just over 3 mm long. They are 

a light reddish-brown color and oval in shape.

a b

Aphthona cyparissiae a. pupa (Neal Spencer, USDA ARS, bugwood.org); b. adult (R. Richard, 

USDA APHIS)

LIFE CYCLE: Overwintering larvae resume feeding on young roots in early 

spring as cypress and leafy spurge are resuming growth. Pupation occurs in the 

soil. Adults are active from early summer to late summer as spurges bolt, flower, 

and mature. Females lay numerous eggs into the soil throughout the growing 

season. Hatching larvae burrow into spurge roots to feed, developing through 

three instars. There is one generation per year.

DAMAGE: Larvae feed on root hairs and young roots, inhibiting root function 

and stunting spurge stem growth. Adults feed on leaves and flowers, decreasing 

photosynthesis and plants’ sugar-making ability for root reserves.

PREFERRED HABITAT: This beetle does best in moderately-dense infestations 

of cypress and leafy spurge found on dry to semi-moist sites. It does poorly in 

soils with too much clay.

RELEASE HISTORY: In the US, beetles from Austria, Hungary, Italy, and 

Switzerland were released on leafy spurge beginning in 1986 (IA, MN, NE, NH, 

NY, ND, RI, SD, WI) and redistributed to cypress spurge starting in 1995 (NH, 

RI). Many US releases contained a mixture of Aphthona species. In Canada, 

beetles from Austria, Hungary, and Switzerland were released on leafy spurge 

beginning in 1982 (MB, NS, ON, SK) and on cypress spurge starting in 1982 

(ON, QC).
Biological Control in Eastern North America 177spurges

Coleoptera: Chrysomelidae

CURRENT STATUS: Aphthona cyparissiae attacks both cypress and leafy spurge 

in North America. In the US, it is present on cypress spurge in two states and 

abundant in at least one (RI). It is well established at a few leafy spurge release 

sites but is overall much less abundant on leafy spurge than other Aphthona

spp. On both spurge species, A. cyparissiae populations are highest at dry, mesic 

sites with sandy loam soils. Under these conditions, stem density may decrease 

quickly, but unattacked roots help plants recover. Numerous years under the right 

conditions are required for this biocontrol agent to decrease spurge populations 

permanently. Damage is typically greatest in combination with other Aphthona 

spp. In Canada, high populations of A. cyparissiae effectively control cypress and 

leafy spurge at dry, open sites, but insect densities are too low and ineffective 

elsewhere.

REDISTRIBUTION: This species is best collected in the adult stage using a net 

and aspirator in mid-summer when plants are flowering. They can be transferred 

to new sites in groups of 200-300. Establishment can be monitored by observing 

adults on spurge foliage the following summer during the heat of the day. Keep 

in mind flea beetles quickly jump away when disturbed. Alternatively, roots can 

be dissected for evidence of larval feeding from autumn through the following 

spring. Note that feeding larvae can be extremely difficult to distinguish from 

other spurge Aphthona species. 

NOTES: Five species of Aphthona are established on cypress and leafy spurge 

in North America. Aphthona nigriscutis typically has a black spot on the back 

while A. flava is generally more orange in color than A. cyparissiae. However, 

coloration differences among brown spurge flea beetles are often unreliable. 

Aphthona czwalinai and A. lacertosa are black spurge flea beetles.

cypress leafy
178 Biological Control in Eastern North America spurgesAphthona czwalinai (Weise)

Black leafy spurge flea beetle

DESCRIPTION: Larvae are up to 5 mm long, slender, whitish and with a brown 

head capsule. Adults are shiny black. Middle and front legs are reddish-brown 

while the entire surfaces of the hind femurs are dark. Males are just under 3 mm 

long, while females are usually just over 3 mm.

a b

Aphthona czwalinai a. pupa (Neal Spencer, USDA ARS, bugwood.org); b. adult (R. Richard, USDA 

APHIS)

LIFE CYCLE: Overwintering larvae resume feeding on young roots in early 

spring as cypress and leafy spurge are resuming growth. Pupation occurs in the 

soil. Adults are active from early summer to late summer as spurges bolt, flower, 

and mature. Females lay numerous eggs in the soil throughout the growing 

season. Hatching larvae burrow into spurge roots to feed, developing through 

three instars. There is one generation per year.

DAMAGE: Larvae feed on root hairs and young roots, inhibiting root function 

and stunting spurge stem growth. Adults feed on leaves and flowers, decreasing 

photosynthesis and plants’ sugar-making ability for root reserves.

PREFERRED HABITAT: This species does best in moderately-dense infestations 

of cypress and leafy spurge found on more mesic sites. It does poorly in soils with 

too much sand or clay.

RELEASE HISTORY: Beetles from Austria and Hungary were released on leafy 

spurge in the western US beginning in 1987; eastern releases began in 1989 (IA, 

MI, MN, NE, NH, ND, RI, SD, WI). Established beetles were redistributed 

to cypress spurge in 1995 (NH, RI). Many US releases contained a mixture of 

Aphthona species. In Canada, beetles from Austria were released on leafy spurge 

in western provinces starting in 1985; eastern releases began on leafy spurge in 
Biological Control in Eastern North America 179spurges

Coleoptera: Chrysomelidae

1986 (MB, ON) and on cypress spurge in 1987 (ON). Established indviduals 

initially from Austria and Hungary were redistributed from the US and released 

in MB and western Canada beginning in 1995.

CURRENT STATUS: Aphthona czwalinai attacks both cypress and leafy spurge 

in North America. In the US, it is established on both cypress and leafy spurge, 

though populations are very limited on cypress spurge. For many years it was 

believed that control of leafy spurge on the local level in the US was achieved 

primarily by A. nigriscutis, A. czwalinai and A. lacertosa. Aphthona czwalinai was 

thought to have been a major component in the early years of the leafy spurge 

biocontrol program, until it was discovered that most of what was being called 

A. czwalinai was in fact A. lacertosa. It was subsequently considered insignificant, 

until large populations were recently found in ND where this beetle does best at 

mesic sites. In Canada, A. czwalinai is established only on leafy spurge, and its 

distribution is limited. Release sites now appear to be dominated by A. lacertosa.

Resampling efforts are currently underway at initially pure A. czwalinai release 

sites and pure A. lacertosa sites throughout Canada for molecular analysis.

REDISTRIBUTION: This beetle is best collected in the adult stage using a net 

and aspirator in mid-summer when plants are flowering. They can be transferred 

to new sites in groups of 200-300. Establishment can be monitored by observing 

adults on spurge foliage the following summer during the heat of the day. Keep 

in mind flea beetles quickly jump away when disturbed. Alternatively, roots can 

be dissected for evidence of larval feeding from autumn through the following 

spring. Note that feeding larvae can be extremely difficult to distinguish from 

other spurge Aphthona species. 

NOTES: Five species of Aphthona are established on cypress and leafy spurge in 

North America. Aphthona czwalinai has solid dark hind femurs compared to the 

other black spurge flea beetle, A. lacertosa. Aphthona cyparissiae, A. flava, and A. 

nigriscutis are all brown spurge flea beetles. This species is occasionally referred 

to by the spelling of A. czwalinae.

cypress leafy
180 Biological Control in Eastern North America spurgesHyles euphorbiae (L.)

Leafy spurge hawk moth

DESCRIPTION: Larvae are up to 10 cm long. They change color upon 

maturation going from dark green, to brown and yellow longitudinally striped, 

to green with white spots, to red, black, yellow, and white with a horn at the 

back end. Larvae contain leafy spurge toxin and are poisonous. Adults have 

wingspans up to 5 cm and are white, pink, and brown.

a b c

Hyles euphorbiae a. larva; b. pupa (Whitney Cranshaw, Colorado State University, bugwood.org); 

c. adult (a,c R. Richard, USDA ARS)

LIFE CYCLE: There are up to two generations per year. Adults emerge in early to 

mid-summer when cypress and leafy spurge are bolting/flowering. Females lay 

70-150 eggs in clumps on leaves and bracts. Hatching larvae feed on these parts 

as cypress and leafy spurge are flowering. Larvae feed through five instars, and 

then pupation occurs in the soil. Next generation adults emerge in late summer 

and repeat the cycle. New hatching larvae move to the soil to pupate; pupae 

overwinter.

DAMAGE: Larval feeding defoliates spurge, though this often does not kill the 

attacked plants.

PREFERRED HABITAT: This species does best in thick spurge infestations 

growing in open areas near trees. Pupae are heavily preyed upon so sites with 

low populations of rodents, ants, etc. are preferred. 

RELEASE HISTORY: Moths from France, Germany and Switzerland were 

released in Canada on cypress spurge beginning in 1965 (ON) and on leafy 

spurge in 1966 (MB, ON). Established populations were redistributed to leafy 

spurge in the western US starting in 1966; eastern releases began in 1974 (MD, 

MN, NE, NY, ND, SD). The same Canadian source material was released on 

cypress spurge starting in 1976 (MD, NY, VA) and on the related invasive 
Biological Control in Eastern North America 181spurges

Lepidoptera: Sphingidae

Euphorbia oblongata in the western US (failed) in 1974. Moths from Hungary 

were then released on leafy spurge in 1980 in the western US (ND, SD 1985). 

CURRENT STATUS: Hyles euphorbia attacks both cypress and leafy spurge in 

North America. It is established on the fertile tetraploid form of cypress spurge 

in NY where initially high densities of this moth have since decreased due to 

high levels of predation. Even where high densities have resulted in total cypress 

spurge defoliation, impact is insignificant as plant populations can tolerate 

yearly defoliation. Both source populations established on leafy spurge in the US 

where they have since intermixed and can no longer be differentiated. Though 

moth densities may be locally high in some years, disease and predation typically 

prevent densities from developing to levels substantial enough to impact leafy 

spurge populations in some areas. Even where high densities have resulted in 

total plant defoliation, impact has been insignificant as this does not kill plants. 

In Canada, H. euphorbia abundance is typically limited to moderate on both 

cypress and leafy spurge due to predation. Even when moth populations are 

high, plants recover from defoliation. It has limited biocontrol value alone, but 

may stress the weeds when in combination with other biocontrol agents.

REDISTRIBUTION: Though this species can be collected in various stages, 

larval is the preferred stage to transport. Both generations are suitable for 

collection, either in spring/early summer as spurges are beginning to flower, or 

late summer/fall as spurges mature. Any instar can be collected, though larger, 

mature larvae are most conspicuous and easy to find. Gently remove larvae by 

hand or with forceps, and place them directly in a waiting container. Larvae 

may regurgitate liquid as a defense measure; this is not harmful to the insect 

or collector. They can be transferred in groups of 50-100 to uninfested spurge 

patches. Establishment can be monitored by observing adults or larvae on 

cypress or leafy spurge foliage throughout the following growing season.

NOTES: This biocontrol agent resembles native hawk moth species but is more 

active during daytime, while native hawk moths 

are more nocturnal.

cypress leafy
182 Biological Control in Eastern North America spurgesOberea erythrocephala (Schrank)

Red-headed leafy spurge stem borer

DESCRIPTION: Mature larvae are up to 20 mm long, slender, and white with a 

yellowish head and a head capsule. Bodies are obviously segmented with inflated 

segments. Adults are slender and 10-12 mm long with long, dark antennae, red 

heads, and black eyes. Adult bodies are dark grey above and lighter grey with 

reddish markings below. Their legs are yellowish-brown.

a b c

Oberea erythrocephala a. larva in root (R. Richard, USDA ARS); b. adult (Mark Schwarzländer, 

University of Idaho); c. damage (Eric Coombs, Oregon Department of Agriculture)(a-c bugwood.org)

LIFE CYCLE: Adults emerge in early to mid-summer and feed on spurge leaves 

and flowers. Females girdle a spurge stem, chew a hole, and deposit a single egg 

(up to 40 in a lifetime). Hatching larvae mine down the stem until reaching the 

root crown and nearby lateral roots. Larvae overwinter and pupate within the 

root crown in spring. Adults chew through remaining plant tissue and emerge 

from the soil. There is one generation per year in Europe, though two years may 

be required for full development in colder parts of North America.

DAMAGE: Adult feeding is insignificant. Larval mining kills shoots and reduces 

root reserves. 

PREFERRED HABITAT: This species prefers mesic sites with tree cover. It 

is believed to do well in riparian areas and has been shown to survive winter 

temperatures below freezing.

RELEASE HISTORY: Individuals from Italy were released on leafy spurge in the 

western US in 1980. After these failed to establish, new individuals were sourced 

from Austria, Hungary and Italy and released on leafy spurge in the western US 

in 1982; eastern releases began in 1985 (IA, MI, MN, NE, NH, NY, ND, RI, 

SD, WI). In Canada, individuals from Switzerland were released on leafy spurge 
Biological Control in Eastern North America 183spurges

Coleoptera: Cerambycidae

in eastern provinces starting in 1979 (MB, ON from 1981) and on cypress 

spurge in MB and ON beginning in 1986. 

CURRENT STATUS: Oberea erythrocephala attacks only leafy spurge in North 

America. In the US, it was initially believed to have the potential to greatly 

depress leafy spurge populations, but beetle densities have remained too low to 

impart significant impact in the field. At some infestations, it may cause declines 

in larger plants. In Canada, O. erythrocephala is established only in the western 

province of AB where it is considered rare. At high densities, small plants can 

be killed, however field populations are too low to have a significant impact in 

Canada.

REDISTRIBUTION: Adults should be collected in early summer as spurge 

flowers. They often fly or drop when disturbed, so sweep netting is less efficient 

than for other species. Alternatively, the beetles can be collected by hand or with 

soft forceps and placed directly in containers. Collect during the heat of the day. 

They can be transferred to new sites in groups of 50-100. Establishment can be 

monitored by observing adults on spurge foliage the following summer during 

the heat of the day or by dissecting stems/root crowns for mining larvae from 

summer through the following spring.

NOTES: This species may attack only specific biotypes of leafy spurge, thus 

limiting its efficacy in many areas.

leafy
184 Biological Control in Eastern North America spurgesPegomya curticornis (Stein) & P. euphorbiae (Kieffer)

Leafy spurge gall flies

SYNONYMS: Pegomya argyrocephala (Meigen)

DESCRIPTION: These two species are virtually 

indistinguishable. Larvae are light gray maggots. 

Adults are dark colored with maroon eyes and 

scattered black hairs on the head and thorax. Wings 

are dark and translucent and span up to 6 mm. 

LIFE CYCLE: Adults emerge in early spring and lay eggs 

in leaf buds of new shoots after spurges have resumed 

growing. Hatching larvae tunnel down young shoots, 

which have less toxic milky latex than older shoots. 

Larvae develop through three instars. Larval vascular 

feeding induces the formation of galls in subterranean 

stems and in spurge roots. They overwinter as pupae 

within galls. There is one generation per year.

DAMAGE: Mined and galled cypress and leafy spurge 

stems wilt and eventually die.

PREFERRED HABITAT: Specific habitat requirements for both species are 

unknown.

RELEASE HISTORY: Pegomya curticornis and P. euphorbiae were collected from 

Hungary and released on leafy spurge in MB and western Canadian provinces in 

1988. Pegomya euphorbiae from the same source was also released on leafy spurge 

in ON in 1990 and on cypress spurge in ON in 1989. 

CURRENT STATUS: Pegomya euphorbiae is thought to be established only on 

leafy spurge in North America. It was initially believed that all introductions of 

Pegomya spp. failed to established on both cypress and leafy spurge in Canada. 

In 2014, however, establishment was confirmed at the original leafy spurge 

release sites in MB and SK. While there is still some uncertainty, it appears the 

established species is P. euphorbiae. Its abundance and impact on leafy spurge 

is unknown. It is still believed that P. euphorbiae failed to establish on cypress 

spurge in Canada. 

REDISTRIBUTION: Populations are likely too limited to field collect, so 

releases should be made using laboratory colonies when available. In the future, 

should Pegomya spp. be further established, field redistributions can be done by 

Pegomya euphorbiae adult 

(André Gassmann, CABISwitzerland)
Biological Control in Eastern North America 185spurges

Diptera: Anthomyiidae

gathering galled stems and roots in summer as spurges are actively growing and 

flowering. Bunch gathered plant material and transfer to new sites as soon as 

possible, and place them upright to help avoid predation. Establishment can be 

monitored the following growing season by cutting stems and observing mining 

larvae and galls.

NOTES: These two species were previously lumped together under the name 

Pegomya argyrocephala. Pegomya spp. were approved in both the US and 

Canada but were released only in Canada.

P. euphorbiae

leafy
186 Biological Control in Eastern North America spurgesSpurgia capitigena (Bremi) & S. esulae Gagné

Leafy spurge tip gall midges

SYNONYMS: Bayeria capitigena Bremi

DESCRIPTION: Both “species” are virtually indistinguishable (see Notes). Eggs 

are orange and cylindrical. Larvae are orange and 1-2 mm long. Adults are dark 

gray with reddish abdomens and tiny, dark heads. Adults are just under 2 mm 

long; males are slightly smaller than females. Males have forceps on the end of 

the abdomen while females have an exposed ovipositor.

a b c

Spurgia esulae a. eggs (L.L. Berry); b. larvae and pupae in galls (Norman Rees, USDA ARS); c. adult 

(USDA APHIS PPQ Archive)(a-c bugwood.org)

LIFE CYCLE: Adults emerge in spring when cypress and leafy spurge are 

resuming growth. They live only a number of hours. Eggs are laid in groups of 

20+ among leaves on spurge growing tips. Hatching larvae feed on tips (through 

three instars), causing galls to form. Pupation occurs in silken cocoons within 

galls; adults emerge and repeat the cycle. There are two generations/year in cold 

climates, and 3-5 in warmer areas if new shoots are available. Last generation 

larvae overwinter and pupate in the soil.

DAMAGE: Larvae attacking spurge growing tips destroy the shoots’ ability to 

flower and produce seeds. Shoots eventually die and are replaced by new stems 

that are attacked by the next generation of midges.

PREFERRED HABITAT: These species prefer dense spurge infestations growing 

on south-facing slopes in cool climates, and can reportedly tolerate some shading.

RELEASE HISTORY: These two species were previously lumped together 

under the name Bayeria capitigena. After their introduction, B. capitigena was 

transferred to the genus Spurgia and split into two species. Consequently, the 

release history is convoluted. What is now S. esulae was introduced from Italy 

and released on leafy spurge in the US beginning in 1985 (IA, MI, MN, NE, 
Biological Control in Eastern North America 187spurges

Diptera: Cecidomyiidae

NH, NY, ND, RI, SD, WI). These were redistributed to cypress spurge in the 

eastern US in 1995 (NH, RI). Spurgia capitigena is believed to have been a 

contaminant of one shipment of S. esulae released on leafy spurge in ND in 

1986. Both species were redistributed to leafy spurge in Canada starting in 1987 

(MB, NS, ON). Following establishment, both species were redistributed to 

cypress spurge in NS in 1990, and S. capitigena alone was also redistributed 

to cypress spurge in ON and QC in 1990. Spurgia capitigena from France was 

intentionally released on leafy spurge in ND, US from 2001-2002.

CURRENT STATUS: Spurgia esulae attacks both cypress and leafy spurge in 

North America. In the US, densities are generally low. Even where abundant, galls 

form after flowering, so its overall impact is insignificant. Spurgia capitigena (from 

both sources) is established only on leafy spurge in ND where its impact is largely 

unknown but assumed to be negligible. In Canada, S. capitigena is established on 

both cypress and leafy spurge in ON; to date S. esulae is confirmed established 

only on leafy spurge. Where established, galls from both species prevent flower 

formation and seed production, though their overall impact appears negligible.

REDISTRIBUTION: Midges are most safely collected by gathering galls infested 

with both larvae and pupae. The first generation is often best synchronized with 

its spurge host, so collect from mid-May to mid-June (depending on location) 

prior to spurge flowering. Clip at least 6 in (15 cm) below galls, bunch the 

clipped stems, and wrap the bottoms in damp paper towels. Transfer these to 

new sites as soon as possible, and place them upright to help avoid predation. 

Establishment can be monitored by observing galls on new spurge shoot tips 

throughout the following growing season.

NOTES: More recent studies with these midges revealed no evidence for two 

species. However, a revision of this group has not been published, so the two 

separate names are retained as valid at the time of publication of this field guide.

S. capitigena

cypress

S. capitigena

leafy

S. esula

cypress

S. esula

leafy
188 Biological Control in Eastern North America spurges

Non-Established Biocontrol Agents

Aphthona abdominalis Duftschmidt

(Coleoptera: Chrysomelidae)

DESCRIPTION AND LIFE CYCLE: 

In Europe, overwintering adults emerge 

from plant litter in late spring and feed 

on leafy spurge foliage during bolting 

or flowering. Adults are 2 mm long and 

grayish-brown with a reddish-yellow 

head and transparent outer wings. 

Females lay eggs at or just below the soil 

surface. Hatching larvae burrow into 

spurge roots to feed, developing through three instars. Larvae are white with a 

yellow head and prominent head capsule and are 1-3 mm long. Pupation occurs 

in the soil near roots. There are up to 4 generations per year.

RELEASE HISTORY: Beetles from Italy were released on leafy spurge in ND 

and the western US from 1993, but failed to establish. Not released in Canada.

Chamaesphecia spp. (Lepidoptera: Sesiidae)

DESCRIPTION AND LIFE CYCLE: 

Three Chamaephecia spp. have been 

released. All three have white larvae up to 

15 mm long. In Europe, overwintering 

larvae resume feeding in root tunnels 

in early spring. They mine upwards in 

the plant stem, pupating within. Adults 

emerge from late spring and lay eggs on 

spurge plants. Adults are dark brown 

with yellow-white bands. Bodies are typically 10-14 mm long; wingspans are 

16-22 mm. Each wing is brown with yellow markings and a few transparent 

windows with dark margins. Body and wing tips are fringed. Hatching larvae 

burrow into the stem, mine down, and feed on roots. There is one generation 

per year. 

RELEASE HISTORY: Chamaesphecia empiformis from Europe was released 

on cypress spurge in ON, CAN (1970, 1989) and the western US (1975). 

Aphthona abdominalis adult (R. Richard, 

USDA APHIS, bugwood.org)

Chamaesphecia crassicornis adult (R. Richard, 

USDA APHIS, bugwood.org)
Biological Control in Eastern North America 189spurges

Non-Established Biocontrol Agents

Chamaesphecia tenthrediniformis from Europe was released on leafy spurge in 

ON (CAN) in 1971 and in the western US beginning in 1975. Starting in 1991, 

C. crassicornis and C. hungarica from Europe were released on leafy spurge, but 

only in western states and provinces not covered in this guide. It ws initially 

believed that all introductions of all species failed; however, what is believed to 

be an individual C. empiformis was photographed on cypress spurge in ON in 

2015. Because the species in question could be C. tenthridiniformis, additional 

confirmation is needed before declaring either species established in North 

America. Chamaesphecia astatiformis was released in western CAN (1993) 

but not released in the US.

Minoa murinata (Scopoli)

(Lepidoptera: Geometridae)

DESCRIPTION AND LIFE CYCLE: 

Pupa overwinter just beneath the soil 

surface. Adults emerge in late spring 

and lay eggs on spurge leaves. Adults 

are gray to tan with a metallic sheen. 

Wings are fringed and span 18-23 mm. 

Hatching larvae feed on the undersides 

of leaves. Larvae are grayish-pink with 

variable black markings, brown heads, 

pink warts, and an orange or yellow stripe along each side. They can be up to 13 

mm long and develop through four instars before dropping to the soil in fall to 

pupate. There can be two generations per year in suitable climates. Adults of the 

second generation emerge in late summer.

RELEASE HISTORY: Moths from Germany and Austria were released on leafy 

spurge in Canada from 1988 (MB and western provinces), but eventually died 

out. Not released in the US.

Minoa murinata adult (Siga)
190 Biological Control in Eastern North America tree-of-heavenTree-of-heaven

Ailanthus altissima (Mill.) Swingle

SYNONYMS: Chinese sumac, stinking sumac, paradise tree, Brooklyn palm

ORIGIN: Native to China and Taiwan and intentionally introduced to 

Pennsylvania, US in 1784 as an ornamental.

DESCRIPTION: Deciduous tree typically growing 55-89 ft tall (17-27 m) with a 

trunk diameter of 3.3 ft (1 m) from a shallow, suckering root system. The bark is 

light gray and smooth, becoming rougher and fissured with age. The compound 

leaves are alternate, 1-3 ft long (30-90 cm), and have 10-41 leaflets arranged in 

pairs. Leaflets are 2-7 in long (5-18 cm) and 1-2 in wide (2.5-5 cm). Each leaflet 

is lance-shaped with smooth margins, a pointed tip, and squared base. Each 

leaflet base has 1-2 teeth with a prominent gland on the back of each tooth. Male 

and female flowers usually appear on separate plants (dioecious). Both flowers are 

small with 5 greenish-yellow petals and appear in large clustered infloresences 4-8 

in long (10-20 cm) at the ends of new shoots. Leaves, branches, and male flowers 

all have a foul odor. Female flowers produce winged fruits (similar in appearance 

to maples) that are twisted, 1 in long (2.5 cm), and turn reddish in fall.

a b

Tree-of-heaven a. tree (Robert Vidéki, Doronicum Kft.); b. infestation (Karan A. Rawlins, 

University of Georgia)(a,b bugwood.org)
Biological Control in Eastern North America 191tree-of-heaven

Family Simaroubaceae

c d e

Tree-of-heaven c. glands on back of leaflet teeth (Annemarie Smith, bugwood.org); d. inflorescence 

(H. Zell); e. mature fruits and foliage (Luis Fernández García)

HABITAT: Tree-of-heaven can thrive in a variety of climates from humid forests to 

arid mountainsides, but does best in full sun in temperate regions. It is a pioneer 

of disturbed sites, such as highway rights-of-way, fallow fields, vacant lots, and 

rail lines, but can move outwards into undisturbed native vegetation. It does 

well in a variety of soil conditions and can tolerate drought but not flooding. 

Prolonged cold and snow cover cause dieback, but the tree resprouts from roots.

ECOLOGY: Tree-of-heaven reproduces by seed and suckering roots. Seeds 

germinate throughout spring, with highest rates occurring in full sun. It is one 

of the fastest-growing trees in North America, growing 1-6.6 ft ( 0.3-2 m) per 

year. Plants can become reproductive in 1-2 years, and flowering occurs in late 

spring to early summer. A single plant can produce over 300,000 seeds per year. 

Seeds are readily spread by wind and water; some are retained on the parent plant 

over the winter. Seeds are typically viable for less than one year. The leaves are 

deciduous, falling from the tree in autumn and winter. 

New leaves emerge in late spring. The shallow root 

system readily produces suckers. These develop 

into new plants and create large tree-of-heaven 

infestations. Most trees live 30-50 years. 

BIOLOGICAL CONTROL: As of 2016, 

there are no classical biocontrol agents 

approved for use in North America. The 

native wilt Verticillium nonalfalfae is 

currently being studied in experimental 

field tests. Additional species are being 

tested for potential future release in North 

America.
192 Biological Control in Eastern North America tree-of-heaven

Tree-of-Heaven, Native Natural Enemy

Verticillium nonalfalfae (Inderbitzin 

et al 2011) (=V. albo-atrum Reinke & Berthold)

(Plectosphaerellaceae: Phyllachorales)

DESCRIPTION AND LIFE CYCLE: 

Once spores penetrate vascular tissue of 

hosts, the pathogen spreads throughout 

the plant, causing shriveled/dead foliage 

and a yellowish-brown discoloration of 

the sapwood directly beneath the bark 

(healthy individuals have white sapwood). 

Wilt spores are spread by herbivorous insects. Resting stages overwinter in the soil. 

CURRENT STATUS: This wilt is naturally occurring in North America. Since 

2002, a strain believed to have evolved to be specific to tree-of-heaven has been 

observed killing large swaths of tree-of-heaven in PA, VA, and OH, US. Following 

extensive host range testing, inoculation techniques were developed, and the 

fungus is being distributed at various test sites in the US. As of 2016, this species is 

still under study in the US, and it is illegal to move it across state lines.

Verticillum wilt on tree-of-heaven (The 

Pennsylvania State University)
Biological Control in Eastern North America 193tree-of-heaven
194 Biological Control in Eastern North America alligatorweedAlligatorweed

Alternanthera philoxeroides (Mart.) Griseb.

SYNONYMS: alligator weed, Achyranthes philoxeroides (Mart.) Standl.

ORIGIN: Native to South America, it was introduced to North America by 1897 

in ship’s ballast.

DESCRIPTION: This perennial species has two growth forms: aquatic and 

terrestrial. Both forms have opposite, stalk-less leaves typically 1-5.5 in long (2-

14 cm). The aquatic form often creates dense floating mats. The aquatic form 

produces hollow stems emerging up to 20 in (50 cm) above water, and its leaves 

are long, lance-shaped, and smooth. The terrestrial form grows much shorter 

and produces stems that are less hollow with shorter, rounder leaves compared 

to the aquatic form. The flowers of both forms appear in ball-like clusters 0.6 

in (1.5 cm) in diameter on long stalks during warm summer months. There are 

6-20 flowers in each cluster. Individual flowers have five white, papery sepals 

a b

Alligatorweed a. plant (Graves Lovell, Alabama Department of Conservation and Natural 

Resources); b. infestation (Chris Evans, University of Illinois)(a,b bugwood.org)
Biological Control in Eastern North America 195Alligatorweed

Family Amaranthaceae

c d e

Alligatorweed c. leaves, stems of the aquatic form; d. leaves, stems of the terrestrial form (c,d James H. 

Miller, USDA Forest Service); e. flowers (Rebekah D. Wallace, University of Georgia)(c-e bugwood.org)

that resemble petals. Seeds are smooth and lens-shaped, but are not typically 

produced (or viable) in North America.

HABITAT: Alligatorweed is most often found growing in shallow water along 

banks of all types of water bodies. The terrestrial form is also found in dried beds 

of water bodies as well as pastures, lawns, and some crops.

ECOLOGY: Alligatorweed grows year-round in warm climates; it primarily 

reproduces vegetatively in North America. Fragmentation of plants (e.g. from 

flooding or mechanical or chemical control) can yield numerous fragments 

with at least one node which are then moved from one place to another on 

currents, boats, machinery, etc., and take root in suitable habitat. The aquatic 

form produces dense floating mats from the hollow stems and may be rooted 

to the shoreline or free-floating. The terrestrial form produces an extensive 

rhizomatous root system from which new stems arise. 

Flowering occurs in mid to late summer, but seeds are 

typically not produced in North America.

BIOLOGICAL CONTROL: Agasicles hygrophila

and Arcola malloi are effective on the aquatic 

form of alligatorweed at warm locations 

in the US. Cold temperatures hinder 

their overwintering at inland sites, and 

they are ineffective on the terrestrial form. 

Amynothrips andersoni attacks both forms of 

alligatorweed, but has only minor impact. 

The weed does not occur in Canada.
196 Biological Control in Eastern North America alligatorweedAgasicles hygrophila Selman & Vogt

Alligatorweed flea beetle

DESCRIPTION: Eggs are pale yellow and cylindrical. Larvae are yellow initially, 

turning black as they age. Larvae can be up to 6 mm long. Pupae are creamcolored initially but darken with age. Adults are 4-6 mm long and black with 

four longitudinal stripes (2 on each elytra). Adults have enlarged hind femurs, 

enabling them to jump large distances. Females are slightly larger than males. 

a b

Agasicles hygrophila a. larvae and feeding damage; b. adult and feeding damage (a,b Gary 

Buckingham, USDA ARS, bugwood.org)

LIFE CYCLE: Adults emerge in early spring and begin mating and ovipositing; 

females lay an average of 1,100 eggs during their lifetime. Eggs are deposited 

in two rows (12-54 eggs per cluster) on the undersides of alligatorweed leaves. 

Larvae feed on leaf tissue, often leaving transparent feeding “windows”. Larvae 

develop through three instars prior to chewing into alligatorweed stems. Pupation 

occurs within the plant stems. Adults emerge and feed on alligatorweed leaves 

and stems. There are 4-6 generations per year. Last generation adults overwinter 

among roots and stems of alligatorweed along water body margins. 

DAMAGE: Larval and adult feeding on leaves and stems is often severe, leading to 

eventual submergence of the floating mat and clearing waterways.

PREFERRED HABITAT: This beetle attacks only the aquatic form of 

alligatorweed, though minor feeding has been observed on alligatorweed plants 

that have only recently become terrestrial (following a water drawdown). It 

overwinters only in warmer locations, but extends its range into colder locations 

during summer and autumn. Hot, dry summers reduce beetle populations at 

some locations.

RELEASE HISTORY: Beetles from Uruguay and Argentina were released on 
Biological Control in Eastern North America 197Alligatorweed

Coleoptera: Chrysomelidae

alligatorweed beginning in 1964 (AL, AR, FL, GA, LA, MS, NC, SC, TN, TX). 

Beetles sourced from the southernmost part of this species range in Argentina 

were released in the southeastern US in 1979 in an attempt to increase cold 

tolerance.

CURRENT STATUS: All releases of A. hygrophila are believed to have established 

in the southeastern US, though there is no evidence that beetles from the later 

release from cold portions of the insect’s native habitat have performed any 

better than those released initially. Overall, the abundance of this flea beetle 

varies by season; populations decline during summer due to reduced fecundity 

associated with high temperature. The flea beetle’s impact is likewise variable. It 

is highly successful in northern FL and warmer coastal areas where insects can 

overwinter, but populations are variable elsewhere. It is not effective against the 

terrestrial form of alligatorweed. 

REDISTRIBUTION: This species is best collected in the adult stage using a 

net in early spring. Adults can be transferred to new sites in groups of 200. 

Establishment can be monitored by observing adults or larvae on alligatorweed 

foliage later in the season or the following year. Alternatively, stems of plants with 

heavy feeding damage can be dissected for evidence of pupation throughout the 

following growing season. 

NOTES: This species has not been released in Canada; the weed reportedly 

does not occur in Canada.
198 Biological Control in Eastern North America alligatorweedArcola malloi (Pastrana)

Alligatorweed stem borer

SYNONYMS: Vogtia malloi Pastrana

DESCRIPTION: Eggs are white and oval-shaped. Larvae are white to yellow 

initially, appearing brown at maturity because of several tan, longitudinal, wavy 

stripes. Last instars are up to 14 mm long. Pupae are found in silken cocoons and 

turn from yellow to dark brown with age. Adults hold their wings tightly against 

their bodies; they are 13-14 mm long with a wingspan of 20 mm. Forewings are 

tan to brown with mottled markings. 

a b

Arcola malloi a. larva (USDA ARS); b. adult (Willey Durden, USDA ARS, bugwood.org)

LIFE CYCLE: Adults emerge in spring, and females lay eggs singly at leaf axils 

or on the undersides of alligatorweed leaves. A single female may lay an average 

of 260 eggs in her lifetime. Larvae bore into stem tips and mine downwards, 

feeding on stem tissue through five instars. At maturity, larvae plug stem nodes 

beneath them with chewed tissue in order to seal out water and prepare adult exit 

“windows” by chewing stem tissue but leaving the epidermis intact. Larvae spin 

cocoons in which to pupate, and adults emerge through exit windows. In North 

America, the number of generations per year is unknown; 3-4 generations per 

year have been observed in the native range. Last generation larvae overwinter in 

alligatorweed stems and pupate the following spring.

DAMAGE: Larval mining causes stems to wilt and eventually die, turning yellow 

as they do so. Entire mats often turn yellow and submerge.

PREFERRED HABITAT: The moth is most commonly found on mats of the 

aquatic form of alligatorweed, though plants of the terrestrial form are also 

occasionally attacked. It overwinters only in warmer locations, but extends its 

range into colder locations during summer and autumn.
Biological Control in Eastern North America 199Alligatorweed

Lepidoptera: Pyralidae

c d

Arcola malloi damage to alligatorweed (c,d USDA ARS, bugwood.org)

RELEASE HISTORY: Motns from Argentina were released in FL, GA, NC, 

and SC beginning in 1971 (AL in 1972). This species subsequently dispersed 

naturally to AR, LA, MS, and TX.

CURRENT STATUS: Arcola malloi is established throughout the southeastern 

US where larval burrowing causes stem collapse and waterlogging. The moth is a 

useful adjunct to (but possibly not as good a competitor as) Agasicles hygrophila. 

The moth contributes effectively to control in MS and FL, as well as in TX 

when populations are not limited by adverse conditions. It has an excellent 

dispersal ability with annual spread of up to 620 miles (1,000 km). It most 

likely overwinters in warmer coastal areas and migrates to inland infestations. 

This moth is most effective against floating plant mats; damage to the terrestrial 

form is minimal.

REDISTRIBUTION:Adults are easily damaged so sweeping is not recommended. 

Instead, place stems infested with larvae and pupae into uninfested alligatorweed. 

This can be done throughout the growing season, though the moth is most 

available from midsummer to early autumn. Take care to keep the collected stems 

cool and moist until they can be transferred. Establishment can be monitored 

by observing alligatorweed stems for evidence of larval mining later in the same 

season or in subsequent years. 

NOTES: This moth has reportedly been collected from the 

native Philoxerus vermicularis (L.) Sm. (whose name has 

since been changed to Blutaparon vermiculare (L.) Mears) 

and the native Alternanthera flavescens Kunth. This species 

has not been released in Canada; the weed reportedly 

does not occur in Canada. 
200 Biological Control in Eastern North America alligatorweedAmynothrips andersoni O’Neill

Alligatorweed thrips

DESCRIPTION: Eggs are elongated and yellow at first but turn reddish with 

age. Nymphs are up to 2 mm long. The first nymphal stage is pale yellow, but 

nymphs turn increasingly orange to red with black legs through subsequent 

stages. Adults can be either wing-less or winged (with fringed wings). Most 

winged forms have only short wings and are flightless; long-winged forms are 

uncommon. Adults are 2 mm long and black with black legs and antennae.

a b c

Amynothrips andersoni a. second instar (USDA ARS); b. adult (US Army Corps of Engineers 

ERCD); c. damage (Gary Buckingham, USDA ARS)(a,c bugwood.org)

LIFE CYCLE: Eggs are laid singly (an average of 200 per female) on hairs at 

stem nodes. Unmated females produce all males, but females that are fertilized 

produce equal amounts of male and female progeny. Adults and nymphs feed 

on new growth of alligatorweed leaves and stems. There are multiple overlapping 

generations per year; 4-5 generations have been observed in the native range. All 

stages can overwinter, though the most common overwintering stage is adult.

DAMAGE: Nymphs and adults pierce alligatorweed leaves and stems and suck 

out cell contents. Feeding causes leaf and tip deformation which stunts plants. 

This typically does not kill plants so the overall impact is not severe.

PREFERRED HABITAT: This thrips attacks both the aquatic and terrestrial 

forms of alligatorweed, and is the most cold tolerant of established alligatorweed 

biocontrol agents. Hot summers limit populations.

RELEASE HISTORY: Thrips from Argentina were released in the southeastern 

US beginning in 1967 (AL, CA, FL, GA, LA, MS, SC, TX).

CURRENT STATUS: Amynothrips andersoni successfully established on 

alligatorweed throughout the southeastern US. Though widely distributed, 
Biological Control in Eastern North America 201Alligatorweed

Thysanoptera: Phlaeothripidae

populations are usually limited. It is the least widespread of the alligatorweed 

biocontrol agents established in the US, but the most cold tolerant. Competition 

from the flea beetles limits populations on the aquatic form. It is the only 

established biocontrol agent to impact the terrestrial form of alligatorweed; 

however, damage to both the aquatic and terrestrial forms is usually only light 

(causing some leaf deformation). Predation limits populations in some areas.

REDISTRIBUTION: Due to the low impact of the alligatorweed thrips, this 

species is a low priority for redistribution. At cold locations where the other two 

alligatorweed biocontrol agents are limited, and/or where other control methods 

are not feasible, the thrips is best redistributed on infested plants transferred to 

alligatorweed mats at uninfested sites. Transfers are best made in spring and 

autumn, taking care to keep the collected stems cool and moist until they can be 

transferred. Establishment can be monitored throughout the following growing 

season by checking for adults or nymphs in the curled leaf tips of attacked 

alligatorweed. 

NOTES: This species has not been released in Canada; the weed reportedly 

does not occur in Canada.
202 Biological Control in Eastern North America chamomileScentless chamomile

Tripleurospermum inodorum (L.) Sch. Bip.

SYNONYMS: scentless false mayweed, Matricaria perforata Mérat, 

Tripleurospermum maritimum (L.) W. D. J. Koch ssp. inodorum (L.) Appleq., 

Tripleurospermum perforatum (Mérat) M. Laínz

ORIGIN: Native to Eurasia. Introduced to North America by the 1920s.

DESCRIPTION: An erect, branching annual or short-lived perennial growing 

0.5-3.2 ft tall (15-100 cm) from a fibrous root system. Leaves are alternate and 

very finely divided, giving the plant a fern-like appearance. Flower heads are 

daisy-like with white outer ray florets and yellow inner disc florets. Flower heads 

are typically 1.25-1.6 in (30-40 mm) in diameter. Seeds are small (0.08 in or 2 

mm long), elongate, brown, and ribbed, with no pappus. 

HABITAT: Scentless chamomile is well adapted to many different habitats, 

thriving in disturbance typical of annual and perennial crops, pastures, wasteland, 

roadsides, and ditches. It germinates readily at sites with periodic flooding.

a b

Scentless chamomile a. plant (Robert Vidéki, Doronicum Kft., bugwood.org); b. infestation (Alec 

McClay, McClay Ecoscience)
Biological Control in Eastern North America 203chamomile

Family Asteraceae

c d

Scentless chamomile c. leaves (Caleb Slemmons, University of Wisconsin, Stevens Point, bugwood.

org); d. flower heads (Alec McClay, McClay Ecoscience)

ECOLOGY: Scentless chamomile reproduces by seed only. Plants germinate 

throughout the growing season. Those germinating before mid-July often 

behave as annuals, bolting and flowering within the same growing season. 

Those germinating after mid-July behave as winter annuals, developing into 

an overwintering rosette which bolts and flowers the following summer. Most 

plants die after flowering and setting seed, though a small proportion overwinter 

and re-grow from the root crown to flower again in the following season. This 

species is a prolific seed producer; dense populations can yield up to 1.8 million 

seeds/m2. Seeds are readily transported by water, birds, and other animals, and 

may stay viable up to 15 years.

BIOLOGICAL CONTROL: This weed is most problematic in midwestern and 

western states and provinces, though biocontrol has also proven beneficial on 

some infestations in the East. Both Rhopalomyia tripleurospermi and Omphalapion 

hookerorum are abundant in western Canada, and O. 

hookerorum has large populations in eastern provinces as 

well. Both species reduce scentless chamomile 

seed production. While this does not kill 

plants, they are useful in combination with 

other control methods or where some 

other control methods are not feasible. 

Microplontus edentulus is established only in 

western Canada and is rare in the field with 

no documented impact. No species have 

been approved for use or released in the 

US.
204 Biological Control in Eastern North America chamomileOmphalapion hookerorum (Kirby)

Scentless chamomile seed weevil

SYNONYMS: Apion hookeri Kirby

DESCRIPTION: Eggs are small and round, changing from white to brown with 

age. Larvae are white, C-shaped, and typically up to 2 mm long. Adult males 

are black and 1.5-2 mm long. Females have a metallic sheen in shades of blue, 

turquoise or purple and are typically 2-2.5 mm long. Both males and females 

have rounded bodies and curved snouts with bulging eyes.

a b c

Omphalapion hookerorum a. larva in damaged flower head; b. adult; c. adults on flower head (a-c 

Alec McClay, McClay Ecoscience)

LIFE CYCLE: Female adults emerge in spring and feed on scentless chamomile 

plants prior to laying eggs in young flower heads. Hatching larvae feed on florets 

and seeds, developing through three instars. Pupation occurs within the flower 

head. Adults emerge in late summer and mate, but females do not oviposit. They 

overwinter in soil or litter and will oviposit the following year. Males die before 

winter. There is one generation per year.

DAMAGE: Larval feeding destroys some seeds. Seed consumption does not kill 

existing plants, but does help reduce the rate of scentless chamomile spread.

PREFERRED HABITAT: The weevil is reportedly not restricted to any particular 

habitat in its native range, though it seems to prefer cold, dry continental 

climates.

RELEASE HISTORY: The weevils used for screening and initial releases were 

introduced from Germany and released in western Canada and MB beginning 

in 1992. An adventive population was discovered in NS in 1990, possibly 

introduced by fishing or pleasure boats or via dry ballast from Europe. Both 

intentional and adventive populations eventually intermixed.
Biological Control in Eastern North America 205chamomile

Coleoptera: Brentidae

CURRENT STATUS: Omphalapion hookerorum is established on scentless 

chamomile in MB and NS, Canada as well as in western provinces not covered 

by this guide. The weevil’s abundance is high, and its overall impact is medium. 

In western provinces, up to 78% of scentless chamomile seed heads are attacked 

by O. hookerorum, and up to 32% by Rhopalomyia tripleurospermi. Estimated 

scentless chamomile seed production is reduced up to 19% by a combination 

of both species. Up to 17 O. hookerorum adults have been found in a single seed 

head (mean 3.9). It disperses up to 1.7 miles/year (2.8 km/year).

REDISTRIBUTION: Wherever it is not currently established, adults can be 

transferred in groups of 200. Releases can be made in spring or late summer. 

Adult females can be collected in spring, using an aspirator, from the young buds 

and shoot tips of scentless chamomile. In late summer, adults can be collected 

as they emerge from the mature seed heads. Releases should be made on patches 

of at least 2,000 m2 (0.5 acres). Establishment can be monitored the following 

spring by checking for adults on shoot tips and flower buds, or in summer by 

dissecting capitula for evidence of feeding larvae. 

NOTES: This species has not been released in the US.
206 Biological Control in Eastern North America chamomileRhopalomyia tripleurospermi Skuhravá & Hinz

Scentless chamomile gall midge

DESCRIPTION: Eggs are bright red and elongate. Larvae are bright red initially, 

changing to white at maturity. Male pupae are gray while female pupae are red to 

dark purple. Adult males and females also have distinct appearances. Males are 

approximately 2.5 mm long with a brown head and thorax and gray abdomen. 

Male legs are long and slender. Adult females are typically 2.5-3 mm long with 

a bright red abdomen and shorter, thicker legs. Females contain fully developed 

eggs; larger females contain more eggs.

a b c

Rhopalomyia tripleurospermi a. eggs; b. male pupa; c. female adult (a-c Alec McClay, McClay 

Ecoscience)

LIFE CYCLE: Pupation occurs in spring. Adults emerge in spring, and females 

lay eggs into scentless chamomile leaf axils or unopened buds. Hatching larvae 

enter and feed on bud tissue, developing through three larval instars. Larval 

feeding induces the formation of galls, which appear as masses of crowded, leaflike growths with a mossy appearance. Galls may develop on growing points, 

leaves, stems, or flowers. In AB Canada there are three generations per year, but 

two are expected in colder climates. Larvae overwinter in galls and pupate within 

galls the following spring.

DAMAGE: Larval-induced galls interrupt and stunt the normal growth of 

scentless chamomile, reducing flowering. High attack rates can kill overwintering 

rosettes.

PREFERRED HABITAT: The midge appears to thrive in all habitats where 

scentless chamomile occurs.

RELEASE HISTORY: Midges from Austria were released in Canada beginning 

in 1999 (MB and western provinces).
Biological Control in Eastern North America 207chamomile

Diptera: Cecidomyiidae

d e

Rhopalomyia tripleurospermi d. gall on rosette; e. gall on shoot tip (d,e Alec McClay, McClay 

Ecoscience)

CURRENT STATUS: Rhopalomyia tripleurospermi is established on scentless 

chamomile only in western Canada provinces not covered in this guide (AB, 

BC, SK). In western Canada, its abundance is high, and its overall impact is 

medium. Up to 78% of seed heads are attacked by Omphalapion hookerorum and 

up to 32% by R. tripleurospermi. Estimated scentless chamomile seed production 

is reduced up to 19% by a combination of both species. Heavy galling stunts 

plants and decreases and/or delays flower production. Anecdotal reports suggest 

scentless chamomile populations are declining in areas (western provinces) with 

heavy attack. This fly disperses up to 3.2 miles per year (5.2 km/yr).

REDISTRIBUTION: Adults are small, short-lived, and delicate so sweeping is 

not feasible. Instead, place infested plants into uninfested patches from spring 

through midsummer. To avoid transferring unwanted parasitoids, other insects, 

or scentless chamomile seeds, gall-infested stems can be collected and adults 

reared out indoors. Refer to Additional Considerations in the Introduction 

for instructions on how to do so. Once they emerge in spring, midges can be 

transferred to new chamomile infestations in groups of 50-100. Establishment 

can be monitored by observing scentless chamomile foliage for galls later in the 

same season or in subsequent years. 

NOTES: Galls are susceptible to parasitoid attack, but 

parasitism levels in the field are not high enough to prevent 

rapid population growth. This species has not been 

released in the US.
208 Biological Control in Eastern North America chamomileMicroplontus edentulus (Schultze)

Scentless chamomile stem-mining weevil

SYNONYMS: Ceutorhynchus edentulus Schultze

DESCRIPTION: Larvae are white, C-shaped, and have brown head capsules. 

They are approximately 3 mm long. Adults are about 3 mm long and 2 mm 

wide. Females are slightly larger than males. Adults are mottled gray with lighter 

patches at the base and sides of wing covers. They have long, curved snouts. 

a b

Microplontus edentulus a. larva in flower head; b. adult (a,b Alec McClay, McClay Ecoscience)

LIFE CYCLE: Adults emerge in early spring and begin mating and ovipositing 

prior to chamomile flowering. Eggs are deposited singly into holes chewed by 

females in upper plant stems, near leaf bases. Hatching larvae mine stems and 

sometimes into flower bases, though they do not feed on or damage seeds. Larvae 

develop through three instars prior to dropping to the ground and burrowing 

into the soil to build cocoons out of soil particles. Pupation occurs within 

cocoons. Adults typically overwinter within cocoons, but some emerge in fall 

and overwinter in soil and litter. There is one generation per year.

DAMAGE: Larval stem mining causes plants to produce thin stems, which reduces 

plant mass and seed production. Large, healthy plants appear less affected.

PREFERRED HABITAT: Specific habitat requirements are unknown.

RELEASE HISTORY: Weevils from Austria were released on scentless chamomile 

in western Canada beginning in 1997 and in MB in 1998. 

CURRENT STATUS: Microplontus edentulus has been confirmed established on 

scentless chamomile only at one site in western Canada (AB). To date there has 

been no evidence of impact in the field. Larval mining in stems occurs too late to 
Biological Control in Eastern North America 209chamomile

Coleoptera: Curculionidae

c d

Microplontus edentulus c. larvae and mining damage in stem (Hariet Hinz, CABI-Switzerland); d. 

emergence hole in plant stem (Alec McClay, McClay Ecoscience)

impact plant fitness, and mining in receptacles does not destroy seeds. Parasitism 

may play a role in the low population levels. 

REDISTRIBUTION: Populations are currently too limited to field collect so 

releases should be made using laboratory colonies when available. In the future, 

should this biocontrol agent become better established, field redistributions can 

be done utilizing a sweep net in early spring to collect adults from stems and 

foliage during the mating stage. These can be transferred to new, uninfested sites 

in groups of 100-200. Establishment can be monitored the following season 

by observing adults on plant foliage or dissecting stems to find larvae mining 

within. 

NOTES: This species has not been released in the US.
210 Biological Control in Eastern North America hemlockPoison hemlock

Conium maculatum L.

ORIGIN: Native to Eurasia. Introduced to North America in the 1800s as a 

garden plant.

DESCRIPTION: An erect plant typically growing as a biennial but may behave 

as a winter annual or short-lived perennial. The plant often grows 3-6 ft tall (90-

180 cm) from a deep taproot. Leaves are alternate and finely divided, giving the 

plant a fern-like appearance. Stems are hollow, smooth, and covered in purple 

spots or splotches. The inflorescence is a compound umbel with 12-16 umbellets. 

Individual flowers have five white petals. Seeds are brown, oval, flattened on one 

side, and have conspicuous wavy ribs.

HABITAT: Poison hemlock often grows in dense stands at shady or moist sites. It 

is frequently found along roadsides, field margins, ditch banks and in low-lying 

waste areas. It also invades native plant communities in riparian woodlands and 

open flood plains of rivers and streams. 

a b

Poison hemlock a. plant (Steve Dewey, Utah State University); b. infestation (Joe DiTomaso, 

University of California)(a,b bugwood.org)
Biological Control in Eastern North America 211hemlock

Family Apiaceae

c d e

Poison hemlock c. leaf; d. stem (Jeff Stachler, Ohio State University); e. inflorescence (c,e Pedro 

Tenorio-Lezama)(c-e bugwood.org)

ECOLOGY: Poison hemlock reproduces by seed only. Plants germinate throughout 

the growing season. Most plants are biennials, remaining as rosettes the first year 

and bolting/flowering only during the second year. Flowering typically occurs in 

mid- to late summer. Most plants die after flowering and setting seed, though a 

small proportion overwinter and re-grow from the root crown to flower again in 

the following season. Seeds are readily transported by farm machinery, vehicles, 

agricultural produce, mud and clothing, as well as being carried by water and, to 

a limited extent, wind. Seeds may stay viable up to three years.

BIOLOGICAL CONTROL:Agonopterix alstroemeriana was accidentally introduced 

to North America by 1973; it spread rapidly throughout the northwestern states 

by 1983. It has since been granted redistribution permits for use on poison 

hemlock in the US, and has been moved around extensively. It is widespread 

in the West, but eastern populations are more limited. High populations cause 

severe defoliation, but many plants recover after larvae 

pupate in midsummer, so overall impact is believed to be 

limited. No species are approved for release 

in Canada for control of poison hemlock.

NOTES: All parts of the plant contain 

alkaloids that are highly toxic to livestock 

and humans.
212 Biological Control in Eastern North America hemlockAgonopterix alstroemeriana (Clerck)

Defoliating hemlock moth

DESCRIPTION: Eggs are pale yellow and cylindrical. Early instars are 

predominantly yellow with black head capsules. Later instars are light green with 

three dark green longitudinal stripes. Mature larvae can be up to 12 mm long. 

Pupal cases are reddish-brown. Adults are approximately 10 mm long with 18 

mm wingspans. Adults are speckled brownish-gray and have a distinctive dark 

brown spot on each wing. 

a b c

Agonopterix alstroemeriana a. eggs; b. larva; c. adult (a-c Eric Coombs, Oregon Department of 

Agriculture, bugwood.org)

LIFE CYCLE: Adults emerge in early spring and begin mating and ovipositing. 

Eggs are deposited on the undersides of poison hemlock leaves. Hatching larvae 

feed on leaves, creating tubes of leaf particles. Leaf tubes are quickly abandoned 

when larvae are disturbed and drop to the ground. Larvae develop through five 

instars; late instars incorporate flower tissue into their tubes. They pupate in 

the soil with new adults emerging in midsummer. Adults overwinter in soil and 

plant litter. There is one generation per year.

DAMAGE: Larval feeding defoliates plants which can lead to reduced reproduction 

and sometimes plant death. Many plants recover and produce more foliage after 

larvae have pupated.

PREFERRED HABITAT: Specific habitat requirements are unknown.

RELEASE HISTORY: Accidentally introduced, this moth was first documented 

in the US (NY) in 1973. It spread rapidly to many additional states including 

those in the West by 1983. Despite being introduced accidentally, the USDA 

APHIS has granted permits for its redistribution, and it is currently commercially 

available.
Biological Control in Eastern North America 213hemlock

Lepidoptera: Oecophoridae

d e

Agonopterix alstroemeriana d. defoliated leaves; e. defoliated stand (a,b Eric Coombs, Oregon 

Department of Agriculture, bugwood.org)

CURRENT STATUS: This moth is established at high densities on poison 

hemlock throughout the western US and in portions of the East. It can reduce 

seed production and cause severe defoliation of poison hemlock, however many 

plants recover after larvae terminate feeding in midsummer. Changes in poison 

hemlock stand density have not been documented, so the overall impact is 

believed to be limited.

REDISTRIBUTION: Agonopterix alstroemeriana populations are widespread 

throughout the western US. Where eastern infestations of poison hemlock are 

sufficiently large to warrant releases of this moth, larvae can be hand-picked 

from other sites during late spring and transferred along with cut leaves of 

poison hemlock in groups of 50-100. As this weed is extremely toxic, gloves 

and protective clothing should be worn when cutting any foliage. Establishment 

can be monitored the following spring and summer by observing new larvae on 

poison hemlock foliage.

NOTES: Adults are nocturnal and hide during the day. This species is not 

approved for release in Canada.
214 Biological Control in Eastern North America hydrillaHydrilla

Hydrilla verticillata (L.) L.A.S. Johnson

SYNONYMS: Florida elodea, water thyme

ORIGIN: Native to Africa, Asia, Australia, and portions of Europe, hydrilla was 

intentionally introduced to North America in the 1950s as an aquarium plant.

DESCRIPTION: Submersed, aquatic perennial with roots typically buried in the 

hydrosoil. Roots are slender, white, and stoloniferous in the hydrosoil or may 

grow from stem nodes. Stoloniferous roots end in potato-like tubers up to 0.5 in 

long (13 mm). Stems are slender (<0.2 in or 4 mm wide), up to 33 ft (10 m) long, 

and become more branched at the surface, forming dense intertwined mats. Leaves 

occur in whorls of 3-8 all along the stem. Most leaves are <0.6 in (15 mm) long; 

they have serrated margins and small teeth on undersides of midveins. Swollen leaf 

buds (turions) are formed in leaf axils. In the US, male and female flowers may 

appear on the same plant (monoeocious) or on separate plants (dioecious). The 

dioecious form is more common in the southern US while the monoeocious is 

dominant in the North. Female flowers are tiny, have 6 white petals, and reach the 

surface on thread-like stalks; each produce 2-6 oblong seeds. Male flowers are tiny, 

green, and closely attached to leaf axils until they break off and free-float.

a b

Hydrilla a. plant (David J. Moorhead, University of Georgia); b. infestation (Cleveland Metroparks)

(a,b bugwood.org)
Biological Control in Eastern North America 215hydrilla

Family Hydrocharitaceae

c d e

Hydrilla c. leaves; d. flowers and foliage (Cleveland Metroparks); e. tubers (c,e Robert Vidéki, 

Doronicum Kft.)(c-e bugwood.org)

HABITAT: This aquatic species has been found growing in any type of freshwater, 

including lakes, springs, marshes, irrigation ditches, and rivers. It can grow 

in water depths from a few inches (7.5 cm) to 33 ft (10 m), and can tolerate 

moderate salinity (up to 33% of seawater). It can be found in both tropical and 

temperate climates and in a variety of nutrient and pH levels.

ECOLOGY: Hydrilla reproduces by seeds and (primarily) vegetatively. Throughout 

the growing season, new stems sprout from the root system and tubers as well as 

from stem fragments and turions that break from the parent plant. Stem fragments 

containing a single node (whorl of leaves) can sprout new plants. Flowering occurs 

from summer to fall. Male flowers break from the plant to free-float, fertilizing 

female flowers after bumping into them. In warm climates, the plant continues to 

grow over the winter. At cold sites, stems die back to the tubers, and new stems 

re-sprout the following spring. While turions die after one year, tubers may remain 

dormant in mud for many years.

BIOLOGICAL CONTROL:Hydrellia pakistanae

is widespread and abundant; high fly densities 

are locally correlated with decreases in hydrilla. 

It was initially believed Bagous hydrillae failed to 

establish, but small populations were observed 

in 2009. To date, populations of B. hydrillae

and Hydrellia balciunasi are too low to have 

significant impact. Despite multiple releases 

in the US, B. affinis failed to establish. Foreign 

exploration for additional biocontrol agents 

is still underway. The weed does not occur 

in Canada.
216 Biological Control in Eastern North America hydrillaHydrellia balciunasi Bock & H. pakistanae Deonier

Australian hydrilla leaf-mining fly & Asian hydrilla leaf-mining fly

DESCRIPTION: Both species are virtually indistinguishable; experts must use 

genitalia features to differentiate adults. Eggs of both species are yellow-white 

and elongate with longitudinal ridges. Larvae are yellow-green to white, have 

two anal spines, and are up to 3.5 mm long at maturity. Pupae are enclosed in 

cocoons that turn dark brown with age. Adults are dark gray with grayish-orange 

legs and typically bronze faces and are up to 1.5 mm long. 

a b

Hydrellia spp. a. egg; b. larva (a,b Lyle J. Buss, University of Florida)

LIFE CYCLE: At warm locations, both Hydrellia spp. and hydrilla develop 

throughout the year; larvae and pupae are the stages most often observed over 

winter. Adults emerge in spring and lay eggs singly or in small groups (though an 

average of 35 per lifetime) on leaves and stems at or just above the water surface. 

Larvae mine within leaves (4-12 per lifetime) through three instars. Leaves 

are mined completely before larvae exit to find another. Mature larvae attach 

themselves to leaf axils and pierce the stems with their anal spines while their skin 

hardens into cocoons. Pupae obtain air from the stems via the anal spines. Adults 

emerge and float to the surface in a bubble of air to repeat the cycle. There are 

multiple generations per year (up to 7) depending on site conditions.

DAMAGE: Leaves mined by larvae decay and fall. Stems with moderate to high 

amounts of H. pakistanae leaf-mining often sink and die. 

PREFERRED HABITAT: Both species are restricted to warm climates but 

perform well in all warm water bodies where hydrilla mats are present.

RELEASE HISTORY: Hydrellia balciunasi from Australia was released in FL 

from 1989 and TX beginning in 1991. Hydrellia pakistanae from three different 

countries was released in the US: India starting in 1987 (AL, CA, FL, GA, LA, 

TX), Pakistan in 1990 (FL), China in 1992 (AL, FL, LA, TX) in an attempt to 
Biological Control in Eastern North America 217hydrilla

Diptera: Ephydridae

c d

Hydrellia spp. c. adult (Lyle J. Buss, University of Florida); d. abdomen comparison between males 

of introduced Hydrellia spp. (left) and native Hydrellia spp. (right)(USDA ARS, bugwood.org)

increase survival at cold locations. India and Pakistan releases were successful and 

subsequently not differentiated; it is unclear if the China releases were successful.

CURRENT STATUS: No major impact has been observed for H. balciunasi as 

populations have remained low and spread has been limited. Hydrellia pakistanae

is much more widespread and abundant; larval mining decreases photosynthesis 

and reduces tuber numbers. High fly densities are locally correlated with decreases 

in weed populations. Some populations of both species are limited by parasitism 

and cold weather. Studies since 2004 indicate the monoecious biotype is not as 

suitable a host for introduced Hydrellia spp. as is dioecious hydrilla. 

REDISTRIBUTION: Hydrellia pakistanae is a higher priority for redistribution.

Hydrilla stems infested with larvae and pupae can be transferred to new hydrilla 

mats, taking care to keep the collected stems cool and moist until they can be 

transferred and to avoid transferring other insects or parasitoids. Establishment 

can be monitored the following growing season observing larvae mining leaves.

NOTES: Both introduced Hydrellia spp. closely resemble native Hydrellia spp. 

Introduced males can be differentiated by their 

abdomen being approximately the same 

size as their thorax, while the abdomen of 

a native male is 1.5 to 2 times as long as 

the thorax. Females of introduced and 

native species must be differentiated by 

their genitalia. Neither species has 

been released in Canada where the 

weed is also reportedly not present. H. balciunasi H. pakistanae
218 Biological Control in Eastern North America hydrillaBagous hydrillae O’Brien

Hydrilla stem weevil

DESCRIPTION: Eggs are white and oval. Larvae are C-shaped, white with brown 

head capsules, and up to 3 mm long. Adults are elongate with long snouts, up 

to 3 mm long, mottled, and tan to dark brown. In many individuals, 2-4 light 

coloration spots can be seen on the far ends of the elytra. 

a b

c

d

Bagous hydrillae a. larva ; b. pupa, c. adult, side view; d. adult, top view (a-d courtesy US Army 

Corps of Engineers, ERDC-EL)

LIFE CYCLE: Overwintering adults emerge in spring, fly from the shore to 

hydrilla mats, and feed on stems and leaves. Females lay eggs (average of 300 per 

lifetime) singly in hydrilla stems near plant nodes. Larvae bore into stems and 

feed through three instars. Adult and larval feeding causes stems to break apart, 

and fragments float to shore where they become stranded. Mature larvae exit 

stems of stranded fragments to pupate in the soil. Some pupate within stranded 

stems, though pupation does not occur in submersed hydrilla. Adults emerge, fly 

to new hydrilla patches, and continue the cycle. There are multiple generations 

per year in the native range (possibly 4-5). Adults overwinter in soil or among 

stranded hydrilla stems.

DAMAGE: Hydrilla stems turn black where larvae bore inside. Adult feeding 

externally on leaves and stem tissue and larvae boring internally in stems causes 

hydrilla stems to break apart, and fragments float to shore where they become 

stranded and die.

PREFERRED HABITAT: Specific habitat requirements are unknown.

RELEASE HISTORY: Weevils from Australia were released in AL, FL, GA, and 

TX from 1991-1996.

CURRENT STATUS: This weevil was temporarily recovered in FL and TX 

following the original releases; however, it was believed this species had failed to 
Biological Control in Eastern North America 219hydrilla

Coleoptera: Curculionidae

e f g

Bagous hydrillae feeding damage (e-g courtesy US Army Corps of Engineers, ERDC-EL)

permanently establish in the field. Small numbers were recovered LA in 2009 

(over 360 miles or 580 km from the nearest release), indicating populations 

persisted throughout the southeastern US. There have been no observed 

reductions to hydrilla mats, and the impacts of any existing weevil populations 

are believed to be negligible. New inventories are warranted to determine the 

overall distribution of this species in the US.

REDISTRIBUTION: Populations are currently too limited to field collect. 

In the future, should this biocontrol agent become better established, field 

redistributions can be done by hand-collecting adults from stranded hydrilla 

stems. These can be transferred to new, uninfested sites in groups of 100-200. 

Establishment can be monitored the following season by observing adults on 

plant foliage or dissecting stems to find larvae mining within. 

NOTES: This species has not been released in Canada; the weed reportedly 

does not occur in Canada.
220 Biological Control in Eastern North America hydrilla

Non-Established Biocontrol Agent

Bagous affinis Hustache

(Coleoptera: Curculionidae)

DESCRIPTION AND LIFE CYCLE: 

Adults are elongate with long snouts, 

3-4 mm long, and a mottled brown. 

Adults emerge in spring and feed on 

hydrilla stems and leaves exposed by 

receding waters. Females lay up to 

230 eggs singly on emerged or drying 

hydrilla stems, moist wood, tubers, 

or soil. Eggs are white and oval. Larvae are C-shaped, white with brown head 

capsules, and up to 5 mm long. Larvae crawl through sediment searching for 

tubers, then feed on or within hydrilla tubers through three instars. Pupation 

typically occurs within tubers. There are multiple generations per year in the 

native range (possibly 2-3). Adults overwinter in soil or among stranded hydrilla 

stems.

RELEASE HISTORY: Individuals from India were released in FL from 1987-

1990 and TX from 1994-1995. Though it was initially recovered in FL, 

permanent establishment has not been reported. Establishment has been limited 

by this species requiring extensive drawdown conditions which expose the 

sediment surface and allow immature weevils access to buried hydrilla tubers.

Bagous affinis adult (Michael Shillingburg)
Biological Control in Eastern North America 221hydrilla

Unapproved Non-Indigenous Natural Enemies

Cricotopus lebetis Sublette

(Diptera: Chironomidae)

DESCRIPTION AND LIFE CYCLE: 

Adults are 3-4 mm long and green with 

multiple dark bands. Females have shorter 

antennae and thicker abdomens than 

males. Females lay 50-250 whitish eggs 

in long strings on the water. Larvae feed 

through four instars on the growing tips of 

hydrilla. Larvae are up to 4 mm long and 

translucent green with a dark band on the thorax. Pupation occurs within hydrilla 

stems. There are multiple generations (up to 11) per year. 

HISTORY AND CURRENT STATUS: This midge was first recorded in LA, 

US in 1957; it is established in FL and LA. It damages hydrilla’s stem tips, 

causing stunting and preventing hydrilla from growing to the surface. However, 

populations are limited and overall field impact is typically minor. This midge 

attacks nontarget species and is not approved for redistribution in the US.

Parapoynx diminutalis Snellen

(Lepidoptera: Crambidae)

DESCRIPTION AND LIFE CYCLE: 

Adults are 8 mm long, white, with brown 

and tan markings and bands. Females lay 

~200 yellow eggs in 30-egg masses on 

hydrilla stems and leaves. Larvae are up 

to 10 mm long, white to yellow, and have 

spotted heads, long hairs, and branched 

gills. Larvae feed on hydrilla leaves 

through seven instars. Late instars construct silk cases from plant tissue. Pupation 

occurs in cocoons within the cases. There are multiple generations per year.

HISTORY AND CURRENT STATUS:This moth was studied for its biocontrol 

potential but rejected. It was accidentally introduced (first recorded in FL, US in 

1975) and is now established in AL, FL, GA, SC, TX. Larval feeding can heavily 

damage hydrilla populations locally. However, this biocontrol agent only occurs 

sporadically so overall impact is typically low. Populations are limited by cold 

weather. This species is not approved for redistribution in the US.

Cricotopus lebetis adult (Jerry F. Butler, 

University of Florida, Professor Emeritus)

Parapoynx diminutalis adult (Jonatan, 

Josve05a)
222 Biological Control in Eastern North America knotweedsBohemian knotweed

Fallopia xbohemica (Chrtek & Chrtková) J.P. Bailey

SYNONYMS: Polygonum xbohemicum (Chrtek & Chrtková) Zika & Jacobson 

Reynoutria xbohemica Chrtek & Chrtková

ORIGIN: Hybrid of Fallopia japonica and F. sachalinensis that is both intentionally 

cultivated and naturally occurring in the field where both parent species overlap. 

Backcrossing with parent species regularly occurs.

DESCRIPTION: Bohemian knotweed has features intermediate to its parent 

giant and Japanese knotweed species. It is an upright herbaceous perennial 

typically 3.2-14 ft (1-4 m) tall with a deep taproot and extensive rhizomes. Stems 

are hollow, smooth, jointed and swollen at the nodes (resembling bamboo), and 

often woody at their base. Leaves are alternate, 3-12 in (8-30 cm) long, and 

2-10 in (5-25 cm) wide. Leaves may have an abruptly pointed or tapering tip; 

their base be flat, tapering, or heart-shaped. Hairs on the undersides of leaves are 

short with broad bases. Flowers are small, greenish to creamy-white, and grow in 

branched clusters from leaf axils near stem ends. Flower clusters are 3-6 in (8-15 

cm) long. Fruits are papery, 3-winged, and up to 0.6 in (15 mm) long.

a b

Bohemian knotweed a. plant (Sasha Shaw, King County Noxious Weed Control Program); 

b. infestation (Jennifer Andreas, Washington State University Extension)
Biological Control in Eastern North America 223knotweeds

Family Polygonaceae

c d e

Bohemian knotweed c. leaves (Robert Vidéki, Doronicum Kft.); d. flowers (Sasha Shaw, King County 

Noxious Weed Control Program); e. fruits (Leslie J. Mehrhoff, University of Connecticut)(c,e bugwood.org)

HABITAT: Bohemian knotweed is frequently found in riparian, wetland, or lowland 

plant communities. It can inhabit a variety of sunlight, soil moisture, and human 

disturbance conditions, but has become especially problematic in full sun locations 

along the banks and floodplains of rivers and streams and moist roadsides. It is 

found growing next to either/both parent species and in their absence.

ECOLOGY: North American Bohemian knotweed reproduces both vegetatively 

and by seed. Rhizome sprouting occurs from late spring through summer. 

Rhizome and stem fragments can give rise to new plants if sufficient moisture 

is present. Seeds are transported by wind, water, and wildlife. Seeds germinate 

during spring; their longevity in the soil is unknown. Flowering occurs in late 

summer to early fall. Leaves fall in winter, and plants die back to rhizomes.

BIOLOGICAL CONTROL: As of 2016, Aphalara itadori has been approved 

by TAG for release on Bohemian, giant, and Japanese 

knotweed, but it is still under review in the US. Releases 

were made in Canada in 2016, but only on 

Japanese knotweed.

NOTES: Bohemian knotweed plants and leaves 

are variable in size and shape compared to 

either parent species, making differentiation 

difficult. Hairs on the undersides of leaves 

are long and wavy for giant knotweed, short 

with broad bases for Bohemian knotweed, 

and reduced to barely visible bumps on 

Japanese knotweed.
224 Biological Control in Eastern North America knotweedsGiant knotweed

Fallopia sachalinensis (F. Schmidt) Ronse Decraene

SYNONYMS: Sakhalin knotweed, Polygonum sachalinense F. Schmidt, Reynoutria 

sachalinensis (F. Schmidt) Nakai

ORIGIN: Native to Asia, it was introduced to North America in the late 1800s as 

an ornamental and for erosion control before it escaped cultivation. 

DESCRIPTION: An upright herbaceous perennial typically growing from 3.2-

13 ft (1-4 m) tall. It has a deep taproot and extensive rhizomes that may extend 

50-65 ft (15-20 m) laterally. Clustered stems are hollow, smooth and pale green, 

jointed and swollen at the nodes (resembling bamboo), and often woody at their 

base. Leaves are alternate, 6-12+ in (15-30+ cm) long, and 4-10 in (10-25 cm) 

wide. They have a tapering tip, heart-shaped base, somewhat wavy margins, and 

long wavy hairs on their undersides. Flowers are small, greenish to creamy-white, 

and grow in branched clusters from leaf axils near stem ends. Flower clusters are 

up to 4 in (10 cm) long. Fruits are papery, 3-winged, and 0.6 in (15 mm) long.

a b

Giant knotweed a. plants (Jennifer Andreas, Washington State University Extension); b. infestation 

(Robert Emanuel, bugwood.org)
Biological Control in Eastern North America 225knotweeds

Family Polygonaceae

c d e

Giant knotweed c. leaf; d. flowers (c,d Jennifer Andreas, Washington State University Extension); e. 

fruits (Barbara Tokarska-Guzik, University of Silesia,bugwood.org)

HABITAT:Giant knotweed is frequently found in riparian, wetland, or lowland plant 

communities. It can inhabit a variety of sunlight, soil moisture, and disturbance 

conditions, but has become especially problematic in full sun locations along the 

banks and floodplains of rivers and streams and moist roadsides. 

ECOLOGY: North American Giant knotweed reproduces primarily vegetatively, 

but it spreads in limited amounts by seed. Rhizome sprouting occurs from late 

spring through summer. Rhizome and stem fragments can give rise to new 

plants if sufficient moisture is present. Seeds are transported by wind, water, and 

wildlife. Seeds germinate during spring; their longevity in the soil is unknown. 

Flowering occurs in late summer to early fall. Leaves fall in winter, and plants 

die back to rhizomes.

BIOLOGICAL CONTROL: As of 2016, Aphalara itadori has been approved 

by TAG for release on Bohemian, giant, and Japanese 

knotweed, but it is still under review in the US. Releases 

were made in Canada in 2016, but only on 

Japanese knotweed. 

NOTES: Japanese knotweed grows shorter 

and has smaller leaves with flat or tapered 

bases, abrupt tips, and no hairs on their 

undersides. Use leaves from the middle of 

the stem for comparison as those at stem 

tips are most variable. Bohemian knotweed 

leaves are variable in size between both 

parent species; hairs on their undersides 

are short with broad bases.
226 Biological Control in Eastern North America knotweedsJapanese knotweed

Fallopia japonica (Houtt.) Ronse Decraene

SYNONYMS: Japanese bamboo, Japanese fleeceflower, Polygonum cuspidatum

Siebold & Zucc., Reynoutria japonica Houtt.

ORIGIN: Native to Asia, it was introduced to North America in the late 1800s as 

an ornamental and for erosion control before it escaped cultivation. 

DESCRIPTION: An upright herbaceous perennial that grows 3.2-10 ft (1-3 m) 

tall from a deep taproot and extensive rhizomes that may extend 23-65 ft (7-20 

m) laterally. Stems are hollow, smooth, purplish turning green with age, jointed 

and swollen at the nodes (resembling bamboo), and often woody at their base. 

Leaves are alternate, 3-6 in (8-15 cm) long, and 2-5 in (5-12 cm) wide; they 

have an abruptly pointed tip and a flat or tapering base. Hairs on the undersides 

of leaves are reduced to barely visible bumps. Flowers are small, creamy-white, 

and grow in branched clusters from leaf axils near stem ends. Flower clusters are 

3-6 in (8-15 cm) long. Fruits are papery, 3-winged, and 0.4 in (10 mm) long.

a b

Japanese knotweed a. plant (Jenn Grieser); b. infestation (Leslie J. Mehrhoff, University of 

Connecticut)(a,b bugwood.org)
Biological Control in Eastern North America 227knotweeds

Family Polygonaceae

c d e

Japanese knotweed c. leaves (John Cardina, Ohio State University); d. flowers; e. fruits (d,e Leslie J. 

Mehrhoff, University of Connecticut)(c-e bugwood.org)

HABITAT: Japanese knotweed is frequently found in riparian, wetland, or lowland 

plant communities. It can inhabit a variety of sunlight, soil moisture, and human 

disturbance conditions, but has become especially problematic in full sun locations 

along the banks and floodplains of rivers and streams and moist roadsides. 

ECOLOGY: North American Japanese knotweed is believed to reproduce primarily 

vegetatively, though increasing attention has been given to its reproduction by 

seed. Rhizome sprouting occurs from late spring through summer. Rhizome and 

stem fragments can give rise to new plants if sufficient moisture is present. Seeds 

are transported by wind, water, and wildlife. Seeds germinate during spring; 

their longevity in the soil is unknown. Flowering occurs in late summer to early 

fall. Leaves fall in winter, and plants die back to rhizomes.

BIOLOGICAL CONTROL: As of 2016, Aphalara itadori has been approved 

by TAG for release on Bohemian, giant, and Japanese 

knotweed, but it is still under review in the US. Releases 

were made in Canada in 2016, but only on 

Japanese knotweed. It is too soon to determine 

if this psyllid has established in the field.

NOTES: Giant knotweed grows taller and has 

larger leaves with heart-shaped bases and 

long hairs on their undersides. Use leaves 

from the middle of the stem for comparison 

as those at the tips are most variable. 

Bohemian knotweed leaves are variable in 

size between both parent species; hairs on 

their undersides are short with broad bases.
228 Biological Control in Eastern North America knotweedsAphalara itadori Shinji

Knotweed psyllid

DESCRIPTION: Eggs are creamy-white and elongated. Early nymphal instars 

are pale yellow to tan and more closely resemble adults through each subsequent 

instar. Adults are typically 2 mm long and are mottled tan and orange at first, 

turning darker brown with age. Their wings have tan veins and are translucent 

with mottled brown markings. 

a b c

Aphalara itadori a. nymph; b. adults on Japanese knotweed stem; c. damage to Japanese knotweed 

plant (deformed leaves and stunted growth)(a-c Rob Bourchier, Agriculture and AgriFood Canada)

LIFE CYCLE: Overwintering adults lay eggs singly or in small groups on 

knotweed leaves during spring. They frequently lay 600-700 eggs in their 

lifetime. Feeding nymphs secrete crystallized honeydew that form white strings 

or flakes on knotweed plant surfaces. Nymphs and adults feed by piercing and 

sucking knotweed leaf and stem cells. Nymphs develop through five instars. 

There are typically 2-3 generations per year, depending on site conditions. Adults 

overwinter in nearby vegetation, oftentimes beneath the bark of evergreen trees.

DAMAGE: Both adults and nymphs feed on knotweeds, but nymphal feeding is 

most damaging. Feeding causes defoliation, deformation of remaining leaves, 

stunted growth, and reduced biomass in both above- and below-ground growth. 

Heavy infestations may kill attacked plants outright. 

PREFERRED HABITAT: This species is tolerant of a wide temperature range 

in its native Japan, and it is believed to do better under humid rather than dry 

conditions.

RELEASE HISTORY: Individuals of the Kyushu strain from Japan, obtained via 

England, were released on Japanese knotweed in Canada in 2016 (ON in the 

East and AB, BC in the West). 
Biological Control in Eastern North America 229knotweeds

Hemiptera: Psyllidae ?

CURRENT STATUS: It is too early following release to confirm establishment 

in the field in Canada. Additional releases are planned for subsequent years.

REDISTRIBUTION: Because populations are not currently confirmed to be 

established in the field, further releases are recommended. Any releases made 

should be done using laboratory colonies and under the guidance of appropriate 

authorities. In the future, should this biocontrol agent become established, 

field redistributions can be done by transferring leaves and stems infested with 

psyllids to new knotweed sites and placing them against uninfested foliage, 

taking care to keep stems cool until the transfer is completed. Establishment can 

be confirmed the following year by observing nymphs and adults or the nymphs’ 

white secretions on knotweed leaves and stems.

NOTES: There are two strains of this biocontrol agent currently under study; the 

Kyushu (southern) strain performs best on Japanese and Bohemian knotweed, 

and the Hokkaido (northern) strain performs best on giant knotweed.

Japanese
230 Biological Control in Eastern North America melaleucaMelaleuca

Melaleuca quinquenervia (Cav.) S. T. Blake

SYNONYMS: broad-leaved paperbark, paperbark, punk tree, white bottlebrush 

ORIGIN: Native to Australia, New Caledonia, New Guinea and intentionally 

introduced to Florida, US several times in the early 1900s as an ornamental, 

timber source, soil erosion inhibitor, and as a means to drain wetlands.

DESCRIPTION: Evergreen tree typically growing 49-80 ft tall (15-24 m) from 

an adapting root system with above- and below-ground roots. Trees in dense 

stands have a single, moderately straight trunk while those in open infestations 

may be multi-stemmed with wide canopies. Branches are ascending on young 

trees and somewhat drooping on older trees. The corky bark is thick, consisting 

of many layers. Outer layers often become ragged and partly unrolled. Leaves are 

alternate, lance-shaped, leathery, gray-green, and give a camphor-like odor when 

crushed. Numerous flowers occur on creamy white “bottle brush” inflorescences 

1-3 in long (2.5-8 cm). Capsule fruits are arranged in tight clusters of 30-70; 

each capsule contains 200-350 tiny brown seeds. 

a b

Melaleuca a. tree (Forest and Kim Starr, Starr Environmental); b. infestation (Amy Ferriter, State of 

Idaho)(a,b bugwood.org)
Biological Control in Eastern North America 231melaleuca

Family Myrtaceae

c d e

Melaleuca c. leaves and bark (Fir0002/Flagstaffotos); d. flowers, fruits, and foliage (Forest and Kim 

Starr, Starr Environmental); e. seeds (Tony Pernas, bugwood.org)

HABITAT: Melaleuca is found in subtropical climates with alternating wet and 

dry seasons. In southern Florida, it can be found in moist habitats including 

sawgrass prairies, freshwater marshes, and cypress and mangrove swamps, as well 

as the drier zones of pine flatwoods and hardwood bottomlands. 

ECOLOGY: Melaleuca reproduces by seed and re-sprouting from cut branches and 

stems. Seeds germinate in moist soil. The adaptive root system follows a receding 

water table, producing vertical sub-soil roots and thread-like “water roots” that 

extend from surface roots and submerged trunk portions during flooding episodes. 

Trees can become reproductive in one year, but most flower only by the third year. 

Flowering occurs primarily in fall and secondarily in summer, though some flowers 

can be observed all year, and some trees flower multiple times a year. Stems continue 

growing beyond fruits and produce leaves or additional flowers. Seeds are released 

after interrupting events such as fire, frost, or wind damage. Seeds may remain on 

trees for 10 years, but are typically only viable for two years 

in the soil. Some trees can live more than 100 years.

BIOLOGICAL CONTROL: In combination, 

Boreioglycaspis melaleucae, Lophodiplosis trifida, 

and Oxyops vitiosa reduce plant height, 

branching, and biomass of surviving coppices 

and increase seedling mortality; repeated 

attack enables other plant species to grow. 

Fergusobia quinquenerviae and Fergusonina 

turneri failed to establish in the US. Additional 

species are being tested for potential future 

release into North America. The weed does 

not occur in Canada.
232 Biological Control in Eastern North America melaleucaBoreioglycaspis melaleucae Moore

Melaleuca psyllid

DESCRIPTION: Eggs are yellow, cylindrical, and have a spine-like projection on 

one end. Nymphs more closely resemble adults through each subsequent instar. 

Early nymphal instars are pale yellow with no markings. Mature nymphal instars 

have gray to black markings and have filamentous wax loosely covering their 

bodies. Adults are up to 3 mm long and pale yellow-orange to white in color 

with gray to black markings. Their wings are transparent with yellow veins. Two 

finger-shaped appendages extend outward and downward from below their eyes.

a b c

Boreioglycaspis melaleucae a. eggs on tip of a melaleuca leaf; b. adult; c. waxy flocculence produced by 

nymphs on melaleuca foliage (a-c Susan A. Wright, USDA ARS Invasive Plant Research Laboratory)

LIFE CYCLE: This species is continuously brooded, creating frequent overlap 

of generations. Female adults insert the spine-like projections of eggs into 

melaleuca stems and leaves. They lay eggs singly or in small groups, but up to 

275 in their lifetime. Nymphs secrete waxy filaments that cover their bodies as 

a form of protection. Wax secretions form a dense, woolly mass on stems and 

leaves. Nymphs and adults feed by piercing and sucking out the cell contents 

of melaleuca leaf and stem cells. Nymphs develop through five instars, each 

secreting copious amounts of honeydew. There are multiple generations per year 

(up to 13) depending on site conditions.

DAMAGE: Both adults and nymphs feed on melaleuca, but nymphal feeding is 

most damaging. Their saliva is thought to be phytotoxic and cause premature 

leaf drop. Heavy infestations kill attacked leaves, young plants, and saplings. 

PREFERRED HABITAT: This species is well adapted to most habitats 

throughout southern Florida. High summer temperatures (above 86°F or 30°C) 

reduce psyllid populations during the summer months.

RELEASE HISTORY: Psyllids from Australia were released in Florida, US 

beginning in 2002.
Biological Control in Eastern North America 233melaleuca

Hemiptera: Psyllidae

CURRENT STATUS: This psyllid is well established throughout Florida, though 

populations are seasonably variable and densities are greatest in the south. In 

combination with Lophodiplosis trifida, Oxyops vitiosa, and the adventive rust 

Puccinia psidii, it causes severe damage to mature melaleuca trees. Cumulative 

damage is reduced plant height, branching, and biomass of surviving coppices 

as well as increased fruit abortion and seedling/sapling mortality. Summer 

temperatures possibly reduce population growth. Predation by generalist species 

may reduce populations as well, though this is likely insignificant. 

REDISTRIBUTION: Stems infested with psyllids can be transferred to new 

melaleuca sites and placed against uninfested foliage, taking care to keep stems 

cool until the transfer is completed. At sites with high summer temperatures 

(above 86°F or 30°C), populations will be low during summer and redistributions 

likely ineffective during that time. Establishment can be confirmed the same or 

following year by observing nymphs and adults or the nymphs’ dense waxy 

secretions on melaleuca leaves and stems.

NOTES: The melaleuca snout beetle O. vitiosa cannot establish at permanently 

flooded melaleuca sites because of its requirement to pupate in soil. Boreioglycaspis 

melaleucae is a good complement at these types of sites because it completes its 

life cycle entirely in the tree canopy.
234 Biological Control in Eastern North America melaleucaLophodiplosis trifida Gagné

Melaleuca gall midge

DESCRIPTION: Eggs are elongated and red-orange in color. Larvae are yellow 

to orange and are up to 1.5 mm long. Pupae are a yellowish-orange, becoming 

darker orange as they mature. Adults are very small (3 mm long) and have dark 

red bodies, tan heads, and pale gray wings and legs. They have fine, delicate legs 

and antennae.

a b

Lophodiplosis trifida a. adult female (Susan A. Wright, USDA ARS Invasive Plant Research 

Laboratory); b. galls on melaleuca foliage (Matthew F. Purcell, USDA ARS Australian Biological 

Control Laboratory)

LIFE CYCLE: This species is continuously brooded, creating frequent overlap 

of generations. Females lay up to 160 eggs singly or in small groups on young 

melaleuca stems, buds, and leaves. Larvae burrow into stem or leaf tissue, and 

enzymes in their saliva initiate the formation of galls. Though galls develop in 

stems, buds, and leaves, it is stems that are most heavily galled. Larvae feed 

within galls through three instars. Galls may have single chambers housing 

one individual or several chambers, each housing a single larvae. Larger galls 

can be a few inches (several cm) long. Pupation occurs within galls. Adults are 

sexually mature upon emergence and live for up to five days. There are multiple 

overlapping generations per year. 

DAMAGE: Galling halts growth of infested stems on young stems of mature trees 

and kills small seedlings and saplings.

PREFERRED HABITAT: This midge does best with high humidity and at sites 

with prolonged flooding or near water. Populations are reduced in dry habitats.

RELEASE HISTORY: Midges from Australia were released in Florida, US in 

2008.
Biological Control in Eastern North America 235melaleuca

Diptera: Cecidomyiidae

CURRENT STATUS: Though this species was introduced more recently than all 

other melaleuca biocontrol agents, it quickly established at all release sites except 

one where biocontrol agents were killed by frost. Populations are moderately 

abundant overall. Populations are high in areas with a long hydroperiod 

(wetlands) but lower in upland systems where they are restricted to the lower 

canopy. Galling reduces melaleuca sapling height by 10.1%, leaf biomass by 

42%, woody biomass by 42.7%, and root biomass by 30.3%. In conjunction 

with the other established biocontrol agents, L. trifida decreases plant growth 

and survival. 

REDISTRIBUTION: Sweeping adult midges is possible, though may be 

damaging. Instead, transfer stems infested with galls to new sites and place 

against uninfested foliage. It is important to keep galled stems moist and cool to 

prevent dessication. Establishment can be monitored throughout the following 

season by observing galls on new melaleuca shoots.

NOTES: The melaleuca snout beetle Oxyops vitiosa cannot establish at permanently 

flooded melaleuca sites because of its requirement to pupate in soil. Lophodiplosis 

trifida is a good complement to this biocontrol agent because it does best at 

moist and humid sites.
236 Biological Control in Eastern North America melaleucaOxyops vitiosa Pascoe

Melaleuca snout beetle

DESCRIPTION: Eggs are 1 mm long and yellow but are coated with a dark 

protective secretion. Larvae produce long, thin coils of feces and are covered in a 

protective oily secretion that turns dark with fecal matter. Early instars are small 

and yellow while mature larvae are up to 14 mm long, grayish, and slug-like in 

appearance. Adults are up to 9 mm long and reddish-brown initially but turn 

darker gray with age.

a b

Oxyops vitiosa a. larvae, fecal coil, and feeding damage (Willey Durden, USDA ARS); b. adult (Gary 

Buckingham, USDA ARS)(a,b bugwood.org)

LIFE CYCLE: This species is continuously brooded, creating frequent overlap of 

generations. Females lay 500-1,000 eggs singly on young melaleuca leaves and 

expanding buds and twigs. Larvae are specialized feeders, feeding on the seasonal 

flush of young melaleuca leaves through four instars. They consume all layers of 

leaf tissue except the cuticle, leaving “window” feeding scars. At maturity, larvae 

drop from the host plant to burrow into the soil for pupation. Adults feed on 

melaleuca leaves, buds, and stems. Adult feeding damage to tough, older leaves 

is often superficial, resulting in narrow scars along the leaf surface. Adults are 

long-lived (over one year), and there are 2-3 generations produced per year in 

Florida’s climate.

DAMAGE: Heavy larval and adult feeding causes defoliation and tip dieback 

which in turn stimulate new growth that acts as a nutrient sink and reduces 

reproductive output. New growth is subsequently attacked by continual 

generations of the beetle, increasing the impact further. 

PREFERRED HABITAT: The snout beetle does best at sites with dry winter 

conditions and abundant young melaleuca foliage. Because this beetle pupates 

in the soil, persistent populations are rare in permanently flooded habitats.
Biological Control in Eastern North America 237melaleuca

Coleoptera: Curculionidae

c d e

Oxyops vitiosa damage c. feeding scars (Willey Durden, USDA ARS); d. normal undamaged branch 

(lower), defoliated branch (upper)(Peggy Greb, USDA ARS); e. severely defoliated (bare twigs) 

upper crown of trees (Ted D. Center)(c-e bugwood.org)

RELEASE HISTORY: Beetles from Australia were released in Florida, US from 

1997.

CURRENT STATUS: This species is well established throughout Florida, 

though densities are greatest in the south. In combination with Boreioglycaspis 

melaleucae, Lophodiplosis trifida, and the adventive rust Puccinia psidii, it causes 

severe damage to mature melaleuca trees. Cumulative damage occurs as reduced 

plant height, branching, and biomass of surviving coppices as well as increased 

seedling mortality. Repeated attack enables other plant species to colonize sites. 

REDISTRIBUTION: Despite being fairly widespread in Florida, it should be 

redistributed to sites where it is not yet established. Because beetles pupate in the 

soil, sites with prolonged flooding are not suitable for redistributions. Adults can 

be collected all year long but are most abundant in winter and spring. Adults can 

be tapped from foliage into collection trays or containers, or aspirated directly 

from the foliage. They can be transferred to new melaleuca sites in groups of 

300-5,000. Establishment can be monitored the following year by observing 

adults or larvae on foliage, or by observing their characteristic feeding damage 

to young leaves and twigs.
238 Biological Control in Eastern North America melaleuca

Non-Established Biocontrol Agents

Fergusonina turneri Taylor

(Diptera: Fergusoninidae) 

& Fergusobia quinquenerviae

Davies & Giblin-Davis

(Secernentea: Tylenchida)

DESCRIPTION AND LIFE CYCLE: 

Fergusonina gall flies and Fergusobia 

nematodes have a mutualistic 

relationship in that female flies oviposit 

both their own eggs as well as juvenile 

nematodes into melaleuca leaf and flower 

buds. Infection with the nematodes stimulates the formation of a gall, and fly 

larvae feed on gall tissue through all three instars. Female nematodes then invade 

third instar female fly larvae, laying eggs in and feeding on their hosts but not 

killing them. Third instars create “windows” in galls through which adults later 

emerge (following pupation within galls). All female flies contain nematodes. 

Juvenile nematodes migrate to the fly’s oviducts in order to be oviposited in new 

melaleuca tissue along with fly eggs, thus repeating the cycle. Galls act as metabolic 

sinks, halting melaleuca stem elongation and preventing flower formation. Mature 

galls are green to reddish-yellow, 0.5 in (1.3 cm) in biology, and often appear as 

grape-like clusters of multiple fly chambers. Adult flies are 3-5 mm long and pale 

yellow with lateral stripes on the abdomen. They have iridescent green eyes and 

transparent wings. Larvae are white and up to 2.5 mm long. Adult nematodes are 

worm-like, unsegmented, and tiny (less than 1 mm long). 

RELEASE HISTORY: Because Fergusobia quinquenerviae is a mutualistic 

nematode of Fergusonina turneri, both were released together. Individuals sourced 

from Australia were released in Florida, US from 2005-2007. This pair failed to 

establish despite multiple introductions and efforts to improve synchronization 

with the susceptible stage of melaleuca (buds). They temporarily colonized 

release sites, but disappeared completely after three generations.

Fergusonina and Fergusobia galls in melaleuca 

(Susan A. Wright, USDA ARS Invasive Plant 

Research Laboratory, bugwood.org)
Biological Control in Eastern North America 239melaleuca

Unapproved Non-Indigenous Natural Enemy

Puccinia psidii (G.Winter)

(Pucciniomycetes: Pucciniales)

DESCRIPTION AND LIFE CYCLE: 

Though Puccinia psidii produces teliospores 

and basidiospores, urediniospores are 

the dominant spore form and most 

characteristic. Urediniospores are yellow 

gold, round, covered in short spines, and 

tiny (27 μm). Spores occur in powdery 

mass clusters (pustules) on both sides 

of infected leaves. Leaves become 

discolored shortly after infection. Even lightly infected leaves turn gray brown at 

the site of infection; severely infected leaves are heavily distorted and ultimately 

defoliated. Infected twigs develop lesions and localized swellings. Urediniospores 

are easily blown to uninfected plants to repeat the entire cycle within two weeks. 

HISTORY AND CURRENT STATUS: This rust was first described in Brazil, 

but recorded from numerous host species throughout Central and South America 

and the Caribbean. It was first recorded on melaleuca in Florida (US) in 1997 

and has since been found on melaleuca throughout southern Florida. Where 

infections are high, damage is significant. In combination with two insects, 

Boreioglycaspis melaleucae and Oxyops vitiosa, it causes reductions in plant height, 

branching, and biomass of mature melaleuca as well as causing increased seedling 

mortality. Though it was studied upon arrival for its potential in biological 

control, this species was rejected and is not approved for redistribution in 

the US.

Puccinia psidii infecting leaves of melaleuca 

(Forest and Kim Starr, Starr Environmental)
240 Biological Control in Eastern North America multiflora roseMultiflora rose

Rosa multiflora Thunb.

SYNONYMS: baby rose, Japanese rose, many-flowered rose

ORIGIN: Native to Asia and intentionally introduced to North America on multiple 

occasions since the early 1800s as an ornamental. Between the 1930s and 1960s, it 

was widely planted for erosion control, wildlife cover, and as a living fence.

DESCRIPTION: Rambling shrub with multiple stems growing up to 15 ft tall 

(4.6 m) and 21+ ft wide (6.5 m) from an extensive fibrous root system. Stems 

are bright green to reddish, 0.6 in (1.5 cm) in cross-section, and usually covered 

with stiff, curved thorns. Stems are typically arching and can root when in 

contact with the ground; stems may occasionally climb among low tree branches. 

The compound leaves are alternate, deeply fringed where they attach to stems, 

and have 5-11 leaflets arranged in pairs with one terminal leaflet. Leaflets are 

elliptical, 1 in long (2.5 cm), and have toothed margins. The undersides of 

leaflets have tiny hairs. Flowers are 0.5-1 in (1.3-2.5 cm) across with 5 notched 

white or slightly pink petals and appear in large clusters. The small, clustered fruits 

(rose hips) each contain up to 20 tan seeds; fruits turn red and leathery in fall.

a b

Multiflora rose a. shrub (Leslie J. Mehrhoff, University of Connecticut); b. infestation (Nancy 

Dagley, USDI NPS)(a,b bugwood.org)
Biological Control in Eastern North America 241multiflora rose

Family Rosaceae

c d e

Multiflora rose c. leaflets, fringed leaf base, thorns on stem (Rob Routledge, Sault College); d. flowers (Karan 

A. Rawlins, University of Georgia); e. mature fruits (James H. Miller, USDA FS)(c-e bugwood.org)

HABITAT: Multiflora rose does best in sunny areas with well-drained soils, but 

it tolerates a wide range of soil, moisture, and light conditions. It can form 

impenetrable thickets in open woodlands, prairies and fields, and along stream 

banks and roadsides. 

ECOLOGY: Multiflora rose spreads by seed, root suckering, and by its arching 

branches rooting when they touch the soil. Seeds germinate throughout spring, 

with highest rates occurring in full sun. Plants may grow slowly for the first 1-2 

years, followed by rapid expansion through root suckering and stem rooting. 

Flowering occurs in spring to early summer. A single mature plant can produce 

over one million seeds per year. Fruits remain on plants over the winter. Most 

new plants arise from seeds dropped near the parent plant, though birds and 

mammals also eat the fruits and disperse seeds large distances. Seeds may remain 

viable in the soil for 10-20 years. The leaves are deciduous, falling from the tree 

in autumn and winter. New leaves emerge in early spring. 

BIOLOGICAL CONTROL: The native mite 

Phyllocoptes fructiphilus vectors the virus Rose 

Rosette Disease which can kill multiflora rose. 

Though the virus has been redistributed and 

studied extensively in the US, it is not an 

effective biocontrol agent and can decimate 

some commercial, ornamental and native 

roses. Redistribution of the mite and virus 

are not recommended, though both are 

widespread and are continuing to spread 

on their own. There are no approved 

biocontrol agents in the US or Canada.
242 Biological Control in Eastern North America multiflora rose

Native and Unapproved Natural Enemies

Rose Rosette Disease 

(Negative-strand RNA virus, genus Emaravirus)

& Phyllocoptes fructiphilus Keifer

(Acari: Eriophyidae)

DESCRIPTION AND LIFE CYCLE: Rose rosette disease is a virus that infects 

rose species (genus Rosa) and is transmitted both by grafting and by the mite 

Phyllocoptes fructiphilus. All stages of the mite are tiny and best viewed through 

a microscope. Adults are spindle-shaped, yellow to amber, 0.14-0.17 mm long, 

and have 4 legs. Females lay eggs on developing rose shoots in spring. Larvae and 

nymphs are translucent and resemble adults but are smaller in size. They develop 

within the leaf folds of new shoots or under leaf petioles. Larvae, nymphs, and 

adults all feed by piercing and sucking cell contents of tender growing tissue 

of multiple rose species. There are multiple generations per year, and adults 

overwinter under rose bark, old bud scales, and on living rose tissues. Mites 

can be distributed by the wind and by contaminated clothing and equipment. 

Symptoms of the virus are highly variable, depending on the rose species, cultivar, 

or even individual plant affected. Some of the more recognizable symptoms 

include leaves that are red for the entire growing season or have mosaic-pattern 

discoloration, leaves that are unusually long and thin, stems with excessive 

thorniness, thickening or flattening, a clustered mass of small branches (witch’s 

broom), a mass of distorted flower buds, a dieback of shoots, and severe yellowing 

and stunting of plants. 

HISTORY AND CURRENT STATUS: While the mite P. fructiphilus is native to 

North America, there is still debate on whether the virus is native as well. The virus 

a b c

Rose Rosette Disease a. head of vector mite magnified (West Virginia University); b. virus-caused 

excessive thorniness and red foliage; c. virus-caused witch’s broom branch and flower bud mass (b,c 

Jennifer Olson, Oklahoma State University)(a-c bugwood.org)
Biological Control in Eastern North America 243multiflora rose

was first identified in Manitoba, Canada in 1940 and in the US in 1941. Both 

the mite and the virus attack native, commercial, and ornamental roses in North 

America. In the absence of the virus, the mite produces no visible symptoms 

on rose plants. Mites can only effectively transmit the virus when feeding on 

rapidly growing tissue, which only occurs in the spring or after abundant rainfall. 

Dispersing mites do not infect many plants that are greater than ~330 ft (100 m) 

from heavily infested plants, so natural spread of the disease is relatively slow except 

within densely populated patches. Rose Rosette Disease has been credited with 

aiding the reclamation of some pastureland within 5-6 years of its introduction.

The virus takes ~2-6 years to kill multiflora rose. Large infected plants can still 

successfully produce seed that can remain viable for up to 20 years. Even if new 

plants become infected with the virus, they will re-seed before they can be killed; 

therefore, the disease is not an effective natural enemy for this weed problem. The 

virus was intentionally redistributed on multiflora rose in IA, MD, and WV, and it 

has been studied extensively. Additional efforts to distribute the virus or mite have 

been curtailed because of public concern over the risk to commercial, ornamental 

and native roses. Both the insect and virus are widespread in eastern and midwestern North America and continue to spread on their own. 
244 Biological Control in Eastern North America PeppertreeBrazilian peppertree

Schinus terebinthifolius Raddi

SYNONYMS: Christmas berry, Florida holly, pink pepper

ORIGIN: Native to South America and intentionally introduced to Florida, US 

in the 1800s as an ornamental; it became naturalized in the 1950s.

DESCRIPTION: Evergreen shrub or small tree typically growing 10-40 ft tall 

(3-12 m) from a shallow, suckering root system. Most plants have a short trunk 

hidden in a sprawling thicket of branches. Branches/stems have gray bark and are 

usually less than 4 in (10 cm) in diamter. The compound leaves are alternate, 3-6 

in long (8-15 cm), and usually have 7-9 leaflets. Leaflets are arranged opposite 

each other with one terminal leaflet. Leaflets are 1-2.8 in long (2.5-7 cm) by 

0.4-1.2 in wide (1-3 cm), oval to elliptical with smooth to toothed margins, and 

have obvious veins. They give off a strong turpentine odor when crushed. Male 

and female flowers usually appear on separate plants (dioecious). Both flowers are 

tiny with 5 white petals and appear in large clustered inflorescences up to 5 in long 

(13 cm) from leaf axils near branch ends. Each female flower produces a single 

dark red, berry-like fruit with a single seed.

a b

Brazilian peppertree a. mature plant (Stephanie Sanchez); b. infestation (Forest and Kim Starr, Starr 

Environmental))(a,b bugwood.org)
Biological Control in Eastern North America 245Peppertree

Family Anacardiaceae

c d e

Brazilian peppertree c. leaves and leaflets (Stephanie Sanchez); d. flowers (James H. Miller, USDA 

Forest Service); e. fruit (USDI National Park Service)(c-e bugwood.org)

HABITAT: Brazilian peppertree grows in tropical to subtropical regions and is 

a pioneer of disturbed sites, such as highway rights-of-way, fallow fields, and 

drained cypress stands, but can move outwards into undisturbed pinelands, 

mangrove forests, coastal shorelines, and marshes. It does well in mesic to 

wet locations below 650 ft (200 m) in elevation. Cold intolerance prevents its 

expansion into more temperate regions.

ECOLOGY: Brazilian peppertree reproduces by seed and by suckering roots. 

Seeds germinate throughout winter and spring. Seedlings can survive (but grow 

slowly) in shade; they can grow 12-20 in (30-50 cm) per year in full sun. Plants 

can become reproductive in three years. Flowering occurs primarily in fall with 

a small amount of flowering in spring/early summer. A single plant can produce 

thousands of ripe fruits that are retained on the plant for up to 8 months and are 

readily eaten/spread by birds and mammals. Seeds are typically only viable for up 

to 5 months after dispersal. Some trees can live up to 35 

years. The shallow root system readily produces suckers. 

These develop into new plants, creating very 

dense Brazilian peppertree infestations. 

BIOLOGICAL CONTROL: As of 2016, 

no biocontrol agents have been approved; 

Pseudophilothrips ichini and Calophya 

latiforceps are expected to be approved and 

released in the near future.

NOTES: The dried fruits of Brazilian pepper 

are used as a spice and are sold in gourmet 

shops in the US as “pink peppercorn.”
246 Biological Control in Eastern North America Peppertree

Unapproved Non-Indigenous Natural Enemy

Megastigmus transvaalensis (Hussey)

(Hymenoptera: Torymidae)

DESCRIPTION AND LIFE CYCLE: 

Adults are 2-3.5 mm long and yellowbrown with clearish wings. Females lay 

up to 25 eggs singly within fruits. Eggs 

are white, smooth, and oval-shaped with 

a long stalk and tiny spur. Larvae are up 

to 3 mm long, white to yellow, and somewhat barrel-shaped. Larvae feed on fruit 

and seed tissue through five instars. Pupation occurs within fruits; pupae remain 

in diapause for several months, emerging during fall. There are two generations 

per year, synchronized with the fall and spring production of fruit.

HISTORY AND CURRENT STATUS: This wasp is likely of South African 

origin and spread to the US via the pink peppercorn trade. It was first found 

in CA, US before 1961 and in FL by 1988. Adults typically attack 22-76% of 

Brazilian peppertree fruits, preventing seed germination. Abundance and impact 

vary, however, by season and location. Despite being intentionally moved around 

in FL prior to 2011, this species has not been officially approved in the US.

Megastigmus transvaalensis adult (Sergio 

Jansen Gonzalez)
Biological Control in Eastern North America 247Peppertree
248 Biological Control in Eastern North America tr. soda appleTropical soda apple

Solanum viarum Dunal

SYNONYMS: sodom apple, yu-a, tutia de vibora, joa bravo, joa amarelo pequeno

ORIGIN: Native to South America, it was introduced to North America by 1988, 

likely adhering to shoes or escaping cultivation.

DESCRIPTION: An herb or partially woody subshrub that grows as a perennial 

or an annual. Tropical soda apple has an extensive root system growing up to 1 

ft deep (30 cm) with shallow, lateral branches extending outwards 3-6 ft (0.9-1.8 

m). Mature plants are 3-6 ft tall (0.9-1.8 m) and have multiple sturdy, branching 

stems. Stems, branches, and leaves are covered in short, fine hairs. Leaves are 

broadly oval, 4-7 in long and 2-6 in wide (10-18 cm x 5-15 cm), and deeply 

lobed with lighter-colored veins. Rigid, yellow spines up to 0.8 in long (2 cm) are 

scattered on stems, branches, and leaf veins. Flowers are 0.6 in across (1.5 cm) 

with five white, recurved petals and occur in small clusters on stems below the 

leaves. Fruits are berries up to 1 in across (2.5 cm) that are mottled green when 

a b

Tropical soda apple a. plant (Florida Division of Plant Industry, Florida Department of Agriculture 

and Consumer Services); b. infestation (J. Jeffrey Mullahey, University of Florida)(a,b bugwood.org)
Biological Control in Eastern North America 249tr. soda apple

Family Solanaceae

c d e

Tropical soda apple c. leaves (Karan A. Rawlins, University of Georgia); d. flower (Rebekah D. 

Wallace, University of Georgia); e. spines, young fruits, leaf (J. Jeffrey Mullahey, University of 

Florida)(c-e bugwood.org)

young (resembling watermelons) but turn yellow at maturity. Each contains up 

to 400 seeds. A single plant may produce more than 50,000 seeds annually.

HABITAT: Tropical soda apple capitalizes on disturbance to invade new areas, 

and can then spread into neighboring undisturbed sites. In the US, it is largely 

a weed of pastures and rangeland, but can also be found in conservation areas, 

cultivated fields, citrus groves, hammocks, roadsides, and ditch banks.

ECOLOGY: Tropical soda apple reproduces by seed and buds on its lateral roots. 

Both germination and flowering occur year-round but primarily in fall through 

spring. Though it is typically a perennial, this weed can sometimes grow as an 

annual germinating, flowering, and dying in the same year. In mild climates, 

the plant is green year-round. In temperate regions, the plant dies back with 

frost and re-sprouts from root buds the following spring. 

Seeds are readily transported by cattle, wildlife, water, 

and hay, and may stay viable for two years.

BIOLOGICAL CONTROL: Gratiana boliviana 

was released in 2003 and is now abundant 

in southern and central FL, US where it is 

highly effective in reducing tropical soda 

apple plant density. Its northern distribution 

is limited by cold. The bioherbicide SolviNix® 

was registered in 2014 in the US for use in 

pastures and wooded areas. Infected plants 

die within ~6 weeks of inoculation. The 

weed does not occur in Canada. 
250 Biological Control in Eastern North America tr. soda appleGratiana boliviana Spaeth

Tropical soda apple leaf beetle

DESCRIPTION: Eggs are oval-shaped, up to 1.8 mm long, and encased in two 

translucent, papery membranes. Larvae are pale green, up to 6 mm long, and 

have spines along their margins on which they accumulate molted skins and 

frass (used as camouflage). Adults are up to 6 mm long and 5 mm wide and have 

a hard protective covering. Females are slightly larger than males. Reproductive 

adults are green while adults in diapause are light brown. 

a b c

Gratiana boliviana a. egg; b. larva with frass and molted skin; c. adult (a-c Rodrigo Diaz, Louisiana 

State University)

LIFE CYCLE: Adults emerge in early spring and feed on tropical soda apple 

foliage, creating a distinctive “shot-hole” feeding pattern. Eggs are deposited 

singly (but up to 300 per female lifetime) onto tropical soda apple leaves. Larvae 

feed on the undersides of young leaves through five instars; their feeding also 

creates “shot-hole” patterns. Pupa are attached to the undersides of tropical soda 

apple leaves. The entire life cycle can be completed in a month; in Florida, there 

are 7-8 generations per year. Last generation adults enter diapause in leaf litter 

during winter, which allows them to survive cold temperatures and food scarcity. 

DAMAGE: Larval and adult feeding reduces photosynthetic capabilities of 

attacked plants and facilitates secondary attack by plant diseases. These stresses 

reduce the growth and reproduction of tropical soda apple plants, decreasing 

competitive ability.

PREFERRED HABITAT: Beetle numbers are greater in open habitats, but 

feeding damage and beetle survivability are higher in shaded habitats. This 

species appears to be hindered by cold temperatures. 

RELEASE HISTORY: Individuals from Argentina and Paraguay were released in 

the southeastern US beginning in 2003 (AL, FL, GA, TX).
Biological Control in Eastern North America 251tr. soda apple

Coleoptera: Chrysomelidae

d e

Gratiana boliviana d. reproductive adult (left) and adult in diapause (right); e. adult feeding damage 

(d,e Rodrigo Diaz, Louisiana State University)

CURRENT STATUS: Gratiana boliviana is now widespread and abundant 

in south and central FL but is limited or absent in northern FL. Successful 

overwintering was initially observed in AL, GA, and TX, but permanent 

establishment has not been confirmed. In FL, larval and adult feeding cause 

defoliation and inhibit fruit production, though insect abundance is variable 

across the landscape. At high densities, beetles have been attributed with up to 

90% decline in plant density within three years of release, and the weed is now 

limited at many sites.

REDISTRIBUTION: The prickles and spines of tropical soda apple impede 

sweep nets at most infestations. Instead, adults can be aspirated directly from 

plant foliage in spring through fall. These can be transferred to new, uninfested 

sites in groups of 100-500. Establishment can be monitored later in the same or 

subsequent year by observing larvae and adults on plant foliage or finding their 

distinctive shot-hole feeding patterns in tropical soda apple foliage. 

NOTES: This species has not been released in Canada; the weed reportedly 

does not occur in Canada.
252 Biological Control in Eastern North America tr. soda appleTobacco mild green mosaic tobamovirus

SolviNix®

DESCRIPTION AND LIFE CYCLE: When this virus is inoculated on its 

host, tropical soda apple, it elicits a lethal hypersensitive response from the 

plant whereby the plant develops necrotic lesions on the leaves, followed by 

wilting and death. Plants of all ages are killed in 2-6 weeks. The virus becomes 

inactive in water and in soils after 6 months. This virus must be transmitted by 

physical contact, but it has no known insect vectors or other natural modes of 

transmission.

HISTORY AND CURRENT STATUS: This virus occurs naturally in many 

parts of the US and around the world. Following extensive host-specificity and 

safety testing, a select strain, U2, was approved and registered as the bioherbicide 

SolviNix® for use on tropical soda apple in the US in 2014. It is commercially 

available in liquid concentrate from the company BioProdex, Inc. When used 

according to label instructions, this bioherbicide kills tropical soda apple plants 

(including roots) within six weeks of inoculation. This bioherbicide is not 

approved for use in Canada; the weed reportedly does not occur in Canada. 

a b

Tropical soda apple a. leaf with tobacco mild green mosaic tobamovirus lesions; b. before (left) and 

after (right) inoculation with the virus (a,b Raghavan Charudattan, BioProdex, Inc.)
Biological Control in Eastern North America 253tr. soda apple
254 Biological Control in Eastern North America waterlettuceWaterlettuce

Pistia stratiotes L.

SYNONYMS: water lettuce, Nile cabbage, water cabbage, shellflower

ORIGIN: Native to the tropical Americas, Asia, Malesia, and Australia. It is 

present in fossil records from North America prior to the Pleistocene, but is 

believed to have been exterminated from the continent and then reintroduced 

(likely accidentally) in the 1700s during European colonization of Florida.

DESCRIPTION: Herbaceous aquatic that grows as a perennial but may behave 

as an annual in temperate regions where it is introduced. As indicated by the 

common name, waterlettuce consists of a rosette that resembles a floating head 

of lettuce. It has stolons and an abundance of feathery roots extending up to 

20 in (50 cm). There are numerous wedge-shaped leaves per rosette. Each leaf 

has parallel veins and is fleshy, 1-6 in long (2.5-15 cm), green to gray-green, 

and covered with dense, white, water repellent hairs. The inflorescence is an 

inconspicuous spadix up to 0.6 in tall (1.5 cm) with 6-8 male flowers in a single 

whorl around the center and one female flower below. Flowers are enclosed by a 

a b

Waterlettuce a. plants b. infestation (a,b Forest and Kim Starr, Starr Environmental)
Biological Control in Eastern North America 255waterlettuce

Family Araceae

c d e

Waterlettuce c. leaves; d. flowers (Keisotyo); e. small plant with roots (c,e Forest and Kim Starr, 

Starr Environmental)

white, hairy, leaf-like spathe. There are up to 6 inflorescences per rosette, hidden 

among interior leaves. Fruits are small green berries.

HABITAT: Waterlettuce prefers slow-moving or stagnant water and is frequently 

found in lakes, ponds, and canals. 

ECOLOGY: This species reproduces both by seeds and stolons. Terminal buds 

on lateral stolons give rise to new rosettes. Up to 15 secondary rosettes may 

be attached to a primary plant and form large mats. Daughter plants break off 

and are carried by water currents, boats or wildlife to start new populations. 

Flowers may be found year-round in warm climates, but peak flowering occurs 

during summer. Seeds remain dormant for long periods in dry sediments when 

water levels recede in dry seasons, and readily germinate when rehydrated during 

rains or flooding. Waterlettuce is sensitive to frost and dies back in winter. In 

temperate regions, the plant behaves as an annual that regrows from the seed bank each year, or it is reintroduced 

annually by aquatic plant enthusiasts. 

BIOLOGICAL CONTROL: Neohydronomus 

affinis was released in the southern US from 

1987. It dispersed well but has had variable 

success. At some sites, it rapidly eliminated 

waterlettuce; at others, the weed persists.

Spodoptera pectinicornis was released in the 

US from 1990 but failed to establish. The 

weed does not occur in Canada. 
256 Biological Control in Eastern North America waterlettuceNeohydronomus affinis Hustache

Waterlettuce weevil

DESCRIPTION: Eggs are small, oval, and cream-colored. Larvae are up to 3 

mm long and have a white or yellow body with a brown head capsule. Adults 

are approximately 2 mm long and have a nearly straight snout with an obvious 

constriction at the base. Adults range from golden-brown to bluish-gray. Bare 

patches form on the elytra where the scales are rubbed off, giving the adults a 

chevron-like pattern. Females are usually slightly larger than males.

a b c

Neohydronomus affinis a. larva (left) and pupa (right); b. adult; c. damage (a-c USDA ARS, 

bugwood.org)

LIFE CYCLE: At warm locations, both Neohydronomus affinis and waterlettuce 

develop throughout the year; adult and pupae are the stages most often observed 

over winter. Adult females lay eggs singly in holes they chew in the upper surface 

of leaves near leaf margins. Larvae mine into leaves and feed towards the spongy 

tissue of leaves through three instars. This leaves a distinctive mining trail clearly 

visible in thin leaf tissue. Pupation occurs within leaves. Emerging adults feed on 

waterlettuce leaves, creating round feeding holes and occasionally chewing into 

the leaf spongy tissue. There are three generations per year in the native range.

DAMAGE: Adult feeding and larval mining destroys leaf bouyancy, and attacked 

plants sink and die under high weevil densities. 

PREFERRED HABITAT: This weevil develops fastest and feeds most actively in 

warmer temperatures and on large nutrient-rich waterlettuce plants.

RELEASE HISTORY: Weevils collected in Brazil were released in Australia, and 

from Australia were redistributed to the US (FL 1987, TX 1991). 

CURRENT STATUS: Neohydronomus affinis disperses well and within 18-30 

months of its release, waterlettuce was eliminated from three of four original 

release sites in FL. Though it has proven effective at many sites in the southeastern 
Biological Control in Eastern North America 257waterlettuce

Coleoptera: Curculionidae

US, establishment has not been universal, and long-term suppression of 

waterlettuce has not been achieved. 

REDISTRIBUTION: Where the weevil has been released and failed (and/or in 

cold climates), further introductions may not prove successful or may be required 

annually. At warm locations where the weevil is not already present, it can be 

introduced by transferring plants infested with larvae and pupae, taking care to 

keep the collected plant material cool and moist until they can be transferred 

and to avoid transferring other insects or parasitoids. Establishment can be 

monitored later in the same or subsequent year by observing larval mining scars 

or adult feeding scars, or by observing actively feeding larvae and adults. 

NOTES: Some early release literature listed their target biocontrol agent as 

Neohydronomus pulchellus. Subsequently it was clarified the early material was

N. affinis and not N. pulchellus. This species has not been released in Canada; 

the weed reportedly does not occur in Canada.
258 Biological Control in Eastern North America waterlettuceWaterlettuce, Non-Established Biocontrol Agent

Spodoptera pectinicornis (Hampson)

(Lepidoptera: Noctuidae)

SYNONYMS: Namangana pectinicornis 

(Hampson), Epipsammea pectinicornis 

(Hampson) 

DESCRIPTION AND LIFE CYCLE: 

Adults have mottled brown forewings 

with light and dark markings and have 

creamy-white hindwings. They have 

a wingspan of 19-23 mm; females are 

slightly larger than males. Adults are generally only active (and mate) at night. 

Females lay up to 1000 eggs in their lifetime, depositing these in masses of up 

to 150 on both sides of waterlettuce leaves. Eggs are tiny, round, and yellowgreen. Larvae feed on the spongy tissue within leaves and on leaf buds. Larvae 

are yellow-green initially but become green intermixed with brown by the final 

instars. They can be up 25 mm long and feed through six instars. Pupation 

occurs within leaves. Adults are short-lived and do not feed on waterlettuce. This 

species is continuously brooded throughout the year, creating frequent overlap 

of generations. 

RELEASE HISTORY: Individuals from Thailand were released in FL and TX, US 

beginning in 1990. The moth was initially believed to have established following 

multiple and varying release attempts. Populations have since dwindled and are 

no longer detectable. This species has not been released in Canada; the weed 

reportedly does not occur in Canada.

Spodoptera pectinicornis adult (USDA ARS, 

bugwood.org)
Biological Control in Eastern North America 259waterlettuce
260 Biological Control in Eastern North America air potatoAir potato

Dioscorea bulbifera L.

SYNONYMS: air potato, air yam, bitter yam

ORIGIN: Native to Africa, Asia, and Australia. Introduced to North America 

intentionally in 1905 (as a possible food crop or ornamental), it quickly became 

invasive.

DESCRIPTION: Herbaceous, perennial twining vine growing from persistent 

subterranean tubers that resemble small, oblong potatoes (up to 6 in or 15 cm 

in diameter). Vines are non-spiny and grow 66 ft (20 m) or longer, blanketing 

trees and surrounding vegetation. Leaves are alternate, smooth-margined, heartshaped, attached by long petioles, and up to 8 in long (20 cm) and nearly as 

wide. Leaf veins are deep; all arise from the same point and terminate at the 

same point. Bulbils (aerial tubers) arise from leaf axils. There are two bulbil 

morphotypes: brown and tan; bulbils are typically round or angled, 0.4-5 in 

wide (1-13 cm), and give the plant its common name of “air potato”. Male and 

female flowers (rarely present in North America) occur on separate plants on 

small hanging spikes arising from leaf axils in summer. Flowers are white to pale 

green, fragrant, and small. Seeds are tiny and partially winged.

a b

Air potato a. vines growing up a tree; b. infestation (a,b Forest & Kim Starr)
Biological Control in Eastern North America 261

Family Dioscoreaceae

air potato

c d e

Air potato c. leaves (James H. Miller, USDA Forest Service, bugwood.org); d. flowers, infrequent in 

the field (Karen Brown, University of Florida, bugwood.org); e. brown bulbil (Forest & Kim Starr)

HABITAT: Air potato can be found growing in moist, mesic, and/or hardwood 

forests. It is frequently found in disturbed areas, forest gaps, and along roadsides. 

Air potato is less common in coastal areas and pine forests.

ECOLOGY: Subterranean tubers and bulbils sprout in spring. Vines can grow 

outwards or climb into the canopy by twining around trees (up to 8 in or 20 cm 

per day in summer). While air potato can reproduce by seed, it rarely flowers in 

North America. Reproduction usually occurs vegetatively when bulbils fall to 

the ground and produce new stems. Up to 200 bulbils are produced per plant 

throughout summer and autumn, and these fall to the ground in autumn and 

winter months. Vines die back in winter. Bulbils are carried long distances by 

water and are frequently transported on machinery and equipment.

BIOLOGICAL CONTROL: Lilioceris cheni was released in the US in 2011 and 

is already having significant impacts by reducing vine 

density and bulbil production. Redistribution of this 

species is recommended, and it is being mass 

reared and released in Florida. One additional 

species is being tested for potential future 

release into North America. The weed does 

not occur in Canada.

NOTES: Some varieties of air potato are edible 

and cultivated as a food crop, especially in 

West Africa.
262 Biological Control in Eastern North America air potatoLilioceris cheni Gressitt & Kimoto

Air potato leaf beetle

DESCRIPTION: Two biotypes have been released: Chinese and Nepalese. Eggs 

are pale yellow, cylindrical, and up to 1 mm long. Early instars of the Chinese 

biotype are reddish while those of the Nepalese biotype are more yellowish; 

both become gray in later instars. Late instars are up to 7 mm long and have a 

black head capsule. Larvae are frequently coated in a sticky secretion to which 

fecal matter adheres. Pupae are pale orange, up to 7 mm long, and enclosed in 

a foam-like matrix covered with soil and other particles. Adults are up to 9 mm 

long with bulging eyes and black heads, legs, abdomens, and antennae. The 

elytra of the Chinese biotype are typically red, while the Nepalese biotype is a 

rusty orange.

a b

c

d

Lilioceris cheni a. eggs; b. larvae (Chinese biotype); c. adult (Chinese biotype)(a-c Melissa C. Smith, 

USDA ARS Invasive Plant Research Laboratory); d. adult (Nepalese biotype, Ellen C. Lake, USDA 

ARS Invasive Plant Research Laboratory)

LIFE CYCLE: Overwintering adults emerge in spring, feed on air potato foliage 

and lay eggs (700-1900+ during their lifetime) in loose clusters on the undersides 

of expanding air potato leaves. Beetles chew through the veins of a young leaf 

prior to ovipositing, causing leaf edges to cup or curl inwards. Larvae feed on 

air potato leaves and occasionally newly forming bulbils through four instars, 

skeletonizing leaves from the undersides. At maturity, larvae enter the soil and 

orally secrete a foam-like substance in which to pupate. The foam-like substance 

becomes covered with soil and other particles and hardens. Many pupae can 

often be found in the same foam matrix. Emerging adults feed on air potato 

foliage and occasionally newly forming bulbils. There are multiple overlapping 

generations per year, and adults overwinter in soil and plant litter.

DAMAGE: Adult and larval feeding on air potato leaves reduces photosynthetic 

capacity and may stunt growth and limit bulbil production. Damage to growing 

tips inhibits vine elongation and may reduce the plant's ability to climb vertical 

structures.
Biological Control in Eastern North America 263

Coleoptera: Chrysomelidae

air potato

e f g

Lilioceris cheni e. pupal foam-like matrix covered with soil and other particles (William A. 

Overholt, University of Florida); f. oviposition damage resulting in leaf cupping; g. heavy feeding 

causing skeletonization of air potato leaves (f,g Ellen C. Lake, USDA ARS Invasive Plant Research 

Laboratory)

PREFERRED HABITAT: Specific habitat requirements are unknown.

RELEASE HISTORY: In FL, the Chinese biotype was released in cages in 2011 

and in the open from 2012 onward. Releases of the Chinese biotype were made 

in GA beginning in 2015. The Nepalese biotype was first released in FL, GA, 

and LA in 2016.

CURRENT STATUS: Following very large mass-rearing and distribution 

programs, leaf beetle populations are now well established and very effective in 

Florida. At many sites, vine density and bulbil production have been reduced by 

25-70%, and impact is still increasing.

REDISTRIBUTION: The beetles are being mass reared in Florida, and most 

releases are currently made from these laboratory colonies. As populations 

increase, field redistributions can be done by tapping adults from stems and 

foliage into cachement containers throughout the growing season. These can 

be transferred to new, uninfested sites in groups of 50-100. Establishment can 

be monitored the following season by observing adults or larvae feeding on air 

potato foliage. 
264 Biological Control in Eastern North America lygodiumOld World climbing fern

Lygodium microphyllum (Cav.) R. Br.

SYNONYMS: Lygodium, climbing maidenhair fern, small-leaf climbing fern

ORIGIN: Native to the wet tropics and subtropics of Australia, Africa, Asia, and 

Oceania, Old World climbing fern was introduced to the US as an ornamental 

in the mid 1900s. It was first found naturalized in Florida in 1965.

DESCRIPTION: Herbaceous, perennial climbing fern growing from brown, 

wiry rhizomes. The rachises (midribs) of fronds are twining and grow up to 90 

ft long (27 m), blanketing trees and surrounding vegetation; old rachis material 

can form dense mats (3.3 ft or 1 m deep) on the ground. Rachises are green 

or brownish when alive and dark brown and wiry when dead. Leafy branches 

off the main stem are 2-5 in (5-12 cm) long and each contain several pairs of 

leaflets. Leaflets are either sterile or fertile. Both types are 1-2.4 in (2.5-6 cm) 

long, triangular-shaped, and attached by small stems. Sterile leaflets generally 

have smooth margins and may be lobed while fertile leaflets are fringed with tiny 

lobes of enrolled leaf tissue that cover the reproductive (spore-producing) parts.

a b

Old World climbing fern a. plant (Ellen C. Lake, USDA ARS Invasive Plant Research Laboratory); 

b. infestation (Tony Pernas, NPS, bugwood.org)
Biological Control in Eastern North America 265

Family Lygodiaceae

lygodium

c d

Old World Climbing Fern c. sterile leaflet (left), fertile leaflet (right)(Peggy Greb, USDA ARS); d. 

fertile leaflet close-up (Amy Ferriter, State of Idaho)(c,d bugwood.org)

HABITAT: This species is frequently found in moist tropical zones and is capable 

of establishing without disturbance. In Florida, it is found invading hardwood 

and hydric hammocks, mesic and wet flatwoods, forested and strand swamps, 

sawgrass prairies, as well as weedy communities. 

ECOLOGY: Old World climbing fern spreads vegetatively via its creeping fronds 

and rhizomes and via spore dispersal. Vegetative growth and spore production 

occur year-round in Florida. Fertile leaflets are usually produced in exposed 

locations where the plant receives sufficient sunlight. Spore production is prolific, 

and spores are easily spread by wind and contaminated hay and equipment and 

may remain viable for more than four years after their release. Germinating 

spores give rise to young Old World climbing fern plants (sporelings).

BIOLOGICAL CONTROL: Releases of the mite Floracarus perrepae and the 

brown lygodium moth, Neomusotima conspurcatalis, began in the US 

in 2008. Both species established, and both are having 

variable impacts on the weed. Despite multiple 

releases since 2004, the white lygodium 

moth, Austromusotima camptozonale, failed 

to establish. Additional species are being 

tested for potential future release into North 

America. The weed does not occur in Canada.

NOTES: Thick skirts of old rachises and 

fronds often encase trees and serve as ladders 

that carry fire into tree canopies, killing 

trees that are normally able to withstand 

ground fires.
266 Biological Control in Eastern North America lygodiumFloracarus perrepae Knihinicki & Boczek

Lygodium mite

DESCRIPTION: All stages of this species are tiny and best viewed through a 

microscope. Eggs are spherical and white. Larvae and nymphs are transparent 

and resemble adults but are smaller in size. Adults have 4 legs and are creamcolored at first, darkening gradually to brown at maturity. 

a b c

Floracarus perrepae a. magnified adults; b. leaf galling/rolling up close; c. leaf galling/rolling on frond 

(a-c Ellen C. Lake, USDA ARS Invasive Plant Research Laboratory)

LIFE CYCLE: All stages of this species are active year-round, but activity is 

highest in south Florida during the dry season when temperatures are moderate 

and rainfall is lower. Adult females lay eggs (~37-58 per lifetime) between newly 

emerging leaflets of Old World climbing fern sporelings (newly germinated 

plants). Larvae, nymphs, and adults all feed by piercing and sucking cell 

contents. Feeding on leaflet edges causes leaflets to roll and gall. Though leaf 

roll galls frequently contain multiple mites, a single adult is capable of inducing 

a gall. Subsequent generations lay eggs and feed within the gall, which provides 

a humid and safe environment from predators. There are multiple generations 

per year. Mites move between plants and sites by walking or jumping; jumping 

allows mites to move great distances via wind dispersal.

DAMAGE: Larval, nymph, and adult feeding damage deforms frond/rachis 

growth tips and may kill sporelings. Feeding causes leaflets to form leaf roll galls 

that act as physiological sinks and reduce plant biomass; galled leaflets sometimes 

turn brown. Mites preferentially feed on young, sterile leaflets.

PREFERRED HABITAT: Mites do best under moderate to high humidity 

and moderate ambient temperatures (~70°F or 21°C) and favor new, soft green 

foliage for gall initiation.

RELEASE HISTORY: Mites sourced in Australia were released in Florida, US 

beginning in 2008.
Biological Control in Eastern North America 267

Acari: Eriophyidae

lygodium

CURRENT STATUS: The mite only established and persisted at a limited 

number of the initial release sites. More recently it has been observed spreading 

to additional locations, including having been discovered over 75 miles south of 

the nearest rearing or release sites. Though it is too soon following its release and 

spread to evaluate its overall impact, the weed has responded variably to mite 

galling. Variations might be attributed to genetic differences in susceptibility to 

gall induction between different populations of Old World climbing fern. 

REDISTRIBUTION: This species is currently being mass reared and released 

in Florida. It is most easily transferred via potted plants or by collecting fronds 

heavily infested with leaf roll galls and placing these against uninfested Old 

World climbing fern plants in new locations. This can be done throughout the 

year, though high humidity and moderate maximum temperatures may aid in 

successful establishment. Throughout the following seasons and subsequent 

years, establishment can be monitored by observing leaf roll galls on Old World 

climbing fern. 
268 Biological Control in Eastern North America lygodiumNeomusotima conspurcatalis (Warren)

Brown Lygodium defoliating moth

DESCRIPTION: Eggs are oval-shaped, pale yellow, and often deposited in 

overlapping clusters. Early instars are translucent yellow-green with black head 

capsules. Fourth and fifth instars are bright green with black head capsules. 

Larvae are up to 11 mm long at maturity. Pupae are cylindrical, dark brown, 

and 6-7 mm long. Adults are small (11 mm wingspan) and brown with a few 

fine, dark bands and a distinctive white boomerang-shaped marking at the tip 

of each forewing. 

a b

Neomusotima conspurcatalis a. larvae; b. adult (a,b Ellen C. Lake, USDA ARS Invasive Plant 

Research Laboratory)

LIFE CYCLE: Adult females lay eggs (65-172 per lifetime) either singly or in 

small clusters on Old World climbing fern leaflets. Larvae typically develop 

through five instars, though some pupate after four instars. First to third instars 

skeletonize the climbing fern leaflets, leaving distinctive clear “windows” that 

eventually turn brown, and leaflets die. Later instars defoliate the plant by 

feeding along the margins of leaflets. Some late instars construct temporary 

refuges of silk and plant particles beneath which they continue to defoliate 

leaflets. Pupation occurs on a stem or in leaf debris, often in thin silken cocoons. 

There are multiple generations per year (potentially 10-12), and all stages may be 

active throughout the year, depending on site conditions.

DAMAGE: Heavy leaf defoliation by larvae causes “brown out” events and leads 

to frond and plant dieback. 

PREFERRED HABITAT: This species does best where temperatures average 80°F 

(26.5°C). Higher and lower temperatures result in slowed development or death.

RELEASE HISTORY: Moths sourced in Australia were released in Florida, US 

beginning in 2008.
Biological Control in Eastern North America 269

Lepidoptera: Crambidae

lygodium

c d e

Neomusotima conspurcatalis c. early instars "window" feeding; d. late instar feeding along leaflet 

margins (Melissa C. Smith, USDA ARS Invasive Plant Research Laboratory); e. damage in the field 

(brown fronds and rachises)(c,e Ellen C. Lake, USDA ARS Invasive Plant Research Laboratory)

CURRENT STATUS: Though is still too soon following its release to evaluate 

its overall impact, this moth is well established across wide areas of southeastern 

Florida. Periodic outbreak populations of this biocontrol agent cause substantial 

damage to Old World climbing fern populations. Regrowth from rhizomes 

and dormant lateral buds occurs after defoliation events; however, regrowth is 

subjected to additional oviposition and subsequent rounds of larval defoliation. 

Low winter temperatures cause drastic population reductions of this moth and 

enable partial recovery of the weed. Attack by this moth, alone, is unlikely to 

provide adequate control, but could be beneficial in combination with other 

biological control agents and other control methods. Multiple species of native 

parasitoids attack this moth in Florida. Ongoing research is assessing parasitism 

and whether or not it is likely to substantially impact biocontrol agent populations.

REDISTRIBUTION: This moth is currently being mass reared and released in 

Florida. Foliage of Old World climbing fern heavily infested with N. conspurcatalis

larvae can be cut and transferred to new sites and manually inserted in between 

the climbing leaves of uninfested L. microphyllum plants. Transfers of at least 

4,000 larvae appear to establish better than transfers using fewer individuals. 

Establishment can be monitored by observing feeding larvae later in the same 

or subsequent years or by observing skeletonizing feeding 

damage on Old World climbing fern leaves.

NOTES: Neomusotima conspurcatalis is similar to the closely 

related biocontrol agent Austromusotima camptozonale, which 

failed to establish on Old World climbing fern in Florida. It is 

believed the higher reproductive output of N. conspurcatalis

is a big contributor to its establishment.
270 Biological Control in Eastern North America lygodium

Non-Established Biocontrol Agent

Austromusotima camptozonale 

(Hampson) 

= Cataclysta camptozonale (Hampson)

(Lepidoptera: Crambidae)

DESCRIPTION AND LIFE CYCLE: 

Adults are small (11 mm wingspan) 

and white with delicate tan bands. 

Adults are short-lived, mating and 

ovipositing shortly after emergence. 

Females lay an average of 60 eggs singly 

or in small clusters Old World climbing 

fern leaflets or stems. Eggs are small and opaque. Larvae develop through five 

instars. The first two instars are pale in color and feed on leaflet cells, creating 

clear “windows.” Later instars are bright green, up to 11 mm long, and are leaf 

defoliators. Fifth instars spin cases made of silk and leaf particles in which to 

feed and then pupate; these are attached to concealed plant parts. There are 

potentially multiple generations per year, and all stages may be active throughout 

the year, depending on site conditions.

RELEASE HISTORY: Moths sourced from Australia was released in Florida, 

US from 2004-2007. Breeding was initially detected for a short time following 

release, but there was no evidence of persistence or establishment. A second 

attempt at field colonization began in 2010 using fresh collections of the 

biocontrol agent again sourced from Australia. All attempts failed. Establishment 

failure was possibly influenced by high ant predation and lower reproductive 

output than for the related species, Neomusotima conspurcatalis.

Austromusotima camptozonale (Christine A. 

Bennett, USDA ARS, bugwood.org)
Biological Control in Eastern North America 271lygodium
272 Biological Control in Eastern North America salviniasCommon salvinia

Salvinia minima Baker

SYNONYMS: water fern, salvinia, water spangles. The names Salvinia auriculata 

Aublet and S. rotundifolia Willd. are occasionally listed as synonyms, though 

this is incorrect as both names refer to a different, distinct species. 

ORIGIN: Native to Mexico, Central America, and South America. It was 

introduced to the US by the 1920s, likely via the aquarium trade.

DESCRIPTION: Aquatic, free-floating fern growing as an annual or short-lived 

perennial. The plant has no true roots. Horizontal branching rhizomes float just 

below the surface and bear three leaves (fronds) at each node. Two leaves are 

floating and one is submersed and divided into several filaments that resemble 

(but do not function as) roots. Floating leaves are up to 0.8 in long (2 cm), have 

smooth margins, have distinct midribs, and are oval-shaped overall but heartshaped at their base. Water repellent, white hairs on the upper surface of floating 

leaves have 4 branches while hairs on the undersides of leaves and filaments 

are unbranched and chestnut-colored. Floating leaves growing in shade remain 

green, small, and flat on the water while those growing in sun may become rusty 

brown, elongate, and fold upright on the midrib. Spore-producing structures 

a b

Common salvinia a. plants (Joseph LaForest, University of Georgia); b. infestation growing in shade 

(Barry Rice, sarracenia.com)(a,b bugwood.org)
Biological Control in Eastern North America 273salvinias

Family Salviniaceae

c d e

Common salvinia c. floating leaves (Joseph LaForest, University of Georgia); d. branching hairs on 

upper surface of floating leaf (Mic Julien, CSIRO); e. senescing plant with rusty floating leaves and 

filaments (Supermartl)(c,d bugwood.org)

(sporocarps) shaped like small lemons (~1 mm wide) are spirally arranged on the 

main axis of submersed filaments.

HABITAT: Common salvinia grows best in still, shallow water with high organic 

content, and is most frequently found in ponds, lakes, bayous, swamps, slow 

streams, canals, and ditches. It can tolerate salinity levels as high as 4-7 ppt.

ECOLOGY: Though sporocarps can be found on submersed filaments, this 

species is not known to produce fertile spores in the US, and all reproduction 

occurs vegetatively. Rhizomes containing numerous lateral buds are easily and 

regularly fragmented. Fragments are readily carried by water currents, animals, 

boats, etc., and give rise to new plants under favorable conditions. Buds remain 

dormant during dry and cold periods, allowing this species to survive in cold 

climates as well as long transports on boats/trailers. The 

numerous leaf hairs prevent drying, further enabling 

leafy plants to survive long distance transport.

BIOLOGICAL CONTROL: The FL ecotype 

of Cyrtobagous salviniae is abundant and 

helps suppress this weed in FL and LA, US.

The weed does not occur in Canada.

NOTES: Common salvinia is smaller than 

giant salvinia, and its upper leaf hairs are 

free near the tips while the upper leaf hairs 

of giant salvinia come together at the tips.
274 Biological Control in Eastern North America salviniasGiant salvinia

Salvinia molesta D.S. Mitch.

SYNONYMS: water fern, salvinia, kariba-weed, African pyle

ORIGIN: Native to Brazil, it was introduced to North America via the aquatic 

plant trade. It was first reported growing in the wild in the US in 1995.

DESCRIPTION: Aquatic, free-floating fern growing as an annual or shortlived perennial. The plant has no true roots. Horizontal branching rhizomes 

float just below the surface and bear three leaves (fronds) at each node. Two 

leaves are floating and one is submersed and divided into several filaments that 

resemble (but do not function as) roots. Floating leaves are oval-shaped and up 

to 1.6 in long (4 cm) and have smooth margins and distinct midribs. Water 

repellent, white hairs on the upper surface of floating leaves have 4 branches 

that join back together at the tip, giving them an “egg beater” appearance. 

Hairs on the undersides of leaves and filaments are unbranched and chestnutcolored. Depending on nutrient and space availability, plants may be slender 

with small leaves or dense mats with large crowded, folded leaves. Sporeproducing structures (sporocarps) shaped like small eggs are arranged in chains 

on submersed filaments.

a b

Giant salvinia a. plant with crowded leaves (Leslie J. Mehrhoff, University of Connecticut); b. infestation 

(Kenneth Calcote, Mississippi Department of Agriculture and Commerce)(a,b bugwood.org)
Biological Control in Eastern North America 275salvinias

Family Salviniaceae

c d e

Giant salvinia c. floating leaves on a non-crowded plant; d. “egg beater” hairs on upper surface of 

floating leaf (Mic Julien, CSIRO); e. senescing plant with rusty floating leaves and filaments with 

sporocarps (c,e Leslie J. Mehrhoff, University of Connecticut)(c-e bugwood.org)

HABITAT: Giant salvinia grows best in still, shallow water with high organic 

content, and is most frequently found in ponds, lakes, bayous, swamps, slow 

streams, canals, and ditches. It does not tolerate saline environments.

ECOLOGY: Though sporocarps can be found on submersed filaments, this 

species is not known to produce fertile spores in the US, and all reproduction 

occurs vegetatively. Rhizomes containing numerous lateral buds are easily and 

regularly fragmented. Fragments are readily carried by water currents, animals, 

boats, etc., and give rise to new plants under favorable conditions. Buds remain 

dormant during dry and cold periods, allowing this species to survive in cold 

climates as well as long transports on boats/trailers. The numerous leaf hairs also 

prevent drying, enabling leafy plants to survive long distance transport as well.

BIOLOGICAL CONTROL: The FL ecotype of 

Cyrtobagous salviniae suppresses the few populations 

of this weed present in FL, US. The Brazilian 

ecotype helps control giant salvinia at coastal 

infestations in LA and TX, but is less effective 

at inland sites where it is hindered by cold 

temperatures. The weed does not occur in 

Canada. 

NOTES: Giant salvinia is larger than 

common salvinia, and its upper leaf hairs 

come together at the tips while common 

salvinia upper leaf hairs are free near the 

tips.
276 Biological Control in Eastern North America salviniasCyrtobagous salviniae Calder & Sands

Salvinia weevil

DESCRIPTION: Eggs are white, elliptical, and tiny (0.5 mm long). Larvae are 

white, C-shaped, and have brown head capsules. They are up to 4 mm long. 

Adults are up to 2.5 mm long and have a long snout. Females are usually slightly 

larger than males. Newly emerged adults are brown, but they change to shiny 

black within a few days. There are two ecotypes of this species present in the US: 

the Florida ecotype is significantly smaller than the Brazilian ecotype.

a b c

Cyrtobagous salviniae a. larva; b. adult (Scott Bauer, USDA ARS); c. larval damage to giant salvinia 

leaves (browning)(a,c Peggy Greb, USDA ARS)(a-c bugwood.org)

LIFE CYCLE: Females lay up to 300 eggs singly in cavities they chew in salvinia 

rhizomes, leaves, and filaments. Larvae feed externally on buds and leaves before 

burrowing to feed within rhizomes. There are three larval instars. Pupation occurs 

underwater in cocoons attached to filaments or leaf bases. Emerging adults feed 

on buds, leaves, and filaments leaving a distinctive “shot-hole” feeding pattern. 

When adults are underwater, a film of air trapped beneath their body allows 

them to breathe. Adults may live 20-38 weeks, depending on site conditions. 

This species is restricted to warm regions where its salvinia hosts actively grow 

year-round. Consequently overwintering information is unknown. In North 

America, the number of generations per year is also unknown, but is believed 

to be one.

DAMAGE: While adult feeding helps suppress plant growth, larval feeding is 

most damaging to salvinia. Larval mining disconnects the flow of nutrients 

from submersed fronds to emergent leaves and buds. Plants attacked by salvinia 

weevil larvae turn brown, disintegrate, and eventually sink. 

PREFERRED HABITAT: This weevil is restricted to warm regions and does best 

between 55 and 91°F (13-33°C). It appears to prefer larger plants and performs 

best on plants with higher nitrogen content. 
Biological Control in Eastern North America 277salvinias

Coleoptera: Erirhinidae

RELEASE HISTORY: Two ecotypes of this species are known in the US. The 

smaller Florida ecotype was likely introduced accidentally to FL along with 

common salvinia prior to 1960, and it spread naturally to giant salvinia in FL. 

This ecotype was subsequently intentionally redistributed to common salvinia 

in LA beginning in 2002 and to giant salvinia in LA and TX in 1999. The 

larger Brazilian ecotype was intentionally released in Australia and from there 

redistributed to giant salvinia in LA and TX from 2001.

CURRENT STATUS: Attacks both common and giant salvina in North 

Amrica. The Florida ecotype failed to establish on giant salvinia in LA. In FL, it 

is abundant on the few giant salvinia infestations present as well as on common 

salvinia populations throughout the state. The Florida ecotype helps control 

both species in FL where both the weeds and the weevils go through numerous 

boom and bust cycles. The Florida ecotype is abundant on common salvinia in 

LA, but at some sites predation by red imported fire ants may decrease weevil 

populations below the threshold needed to provide control. The Brazilian ecotype 

successfully suppresses most giant salvinia infestations along the Gulf Coast. 

Further inland in LA and TX, control is reduced because colder temperatures 

slow weevil growth and hinder overwintering. Research is underway to find 

more cold tolerant populations of the weevil in South America.

REDISTRIBUTION: Plants infested with weevil larvae can be transferred to new 

sites and placed against uninfested salvinia plants. This should only be done at 

sites with large salvinia populations to ensure the plant transfer does not increase 

the weed problem. Alternatively adults can be collected with a Berlese funnel or 

by submerging infested plant material and hand-collecting adults as they rise 

to the surface. This can be done year-round. Adults can be transferred to new 

sites in groups of 200-500. Establishment can be monitored the following year 

by observing adults or their shot-hole feeding on foliage. Rhizomes can also be 

dissected for evidence of larval feeding. 

NOTES: When this weevil was first collected 

in both Florida and southeastern 

Brazil, it was thought to be Cyrtobagous 

singularis or a biotype of this species. 

Detailed comparative studies following 

releases in Australia helped researchers 

determine it was a new, undescribed 

species, later to be named Cyrtobagous 

salviniae. common giant
278 Biological Control in Eastern North America New ProjectsCurrent Studies in Weed Biocontrol

Earlier portions of this guide focus on biocontrol agents that have been intentionally 

released and/or are already established in eastern North America. Multiple studies 

are currently underway to obtain approval for additional biocontrol agents for use 

against some of the weed systems already described as well as some entirely new 

weeds. The current status of these studies is summarized in the following tables. 

Biocontrol agents that have already been approved by the Technical Advisory Group 

(TAG) and are closest to release in eastern North America are described below. As 

of 2016, these are still within the regularoty process and are not yet fully approved 

for field release. Potential biocontrol agents that are further behind in the approval 

process are listed briefly on the following pages. It is important to note that some of 

the species described on the following pages have already been rejected, and many 

of the species still showing promise may not receive final approval. 

Potential Biocontrol Agents Approved by the 

Technical Advisory Group (TAG)

Host Biocontrol Agent Impact

Brazilian peppertree

Schinus terebinthifolius

Pseudophilothrips ichini

(Thysanoptera: 

Phlaeothripidae)

Pierces/sucks leaf cell contents. 

This often kills leaves, reduces 

photosynthetic capacity, and 

stunts plant growth

Brazilian peppertree

Schinus terebinthifolius

Calophya latiforceps

(Hemiptera: 

Calophyidae)

Pierces/sucks plant cell contents, 

killing shoot tips, reducing the 

growth of young plants, and 

inhibiting seed production

Chinese tallow

Triadica sebifera

Bikasha collaris

(Coleoptera: 

Chrysomelidae)

Larval root-feeding and adult 

leaf-feeding reduce stem height, 

total biomass, number of leaves 

and stem diameter

Garlic mustard

Alliaria petiolata

Ceutorhynchus scrobicollis

(Coleoptera: 

Curculionidae)

Larval feeding on the root crown 

reduces plant stature and may 

kill plants outright

Russian thistle

Salsola tragus

Uromyces salsolae

(Pucciniomycetes: 

Pucciniales)

Infection can stunt plant growth 

and reduce seed production
Biological Control in Eastern North America 279New Projects

Potential Biocontrol Agents Further Behind 

in the Approval Process

Host 2016 Status

Air potato

Dioscorea bulbifera The beetle Lilioceris egena is under investigation.

Australian pine

Casuarina spp.

Foreign exploration is currently underway in the weed’s 

native range, and preliminary testing has started on the most 

promising candidates.

Brazilian 

peppertree

Schinus terebinthifolius

Three species that have been petitioned were denied approval. 

One of these (the sawfly Heteroperreyia hubrichi) is still of 

interest. Two additional psyllids are under investigation.

Canada thistle

Cirsium arvense

The pathogen Pustula spinulosa was a species of interest, but 

was recently abandoned after it was found infecting nontarget 

species in field experiments.

Chinese privet

Ligustrum sinense

One potential biocontrol agent has been denied approval. The 

beetle Argopistes tsekooni is under investigation.

Chinese tallow

Triadica sebifera

One potential biocontrol agent has been denied approval. The 

moth Gadirtha fusca is under investigation.

Cogongrass

Imperata cylindrica

Foreign exploration is currently underway, and preliminary 

testing has started on the most promising candidates.

Earleaf acacia

Acacia auriculiformis

Under investigation to determine the feasibility of biological 

control.

Eurasian 

watermilfoil

Myriophyllum 

spicatum

The fungus Mycoleptodiscus terrestris was originally studied for its 

use as a bioherbicide against Hydrilla verticillata but was found 

to be ineffective. It is currently being studied for its efficacy 

against Eurasian watermilfoil in field trials in Michigan.

Fig buttercup

Ficaria verna

Under investigation to determine the feasibility of biological 

control.

Flowering rush

Butomus umbellatus

Two weevils (Bagous nodulosus and B. validus) and the fly 

Phytoliriomyza ornata are under investigation.
280 Biological Control in Eastern North America New ProjectsCurrent Studies in Weed Biocontrol

Potential Biocontrol Agents Further Behind 

in the Approval Process

Host 2016 Status

Garlic mustard

Alliaria petiolata

In addition to Ceutorhynchus scrobicollis, which has been 

approved by TAG, three other Ceutorhynchus species are under 

investigation.

Himalayan balsam

Impatiens glandulifera

The rust fungus Puccinia komarovii var. glanduliferae is under 

investigation.

Hydrilla

Hydrilla verticillata

The fungus Mycoleptodiscus terrestris was studied for its use as 

a bioherbicide but was found to be ineffective in several trials. 

Foreign exploration for additional biocontrol candidates is still 

underway.

Invasive common reed

Phragmites australis 

ssp. australis

Petitions are currently being prepared for the release of two 

moths, Archanara geminipuncta and A. neurica.

Japanese stiltgrass

Microstegium 

vimineum

Two Bipolaris pathogens already present in eastern North 

America are currently being studied for specificity and 

efficacy as potential biocontrol agents. Differential response in 

susceptibility to Bipolaris microstegii has been discovered; much 

of the population is not susceptible, but the remaining portion 

is severely damaged. An aphid is also being studied in China.

Kudzu

Pueraria lobata

Two Chinese insects tested thus far have failed host specificity 

tests. Foreign exploration is still underway to identify additional 

potential agents.

Melaleuca

Melaleuca 

quinquenervia

The sawfly Lophyrotoma zonalis was rejected following concerns 

it would be toxic to native fauna if ingested. The midge 

Lophodiplosis indentata is under investigation.

Mile-a-minute 

weed

Persicaria perfoliata

The fungal pathogen Colletotrichum gloeosporioides is under 

investigation.

Old World 

climbing fern

Lygodium 

microphyllum

The sawfly Neostromboceros albicomus and the moth 

Lygomusotima stria are well along in the host range testing 

process. Also under evaluation, but in the very preliminary 

stages, are two stem borers: Siamusotima disrupta and another 

unidentified crambid species, as well as a Callopistria sp.

Oxeye daisy

Leucanthemum vulgare

Four species are currently being studied as potential biocontrol 

agents.
Biological Control in Eastern North America 281New Projects

Potential Biocontrol Agents Further Behind 

in the Approval Process

Host 2016 Status

Parrotfeather

Myriophyllum 

aquaticum

Foreign exploration is currently underway in the weed’s native 

range. Insects native to North America are also being studied as 

potential biocontrol agents.

Perennial 

pepperweed

Lepidium latifolium

The weevil Ceutorhynchus marginellus and the mite Metaculus 

lepidifolii are under investigation.

Rose myrtle

Rhodomyrtus tomentosa

Numerous species have been tested and found to lack specificity. 

The moths Mesophleps albinella and Casmara spp. are still 

undergoing testing.

Russian olive

Elaeagnus angustifolia

The mites Aceria angustifoliae and A. eleagnicola are under 

investigation.

Skunk vine

Paederia foetida

Numerous species have been tested and found to lack specificity. 

Foreign exploration is still underway to identify additional 

potential agents.

Swallow-worts

Vincetoxicum spp.

The leaf beetle Chrysochus (Eumolpus) asclepiadeus and the fly 

Euphranta connexa are under investigation.

Toadflaxes

Linaria spp.

Additional species of Rhinusa and also Mecinus weevils are 

currently under investigation.

Tropical soda 

apple

Solanum viarum

Two leaf beetles (Gratiana graminea and Metriona elatior) and 

the flower bud weevil Anthonomus tenebrosus were petitioned for 

release, but all three were denied approval.

Tree-of-heaven

Ailanthus altissima

The weevil Eucryptorrhynchus brandti was initially denied 

approval. Additional host testing was conducted, and the 

petition has since been revised for resubmission.

Water chestnut 

Trapa natans The leaf beetle Galerucella birmanica is under investigation.

Waterhyacinth

Eichhornia crassipes

The planthopper Taosa longula and the fly Thrypticus truncatus

are under investigation.
Glossary

282 Biological Control in Eastern North America

Glossary

Term Definition

abdomen The last of the three insect body regions; usually containing 

the digestive and reproductive organs

achene A small, one-seeded fruit that does not split at maturity

adventive Species that arrived in the geographical area from elsewhere 

by any means

aestivation A period of dormancy to survive predictable, unfavorable 

environmental conditions, such as temperature extremes, 

drought, or reduced food availability

alternate Where leaves appear singly at stem nodes, on alternate sides 

of the stem

antenna 

(pl. antennae)

In arthropods, one of a pair of appendages on the head, 

normally many jointed and of sensory function

aspirator An apparatus used to suck insects into a container. Can be as 

simple as in a mouth aspirator, or mechanical as in a gasolineor battery-powered vacuum aspirator

basal Located at the base of a plant or plant part

biennial A plant that flowers and then dies in its second year

biological control Reducing a pest’s abundance through intentional use of its 

natural enemies (predators, parasitoids, and pathogens)

bolting Plant stage at which the flower stalk begins to grow

bract A small, leaf-like structure below a flower

bulbil Bulbs or tubers that form at leaf axils or in place of flowers on 

certain plants. Bulbils give rise to new plants.
Glossary

Biological Control in Eastern North America 283

Term Definition

capitulum (pl. 

capitula) 

Seed head of a plant in the sunflower family

complete 

metamorphosis

An insect life cycle with four distinct stages (egg, larva, pupa, 

adult)

compound eyes Paired eyes consisting of many facets, or ommatidia, in most 

adult Arthropoda

compound leaf A leaf consisting of two or more leaflets borne on the same 

leaf stalk

coordinates A set of numbers used to specify a location 

crown Location of where a plant's stems meets its roots

diapause A suspension of development in response to regularly and 

recurring periods of adverse environmental conditions, 

such as extreme temperatures, drought, or reduced food 

availability

deciduous Sheds its leaves annually

density Number of individuals per unit area (e.g. plants, stems, or 

leaves)

dissemination Dispersal. Can be applied to seeds or insects

elytron (pl. elytra) Hardened front wing of a beetle

emergence Act of adult insect leaving the pupal exoskeleton, or leaving 

winter or summer dormancy

erect Grows upright and vertical as opposed to prostrate (spreading 

on the ground)

exoskeleton Hard, external skeleton of the body of arthropods, including 

insects and mites

exotic Not native 

floret One of the small, closely clustered flowers forming the head 

of a composite flower in the sunflower family
Glossary

284 Biological Control in Eastern North America

Term Definition

flower head A special type of inflorescence consisting of numerous florets 

that actually look like one flower

forb Herbaceous plant (does not have solid woody stems)

frass The fecal matter of insects

genus (pl. genera) A taxonomic category ranking below family and above  

species and consisting of a group of species exhibiting 

similar characteristics. The genus name is followed by a Latin 

adjective or epithet to form the name of a species

head Insect body region with the mouthparts, antennae, and eyes

head capsule Hardened covering of the head of an immature insect

herbivory Feeding on plants

host The plant or animal on which an organism feeds; the organism 

utilized by a parasitoid; a plant or animal susceptible to attack 

by a pathogen

host specificity The highly-evolved, often obligatory association between an 

organism and its host (i.e. weed). A highly host-specific insect 

feeds only on its host and on no other species

incomplete 

metamorphosis

An insect life cycle with three distinct stages (egg, nymph, 

adult)

inflorescence The flowering part of a plant

instar The phase of an arthropod’s nymphal or larval development 

between molts

involucre A circle of bracts under an inflorescence

larva (pl. larvae) Immature stage of some animals, including insects and 

mites. In insects with complete metamorphosis, it is the 

stage between the egg and pupa (examples include grubs, 

caterpillars and maggots)

leaflet A leaf-like part of a compound leaf. Though it resembles an 

entire leaf, a leaflet is not attached to the main plant stem or 

branch as a leaf is, but rather on the leaf stalk

lobed A leaf with shallow or deep, rounded segments, as in a thistle 

rosette leaf
Glossary

Biological Control in Eastern North America 285

Term Definition

membranous Thin and transparent

molting Process of arthropod development that involves shedding its 

exoskeleton and producing another as the arthropod grows

NAD 83 North American Datum, the official datum used for the 

UTM geographic coordinate system in North America

node Part of the stem of a plant from which a leaf, branch, or root 

grows

nontarget effect When control efforts affect a species other than the species 

they were enacted to control (can be positive or negative)

nymph Immature form of invertebrates, including mites and insects 

that undergo incomplete metamorphosis. Resembles adults

ocrea Plant structure formed of stipules fused into a sheath 

surrounding the stem

opposite Where leaves appear in twos at stem nodes, on opposite sides 

of the stem

oviposit To lay or deposit eggs

pappus A tuft of hairs, scales, or bristles at the base of an achene in 

flowers of the sunflower family

parasitoid An insect (e.g., a wasp) whose larvae live as parasites, 

eventually killing their hosts (typically other insects)

perennial A plant that lives for more than two years

petiole Leaf stalk that attaches it to a plant stem

proleg A fleshy, unsegmented, abdominal walking appendage of 

some insect larvae, common among caterpillars

prostrate Grows flat along the ground as opposed to growing erect 

(upright)

pupa (pl. pupae) 

(v. pupate)

Non-feeding, inactive stage between larva and adult for an 

insect with complete metamphorsis

qualitative Measurement of descriptive elements (e.g., age class, 

distribution)
Glossary

286 Biological Control in Eastern North America

Term Definition

quantitative Measurement of quantity; the number or amount (e.g., seeds 

per capitula)

rachis Main stem of a compound plant structure. In ferns, the rachis 

is the midrib of the frond

receptacle Part of the stem to which the flower is attached

rhizome A modified stem of a plant that grows horizontally 

underground, often sending out roots and shoots from its 

nodes

rosette A compact, circular, and normally basal cluster of leaves

seed head Synonym for capitulum of a plant in the sunflower family. 

Consists of a receptacle and florets

senescence Transition from living cells to dead ones as a function of age; 

the final stage in a life cycle

sepal Part of a flowering plant occurring beneath flower petals, 

sepals function as protection for the flower in bud and petals 

when in bloom. Sepals are typically green, but some may 

resemble petals.

spadix Inflorescence with several tiny flowers clustered on a narrow, 

fleshy stem

spathe Leaf-like curved bract surrounding a spadix

species A fundamental category of taxonomic classification, ranking 

below a genus or subgenus and consisting of related organisms 

capable of interbreeding

spillover feeding When a biocontrol agent population reaches outbreak 

densities, some feeding may occur on adjacent nontarget 

plant species. Spillover feeding is temporary and is unlikely 

to have negative consequences at the population level of 

nontarget species

sporocarp Specialized structure found on ferns; their primary function is 

the production and release of spores.

spore Unit of asexual reproduction that is part of the life cycle of 

many plants (e.g. ferns), algae, fungi and protozoa. Similar to 

a seed produced by flowering plants
Glossary

Biological Control in Eastern North America 287

Term Definition

sporeling A young plant or fungus produced by a germinated spore, 

similar to a seedling derived from a germinated seed

stolon Stem which grows at the soil (or water) surface or just below 

ground that forms adventitious roots at nodes and new plants 

from buds (also called runner)

synchrony Occurring at the same time (e.g. plant flowering and insect 

oviposition)

taxonomy The classification of organisms in an ordered system that 

indicates natural relationships. The science, laws, or principles 

of classification; systematics

thorax Body region of an insect behind the head and abdomen, 

bearing the legs and wings

toothed (margin) Saw-like leaf margin with somewhat regular teeth on the edge 

that may be different in size. Also called serrated

transect A straight line of varying length along which items (e.g. 

plants) are periodically sampled individually or in quadrants

turion Swollen leaf bud that gives rise to a new plant after it breaks 

free from the parent plant and sprouts

umbel An inflorescence which consists of a number of short flower 

stalks which spread from a common point, somewhat like 

umbrella ribs. They can be simple or compound (the single 

flowers are replaced by many smaller umbels called umbellets).

UTM Universal Transverse Mercator, a grid-based geographic 

coordinate system 

WGS 84 The World Geodetic System, a datum for latitude/longitude 

geographic coordinate systems

whorled Where multiple leaves radiate outward from a single stem 

node

winged A membranous expansion of tissue extending beyond the 

normal outline of a structure
references

288 Biological Control in Eastern North America

Selected References

Air potato

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Center, T.D. 2013. (personal communication) (Retired) United States Department of Agriculture, 

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Lauderdale, FL 33314 USA. 

Center, T.D., W.A. Overholt, E. Rohrig, and M. Rayamajhi. 2015. Classical biological control of air 

potato in Florida. EENY-864. University of Florida IFAS Extension. 4 pp. 

Center, T.D., M.B. Rayamajhi, F.A. Dray Jr, P.T. Madeira, G.L. Witkus, E. Rohrig, E.D. Mattison, 

E.C. Lake, M. Smith, J. Zhang, M. Purcell, A.S. Konstantinov, and D. Schmitz. 2013. Host 

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Dioscorea bulbifera L. in the southern United States. Biocontrol Science and Technology 23(7): 

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Center, T., M.B. Rayamajhi, M.F. Purcell, M. Markinson, and J. Ding. 2011. Pre-release 

colonization of Lilioceris sp nr. impressa (Coleoptera: Chrysomelidae: Criocerinae) for control 

of air potato. Invasive Plant Management Research and Outreach Newsletter 3(1): 9-10. 

Croxton, M.D., M.A. Andreu, D.A. Williams, W.A. Overholt, and J.A. Smith. 2011. Geographic 

origins and genetic diversity of air-potato (Dioscorea bulbifera) in Florida. Invasive Plant 

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Lake, E.C., M.C. Smith, F.A. Dray Jr., and P.D. Pratt. 2015. Ecological host-range of Lilioceris 

cheni (Coleoptera: Chrysomelidae), a biological control agent of Dioscorea bulbifera. Biological 

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of Lilioceris cheni Gressitt and Kimoto (Coleoptera: Chrysomelidae), biological control agents 

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America. https://doi.org/10.1093/aesa/saw100.

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impressa (Coleoptera: Chrysomelidae)—a potential biological control agent of air potato, 

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Dioscorea bulbifera L. (Air-Potato) plants generated from bulbils in Florida. Invasive Plant 

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Alligatorweed

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Carley M., and S. Brown. 2006. Invasive plants; Established and potential exotics, Gulf of Mexico 

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Brazilian peppertree

Burckhardt, D., J.P. Cuda, V. Manrique, R. Diaz, W.A. Overholt, D.A. Williams, L.R. Christ, and 

M.D. Vitorino. 2011. Calophya latiforceps, a new species of jumping plant lice (Hemiptera: 

Calophyidae) associated with Schinus terebinthifolius (Anacardiaceae) in Brazil. Florida 

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Cuda, J.P., G.S. Wheeler, and D.H. Habeck. 2014. Brazilian peppertree seed Chalcid, Megastigmus 

tranvaalensis (Hymenoptera: Torymidae). EENY 270. University of Florida IFAS Extension. 5 pp.

Habeck, D.H. and F.D. Bennett. 1989. First record of a phytophagous seed chalcid from Brazilian 

peppertree in Florida. Florida Entomologist 72(2): 378-379. 

McKay, F., M. Oleiro, G. Cabrera Walsh, D. Gandolfo, J.P. Cuda, and G.S. Wheeler. 2009. Natural 

enemies of Brazilian peppertree (Sapindales: Anacardiaceae) from Argentina: their possible use 

for biological control in the USA. Florida Entomologist 92(2): 292-303.

Meyer, R. 2011. Schinus terebinthifolius. In: Fire Effects Information System, [Online]. U.S. 

Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences 

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and DNA; thrips as a potential biocontrol agent of Brazilian peppertree, with a new species 

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induced by Calophya latiforceps (Hemiptera: Calophyidae) reduce leaf performance and growth 

of Brazilian peppertree. Biocontrol Science and Technology 26(1): 23-34.

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(Hymenoptera: Torymidae): an African wasp feeding on a South American plant in North 

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Wheeler, G.S., L.M. Massey, and M. Endries. 2001. The Brazilian peppertree drupe feeder 

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Multiflora rose

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Appendix

324 Biological Control in Eastern North America

I. Biocontrol Agent Monitoring Form

SITE: ______________________________ STATE: _________ DATE: ________ _________ _______

 year month day

NAME: ________________________________________________________________________________

GPS: Lat N _____°___________’ Long W_____°___________’ Elevation: ___________________ ft m 

UTM: Datum Zone:________ Year: _______ Easting:_______________ Northing: _________________

TIME: ___________ TEMPERATURE: ____________ WEATHER: ___________________________

Species Type Counting Method

Hard-bodied adults present 

on foliage during growing 

season (e.g. beetles)

Perform a series of 10 sweeps, counting the adults of all monitored 

species separately. Following each count, move to a new part of 

the infestation and repeat for a total of 10 counts. Record your 

counts in the table below, and then sum your measurements.

Larvae feeding within plant 

parts during growing season 

(e.g. seed heads, stems, galls, 

roots)

Randomly select 10 plants throughout the infestation. Dissect 

the tissue attacked by the target biocontrol agent (e.g. seed heads, 

stems, galls, roots) and in the table below, record the number of 

larvae found.

Species cryptic or too small 

to see/collect; feeding 

damage is best indicator of 

presence/abundance (e.g. 

fungi, mites, thrips)

Walk throughout the infestation and look closely at target weeds 

to identify biocontrol agent damage. Estimate the overall damage 

infection level in the “Total” column of the table below by 

using the letter for the most appropriate choice: A: No feeding 

or infection; B: Occasional, scattered feeding or infection; C: 

Conspicuous, widespread feeding or infection.

Count

Species 1 2 3 4 5 6 7 8 9 10 Total

Notes 

 
Appendix

Biological Control in Eastern North America 325

II. Vegetation Monitoring Form

SITE: ______________________________ STATE: _________ DATE: ________ _________ _______

 year month day

NAME: ________________________________________________________________________________

GPS: Lat N _____°___________’ Long W_____°___________’ Elevation: ___________________ ft m 

UTM: Datum Zone:________ Year: _______ Easting:_______________ Northing: _________________

TIME: ___________ TEMPERATURE: ____________ WEATHER: ___________________________

A transect is made in year 1, with 10 permanent markers inserted along the transect (1 marker per 

quadrat). All 10 quadrats are re-measured in subsequent site visits (preferably once/year). Position the 

quadrat frame along the transect, as close to the ground as possible. Gently arrange vegetation so that 

plant parts are either within or outside (rather than underneath) the frame. The quadrat should be in 

the same location as the previous year’s quadrat. Standing over the frame, estimate how much of each 

quadrat is covered by the target weed and the other cover categories listed in the table, in increments 

of 5%. All cover readings should add up to 100% for each quadrat. Count the number of target 

weed species stems/plants in each quadrat and measure the height of the tallest (cm). List other major 

species present at the site and check if they are present in each quadrat.

Quadrat

% of Quadrat

(to the nearest 5%) 1 2 3 4 5 6 7 8 9 10

Soil, litter

Rock

Water

Target weed

Other forbs, vines

Other grasses, sedges

Other woody plants

target weed 1 2 3 4 5 6 7 8 9 10

# plants/stems

Height tallest stem (cm)

other species

(write name, üif present) 1 2 3 4 5 6 7 8 9 10
Species Index

Index

326 Biological Control in Eastern North America

A

Acacia auriculiformis 279

Acentria ephemerella 73

Aceria angustifoliae 281

Aceria anthocoptes 105

Aceria eleagnicola 281

Achyranthes philoxeroides, See Alternanthera 

philoxeroides

Agapeta zoegana 42

Agasicles hygrophila 196

Agonopterix alstroemeriana 212

Agrilus hyperici 134

Ailanthus altissima 190, 281

Air-potato 260, 279

Air-potato leaf beetle, See Lilioceris cheni

Alliaria petiolata 278, 280

Alligatorweed 194

Alligatorweed flea beetle, See Agasicles hygrophila

Alligatorweed stem borer, See Arcola malloi

Alligatorweed thrips, See Amynothrips andersoni

Alternanthera philoxeroides 194

Altica carduorum 102

Amynothrips andersoni 200

Anthonomus tenebrosus 281

Aphalara itadori 228

Aphis chloris 136

Aphthona abdominalis 188

Aphthona cyparissiae 176

Aphthona czwalinai 178

Aphthona flava 172

Aphthona lacertosa 168

Aphthona nigriscutis 170

Apion hookeri, See Omphalapion hookerorum

Aplocera plagiata 138

Archanara 280

Arcola malloi 198

Argopistes tsekooni 279

Arzama densa, See Bellura densa

Asian hydrilla leaf-mining fly, See Hydrellia 

pakistanae

Atteva punctella, See Atteva aurea

Australian hydrilla leaf-mining fly, See Hydrellia 

balciunasi

Australian pine 279

Austromusotima camptozonale 270

B

Bagous affinis 220

Bagous hydrillae 218

Bagous nodulosus 279

Bagous validus 279

Banded knapweed gall fly, See Urophora affinis

Bangasternus fausti 48

Bayeria capitigena, See Spurgia capitigena and

Spurgia esulae

Bellura densa 116

Bikasha collaris 278

Bipolaris spp. 280

Black dot leafy spurge flea beetle, See Aphthona 

nigriscutis

Black knapweed 29

Black leafy spurge flea beetle, See Aphthona 

czwalinai

Black-margined loosestrife beetle, See

Galerucella calmariensis

Black swallow-wort 74

Blunt knapweed flower weevil, See Larinus 

obtusus

Bohemian knotweed 222

Boreioglycaspis melaleucae 232

Botanophila seneciella 124

Brachypterolus pulicarius 150

Brazilian peppertree 244, 278, 279

Broad-nosed knapweed seedhead 

weevil, See Bangasternus fausti

Bronze knapweed root borer, See Sphenoptera 

jugoslavica

Brown dot leafy spurge flea beetle, See

Aphthona cyparissiae

Brown knapweed 29

Brown-legged leafy spurge flea beetle, See

Aphthona lacertosa

Brown Lygodium defoliating moth, See

Neomusotima conspurcatalis

Brown-winged knapweed root moth, See

Pelochrista medullana

Bull thistle 81, 82

Bull thistle seedhead gall fly, See Urophora stylata

Butomus umbellatus 279

C

Callopistria sp. 280

Calophasia lunula 156

Calophya latiforceps 278

Canada thistle 81, 84, 279

Canada thistle stem gall fly, See Urophora cardui

Canada thistle stem weevil, See Hadroplontus 

litura

Carduus acanthoides 81

Carduus nutans 81, 86

Carduus pycnocephalus 81

Carduus tenuiflorus 81

Carduus thoermeri, See Carduus nutans
Index

Biological Control in Eastern North America 327

Casmara spp. 281

Cassida rubiginosa 105

Casuarina spp. 279

Cataclysta camptozonale, See Austromusotima 

camptozonale

Centaurea biebersteinii, See Centaurea stoebe

Centaurea diffusa 29, 30

Centaurea jacea nothosubsp. pratensis 29

Centaurea jacea ssp. jacea 29

Centaurea jacea ssp. nigra 29

Centaurea maculosa, See Centaurea stoebe

Centaurea stoebe 29, 32

Centaurea virgata ssp. squarrosa 29

Cercospora piaropi 116

Cercospora rodmanii, See Cercospora piaropi

Ceuthorhynchidius horridus, See Trichosirocalus 

horridus

Ceutorhynchus edentulus, See Microplontus 

edentulus

Ceutorhynchus litura, See Hadroplontus litura

Ceutorhynchus marginellus 281

Ceutorhynchus scrobicollis 278

Ceutorhynchus spp. 280, See also Ceutorhynchus 

edentulus, Ceutorhynchus litura, Ceutorhynchus 

marginellus, Ceutorhynchus scrobicollis

Chaetorellia acrolophi 50

Chamaesphecia empiformis 188

Chamaesphecia hungarica 189

Chamaesphecia tenthrediniformis 189

Cheilosia corydon, See Cheilosia grossa

Cheilosia grossa 96

Chinese privet 279

Chinese tallow 279

Chrysochus (Eumolpus) asclepiadeus 281

Chrysolina hyperici 132

Chrysolina quadrigemina 132

Cinnabar moth, See Tyria jacobaeae

Cirsium arvense 81, 84, 279

Cirsium palustre 81

Cirsium vulgare 81, 82

Cleonis pigra 106

Cochylis atricapitana 122

Cogongrass 279

Colletotrichum gloeosporioides 280

Common salvinia 272

Common St. Johnswort 130

Conium maculatum 210

Copper leafy spurge flea beetle, See Aphthona 

flava

Cricotopus lebetis 221

Cynanchum rossicum, See Vincetoxicum rossicum

Cyphocleonus achates 34

Cypress spurge 164

Cyrtobagous salviniae 276

D

Dalmatian toadflax 142

Defoliating hemlock moth, See Agonopterix 

alstroemeriana

Diffuse knapweed 29, 30

Dioscorea bulbifera 260, 279

E

Earleaf acacia 279

Eichhornia crassipes 108, 281

Elaeagnus angustifolia 281

Epipagis albiguttalis, See Niphograpta albiguttalis

Epipsammea pectinicornis, See Spodoptera 

pectinicornis

Eteobalea intermediella 158

Eteobalea serratella 158

Eucryptorrhynchus brandti 281

Euhrychiopsis lecontei 72

Euphorbia crassipes 164

Euphorbia esula 166

Euphranta connexa 281

Eurasian watermilfoil 70

European water chestnut 281

F

Fallopia japonica 226

Fallopia sachalinensis 224

Fallopia xbohemica 222

Fergusobia quinquenerviae 238

Fergusonina turneri 238

Ficaria verna 279

Fig buttercup 279

Floracarus perrepae 266

Flowering rush 279

G

Gadirtha fusca 279

Galerucella birmanica 281

Galerucella calmariensis 64

Galerucella pusilla 64

Garlic mustard 278, 280

Giant knotweed 224

Giant salvinia 274

Golden loosestrife beetle, See Galerucella pusilla

Gratiana boliviana 250

Gratiana graminea 281

Green clearwing knapweed fly, See Terellia 

virens
Index

328 Biological Control in Eastern North America

Grey-winged knapweed root moth, See

Pterolonche inspersa

Gymnetron antirrhini, See Rhinusa antirrhini

Gymnetron linariae, See Rhinusa linariae

Gymnetron netum, See Rhinusa neta

H

Hadroplontus litura 90

Heteroperreyia hubrichi 279

Himalayan balsam 280

Hydrellia balciunasi 216

Hydrellia pakistanae 216

Hydrilla 214, 280

Hydrilla stem weevil, See Bagous hydrillae

Hydrilla verticillata 214, 280

Hylemyia seneciella, See Botanophila seneciella

Hyles euphorbiae 180

Hylobius transversovittatus 66

Hypena opulenta 78

Hypericum perforatum 130

I

Impatiens glandulifera 280

Imperata cylindrica 279

Invasive common reed 280

Italian thistle 81

J

Jacobaea vulgaris 118

Japanese knotweed 226

Japanese stiltgrass 280

K

Klamathweed beetle, See Chrysolina hyperici and 

Chrysolina quadrigemina

Knapweed peacock fly, See Chaetorellia acrolophi

Knapweed root weevil, See Cyphocleonus achates

Knapweeds 28, 29, 31, 32, 33

Knotweed psyllid, See Aphalara itadori

Knotweeds 222, 224, 226

Kudzu 280

L

Larinus carlinae 106

Larinus minutus 36

Larinus obtusus 38

Larinus planus, See Larinus carlinae

Leafy spurge 166

Leafy spurge gall fly, See Pegomya curticornis and 

Pegomya euphorbiae

Leafy spurge hawk moth, See Hyles euphorbiae

Leafy spurge tip gall midge, See Spurgia 

capitigena and Spurgia esulae

Lema cyanella 102

Lepidium latifolium 281

Lesser knapweed flower weevil, See Larinus 

minutus

Leucanthemum vulgare 280

Ligustrum sinense 279

Lilioceris cheni 262

Lilioceris egena 279

Linaria dalmatica 142

Linaria genistifolia, See Linaria dalmatica

Linaria spp. 281, See also Linaria dalmatica and 

Linaria vulgaris

Linaria vulgaris 144

Lobesia euphorbiana 174

Longitarsus jacobaeae 120

Longitarsus spp. 128, See also Longitarsus 

jacobaeae

Loosestrife flower-feeding weevil, See

Nanophyes marmoratus

Loosestrife root weevil, See Hylobius 

transversovittatus

Lophodiplosis indentata 280

Lophodiplosis trifida 234

Lophyrotoma zonalis 280

Lygodium microphyllum 264, 280

Lygodium mite, See Floracarus perrepae

Lygodium spp. 264, See also Lygodium 

microphyllum

Lygomusotima stria 280

Lythrum salicaria 62

M

Marsh thistle 81

Matricaria perforata, See Tripleurospermum 

inodorum

Meadow knapweed 29

Mecinus janthiniformis 146

Mecinus janthinus 146

Mecinus spp. 281, See also Mecinus 

janthiniformis and Mecinus janthinus

Megamelus scutellaris 110

Megastigmus transvaalensis 246

Melaleuca 230, 280

Melaleuca gall midge, See Lophodiplosis trifida

Melaleuca psyllid, See Boreioglycaspis melaleucae
Index

Biological Control in Eastern North America 329

Melaleuca quinquenervia 230, 280

Melaleuca snout beetle, See Oxyops vitiosa

Mesophleps albinella 281

Metaculus lepidifolii 281

Metriona elatior 281

Metzneria paucipunctella 52

Microplontus edentulus 208

Microstegium vimineum 280

Mile-a-minute weed 160, 280

Mile-a-minute weevil, See Rhinoncomimus latipes

Milk thistle 81

Minoa murinata 189

Multiflora rose 240

Musk thistle 81, 86

Musk thistle crown weevil, See Trichosirocalus 

horridus

Musk thistle seedhead fly, See Urophora solstitialis

Mycoleptodiscus terrestris 279, 280

Myriophyllum aquaticum 281

Myriophyllum spicatum 70, 279

N

Namangana pectinicornis, See Spodoptera 

pectinicornis

Nanophyes marmoratus 68

Neochetina bruchi 112

Neochetina eichhorniae 112

Neohydronomus affinis 256

Neomusotima conspurcatalis 268

Neostromboceros albicomus 280

Niphograpta albiguttalis 114

O

Oberea erythrocephala 182

Old World climbing fern 264, 280

Omphalapion hookerorum 204

Onopordum acanthium 81

Orthogalumna terebrantis 117

Oxeye daisy 280

Oxyops vitiosa 236

P

Paederia foetida 281

Pale swallow-wort 76

Parapoynx diminutalis 221

Parrotfeather 281

Pegohylemyia seneciella, See Botanophila seneciella

Pegomya argyrocephala, See Pegomya curticornis 

and Pegomya euphorbiae

Pegomya curticornis 184

Pegomya euphorbiae 184

Pelochrista medullana 54

Perennial pepperweed 281

Persicaria perfoliata 160, 280

Phragmites australis ssp. australis 280

Phyllocoptes fructiphilus 242

Phytoliriomyza ornata 279

Pistia stratiotes 254

Plumeless thistle 81

Poison hemlock 210

Polygonum perfoliatum, See Persicaria perfoliata

Pseudophilothrips ichini 278

Psylliodes chalcomera 103

Pterolonche inspersa 56

Puccinia carduorum 107

Puccinia komarovii var. glanduliferae 280

Puccinia psidii 239

Puccinia punctiformis 104

Pueraria lobata 280

Purple loosestrife 62

Pustula spinulosa 279

R

Ragwort seedhead fly, See Botanophila seneciella

Ragwort stem and crown boring 

moth, See Cochylis atricapitana

Red-headed leafy spurge stem borer, See Oberea 

erythrocephala

Rhinocyllus conicus 98

Rhinoncomimus latipes 162

Rhinusa antirrhini 152

Rhinusa linariae 154

Rhinusa neta 159

Rhinusa pilosa 148

Rhinusa spp. 281, See also Rhinusa antirrhini, 

Rhinusa linariae, Rhinusa neta, and Rhinusa 

pilosa

Rhodomyrtus tomentosa 281

Rhopalomyia tripleurospermi 206

Rosa multiflora 240

Rose myrtle 281

Rose Rosette Disease 242

Russian olive 281

Russian thistle 278

S

Salsola tragus 278

Salvinia minima 272

Salvinia molesta 274

Salvinia weevil, See Cyrtobagous salviniae
Index

330 Biological Control in Eastern North America

Sameodes albiguttalis, See Niphograpta albiguttalis

Scentless chamomile 202

Scentless chamomile gall midge, See

Rhopalomyia tripleurospermi

Scentless chamomile seed weevil, See

Omphalapion hookerorum

Scentless chamomile stem-mining weevil,

See Microplontus edentulus

Schinus terebinthifolius 244, 278, 279

Scotch thistle 81

Senecio jacobaea, See Jacobaea vulgaris

Siamusotima disrupta 280

Silybum marianum 81

Skunk vine 281

Slenderflower thistle 81

Solanum viarum 248, 281

Sphenoptera jugoslavica 40

Spodoptera pectinicornis 258

Spotted knapweed 29, 32

Spotted knapweed seedhead moth, See

Metzneria paucipunctella

Spurge, See Cypress spurge and Leafy spurge

Spurge leaf tying moth, See Lobesia euphorbiana

Spurgia capitigena 186

Spurgia esulae 186

Squarrose knapweed 29

St. Johnswort 130

St. Johnswort aphid, See Aphis chloris

St. Johnswort gall midge, See Zeuxidiplosis giardi

St. Johnswort inchworm, See Aplocera plagiata

St. Johnswort root borer, See Agrilus hyperici

Sulfur knapweed moth, See Agapeta zoegana

Swallow-worts 281, See also Black swallow-wort 

and Pale swallow-wort

T

Tansy ragwort 118

Tansy ragwort flea beetle, See Longitarsus 

jacobaeae

Taosa longula 281

Terellia ruficauda 107

Terellia virens 58

Thistles 80, 81, 82, 83, 84, 85, 86, 87, 279

Thistle seedhead weevil, See Rhinocyllus conicus

Thistle stem hover fly, See Cheilosia grossa

Thrypticus truncatus 281

Toadflaxes 281, See also Dalmatian toadflax and 

Yellow toadflax

Toadflax flower-feeding beetle, See

Brachypterolus pulicarius

Toadflax moth, See Calophasia lunula

Toadflax root-galling weevil, See Rhinusa linariae

Toadflax seed capsule weevil, See Rhinusa 

antirrhini

Toadflax stem weevil, See Mecinus janthiniformis 

and Mecinus janthinus

Tobacco mild green mosaic tobamovirus 252

Trapa natans 281

Tree-of-heaven 190, 281

Triadica sebifera 279

Trichosirocalus horridus 100

Tripleurospermum inodorum 202

Tripleurospermum maritimum ssp inodorum, See

Tripleurospermum inodorum

Tripleurospermum perforatum, See

Tripleurospermum inodorum

Tropical soda apple 248, 281

Tropical soda apple leaf beetle, See Gratiana 

boliviana

Tyria jacobaeae 126

U

Ukranian swallow-wort moth, See Hypena 

opulenta

Uromyces salsolae 278

Urophora affinis 44

Urophora cardui 92

Urophora jaceana 60

Urophora quadrifasciata 46

Urophora solstitialis 94

Urophora stylata 88

UV knapweed seedhead fly, See Urophora 

quadrifasciata

V

Verticillium albo-atrum, See Verticillium 

nonalfalfae

Verticillium nonalfalfae 192

Vincetoxicum 281, See also Vincetoxicum 

rossicum and Vincetoxicum nigrum

Vincetoxicum nigrum 74

Vincetoxicum rossicum 76

Vogtia malloi, See Arcola malloi

W

Waterhyacinth 108, 281

Waterhyacinth moth, See Niphograpta 

albiguttalis

Waterhyacinth planthopper, See Megamelus 

scutellaris

Waterhyacinth weevil, See Neochetina bruchi and 
Index

Biological Control in Eastern North America 331

Neochetina eichhorniae

Waterlettuce 254

Waterlettuce weevil, See Neohydronomus affinis

Y

Yellow toadflax 144

Yellow toadflax stem-galling weevil, See Rhinusa 

pilosa

Z

Zeuxidiplosis giardi 140