FIELD GUIDE

BIOLOGICAL CONTROL OF WEEDS

Rachel Winston, Carol Bell Randall, Rosemarie De Clerck-Floate, 

Alec McClay, Jennifer Andreas and Mark Schwarzländer

US Department

of Agriculture

FOR THE

IN THENORTHWEST

FHTET-2014-08 

Reprinted August 2016

Forest Health Technology

Enterprise Team
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/

The use of trade, firm, or corporation names in this publication is for the information and 

convenience of the reader. Such use does not constitute an official endorsement or approval by the 

U.S. Department of Agriculture or the Forest Service of any product or service to the exclusion of 

others that may be suitable.

Cover photos: Aphthona nigriscutis (R. Richard, USDA APHIS), Mecinus spp. (Bob Richard, USDA APHIS 

PPQ), Chrysolina hypericic quadrigemina, Eustenopus villosus (Laura Parsons & Mark Schwarzländer, 

University of Idaho), Cyphocleonus achates (Jennifer Andreas, Washington State University Extension)

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Rachel L. Winston

Environmental Consultant

MIA Consulting, LLC

Sandpoint, ID, USA

rachel@getmia.net

Mark Schwarzländer

Associate Professor for Entomology

University of Idaho, Department of Plant, 

Soil and Entomological Sciences

Moscow, ID, USA

markschw@uidaho.edu

For additional copies of this publication, contact: 

Richard Reardon

USDA Forest Service

180 Canfield Street

Morgantown, WV 26505

304.285.1566

rreardon@fs.fed.us

Mark Schwarzländer

University of Idaho

PSES Department

Moscow, ID 83844

208.885.9319

markschw@uidaho.edu

Significant help in reviewing and compiling the content in this field guide was provided by Eric 

Coombs (Oregon Department of Agriculture), Jeffrey Littlefield (Montana State University), 

Dan Bean (Colorado Department of Agriculture), Robert Bourchier (Agriculture and AgriFood Canada), and Susan Turner (British Columbia Ministry of Forests and Range). We would 

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

extend our gratitude to Denise Binion, Forest Service-Forest Health Technology Enterprise 

Team (FHTET) for help with editing, layout and graphics, and Richard Reardon (FHTET) 

for producing this guide.

Acknowledgments

BIOLOGICAL CONTROL OF WEEDS

IN THENORTHWEST

Carol Bell Randall

Entomologist, Forest Health Protection

USDA Forest Service

Coeur d’Alene, ID, USA

crandall@fs.fed.us

Jennifer E. Andreas

Integrated Weed Control Project

Washington State University Extension

Puyallup, WA

jandreas@wsu.edu

Alec S. McClay

McClay Ecoscience

Sherwood Park, Alberta, Canada

alec.mcclay@shaw.ca

Rosemarie A. De Clerck-Floate

Weed Biocontrol, Lethbridge Research Centre

Agriculture and Agri-Food Canada

Lethbridge, Alberta, Canada

rosemarie.declerck-floate@agr.gc.ca
Table of ContentsField Guide Components

About This Field Guide 10

Biological Control of Weeds 12

Weed Botanical Traits 14

Life Cycle 14

Duration 14

Leaf Arrangement and Margination 15

Flower heads 15

Biological Control Agent Life Cycles 16

Insects 16

Butterflies and Moths (Order Lepidoptera) 17

Beetles (Order Coleoptera) 17

Flies (Order Diptera) 17

Aphids (Order Hemiptera) 18

Mites 18

Nematodes 18

Fungi 18

Scientific Name Changes 19

Collection Methods 20

Sweep netting 20

Aspirating 20

Hand-picking/Tapping 21

Vacuuming 21

Light trap 21

Transport Considerations 22

Containers 22

Transporting Biological Control Agents 22

Shipping long distances 22

Other factors to consider 23

Releasing Biocontrol Agents 24

Select release site 24

Establish permanent location marker 24

Record geographical coordinates at release point using GPS 24

Prepare map 24

Complete relevant paperwork at site 25

Set up photo point 25

Release as many agents as possible 25
Table of Contents

Monitoring Biocontrol Agents 26

Assessing biocontrol agent populations 26

Assessing the status of the target weed and co-occurring plants 27

Qualitative (descriptive) vegetation monitoring 27

Quantitative vegetation monitoring 28

Assessing impacts on nontarget plants 28

Additional Considerations 29

Avoiding Parasitism 29

Pinkish-Purple Flowers 30

Houndstongue, Cynoglossum officinale 30

Houndstongue Biological Control 32

Longitarsus quadriguttatus (Pontoppidan) 34

Mogulones crucifer (Pallas) 36

Knapweed species comparison (Centaurea) 38

Diffuse knapweed, Centaurea diffusa 40

Spotted knapweed, Centaure stoebe 42

Knapweed Biological Control 44

Agapeta zoegana 46

Bangasternus fausti 48

Chaetorellia acrolophi 50

Cyphocleonus achates 52

Larinus minutus 54

Larinus obtusus 56

Metzneria paucipunctella 58

Pelochrista medullana 60

Pterolonche inspersa 62

Sphenoptera jugoslavica 64

Terellia virens 66

Urophora affinis 68

Urophora quadrifasciata 70

Russian knapweed, Rhaponticum repens 72
Table of Contents

Russian Knapweed Biological Control 74

Aulacidea acroptilonica 76

Jaapiella ivannikovi 78

Subanguina picridis 80

Russian Knapweed, Unapproved Agents 82

Puccinia acroptili. 82

Purple loosestrife, Lythrum salicaria 84

Purple Loosestrife Biological Control 86

Galerucella calmariensis 88

Hylobius transversovittatus 90

Nanophyes marmoratus 92

Saltcedar, Tamarix chinensis & T. ramosissima 94

Smallflower tamarisk, Tamarix parviflora 96

Saltcedar Biological Control 98

Saltcedars, Unapproved Agents 99

Coniatus splendidulus 99

Diorhabda spp. 100

Thistle species comparison 102

Bull thistle, Cirsium vulgare 104

Canada thistle, Cirsium arvense 106

Musk thistle, Carduus nutans 108

Thistle Biological Control 110

Cheilosia grossa 112

Hadroplontus litura 114

Rhinocyllus conicus 116

Trichosirocalus horridus 118

Urophora cardui 120

Urophora stylata 122

Thistles, Non-Established Agents 124

Altica carduorum 124

Lema cyanella 124
Table of Contents

Psylliodes chalcomera 125

Urophora solstitialis 125

Thistles, Unapproved Agents 126

Puccinia punctiformis 126

Aceria anthocoptes 127

Cassida rubiginosa 127

Cleonis pigra 128

Larinus carlinae (=L. planus) 128

Puccinia carduorum 129

Terellia ruficauda 129

Yellow Flowers 130

Scotch broom, Cytisus scoparius 130

Broom Biological Control 132

Bruchidius villosus 134

Exapion fuscirostre 136

Leucoptera spartifoliella 138

Broom, Unapproved Agents 140

Aceria genistae 140

Agonopterix nervosa 141

Arytainilla spartiophila 141

Gorse, Ulex europaeus 142

Gorse Biological Control 144

Exapion ulicis 146

Tetranychus lintearius 148

Gorse, Unapproved Agents 150

Agonopterix nervosa 150

Orange hawkweed, Pilosella aurantiaca 152

Whiplash hawkweed, Pilosella flagellaris 154

Hawkweed Biological Control 156

Aulacidea subterminalis 158

Puncturevine, Tribulus terrestris 160
Table of Contents

Puncturevine Biological Control 162

Microlarinus lareynii 164

Microlarinus lypriformis 166

Tansy ragwort, Jacobaea vulgaris 168

Tansy Ragwort Biological Control 170

Botanophila seneciella 172

Cochylis atricapitana 174

Longitarsus jacobaeae 176

Tyria jacobaeae 180

Tansy Ragwort, Unapproved Agents 182

Longitarsus spp. 182

Rush skeletonweed, Chondrilla juncea 184

Rush Skeletonweed Biological Control 186

Aceria chondrillae 188

Bradyrrhoa gilveolella 190

Cystiphora schmidti 192

Puccinia chondrillina 194

Yellow starthistle, Centaurea solstitialis 196

Yellow Starthistle Biological Control 198

Bangasternus orientalis 200

Chaetorellia australis & C. succinea 202

Eustenopus villosus 204

Larinus curtus 206

Puccinia jacea var. solstitialis 208

Urophora sirunaseva 210

Common St. Johnswort, Hypericum perforatum 212

Common St. Johnswort Biological Control 214

Agrilus hyperici 216

Aphis chloris 218

Aplocera plagiata 220

Chrysolina hyperici & C. quadrigemina 222

Zeuxidiplosis giardi 224
Table of Contents

Dalmatian toadflax, Linaria dalmatica ssp. dalmatica 226

Yellow toadflax, Linaria vulgaris 228

Toadflax Biological Control 230

Brachypterolus pulicarius 232

Calophasia lunula 234

Mecinus janthiniformis & M. janthinus 236

Rhinusa antirrhini 238

Rhinusa linariae 240

Toadflaxes, Non-Established Agents 242

Eteobalea intermediella 242

Toadflaxes, Unapproved Agents 243

Rhinusa neta 243

Green Flowers 244

Leafy spurge, Euphorbia esula 244

Leafy Spurge Biological Control 246

Aphthona cyparissiae 248

Aphthona czwalinai 250

Aphthona flava 252

Aphthona lacertosa 254

Aphthona nigriscutis 256

Hyles euphorbiae 258

Lobesia euphorbiana 260

Oberea erythrocephala 262

Spurgia capitigena & S. esulae 264

Leafy Spurge, Non-Established Agents 266

Aphthona abdominalis 266

Chamaesphecia spp. 266

Minoa murinata 267

Pegomya curticornis & P. euphorbiae 267

White Flowers 268

Field bindweed, Convolvulus arvensis 268
Table of Contents

Bindweed Biological Control 270

Aceria malherbae 272

Tyta luctuosa 274

Scentless chamomile, Tripleurospermum inodorum 276

Chamomile Biological Control 278

Microplontus edentulus 280

Omphalapion hookerorum 282

Rhopalomyia tripleurospermi 284

Poison hemlock, Conium maculatum 286

Poison hemlock Biological Control 288

Agonopterix alstroemeriana 290

Glossary 292

Selected References 298

Houndstongue 298

Knapweeds 300

Russian knapweed 305

Purple loosestrife 307

Saltcedars 309

Thistles 311

Broom and Gorse 315

Hawkweeds 317

Puncturevine 318

Tansy ragwort 320

Rush skeletonweed 322

Yellow starthistle 324

Common St. Johnswort 326

Toadflaxes 327

Leafy spurge 328

Field bindweed 330

Scentless chamomile 331

Poison hemlock 332
Table of Contents
10 Biological Control OF WEEDS in the Northwest Introduction 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 travel, exotic plant 

introductions are on the rise. Biological control of weeds (also called “biocontrol”) 

is the deliberate use of living organisms to limit the abundance of a target weed. 

In this field guide, biological control 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 classical biological control of 

weeds include different organisms, such as insects, mites, nematodes, and fungi. In 

North America, most weed biocontrol agents (also called “agents”) are plant-feeding 

insects, of which beetles, flies, and moths are among the most commonly used. 

This field guide focuses on the most problematic weeds in northwestern North 

America for which there are at least some biocontrol agents established. Multiple 

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

identification traits and plant ecology. Comparison tables are included to further 

aid in identification of related weed species, where applicable. For each weed 

included in this guide, all biocontrol agents 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 for each 

agent are described in great detail. Because current impact and recommendations 

often vary between the USA and Canada, information is presented separately for 

each country.

Symbology has been added for each biocontrol agent described in this manual to 

allow for a quick redistribution recommendation:

About This Field Guide

Many agents are already widespread. All target weed infestations should be surveyed 

USA Can Recommendation

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

Still actively released, but establishment is not yet confirmed

Released, but failed to establish

? ?
Biological Control OF WEEDS in the Northwest 11Introduction

prior to release to ensure the desirable biocontrol agents are not already present. 

Keep in mind that many species are approved for use in only the USA or Canada, 

but not both. In addition, some agents cause nontarget damage to desirable species. 

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

Plant distribution data from the USDA-PLANTS 

database is presented in a map for each weed. Though 

significant effort is put into keeping the PLANTS 

database 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.

Maps depicting each agent’s current establishment 

were created using available literature and numerous 

personal communications with regional land 

managers. Like weeds, biocontrol agents can spread 

rapidly, making accurate distribution information elusive. EDDMapS is a webbased mapping system for documenting invasive species as well as biocontrol agent 

distribution in the USA. EDDMapS combines data from existing sources (e.g. 

databases and organizations) while soliciting and verifying volunteer observations, 

creating an inclusive invasive species geodatabase that is shared with educators, land 

managers, conservation biologists, and beyond. Information can be added in online 

forms through home computers and/or apps created for smartphones. For more 

information on how to utilize or contribute to these tools, visit www.eddmaps.org/

about/ and apps.bugwood.org/.

Agents that were released but did not establish or are not currently approved for 

redistribution in the USA and/or Canada are addressed separately from approved 

agents. The description, ecology, and history/status are described for each 

species, accompanied by a photo. Should you encounter agents not believed to 

be established during field surveys, contact your local weed superintendent, land 

grant university, or extension service personnel to confirm and document their 

establishment. Caution must be taken during field redistribution to ensure that 

agents not approved for use are not inadvertently collected and redistributed along 

with approved agents. 

The remainder of this introduction describes biocontrol regulations, agent life 

cycles, and techniques for collecting, transporting, and releasing established agents. 

Cytisus

scoparius
12 Biological Control OF WEEDS in the Northwest Introduction 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, or facilitate secondary infection from pathogens—all of which reduce the 

weed’s ability to compete with other plants. Root- and crown-feeding biocontrol 

agents are usually more effective against perennial plants that primarily spread by 

root buds. Alternatively, flower- and seed-feeding biocontrol agents are typically 

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

To be considered for release in North America, it is crucial that biocontrol agents 

are host-specific, meaning they must feed and develop only on the target weed; 

or in some cases, on a few closely related plant species. They must never feed on 

any crop or any protected plant species. Tests are necessary in order to ensure that 

the biocontrol agents are effective and that they will damage only the target weed. 

Potential biocontrol agents often undergo more than five or more years of rigorous 

testing to ensure that host specificity requirements are met.

The United States Department of Agriculture’s Animal and Plant Health Inspection 

Service - Plant Protection and Quarantine (USDA-APHIS-PPQ) is the federal agency 

responsible for providing the testing guidelines and authorizing the importation of 

biocontrol agents into the USA. The Canadian Food Inspection Agency (CFIA) 

serves the same role in Canada. Federal laws and regulations are in place to minimize 

the risks to native plant and animal communities associated with introduction 

of exotic organisms to manage weeds. The Technical Advisory Group (TAG) for 

Biological Control Agents of Weeds is an expert committee with representatives 

from regulatory agencies, federal land management offices, environmental 

protection agencies from the USA, and representatives from Canada and Mexico. 

TAG reviews all petitions to import new biocontrol agents into the USA and makes 

recommendations to USDA-APHIS-PPQ regarding the safety and potential impact 

of prospective biocontrol agents. Weed biocontrol researchers work closely with 

USDA-APHIS-PPQ and TAG to accurately assess the environmental safety of 

potential weed biocontrol agents and programs. In addition, some states in the USA 

have their own approval process to permit field release of weed biocontrol agents. 

The Canadian counterpart to TAG is the Biological Control Review Committee 

(BCRC) which uses the North American Plant Protection Organization’s (NAPPO) 

Regional Standards for Phytosanitary Measures (RSMP) number 7 (NAPPO RSMP 

NO.7)- as their review/petition requirement.

Biocontrol practitioners have adopted the International Code of Best Practices 

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

and participants of the Tenth International Symposium for Biological Control of 

Biological Control of Weeds
Biological Control OF WEEDS in the Northwest 13Introduction

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

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

causing environmental damage through the use of biological control by voluntarily 

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

INTERNATIONAL CODE OF BEST PRACTICES 

FOR CLASSICAL BIOLOGICAL CONTROL OF WEEDS1

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

non-endemic agents

2. Obtain multi-agency approval for target

3. Select agents with potential to control target

4. Release safe and approved agents

5. Ensure that only the intended agent is released

6. Use appropriate protocols for release and documentation

7. Monitor impact on the target

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

9. Monitor impacts on potential non-targets

10. Encourage assessment of changes in plant and animal communities

11. Monitor interaction among 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, biocontrol agents that have 

not been approved are illegal to introduce to the USA and Canada. When 

biocontrol agents arrive accidentally, it is generally illegal to redistribute them 

intentionally within the USA. A few cases where this is legal are described in this 

manual. Some agents introduced accidentally to Canada are safe to utilize, however 

redistribution of accidentally introduced agents 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 completely 

eradicate the target weed. Even in the most successful cases, bioontrol 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.
14 Biological Control OF WEEDS in the Northwest IntroductionWeed Botanical Traits

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 others. Traits referred to most commonly include:

Life Cycle

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

only 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 obvious rosette stages. Plants then grow a flowering 

stem in a stage called bolting. In bud, immature flowers appear on the ends of 

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.

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

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

State University; c K. George Beck & James Sebastian, Colorado State University; e Michael Shephard, 

Forest Service (all www.bugwood.org)

d

e

f b

a

c

Duration

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

seed) within one year and then die. Summer annuals germinate during spring/early 
Biological Control OF WEEDS in the Northwest 15Introduction

Jacqi Moulton, MIA Consulting

alternate opposite whorled smooth lobed toothed

a) Canada thistle, all disc florets, b) rush skeletonweed, all ray florets, c) tansy ragwort, both disk (center) 

and ray (outer) florets (photo credits on respective weed pages)

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 

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.

Leaf Arrangement and Margination

a b c

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.
16 Biological Control OF WEEDS in the Northwest IntroductionBiological Control Agent Life Cycles

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. Most adult insects also 

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. The process of an insect shedding its 

“skin” in order to grow is called molting, and 

larval stages between molts are called “instars.” 

Larvae generally complete three to five instars 

before they molt into pupae. During the pupal 

stage, insects change from larvae to adults. 

Insects do not feed during the pupal stage. 

Aphids (in the order Hemiptera) are a group 

a) Complete metamorphosis of an insect (L. 

Wilson), b) body parts of adult insects A. 

head, B. antenna, C. thorax, D. abdomen, 

E. wing (Biocontrol of Weeds in the West)

a

b

of insects included in this manual that have gradual metamorphosis. In this process, 

there is no pupal stage. Instead, their young are called nymphs, and resemble the 

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

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

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

majority of approved biocontrol agents are arthropods in the class Insecta. More 

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

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

there are also nematodes and fungi biocontrol agents.

Insects
Biological Control OF WEEDS in the Northwest 17Introduction

Butterflies and Moths (Order Lepidoptera)

Adult Lepidoptera have two pair of membranous wings, covered (usually 

completely) by minute powder-like scales. Antennae are prominent. The larvae 

(caterpillars) have a toughened head capsule, chewing mouthparts, and a soft body 

that may have hair-like or other projections, three pairs of true legs, and up to five 

pairs of abdominal prolegs. The pupal stage of Lepidoptera is known as a chrysalis 

and is often enclosed in a cocoon.

Beetles (Order Coleoptera)

Most adult beetles are hard-bodied with tough exoskeletons. They have two pairs 

of wings. The two front wings, called elytra, are thickened and meet in a straight 

line down the abdomen of the adult insect, forming a hard, shell-like, protective 

covering. The two hind wings are membranous and used for flight. These are larger 

and are folded under the elytra when not in use. Beetle larvae are grub- or wormlike with three small pairs of legs. Most are pale white with a brown or black head.

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 and 

mayfly in the order Ephemeroptera). 

Identification key to to differentiate biological control insects as a) larvae and b) pupae (both L. Wilson)
18 Biological Control OF WEEDS in the Northwest Introduction Aphids (Order Hemiptera)

Most aphids have soft bodies and vary in color from green, black, brown, pink to 

almost colorless. The mouthpart is unique from other insects described in this manual 

in that it consists of a stylet enclosed in a sheath (rostrum). This combination allows 

them to pierce and suck plant tissue (typically sap) for feeding. Most aphids have 

a pair of abdominal tubes through which they exude droplets of a defensive fluid. 

Mites

Like insects, mites are in the phylum Arthropoda. 

However, they belong to a different class, Arachnida, 

whose adult members are characterized by having 8 

legs (compared to the 6 legs of insects). Mites have 

gradual metamorphosis. The first immature stage in 

mites is called larva; mites in this stage have only 

6 legs. The second immature stage is called nymph 

and has 8 legs. Nymphs are usually very similar in 

appearance to adults. 

Nematodes

Nematodes, or roundworms, belong to 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. In free-living nematodes 

(such as the species in this manual), eggs hatch into larvae, which appear essentially 

identical to the adults, except for an underdeveloped reproductive system.

Fungi

Fungi belong to their own kingdom (Fungi). The 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. Rusts 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 which land on vegetation and produce 

pustules, or uredia, that form 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. 

Biological Control Agent Life Cycles

Egg

Larva

Nymph/

Adult

Rachel Winston, MIA Consulting
Biological Control OF WEEDS in the Northwest 19Introduction

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 updates with 

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).

Weed Common Scientific Name Previous names

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

micranthos, C. maculosa

Russian knapweed Rhaponticum repens Centaurea repens, Acroptilon repens

Musk thistle Carduus nutans Carduus thoermeri

Scotch broom Cytisus scoparius Cytisus scoparius subsp. scoparius, 

Sarothamnus scoparius

Orange hawkweed; 

Whiplash hawkweed

Pilosella aurantiaca; 

Pilosella flagellaris

Hieracium aurantiacum; 

Hieracium flagellare

Tansy ragwort Jacobaea vulgaris Senecio jacobaea

Dalmatian toadflax Linaria dalmatica ssp. 

dalmatica Linaria genistifolia, L. genistifolia ssp. dalmatica, L. dalmatica

Scentless chamomile Tripleurospermum inodorum Matricaria perforata, Tripleurospermum 

maritimum subsp. inodorum, T. perforatum

Agent Current Name Target(s) Previous names

Mogulones crucifer Houndstongue Mogulones cruciger

Subanguina picridis Russian knapweed Paranguina picridis, Mesoanguina picridis

Cheilosia grossa Thistles Cheilosia corydon

Hadroplontus litura Thistles Ceutorhynchus litura

Larinus carlinae Thistles Larinus planus

Trichosirocalus horridus Thistles Ceuthorhynchidius horridus

Exapion fuscirostre Scotch broom Apion fuscirostre

Exapion ulicis Gorse Apion ulicis

Botanophila seneciella Tansy ragwort Hylemyia seneciella, Pegohylemyia seneciella

Aceria chondrillae Rush skeletonweed Eriophyes chondrillae

Rhinusa antirrhini; R. 

linariae; R. neta

Toadflaxes Gymnetron antirrhini; G. linariae; G. netum

Spurgia capitigena, S. esulae Leafy spurge Bayeria capitigena

Pegomya curticornis, P. euphorbiae Leafy spurge Pegomya argyrocephala

Microplontus edentulus Scentless chamomile Ceutorhynchus edentulus

Omphalapion hookerorum Scentless chamomile Apion hookeri
20 Biological Control OF WEEDS in the Northwest IntroductionCollection 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” insects off weeds. 

A sweep is made by swinging the net through the plant 

canopy. If insects are suitable for aspiration (see below for a 

description of aspiration and aspirators), it is best to alternate 

between sweeping insects off the weed and aspirating them 

out of the net. Sweep no more than 25 times before aspirating 

hard-bodied beetles or as few as five times for fragile adult 

moths and flies. Aspirating or removing insects at regular 

intervals reduces the potential harm that could result from knocking biocontrol 

agents around with debris and reduces the opportunity for predator insects swept 

up with the biocontrol agents from finding and devouring the agents. 

Sweep netting is an easy and efficient method for collecting insects from the aboveground portion of plants, and is particularly useful for adult flea beetles. The best 

time for sweeping is during the warmest part of the day (1 -6 p.m.) as this is when 

the beetles are most active. In general, adult moths and flies 

are very delicate, and collecting them with sweep nets can 

be damaging or fatal. It is best to use other methods for 

collecting delicate species. 

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 Laura Parsons, University 

of Idaho

Laura Parsons, University 

of Idaho
Biological Control OF WEEDS in the Northwest 21Introduction

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.

Hand-picking/tapping

Stationary or slow-moving insects can be picked from foliage 

by hand using forceps or tweezers. When sweeping agents is 

inefficient or damages tap them onto a beat sheet or tray using 

a tool such as a racquet. Plants infested with galls or fungal 

spores can be hand-picked and moved to new infestations. 

Take care when moving plant material to ensure seeds are not 

included as 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 insects. 

This is particularly useful for collecting small agents such as 

flea beetles from weed rosettes. Rocks or debris vacuumed up 

may harm collected adults, so this method should be applied 

to foliage collections only. Adding rosette leaves to the net 

gives agents substrates to crawl and hide on and reduces the 

suction strength. Net contents should be aspirated to separate 

agents from unwanted material. 

Light trap

Light traps are used to collect nocturnal agents (typically 

moths) that are otherwise difficult to collect during the day. 

Construct a wire or wooden framework to support a batteryoperated 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 insects attracted to 

the sheet as they land on the surface.

Eric Coombs, Oregon 

Department of Agriculture

Ray Willard , Washington 

State Department of 

Transportation

Jerry Payne, USDA ARS
22 Biological Control OF WEEDS in the Northwest IntroductionTransport Considerations

Containers

Collected insects must be transferred to containers intended to protect and prevent 

them from escaping. Containers should be rigid enough to resist crushing but 

also ventilated to provide adequate air flow and prevent condensation. Unwaxed 

paperboard cartons are ideal for most biocontrol species. As an alternative, you 

can use light-colored, lined or waxed-paper containers (e.g., ice cream cartons 

are particularly suitable) or plastic containers, providing they are ventilated and 

colored or transluscent. Cut holes in the container or its lid, and cover the holes 

with a fine mesh screen. These ventilation procedures are not necessary for galls or 

fungus-infected foliage. Do not use glass or metal containers; they are breakable 

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

Again for insects, fill the containers two-thirds full with crumpled paper towels 

or tissue paper to provide a substrate for insects to rest on and hide in and to 

help regulate humidity. Include a few fresh sprigs of the target weed foliage (as 

food) before adding the agents. Sprigs should be free of seeds, flowers, dirt, spiders, 

and other insects. Do not place sprigs in water-filled containers; they may crush 

the agents or drown the agents upon leaking. Sprigs are not needed for galls or 

fungus-infected foliage. Seal the container lids either with masking tape or label 

tape. Be sure to label each container with (at least) the biocontrol agent(s) name, 

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 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

You might need to use a bonded carrier service with overnight delivery (e.g., USPS, 

FedEx, UPS, or DHL) if your release sites are far from your collection sites or you 

have to deliver your agents to several sites. In such cases, the containers should be 

placed in insulated shipping containers 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 container to 

prevent them from having direct contact with the insect containers and also to 

prevent crushing should they move about during shipping. Empty spaces in the 

shipping container should be loosely filled with crumpled paper, packing peanuts, 
Biological Control OF WEEDS in the Northwest 23Introduction

REGULATIONS FOR THE TRANSFER 

OF BIOLOGICAL CONTROL AGENTS

USA, intrastate Generally, there are few if any restrictions governing 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 governing the release and intrastate transport 

of your specific biological control agent. The state of California regulates release 

permits at the county level.

USA, interstate The interstate transportation of biological control 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 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 at http://www.aphis.usda.gov/plant_health/

permits/organism/biological_control/index.shtml. This allows the complete 

online processing of biological control agent permit requests.

Canada Canada requires an import permit for any new or previously released 

biological control agent. Permits are issued by the Plant Health Division of the 

Canadian Food Inspection Agency. Redistribution of biological control agents 

within a province is generally not an issue; however, you should consult with 

provincial authorities and specialists prior to moving any biological control 

agent across provincial boundaries.

etc. Enclose all paperwork accompanying the agents (including any needed permits) 

before sealing the shipping container with tape. 

Other factors to consider

• Make your shipping arrangements well before you collect the agents, and make 

sure the carrier you select can guarantee overnight delivery as well as the proper 

treatment of the package contents.

• Plan collection and packaging schedules so that overnight shipments can be 

made early in the week rather than delivery on Friday-Sunday. 

• Clearly label the contents of containers and specify that they are living insects.

• Contact personnel at the receiving end, tell them what you are shipping and 

when it is due to arrive, provide a tracking number, verify that someone will be 

there to accept the shipment, and instruct them not open the container prior 

to releasing the agents.
24 Biological Control OF WEEDS in the Northwest IntroductionReleasing Biocontrol Agents

Select release site

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

present. Release sites should typically contain large (4,000 m2

, 1 acre) patches of the 

target weed. Different 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 the biocontrol agents. 

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

it is best to redistribute the agents the same day they are collected. Releases of all 

biocontrol agents should be made under moderate weather conditions (mornings 

or evenings of hot summer days, mid-day for cold season releases). Avoid making 

releases on rainy days. If you encounter an extended period of poor weather, 

however, it is better to release the 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 fence post or plastic/fiberglass pole at least 4 ft (1.2 m) tall as a marker 

at the release point. Avoid wooden posts; they are vulnerable to weather and decay. 

Markers should be colorful and conspicuous. White, bright orange, pink, and red 

are preferred over yellow and green, which may blend into surrounding vegetation. 

Where conspicuous posts may encourage vandalism, mark your release sites with 

short, colorful plastic tent/surveyor’s stakes or steel plates that can be tagged with 

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

Record geographical coordinates at 

release point using GPS 

Map coordinates of the site marker should be determined using 

a global positioning system (GPS) device of a GPS capable 

tablet/smartphone. Coordinates should complement but not 

replace a physical marker. Accurate coordinates will help relocate 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 

biological control 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 

Geonarva
Biological Control OF WEEDS in the Northwest 25Introduction

remote locations or places physically difficult or confusing to access.

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 latitude, longitude, 

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

use; the name(s) of the 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. Once back in the office, submit 

the information to your local weed control authority or land management agency. 

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 year and location.

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

Release as many 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 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; 1 km (2⁄3 mile) is ideal.
26 Biological Control OF WEEDS in the Northwest IntroductionMonitoring 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 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 biotic/abiotic factors have changed over time

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 agents or the same agent in an area where they were 

previously released, and/or helping them avoid land management activities that 

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

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, the 

decline of the target weed, changes in the plant community, and other biotic and 

abiotic (e.g. climate, soil) changes.

Monitoring: a) checking biocontrol agent abundance, b) measuring vegetation along a transect, c) 

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

a b c

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 agents in one or more of their life stages, 
Biological Control OF WEEDS in the Northwest 27Introduction

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 to three years to reach detectable 

levels. Thus if no 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 biological control of weeds expert for assistance.

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

monitoring approach is needed. The Standardized Impact Monitoring Protocol 

(SIMP) is one such approach to monitoring biocontrol agent populations, 

weed populations, and the surrounding plant community over time. This 

simplified protocol was developed through cooperation among the Bureau of 

Land Management, the University of Idaho, Forest Health Protection, the Nez 

Perce Biocontrol Center, and the Idaho State Department of Agriculture. SIMP 

monitoring forms and additional information regarding this method can be found 

at www.agri.state.id.us/Categories/PlantsInsects/NoxiousWeeds/Bio_Control.php. 

Assessing the status of the target weed and cooccurring plants

The ultimate goal of a biological control program is to permanently reduce the 

abundance of the target weed and enable the recovery of more desirable vegetation 

on the site. To determine the efficacy of biocontrol efforts, 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 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, estimates of density, age and distribution classes, 

visual infestation mapping, and maintaining a series of photos from designated 

photo points. Qualitative monitoring provides insight into the status or change of 
28 Biological Control OF WEEDS in the Northwest IntroductionMonitoring Biocontrol Agents

target weed populations. However, its descriptive nature does not generally allow 

for detailed statistical analyses. Data obtained in qualitative monitoring may trigger 

more intensive monitoring later.

Quantitative vegetation monitoring

The purpose of quantitative monitoring is to measure changes in the target weed 

population as well as the vegetative community as a whole before and after a 

biocontrol agent release. It may be as simple as counting the number of stems 

of the target weed in an area, or as complex as measuring plant height, flower 

and production, biomass, species diversity, and species cover. If designed properly, 

quantitative data can be statistically analyzed and give measurable information 

on plant community changes. Pre- and post-release monitoring should follow the 

same protocol and be employed at the same time of year. Post-release assessments 

should be planned annually for at least three to five years after the initial biocontrol 

agent release. The SIMP approach is a combination of qualitative and quantitative 

elements and can be easily modified to meet your personal or agency needs. 

Assessing impacts on nontarget plants

To address possible nontarget attacks on species related to the target weed, 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 all 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 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. 

If you observe approved biological control agents feeding on and/or developing on 

native species, collect samples and take them to a biocontrol specialist in your area. 

Alternatively, you may send the specialist the site data so he or she can survey the 

site for nontarget impacts.
Biological Control OF WEEDS in the Northwest 29Introduction

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 

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

Additional Considerations
30 Biological Control OF WEEDS in the Northwest HoundstongueHoundstongue

Cynoglossum officinale L.

a) plant (Robert Vidéki, Doronicum Kft., www.bugwood.org), b) infestation (Rachel Winston, MIA 

Consulting)

SYNONYMS: gypsy flower, beggar’s lice

ORIGIN: Native to Eurasia; first recorded in North America in Ontario in 1859. 

DESCRIPTION: Upright, herbaceous biennial or short-lived perennial typically 

growing 1-4 ft tall (1⁄3-1.2 m) from a stout taproot. Leaves are grayish green, 

have smooth margins, and are softly to roughly hairy on both surfaces. Basal 

leaves are up to 12 in long (30 cm); stem leaves are smaller, without stalks, and 

grow alternately. An individual plant may have one to several rosettes on one 

root system. Flowering stems are cymes with 10-35 flowers, though usually 2-3 

flowers are open at once. Flowers have five reddish-purple petals, turning blue 

with age. Each flower produces up to four nutlets, each densely covered with 

small hooks.

 

HABITAT: Capitalizes on disturbance to invade areas with a wide variety of 

a b
Biological Control OF WEEDS in the Northwest 31Houndstongue

conditions. Can be found in rangeland, pastures, abandoned crops, roadsides, 

and other waste places, but does especially well in forest clearings opened by 

logging operations and road construction.

ECOLOGY: Spreads only by seed. The barbed hooks on the surface of nutlets 

readily adhere to animal fur, feathers, machinery or human clothing. Seeds only 

remain viable in the soil for up to three years. Germination typically occurs in 

early spring. Plants are rosettes the first year, not producing flowering stems 

until the second year. Flowering occurs throughout summer. Most plants die 

following flowering, but some continue to flower for one or two more years.

APPROVED BIOLOGICAL CONTROL AGENTS: USA: There are no 

approved biocontrol agents; CAN: Longitarsus quadriguttatus and Mogulones 

crucifer (=Mogulones cruciger).

NOTES: All parts of the plant contain 

pyrrolizidine alkaloids that are toxic to livestock 

and humans.

Family Boraginaceae

d

c) rosette (Rachel Winston, MIA Consulting), d) flowers (Fornax), e) nutlets (Richard Old, XID 

Services, Inc, www.xidservices.com, www.bugwood.org)

c e

Cyno

offici
32 Biological Control OF WEEDS in the Northwest Houndstongue HISTORY IN THE NORTHWEST: European exploration for potential 

biological control agents began in 1988. Following the testing of six species, 

Mogulones crucifer and Longitarsus quadriguttatus were approved for release in 

Canada in 1997 and 1998, respectively. A petition for the release of M. crucifer 

in the USA was denied due to concerns about the agent’s host specificity. Despite 

its denial in the USA, M. crucifer naturally migrated there from Canadian release 

sites and is presently established in three states. The USDA APHIS issued a pest 

alert in 2010 which outlines the legal penalties that can be imposed on any 

individual who is affiliated with the unauthorized collection, transportation, and 

release of M. crucifer within and to the USA.

CURRENT STATUS: Both M. crucifer and L. quadriguttatus established in 

Canada, though M. crucifer has proven to be a far superior agent. Its high impact 

has negatively affected populations of L. quadriguttatus, which is now only 

confirmed established in low numbers in BC where it has limited impact. M. 

crucifer is established in AB, BC, ID, MT and WA. At sites where M. crucifer

has been present for multiple years, houndstongue is now typically rare or 

completely absent. Nontarget attack has been documented in both Canada 

and the USA, though to date this attack appears to be only minor, sporadic, 

and temporary spillover. It should be noted that M. crucifer has been shown 

capable of developing on several plant species that are considered threatened and 

endangered in the USA. To date, M. crucifer does not yet occur in areas of the 

USA with populations of these protected species. In addition, there are regions 

of the USA not yet established by M. crucifer where there exists large populations 

of related plant species known to be more prone to M. crucifer attack. Both are 

significant concerns for the future. The incidence of nontarget feeding is still 

being monitored in both Canada and the USA.

RECOMMENDATIONS: USA: Both L. quadriguttatus and M. crucifer

are not approved for release. Though M. crucifer naturally migrated from 

Canada, its redistribution within the USA is illegal and is punishable with 

steep penalties. CAN: Due to the high impact of M. crucifer, continued use of 

L. quadriguttatus is not recommended in Canada. Redistribution of M. crucifer

is recommended and is best accomplished using an industrial strength wet-dry 

vacuum cleaner from April to May.

Houndstongue Biological Control
Biological Control OF WEEDS in the Northwest 33Houndstongue

Longitarsus, Mogulones: Mark Schwarzländer, University of Idaho

Agent Adult Impact Recommendation

Longitarsus 

quadriguttatus

Defoliation and root- feeding 

now have limited impact in 

CAN due to success of M. 

crucifer.

Not released in USA. No 

longer recommended for 

redistribution in CAN due 

to tremendous success of M. 

crucifer.

Mogulones 

crucifer

Root-feeding extremely 

effective throughout weed 

range in Canada, causing high 

mortality.

Naturally spread to USA; 

illegal to redistribute. 

Increasingly distributed in 

CAN, but recommended 

where not already established.
34 Biological Control OF WEEDS in the Northwest Houndstongue DESCRIPTION: Eggs are elliptical, yellowish-orange, and laid at houndstongue 

leaf petiole bases, on root crowns or into the soil within 2 cm from first year 

rosettes. Larvae are 1-4 mm long, have short legs, a white body and yellow head 

with thick head capsule. Adults are up to 3 mm long, shiny black, and have long 

antennae. Both wing covers have 2-4 reddish spots that vary in size and shape. 

It is the reddish spots that gives this agent its Latin name, and helps differentiate 

this species from other Longitarsus.

Longitarsus quadriguttatus (Pontoppidan)

Houndstongue flea beetle

LIFE CYCLE: Eggs hatch in spring; emerging larvae feed on secondary roots and 

the main tap root cortex. Larvae overwinter in plant roots and resume feeding 

in early spring. There are three larval instars. Pupation occurs in the soil. Adults 

emerge in late spring, feed, mate, and oviposit within a week of emergence. 

There is one generation per year.

DAMAGE: Adults feed on foliage leaving a characteristic shot-hole appearance 

over the entire leaf that provides little control of the weed. Larvae feed on roots, 

often leading to plant mortality.

PREFERRED HABITAT: Hot, dry sites with a mild continental climate.

HISTORY: Introduced from Austria to Canada (BC 1998, AB 1999).

CURRENT STATUS: Established in AB and BC initially, but Mogulones crucifer 

subsequently destroyed all known houndstongue at the AB release sites. L. 

Longitarsus quadriguttatus: a) adult (Mark Schwarzländer, University of Idaho), b) feeding damage 

(© Province of British Columbia. All rights reserved. Reproduced with permission of the Province of 

British Columbia)

a b
Biological Control OF WEEDS in the Northwest 35Houndstongue

quadriguttatus is now only confirmed established in low numbers in BC where 

it has limited impact. 

REDISTRIBUTION: In Canada, given the high success of M. crucifer, continued 

use of L. quadriguttatus is not recommended.

NOTES: This agent is not approved for release in the USA. Typical of all flea 

beetles, adults are capable of jumping great distances and do so when disturbed.

Coleoptera: Chrysomelidae

Longitarsu

quadrigut
36 Biological Control OF WEEDS in the Northwest Houndstongue SYNONYMS: Mogulones cruciger Herbst

DESCRIPTION: Eggs are white (turning yellow-orange with age) and laid at the 

bases of houndstongue leaf petioles. Larvae are white with brown head capsules, 

1-4 mm long, and have the typical weevil “C-shape.” Adults are 2-3 mm long 

and a mottled dull brown with a white cross pattern on their wing covers.

Mogulones crucifer (Pallas)

Houndstongue root weevil

Mogulones crucifer: a) eggs, b) larva (a,b Rachel Winston, MIA Consulting), c) adult (Mark 

Schwarzländer, University of Idaho)

a b c

LIFE CYCLE: Overwintering adults emerge in spring from the soil litter and 

feed on houndstongue rosette leaves prior to mating and laying eggs from AprilMay. Hatching larvae feed on roots and develop through three instars. Mature 

larvae exit roots to pupate in the soil in prepared silk oval cocoons covered in 

soil particles. New adults emerge in late summer and early fall and feed on 

houndstongue foliage prior to mating and laying eggs. Autumn oviposition 

is typically much less frequent than in spring. Adults may live 1-2 years, so 

overlap in generations has been documented, and larvae can typically be found 

throughout the year. Overwintering can occur in three forms: mature adults in 

soil, pupae and new adults in cocoons, or larvae in roots.

DAMAGE: Adults feed on foliage, leaving characteristic circular and oval feeding 

holes over the entire leaf and petioles. 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: Does well at all houndstongue sites in BC and AB at 

which it has been released.

HISTORY: Introduced from Hungary and Serbia to Canada (BC 1997, AB 

1998). Spread naturally to the USA by 2008.
Biological Control OF WEEDS in the Northwest 37Houndstongue

CURRENT STATUS: Though this agent is approved for use in Canada, it was 

rejected for release in the USA due to concerns of nontarget attack. It has since 

migrated naturally from Canada to bordering states in the USA. This agent has 

been very effective in Canada and in the portions of the USA to which it has 

naturally migrated. At sites where the agent has been present for multiple years, 

houndstongue is now typically rare or completely absent. Nontarget attack has 

been documented in both Canada and the USA, though to date this attack 

appears to be only minor, sporadic, and temporary spillover. M. crucifer has been 

shown capable of developing on several plant species considered threatened and 

endangered in the USA. To date, M. crucifer does not yet occur in areas of the 

USA with populations of these protected species. In addition, there are regions 

of the USA not yet established by M. crucifer where there exists large populations 

of related plant species known to be more prone to M. crucifer attack. Both are 

significant concerns for the future. The incidence of nontarget feeding is still 

being monitored in both Canada and the USA

REDISTRIBUTION: It is illegal to release or redistribute this species within 

the USA. The USDA APHIS issued a pest alert in 2010 which outlines the 

legal penalties that can be imposed on any individual who is affiliated with 

the unauthorized collection, transportation, and release of M. crucifer in 

and to the USA. In Canada, adult field collections can be difficult as adults 

drop easily from leaves and are readily camouflaged in the soil. The most 

efficient method is to aspirate adults from leaves, petioles, the 

root crown and surrounding soil by using an industrial strength 

wet-dry vacuum cleaner (with a catchment container) from April 

through May and sieving the resulting material. Adults are most 

active following periods of sunny, warm days and in the morning 

to early afternoon. Releases of 300 individuals should be made on 

patches of at least 400 m2 (1/10 acre) containing plants in a variety 

of stages. Establishment can be monitored the following spring.

Mogulones crucifer damage to d) leaves, e) leaf petioles, f) roots (all Rachel Winston, MIA Consulting)

Coleoptera: Curculionidae

d e f

Mogulo

crucifer
38 Biological Control OF WEEDS in the Northwest 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. Below is a 

comparison of these two 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, Rhaponticum, and comprises its 

own, distinct biocontrol program. It is treated separately in this guide.

Tr a it

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

11⁄2’

(0.45 m)

21⁄2’

(0.75 m)

11⁄2’

(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 OF WEEDS in the Northwest 39KNAPWEEDS

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

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

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

Roche, www.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)

11⁄2’

(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
40 Biological Control OF WEEDS in the Northwest 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 or short-lived perennial. Stems are 1-31⁄2 ft tall (1⁄3-1 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. This plant has a deep and fibrous taproot.

 

b

a) plant (K. George Beck & James Sebastian), b) infestations (Eric Coombs, Oregon Department of 

Agriculture) (both www.bugwood.org)

a
Biological Control OF WEEDS in the Northwest 41KNAPWEEDS

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) (all www.bugwood.org)

HABITAT: Rapidly colonizes roadsides and disturbed lands, especially dry sites. It 

prefers habitats in the shrub-steppe zones and dry, open forests. 

ECOLOGY: 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.

APPROVED BIOLOGICAL CONTROL AGENTS: USA: Agapeta 

zoegana, Bangasternus fausti, Cyphocleonus achates, Larinus minutus, L. obtusus, 

Metzneria paucipunctella, Pelochrista medullana, 

Pterolonche inspersa, Sphenoptera jugoslavica, 

Urophora affinis, and U. quadrifasciata; CAN: A. 

zoegana, C. achates, L. minutus, M. paucipunctella, 

P. medullana, P. inspersa, S. jugoslavica, U. affinis. 

and U. quadrifasciata.

NOTES: A diploid, fertile hybrid between diffuse 

knapweed and spotted knapweed has been 

identified and is known as C. x psammogena.

Family Asteraceae

c d e

Centa

diffus
42 Biological Control OF WEEDS in the Northwest KNAPWEEDSSpotted knapweed

Centaurea stoebe L. sensu latu

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

subsp. 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 1-31⁄2 ft (1⁄3-1 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.” 

 

b

a) plant (Angelica Velazquez, Cowlitz County Noxious Weed Control Board), b) infestation (Jennifer 

Andreas, Washington State University Extension)

a
Biological Control OF WEEDS in the Northwest 43KNAPWEEDS

c) rosette (Jennifer Andreas, Washington State University Extension), d) leaf (John Cardina, The 

Ohio State University), e) flower head (Michael Shephard Forest Service) (d,e www.bugwood.org)

HABITAT: Rapidly colonizes roadsides and disturbed lands, especially dry sites, 

then invades adjacent undisturbed grasslands and open forests. 

ECOLOGY: Spreads only by seeds, which are equipped for dispersal 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. 

APPROVED BIOLOGICAL CONTROL AGENTS: USA: Agapeta zoegana, 

Bangasternus fausti, Chaetorellia acrolophi, Cyphocleonus achates, Larinus minutus, 

L. obtusus, Metzneria paucipunctella, Pelochrista medullana, Pterolonche inspersa, 

Sphenoptera jugoslavica, Terellia virens, Urophora affinis, and U. quadrifasciata; 

CAN: A. zoegana, C. acrolophi, C. achates, 

L. minutus, L. obtusus, M. paucipunctella, P. 

medullana, P. inspersa, S. jugoslavica, T. virens, 

U. affinis, and U. quadrifasciata.

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. Spotted knapweed has the widest 

distribution in North America of all knapweed 

species.

Family Asteraceae

c d e

Centa

stoeb
44 Biological Control OF WEEDS in the Northwest KNAPWEEDS HISTORY IN THE NORTHWEST: Six knapweed species (genus Centaurea) 

are highly problematic in North America, though diffuse and spotted are by far 

the most common. Knapweed biological control began in North America in 

1970 with the importation of the knapweed banded gall fly, Urophora affinis. 

Since then, an additional 12 insect species have been introduced to North 

America as classical biological control agents of knapweed. Diffuse and spotted 

knapweed are the primary targets, though other knapweed species serve as 

occasional hosts to established agents.

CURRENT STATUS: All 13 knapweed insects have established in North 

America, though at varying levels. The eight seed-feeding agents reduce seed 

production. This does not kill existing plants, but does help reduce the rate of 

spread of weed populations. Unfortunately most knapweed species are not seedlimited, so seed-feeding agents alone typically do not provide control. The five 

root-feeding agents decrease plant function, stature, reproductive output, and 

sometimes density. However, populations of root-feeding insects are typically 

much less abundant than their seed-feeding counterparts. While they may 

have significant impacts locally, they typically do not provide control overall 

when used alone. The seed-feeding Larinus beetles have proven to be some of 

the most effective knapweed biocontrol agents because in addition to larval 

feeding reducing seed production, adult feeding defoliates leaves and stems. This 

defoliation can be severe, which can stunt and even kill affected plants. The 

most successful North American knapweed biocontrol programs to date utilize a 

combination of insects attacking seeds, foliage and roots of knapweed plants. In 

this manner, diffuse and spotted knapweed have reportedly been controlled in 

certain portions of their invaded range, though certain other infestations persist.

RECOMMENDATIONS: USA: The most effective agents established on 

diffuse knapweed include Larinus spp. (especially L. minutus), Sphenoptera 

jugoslavica, and Urophora spp. Cyphocleonus achates is becoming increasingly 

important on diffuse knapweed at some locations. Both Urophora flies are largely 

already distributed throughout knapweed ranges in North America. Adult 

Larinus and S. jugoslavica can be collected using a sweep net when plants are in 

early flowering. Both favor hot, dry climates. The most effective combination 

of agents for spotted knapweed include Larinus spp. (especially L. obtusus), C. 

achates, and Urophora spp. Adult C. achates can be netted or hand-picked in late 

summer when plants are mature flowering, and released at hot sites with sandy, 

coarse soil. CAN: The same combinations of insects are also the most effective 

against diffuse and spotted knapweed in Canada and can be redistributed in the 

same manner.

Knapweed Biological Control

Credits for photos at right: See individual agent pages
Biological Control OF WEEDS in the Northwest 45KNAPWEEDS

Agent Adult Impact Recommendation

Agapeta 

zoegana

Prefers spotted. Established 

USA, CAN. Root feeding low 

to moderate impact overall. 

Abundance generally low in 

USA, CAN. Not high priority 

for redistribution.

Bangasternus 

fausti

Reduces seed production 

diffuse, spotted, squarrose in 

USA. Limited impact overall.

Not released in CAN. Limited 

abundance and impact in USA 

so not high priority agent.

Chaetorellia 

acrolophi

Prefers spotted. Reduces 

seed production but limited 

impact overall.

Abundance generally low in 

USA, unknown (likely rare) in 

CAN. Not high priority agent.

Cyphocleonus 

achates

Often prefers spotted. Root 

feeding effective at hot, sandy sites 

in USA, CAN; less elsewhere.

Recommended for redistribution 

to hot, sandy sites USA/CAN; 

Especially with Larinus spp.

Larinus 

minutus

Prefers diffuse. Reduces seed 

production & plant function 

in USA, CAN. Impact high. 

Recommended for 

redistribution to hot, dry sites 

in USA, CAN.

Larinus 

obtusus

Often prefers spotted. Reduces 

seed production & plant function 

in USA, CAN. Impact variable. 

Recommended for 

redistribution to mesic sites in 

USA, CAN.

Metzneria 

paucipunctella

Prefers spotted. Reduces seed 

production in USA, CAN. 

Limited impact overall.

Abundance generally low in 

USA and CAN. Not high 

priority for redistribution.

Pelochrista 

medullana

Established only in USA. 

Prefers diffuse. Root feeding, 

low impact overall.

Populations very limited. Not 

high priority for redistribution.

Pterolonche 

inspersa

Established only on diffuse 

in USA, CAN. Root damage 

moderate but only locally.

Populations low in USA, 

CAN. Not high priority for 

redistribution. 

Sphenoptera 

jugoslavica

Prefers diffuse. Established 

USA, CAN. Root damage 

moderate locally.

Recommended for redistribution 

to hot, dry diffuse sites. Spotted 

sites typically too moist.

Terellia 

virens

Established only in USA and 

on spotted. Reduces seed 

production but limited impact.

Abundance and impact 

low. Not high priority for 

redistribution in USA.

Urophora 

affinis

Established on diffuse, spotted 

USA, CAN. Ineffective alone; 

okay in combination.

Typically already widespread in 

USA, CAN. Moderate priority 

where not established.

Urophora 

quadrifasciata

Established on diffuse, spotted 

USA, CAN. Ineffective alone; 

okay in combination.

Typically already widespread in 

USA, CAN. Moderate priority 

where not established.
46 Biological Control OF WEEDS in the Northwest KNAPWEEDS 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.

Agapeta zoegana (L.)

Sulfur knapweed moth

LIFE CYCLE: Larvae overwinter in roots, and feed in those 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 morning or evenings, and rest 

low on the 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, and develop through six instars. As they mine the 

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: 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 (21⁄2 mm).

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) (all www.

bugwood.org)

a b c
Biological Control OF WEEDS in the Northwest 47KNAPWEEDS

HISTORY: Introduced from Austria and Hungary and released on spotted 

and diffuse knapweed in the USA from 1984 (CA, ID, MT, NV, OR, WA). 

Redistributions attempted to squarrose knapweed in UT in 1994. Austrian 

and Hungarian populations were also used for releases on spotted and diffuse 

knapweed in Canada (AB 1989, BC 1982).

CURRENT STATUS: In the USA, it is unknown if the redistributions to 

squarrose knapweed were successful. Can cause significant reduction of spotted 

knapweed above-ground biomass and number of capitula per plant, but has not 

demonstrated any obvious effect on plant density. Expected to primarily affect 

large plants. Damages diffuse knapweed to an even lesser extent than spotted. 

Abundance is limited on both species so overall impact is low. In Canada, high 

populations may have significant impact on diffuse and spotted knapweed 

populations, especially in conjunction with other biocontrol agents. Although 

widely distributed, abundance is typically low because densities decrease as 

distribution/dispersal increase.

REDISTRIBUTION: Adult moths are delicate so are best transferred as 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 Agapeta zoegana larvae and 20 Cyphocleonus achates larvae were found 

attacking one very long segment of knapweed 

root.

Lepidoptera: Tortricidae

diffuse spotted

Agapeta

zoegana, 

stoebe

Agapeta

zoegana, C

diffusa
48 Biological Control OF WEEDS in the Northwest KNAPWEEDS DESCRIPTION: Eggs are yellow ovals covered with dark egg caps. Larvae are 

white, C-shaped grubs with brown head capsules and can be 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 have shorter, more blunt snouts compared to the 

Larinus weevils.

Bangasternus fausti (Reitter)

Broad-nosed knapweed seedhead weevil

Bangasternus fausti: a) pupa (USDA ARS European Biological Control Laboratory), b) adult (Laura 

Parsons & Mark Schwarzländer, University of Idaho) (both www.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 the 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 the 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 spread of knapweed 

populations. 

PREFERRED HABITAT: Prefers hot, dry areas and does not do well in areas 

with prolonged rain or at high elevations.

a b
Biological Control OF WEEDS in the Northwest 49KNAPWEEDS

HISTORY: Introduced from Greece and originally released on diffuse knapweed 

in the USA from 1990 (CA, CO, ID, MT, OR, WA). Successfully redistributed 

to spotted knapweed from 1992 (CO, ID, MN, OR, WA) and squarrose 

knapweed from 1993 (CA, UT). Failed redistributions were attempted on 

meadow knapweed from 1998 (CA, OR) and on purple starthistle in CA in 

1999.

CURRENT STATUS: Larvae can consume up to 100% of seed in attacked 

capitula of diffuse, spotted, and squarrose knapweed, though a proportion of 

seeds often escape attack in large flower heads. Abundance is low in the USA, 

but not likely due to interspecific competition. Overall impact is limited. 

REDISTRIBUTION: Though populations are typically low in the USA, 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 (1⁄2 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 weevil species.

NOTES: This agent is not approved for release in Canada.

Coleoptera: Curculionidae

diffuse spotted

Bangaste

fausti, C

stoebe

Bangasternus

fausti, C

diffusa
50 Biological Control OF WEEDS in the Northwest KNAPWEEDS 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.

Chaetorellia acrolophi White & Marquardt

Knapweed peacock fly

Chaetorellia acrolophi: a) larva (Rachel Winston, MIA Consulting), b) adult (USDA APHIS PPQ 

Archive, www.bugwood.org)

a b

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 

the bracts of unopened buds. A single female may lay 70 eggs in her lifetime. 

Larvae hatch in 4-5 days and penetrate the buds, and feed 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. Typically, first 

generation adults emerge throughout July, mate and lay eggs. New larvae of 

this generation continue to feed on developing seed tissue. Third instar larvae 

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 spread of knapweed populations.

PREFERRED HABITAT: Most effective in areas with low density knapweed, 

which is less preferred by other capitulum feeders. It generally does better at 

higher elevations and in regions with high rainfall.
Biological Control OF WEEDS in the Northwest 51KNAPWEEDS

HISTORY: Introduced from Switzerland and released on spotted knapweed in 

the USA from 1992 (CO, MT, OR, WA, WY). Introduced from Austria and 

Switzerland and released on spotted knapweed in Canada (BC 1991, AB 1995).

CURRENT STATUS: Established only on spotted knapweed in North America. 

In the USA, larval feeding reduces seed production, however populations are 

limited throughout its established range so overall impact is minimal. Diffuse and 

squarrose knapweed may occasionally be attacked, though damage is likely even 

less significant than on spotted. Initially believed to have failed establishment on 

spotted knapweed in Canada, but establishment was confirmed in BC in 2008. 

Abundance and impact in Canada are currently 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. Consequently, 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 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 distinguished by their dark brown anal plates 

and by their presence within galls.

NOTES: In ID, populations do not vary with abundance of other agents; at some 

OR sites interspecific competition limits populations.

Diptera: Tephritidae

diffuse spotted

Chaetore

acrolophi

stoebe

Chaetorellia

acrolophi, C

diffusa
52 Biological Control OF WEEDS in the Northwest KNAPWEEDS 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. 

Cyphocleonus achates (Fåhraeus)

Knapweed root weevil

Cyphocleonus achates: a) larva and root damage (Laura Parsons & Mark Schwarzländer, University 

of Idaho, www.bugwood.org), b) pupa in root, c) adult (b,c Jennifer Andreas, Washington State 

University Extension)

a b c

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 crowns, 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-instar 

larvae 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 the 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: Prefers hot and dry sites, with loose well-drained 

coarse soils in temperate areas. It establishes in undisturbed bunchgrass habitat, 

but favors bare soil surfaces where grasses do not crowd the target plants. Sites 
Biological Control OF WEEDS in the Northwest 53KNAPWEEDS

need to be somewhat large with a corridor of plants, into which the weevil 

disperses by walking.

HISTORY: Introduced from Austria, Hungary and Romania and released on 

both spotted and diffuse knapweed in the USA from 1988 (CA, CO, ID, MT, 

NV, OR, UT, WA, WY) and in Canada (AB, BC) from 1987. Successfully 

redistributed to squarrose knapweed in UT in 1995. Attempted redistributions 

to meadow knapweed in OR (1998), CA (2001) and WA (2007) failed to 

establish.

CURRENT STATUS: In the USA, the principal host is spotted knapweed, on 

which its abundance and impact vary. In some locations, it has been attributed 

with reducing plant longevity, reproductive output, and density. In other studies, 

reproductive output remains unchanged as does the weed population overall. 

Numerous studies claim the 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 is usually less extensive and its abundance 

is also typically decreased on this species. However, diffuse knapweed is the 

primary host for C. achates in WA, and increasing populations are being recovered 

from diffuse knapweed in ID. Established on squarrose knapweed in UT, but 

only in limited numbers and with unknown impact. Spotted knapweed is also 

the preferred host in Canada, on which high weevil populations can decrease 

plant density and stature, though evidence supporting this is anecdotal. Impact 

is greatest in conjunction with other biocontrol agents. Weevil populations are 

much smaller on diffuse knapweed in Canada.

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

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

the heat of day. Releases of 50-100 individuals should be made at large sites 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.

Coleoptera: Curculionidae

diffuse spotted

Cyphocle

achates, C

stoebe

Cyphocleonus

achates, C

diffusa
54 Biological Control OF WEEDS in the Northwest KNAPWEEDS 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 grubs with 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.

Larinus minutus Gyllenhal

Lesser knapweed flower weevil

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)

a b d

LIFE CYCLE: Overwintering adults emerge from soil litter throughout the 

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

the leaves of rosettes and flowering plants, 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 flowering period of knapweeds and develop through three instars in 

four weeks. The number of larvae per flower head depends on the size of the 

flower head and the knapweed species. Pupation occurs in chambers made of 

chewed seeds and pappus hair 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 even further.

PREFERRED HABITAT: Typically prefers sites more dry and hot than those 

tolerated by Larinus obtusus. It favors dense knapweed stands with little plant 

c
Biological Control OF WEEDS in the Northwest 55KNAPWEEDS

competition and requires well-drained, coarse soils. Compacted sites (especially 

those grazed with livestock during the bolting stage) or places with prolonged 

rainfall are not suitable for this insect.

HISTORY: Introduced from Greece and Romania and originally released on 

diffuse and spotted knapweed in the USA from 1991 (CA, CO, ID, IN, MT, 

NV, OR, WA, WY). Spread naturally and via intentional redistributions to 

meadow knapweed from 1998 (CA, OR, WA) and squarrose knapweed in CA 

from 1997. A failed redistribution to purple starthistle was attempted in CA in 

1998. Introduced from Greece and released on diffuse and spotted knapweed in 

Canada from 1991 (AB, BC). 

CURRENT STATUS: Larval feeding decreases knapweed seed output while 

adult feeding decreases plant function. In the USA, causes widespread decreases 

in density of diffuse knapweed, which is the preferred host over spotted. Impact 

on spotted knapweed is variable; it can reportedly be high, but is typically less 

dramatic than on diffuse. Established at lower densities on meadow knapweed in 

CA, OR and WA and on squarrose in CA and UT. Impact on both species in CA 

can be high locally, but elsewhere is typically much less than that observed on 

diffuse knapweed. In Canada, diffuse is typically the preferred host as well. High 

weevil populations correspond to widespread decreases in density and cover of 

diffuse knapweed, with less impact on spotted. In Canada, more than five years 

are generally required post release before reductions are noticeable.

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 on patches of at least 2,000 m2 (1⁄2 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 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 agent likely contained a mixture of both. 

Rodent predation can be high at some sites.

Coleoptera: Curculionidae

diffuse spotted

Larinus

minutus, 

stoebe

Larinus

minutus, C

diffusa
56 Biological Control OF WEEDS in the Northwest KNAPWEEDS 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 grubs with 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. 

Larinus obtusus Gyllenhal

Blunt knapweed flower weevil

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, www.bugwood.org)

a b c

LIFE CYCLE: Overwintering adults emerge from soil 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 flowering period of knapweeds, and develop through three instars in 

3-4 weeks. Pupation occurs in 9 days in pupal chambers made of chewed seeds 

and pappus hair 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 even further.

PREFERRED HABITAT: Favors more moist sites with cooler temperatures 

than those tolerated by Larinus minutus. It establishes on south and west slopes 

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

may discourage establishment.
Biological Control OF WEEDS in the Northwest 57KNAPWEEDS

HISTORY: Introduced from Romania and Serbia and originally released on 

diffuse and spotted knapweed in the USA from 1992 (CO, ID, MT, OR, WA, 

WY). Spread naturally and via intentional redistributions to meadow knapweed 

from 1999 (CA, OR, WA) and spread naturally to black and brown knapweed 

in OR by 2004. Introduced from Romania and released on spotted knapweed 

in BC, Canada from 1992. 

CURRENT STATUS: Larval feeding decreases knapweed seed output while adult 

feeding may decrease plant function. In the USA, spotted knapweed is typically 

the preferred host, on which it successfully reduces abundance in parts of the 

Pacific Northwest. In other areas, even high weevil densities and attack rates 

have little to no impact on knapweed infestations. The distribution listed below 

for spotted knapweed in the USA is likely incomplete. Populations are much 

more limited and with less impact on diffuse knapweed. May provide moderate 

control to meadow (CA, OR, WA), black (OR), and brown knapweed (OR), 

largely via seed reduction. In Canada, it is well established on spotted knapweed 

in BC where it frequently occurs in mixed populations with L. minutus. Similar to 

the USA, larval feeding decreases seed output while adult feeding decreases plant 

function. High weevil populations correspond to widespread density decreases 

of spotted knapweed. Prefers moister conditions, so has smaller distribution 

than L. minutus and overall impact in Canada is moderate.

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 on patches of at least 2,000 m2 (1⁄2 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 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 agent likely 

contained a mixture of both. Rodent predation 

can be high at some sites. The number of larvae 

per seed head is often correlated with seed head 

diameter; up to 6 larvae have been observed in a 

large capitulum of meadow knapweed compared 

with the single larvae typically observed in diffuse 

knapweed seed heads.

Coleoptera: Curculionidae

diffuse spotted

Larinus

obtusus, 

stoebe

Larinus

obtusus, C

diffusa
58 Biological Control OF WEEDS in the Northwest KNAPWEEDS 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.

Metzneria paucipunctella Zeller

Spotted knapweed seedhead moth

Metzneria paucipunctella: a) larva and pupa, b) adult (all Norman Rees, USDA ARS www.bugwood.org)

a b

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 the bracts at the base of young flower heads, or on 

the stems just below the capitula. Larvae hatch in 10-12 days as flower heads 

are opening. Larvae enter the 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 the 

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 others. Older larvae bind seeds together, preventing seeds 

from dispersing over long distances.

PREFERRED HABITAT: Does not tolerate severe winter temperatures. Favored 

sites are south slopes in dry, mild-winter climates. Snow cover during winter 

enhances larval survival. It appears to do best in areas where spotted knapweed 

flowers early in the season.
Biological Control OF WEEDS in the Northwest 59KNAPWEEDS

HISTORY: Introduced from Switzerland and released on spotted knapweed in 

AB and BC, Canada from 1973; redistributed to diffuse knapweed from 1981. 

Redistributed from Canada to spotted knapweed in the USA from 1980 (CO, 

ID, MT, OR, WA, WY). Spread naturally and via intentional redistributions 

to diffuse knapweed from 1980 (MT, OR, WA). Redistributed within OR 

to meadow knapweed in 1983 in releases intended to contain Urophora 

quadrifasciata.

CURRENT STATUS: Spotted knapweed is the preferred host, though even 

on this species abundance is rarely high. Seed reduction is typically insufficient 

to impact knapweed populations. Attack to diffuse and meadow knapweed 

(OR) is far less common; impact is insignificant on these species. In Canada, 

populations are moderate on spotted knapweed but have only limited impact 

on plant populations. Diffuse knapweed is rarely attacked- largely only when 

growing amongst spotted 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. Consequently, 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 both the USA and Canada are limited by overwintering 

mortality, parasitism, and predation (frequently deer mice). 

Lepidoptera: Gelechiidae

diffuse spotted

Metzneria

paucipunc

C stoebe

Metzneria

paucipunctella,

C diffusa
60 Biological Control OF WEEDS in the Northwest KNAPWEEDS 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.

Pelochrista medullana (Staudinger)

Brown-winged knapweed root moth

Pelochrista medullana: a) larva in root (USDA APHIS PPQ Archive), b) adult (Bob Nowierski, 

Montana State University) (both www.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 the outer layers of root tissue, similar to 

Agapeta zoegana. Webbed tubes are produced along feeding tracks, which can be 

irregular, downward or spiralling, and the tunnels are lined with a silken web. 

There are six larval instars. This species seems to prefer rosette plants; larvae that 

feed on the roots of flowering plants develop poorly. Larvae overwinter in the 

roots and complete development in the spring or early summer. Pupation occurs 

within the webbing inside the root. There is one generation per year.

DAMAGE: Larval damage to the roots is similar to that caused by Agapeta 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 

are usually smaller and produce fewer flower heads than uninfested plants. 

a b
Biological Control OF WEEDS in the Northwest 61KNAPWEEDS

PREFERRED HABITAT: Prefers hot, dry areas and dense knapweed patches. 

Populations growing in poor, coarse, or gravel soils are ideal.

HISTORY: Introduced from Austria and Hungary and released in the USA 

from 1984 on diffuse (MT) and spotted knapweed (MT, OR). Introduced 

from Austria and released in BC on diffuse knapweed (from 1982) and spotted 

knapweed (from 1986 in rearing tents).

CURRENT STATUS: Preferred host is diffuse knapweed, though it is established 

on both diffuse and spotted knapweed in the USA. Populations remain limited 

for unknown reasons, causing minimal damage at localized sites. 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.

Lepidoptera: Tortricidae

diffuse spotted

Pelochrista

medullana, 

stoebe

Pelochrista

medullana, C

diffusa
62 Biological Control OF WEEDS in the Northwest KNAPWEEDS DESCRIPTION: Eggs are black and oval-shaped with a slightly depressed center. 

Larvae are pearly white with inflated segments and have small, brown head 

capsules. 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, the wings 

are held close to their sides.

Pterolonche inspersa Staudinger

Grey-winged knapweed root moth

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) (all www.bugwood.org)

a b c

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 under-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 woody central portion of the root or the soft tissue near the outer 

edges, causing galls to form. There are five larval instars; third instars typically 

overwinter within the root 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 

the emerging adults. Pupation is 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 to 

the 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: Prefers hot, dry sites with low to moderate plant 

density. 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 OF WEEDS in the Northwest 63KNAPWEEDS

HISTORY: Introduced from Austria, Hungary and Greece and released in the 

USA on diffuse knapweed from 1986 (ID, MT, OR, UT, WA). Reintroduced 

from Hungary and released on spotted knapweed from 1988 (CO, MT, OR). 

Eggs imported from Greece were distributed on squarrose knapweed in UT in 

1990. Introduced from Austria and Hungary and released in BC, Canada on 

diffuse knapweed from 1986 and spotted knapweed in 1987.

CURRENT STATUS: Established on diffuse knapweed in one region in OR, 

USA where insect populations are now rare and provide no impact because of 

dramatic control of diffuse knapweed by Larinus spp. Releases on spotted and 

squarrose knapweed failed. In Canada, it is established only on diffuse knapweed, 

even in patches with spotted and diffuse knapweed interspersed. Populations 

on diffuse knapweed are moderately abundant and may stunt plants, though 

evidence is anecdotal, and impact due to this 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 have been observed 

containing up to four. The moth can co-occur with Sphenoptera jugoslavica by 

feeding below S. jugoslavica galls.

Lepidoptera: Pterolonchidae

diffuse spotted

Pterolonch

inspersa, C

stoebe

Pterolonche

inspersa, C

diffusa
64 Biological Control OF WEEDS in the Northwest KNAPWEEDS 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 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.

Sphenoptera jugoslavica Obenberger

Bronze knapweed root borer

LIFE CYCLE: Adults emerge in summer with the onset of knapweed flowering. 

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 instar larvae 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 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: Prefers arid environments with a period of drought in 

summer. Thrives in well-drained, coarse soils with southern aspects. Exposed soil 

between plants increases the soil temperature, making sites even more suitable.

HISTORY: Introduced from Greece and released in the USA on diffuse knapweed 

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) (all www.bugwood.org)
Biological Control OF WEEDS in the Northwest 65KNAPWEEDS

from 1980 (CA, CO, ID, MT, NV, OR, UT, WA, WY). Spread naturally and 

via intentional redistributions to spotted knapweed from 1987 (CO, ID, MT, 

OR). Redistributed to squarrose knapweed from 1996 (CA, UT). Attempted 

redistributions to meadow knapweed in 1998 (OR) failed to establish. 

Introduced from Greece and released in BC, Canada on diffuse knapweed from 

1976. Redistributed from diffuse to spotted knapweed in BC from 1987.

CURRENT STATUS: In the USA, causes some reductions in diffuse knapweed 

density and seed output, especially among competing vegetation. Overall 

impact on diffuse is moderate as the agent is largely restricted to hot, dry sites. 

Diffuse is the preferred host; while spotted can be attacked, agent distribution 

and impact are typically very limited on spotted knapweed compared to diffuse. 

Moderately effective on squarrose in CA, but populations are limited in UT. In 

Canada, diffuse is again the preferred host, on which high agent populations can 

be found throughout the driest part of the weed’s range. High beetle numbers 

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

impact is only localized rather than widespread throughout the province. Best in 

combination with other agents. Can decrease seed production and plant stature 

of spotted knapweed 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 plants are in flower. Releases of 50-200 

individuals should be made at large sites with hot climates and loose, welldrained 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.

Coleoptera: Buprestidae

diffuse spotted

Sphenopte

jugoslavica

stoebe

Sphenoptera

jugoslavica, C

diffusa
66 Biological Control OF WEEDS in the Northwest KNAPWEEDS DESCRIPTION: Eggs are elongate, about 1 mm long, and shiny white. Larvae 

are a plump barrel shape 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.

Terellia virens (Loew)

Green clearwing knapweed fly

LIFE CYCLE: Adults emerge in spring when knapweed is still in the rosette 

or bolting stages. Adults feed heavily on nectar when knapweed flower 

heads bloom. Mating begins with the onset of warm weather and continues 

throughout summer. In the 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: Prefers plants on south-facing slopes and dry locations.

HISTORY: Introduced from Austria and Switzerland and initially released in 

the USA on spotted knapweed from 1992 (CA, CO, MT, OR, WA, WY). 

Terellia virens: a) larva, b) adult (both Eric Coombs, Oregon Department of Agriculture)

a b
Biological Control OF WEEDS in the Northwest 67KNAPWEEDS

Redistributions were attempted on purple starthistle and squarrose knapweed in 

CA in 1998 but failed to establish. Introduced from Austria and Switzerland to 

spotted knapweed in Canada (BC 1991, AB 1995) but failed to establish.

CURRENT STATUS: Established only in the USA and only on spotted 

knapweed. Populations are limited, likely due to competition with Urophora

spp. and Larinus spp. Causes only minor reductions in seed production with 

minor impact overall.

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. 

Consequently, 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 

distinguished by their dark brown anal plates and by their presence within galls.

NOTES: May attack diffuse knapweed, but to a much smaller extent than spotted. 

Diptera: Tephritidae

diffuse spotted

Terellia vire

C stoebe

Terellia virens,

C diffusa
68 Biological Control OF WEEDS in the Northwest KNAPWEEDS 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.

Urophora affinis (Frauenfeld)

Banded knapweed gall fly

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) (all www.bugwood.org)

a b c

LIFE CYCLE: There is usually one generation per year, though in warm climates, 

a second generation may occur. Overwintering as third instar larvae, flies pupate 

for about 14 days in the spring and emerge as adults at the time knapweed is 

in the bud stage. 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 where they feed on receptacle tissue. Larval feeding 

triggers the formation of a hard, woody gall which surrounds the larva. The 

majority of 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. 

Between 2-4 galls in a single capitulum are common, though this depends on 

capitulum size (often directly related to the species attacked).

PREFERRED HABITAT: Well adapted to a variety of environmental conditions 

and can be found throughout the majority of spotted and diffuse knapweed 

infestations in North America. Shows a preference for mesic sites and appears to 
Biological Control OF WEEDS in the Northwest 69KNAPWEEDS

do better on dense weed populations.

HISTORY: Introduced from Austria, France and Russia (some via Canada) and 

released in the USA on diffuse and spotted knapweed from 1973 (CA, CO, ID, 

MT, NV, OR, WA, WY). Spread naturally and via intentional redistributions to 

squarrose knapweed in CA, OR, UT from 1988. Introduced from France and 

Russia to Canada and released on diffuse and spotted knapweed in BC from 

1970 (redistributed to AB from 1976).

CURRENT STATUS: Well established on diffuse and spotted knapweed in the 

USA. With U. quadrifasciata contributes to seed reduction of >50% at some sites. 

Seed reduction may retard rate at which weed spreads, but has not appreciably 

lowered stand density because sufficient seeds remain. At other sites, the direct 

effect of Urophora galls on seed production is negligible. Not considered as 

important or effective as other knapweed agents. Established in only limited 

amounts on squarrose knapweed (CA, OR, UT), on which it is not effective. In 

Canada, high fly populations stunt plant growth and decrease seed production 

but result in no apparent decline in knapweed density.

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. Consequently, 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 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 throughout 

the following spring. Note that feeding larvae can be difficult to distinguish from 

other knapweed fly species. Urophora species can 

be distinguished by their dark brown anal plates 

and their presence within galls.

NOTES: It does not disperse as rapidly as Urophora 

quadrifasciata, but is often the dominant species 

at sites where both flies coexist. Deer mice feed 

heavily on Urophora larvae, and mice populations 

are known to increase as a result.

Diptera: Tephritidae

diffuse spotted

Urophora

affinis, C st

Urophora

affinis, C diffusa
70 Biological Control OF WEEDS in the Northwest KNAPWEEDS 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.

Urophora quadrifasciata (Meigen)

UV knapweed seedhead fly

Urophora quadrifasciata: a) larva (USDA ARS), b) adult (Laura Parsons & Mark Schwarzländer, 

University of Idaho) (both www.bugwood.org)

LIFE CYCLE: There are usually two generations per year. Overwintering as third 

instar larvae, flies pupate for 14 days in spring, and adults emerge as knapweed 

is budding. Females lay up to 120 eggs in groups of 1-5 among immature florets 

inside closed flower heads. Unlike Urophora affinis, U. quadrifasciata females 

prefer well-developed capitula. After 3-4 days, larvae hatch and tunnel into the 

base of the capitulum where, through three instars, they feed on receptacle tissue. 

Larval feeding induces the formation of a papery gall which surrounds the larva. 

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. 

Between 2-4 galls in a single capitulum are common, though this depends on 

capitulum size (often directly related to the species attacked).

PREFERRED HABITAT: Well adapted to a variety of environmental conditions 

and can be found throughout the majority of spotted and diffuse knapweed 

infestations in North America. Tolerant of severe winter conditions and requires 

considerably more protective snow cover than U. affinis. 

a b
Biological Control OF WEEDS in the Northwest 71KNAPWEEDS

HISTORY: Introduced from Russia and released in BC, Canada on diffuse 

knapweed in 1972 and meadow knapweed in 1987. Spread naturally to spotted 

knapweed by 1975. Spread to the USA naturally by 1979 (diffuse and spotted 

knapweed) from releases made in Canada and likely redistributed accidentally 

in seed heads thought to contain only the approved Urophora affinis. Spread 

naturally to bachelor’s button as well as brown, meadow and squarrose knapweed 

Many intentional redistributions made on these species post 1979. Officially 

approved for redistribution in the USA in 1989.

CURRENT STATUS: Well established on diffuse and spotted knapweed in the 

USA. 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 retard rate at which weed spreads, but has not appreciably lowered stand 

density because sufficient seeds remain. Not considered as important or effective 

as other agents. Established in smaller amounts on bachelor’s button (Centaurea 

cyanus in OR, WA) and brown (OR, WA), meadow (CA, OR, WA) and squarrose 

knapweed(CA, OR, UT) on which it is even less effective than on diffuse. In 

Canada, high fly populations stunt plant growth and decrease seed production 

but result in no apparent decline in knapweed density. Established on meadow 

knapweed in BC, on which impact is even less.

REDISTRIBUTION: Sweeping adult flies is possible, though may be damaging. 

Instead, place plants with infested capitula into uninfested patches during 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 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 throughout 

the following spring. Note that feeding larvae can be difficult to distinguish from 

other knapweed fly species. Urophora species can 

be distinguished by their dark brown anal plates 

and their presence within galls.

NOTES: Disperses more rapidly than U. affinis, 

but U. affinis is often the dominant species at sites 

where both flies coexist. Deer mice feed heavily 

on Urophora larvae, and mice populations are 

known to increase as a result.

Diptera: Tephritidae

diffuse spotted

Urophora

quadrifasc

C stoebe

Urophora

quadrifasciata,

C diffusa
72 Biological Control OF WEEDS in the Northwest R.KNAPWEEDRussian knapweed

Rhaponticum repens (L.) Hidalgo

SYNONYMS: Centaurea repens L., Acroptilon repens (L.) DC.

ORIGIN: Native to central Asia; introduced to North America as a contaminant 

in alfalfa by 1898.

DESCRIPTION: An upright perennial forb often found in dense infestations. 

Plants grow from 1-3 ft (1⁄3-0.9 m) in height and are supported by creeping 

horizontal roots. Rosette leaves are gray-green, woolly, and deeply divided. Stem 

leaves are oblong and toothed, becoming smaller towards the tips of multiple 

woolly, hairy stems. Mid-plant branches are topped by a few to many flower 

heads with pink, purple, or sometimes blue florets. Flower heads are 0.2-0.4 

in (1⁄2-1 cm) in diameter and produce numerous tiny, bristle-topped seeds. 

Receptacles are covered by bracts with thin, papery margins. 

 

HABITAT: A problematic weed of arid regions, it is widespread in rangelands, 

b

a) plant (Eric Coombs, Oregon Department of Agriculture), b) infestation (Norman Rees, USDA 

ARS) (both www.bugwood.org)

a
Biological Control OF WEEDS in the Northwest 73R.KNAPWEED

c) leaves (Bonnie Million, National Park Service), d) flower heads (Steve Dewey, Utah State University) 

(both www.bugwood.org)

grazing land, grain and other crops, waste places, roadsides, and ditches.

ECOLOGY: Reproduces both vegetatively through its roots and by seed. Seeds 

are equipped for dispersal by wind (short distances), water, livestock, wildlife, 

and human activity and can remain viable in the soil for up to years. Flowering 

occurs from June to September with the majority of germination occurring in 

spring.

APPROVED BIOLOGICAL CONTROL AGENTS: USA and CAN: 

Aulacidea acroptilonica, Jaapiella ivannikovi and Subanguina picridis.

NOTES: Horses feeding on Russian knapweed can develop a fatal nervous disorder 

called chewing disease.

Family Asteraceae

c d

Rhap

repen
74 Biological Control OF WEEDS in the Northwest R.KNAPWEEDHISTORY IN THE NORTHWEST: Exploration throughout the 1970s 

resulted in the release of Subanguina picridis in North America beginning in 

1977. Impact of this agent was lower than expected so two additional agents 

have since been released (Aulacidea acroptilonica and Jaapiella ivannikovi in 

2008 and 2009, respectively).

CURRENT STATUS: Subanguina picridis is widespread in both the USA 

and Canada, but abundance and impact are limited to areas with high soil 

moisture. It is too early following release to determine the overall impact of 

A. acroptilonica and J. ivannikovi in the USA, though early results indicate 

A. acroptilonica populations may remain limited and are already hindered by 

parasitism. Populations of J. ivannikovi are also slow to increase, but at the 

original USA release sites they are significantly reducing seed output and aboveground biomass. Establishment of A. acroptilonica and J. ivannikovi have yet to 

be officially confirmed in Canada.

RECOMMENDATIONS: USA and CAN: Subanguina picridis is not a costeffective agent. Its inability to spread unaided and restriction to moist sites make 

it a low priority for Russian knapweed control. More time is needed to fully 

understand the effects of A. acroptilonica and J. ivannikovi. Redistributions of 

both are recommended in the USA, with greater emphasis placed on J. ivannikovi 

whose greater impact and shorter generation time make this species the more 

encouraging agent. Additional releases of A. acroptilonica and J. ivannikovi are 

recommended in Canada utilizing lab colonies. The adventive Puccinia acroptili 

has been observed in Canada with mixed results. P. acroptili is not approved for 

release in the USA.

Russian Knapweed Biological Control
Biological Control OF WEEDS in the Northwest 75R.KNAPWEED

Aulacidea, Jaapiella: Urs Schaffner, CABI-Switzerland, Subanguina: Tony Caesar, USDA ARS, www.

bugwood.org

Agent Adult Impact Recommendation

Aulacidea 

acroptilonica

Galls stunt plants, reduce seed 

production. Populations still 

limited in USA with minor 

impact. Parasitized

Recommended for new releases 

or redistribution; best done by 

rearing out adults so parasitoids 

are excluded

Jaapiella 

ivannikovi

Larval galls stunt plants, 

reduce seed production 

significantly at original USA 

sites; populations still limited

Recommended for new 

releases with lab colonies or 

field redistribution by moving 

infested plants or rearing adults

Subanguina 

picridis

Galls reduce biomass and 

seed production, but impact 

limited to moist sites and 

times

Not recommended for 

redistribution as low impact 

and inability to spread unaided 

make this agent not cost-effective
76 Biological Control OF WEEDS in the Northwest R.KNAPWEEDDESCRIPTION: Larvae are milky white with a curved body and a small, whitish 

head capsule. Adults are small, typically around 2 mm long. Females are typically 

slightly longer than males and have larger abdomens. Both males and females 

have dark bodies with brown slender legs and lighter colored transparent wings. 

Antennae are long and dark brown.

Aulacidea acroptilonica Tyurebaev

Russian knapweed gall wasp

Aulacidea acroptilonica: a) adult, b) galls (both Urs Schaffner, CABI-Switzerland)

LIFE CYCLE: Adults emerge in early spring. More females than males typically 

emerge and do so with all eggs fully developed. Oviposition begins immediately, 

regardless of whether they have mated or not. Unfertilized eggs are typically 

male. Eggs are laid in meristematic tissue of stems and leaves. Within a few 

weeks, galls become noticeable around feeding larvae. There are three larval 

instars, with the third instar becoming dormant during summer. The third 

instar larvae overwinter, and pupation occurs inside the galls in early spring. 

A small number of larvae remain in hibernation after the first winter, pupating 

only after the second winter.

DAMAGE: Gall development diverts nutrients from flower formation, seed 

production, and plant growth. Under some conditions, galls may stress plants 

sufficiently to reduce their competitive ability.

PREFERRED HABITAT: Well adapted to a variety of environmental conditions 

in its native range, including roadsides, irrigated croplands, wastelands and semideserts. Most common where disturbance from grazing animals or cultivation 

is minimal. 

HISTORY: Introduced from Uzbekistan and released in MT, USA from 2009 

(WY from 2012) and AB, Canada from 2008. 

a b
Biological Control OF WEEDS in the Northwest 77R.KNAPWEED

CURRENT STATUS: It is too soon following release to determine its overall 

impact and abundance in the USA, though populations have already significantly 

increased at one MT site. The wasp is unlikely to control Russian knapweed 

alone, and parasitism is already becoming apparent. Establishment has yet to be 

officially confirmed in Canada.

REDISTRIBUTION: Adults are small and delicate so sweeping is not advised. 

Instead, place plants with infested galls into uninfested patches during fall or 

early spring. Transferring galls may also transfer unwanted parasitoids, insects, 

or Russian knapweed 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, the 

adult wasps can be transferred to new Russian knapweed infestations in groups 

of 50-100. Establishment can be monitored by observing Russian knapweed 

foliage for galls one or two years later during summer.

NOTES: Males appear to be rare or uncommon.

? Hymenoptera: Cynipidae

Aulacide

acroptilo
78 Biological Control OF WEEDS in the Northwest R.KNAPWEEDDESCRIPTION: Larvae are white with rosy hues and with a small white head 

capsule. They are curved and legless and up to 2 mm long. Pupae are pale in color 

and approximately 2 mm long. Adults are light brown with large transparent 

wings. They have long, slender legs and large eyes. Males are just under 2 mm 

long while females are just over.

Jaapiella ivannikovi Fedotova

Russian knapweed gall midge

Jaapiella ivannikovi a) galls, b) adult (both Urs Schaffner, CABI-Switzerland)

LIFE CYCLE: Adults are short-lived and mate soon after emergence. Eggs are 

laid on the tips of growing shoots. Larvae develop through three instars in silky 

webs between the growing leaves of the infested shoot, causing leaves to grow 

together. Pupation occurs in this fusion of leaves, with pupae overwintering. First 

generation larvae emerge in early spring. In its native range there are typically 

four overlapping generations per year, each typically one month long.

DAMAGE: Larval feeding causes stunted growth of the shoot and a fusion of 

leaves, resulting in what is referred to as a “rosette gall.” This reduces overall seed 

production and plant height.

PREFERRED HABITAT: Well adapted to a variety of environmental conditions 

in its native range, including roadsides, irrigated croplands, wastelands and 

semi-deserts. Can build up large populations in habitats with high disturbance 

and irrigation during the summer months. Both factors cause Russian knapweed 

to produce new shoots, and young shoots are the preferred stage for egg-laying 

adults. Moist sites appear to have higher establishment success.

HISTORY: Introduced from Uzbekistan and released in MT and WY, USA from 

2009 (CA, CO, ID, OR, UT, WA subsequently) and AB, Canada from 2009. 

a b
Biological Control OF WEEDS in the Northwest 79R.KNAPWEED

CURRENT STATUS: It is too soon following release to determine its overall 

impact and abundance in the USA, though initial results from the first WY 

release site indicate attack reduces seed output per shoot by 91% and aboveground biomass by 34%. Established at several sites in MT, but populations 

have not significantly increased to date. Establishment has yet to be officially 

confirmed in Canada.

REDISTRIBUTION: Adults are small and delicate so sweeping is not advised. 

Instead, place infested plants into uninfested patches throughout the growing 

season from early spring through fall. Transferring infested plants may also 

transfer unwanted parasitoids, insects, or Russian knapweed seeds. To avoid 

this, 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, midges can be transferred to new Russian 

knapweed infestations in groups of 50-100. As young shoots are the preferred 

stage for egg-laying, mowing the release site one week prior to release may 

increase establishment. This should not be done at overly dry sites where Russian 

knapweed may be incapable of re-sprouting. Establishment can be monitored 

by observing gall presence on Russian knapweed foliage later in the same season 

or in subsequent years. 

NOTES: Dissection of field-collected galls revealed up to 14 larvae feeding within. 

Possibly also established in CA (USA).

? Diptera: Cecidomyiidae

Jaapiella

ivanniko
80 Biological Control OF WEEDS in the Northwest R.KNAPWEEDSYNONYMS: Paranguina picridis (Kirjanova) Kirjanova & Ivanova, Mesoanguina 

picridis (Kirjanova) Chizhov & Subbotin

DESCRIPTION: All stages of this nematode are small and most easily viewed 

with a microscopic. Both juveniles and adults are long and slim in shape, often 

curling in on themselves, and are at least partially transparent. Adults can be up 

to 11⁄2 mm long.

Subanguina picridis (Kirjanova) Brzeski

Russian knapweed nematode

Subanguina picridis: a) galls (Eric Coombs, Oregon Department of Agriculture), b) adult magnified 

greatly with microscope (Tony Caesar, USDA ARS) (both www.bugwood.org)

LIFE CYCLE: ln early spring as stems are bolting, juveniles penetrate rosette leaf 

stems and shoots. Galls form around their feeding sites. There are two or more 

generations per year, with all development, feeding, and reproduction occurring 

in galls. Juveniles overwinter in gall remnants on or just below the soil surface.

DAMAGE: Juveniles and adults cause the formation of galls which reduces aboveground growth and reproduction.

PREFERRED HABITAT: Though it is established in a variety of climates, 

impact and abundance are limited throughout much of its introduced range. 

Populations do best in moist areas, especially those regularly irrigated throughout 

the growing season. 

HISTORY: Introduced from Kazakhstan and released in Canada (AB, BC) from 

1977. Redistributions from Canada to WA, USA in 1984 failed to establish. A 

different population sourced from Turkey and Uzbekistan was released in MT, 

OR, WA in 1990.

a b
Biological Control OF WEEDS in the Northwest 81R.KNAPWEED

CURRENT STATUS: Populations are limited in the USA, and impact has 

been less than expected. A lack of moisture limits survival, so any infections 

are not consistent from year to year due to varying moisture conditions. It does 

not move readily so needs to be propagated and redistributed on a large scale. 

Consequently, this is not a cost-effective agent. Though initially established 

in BC, Canada, many release sites were lost due to subsequent land use. No 

evaluations have been conducted since 2002 to confirm current establishment, 

abundance and impact. If still present, it is likely limited in establishment and 

impact, but most promising for spring-moist and irrigated sites.

REDISTRIBUTION: Best redistributed by transferring galls to the soil of 

uninfested patches during fall. Juveniles will emerge from disintegrating galls in 

early spring to infect new shoots. Establishment can be confirmed by observing 

galls on new Russian knapweed foliage throughout the following growing season.

NOTES: Also attacks to a lesser extent the native Centaurea rothrockii (whose 

name has since been changed to Plectocephalus rothrockii, the cultivated Cynara 

scolymus (whose name has since been changed to Cynara cardunculus subsp. 

cardunculus), and perhaps also the invasive diffuse knapweed.

Tylenchida: Anguinidae

Subangu

picridis
82 Biological Control OF WEEDS in the Northwest R.KNAPWEED

Russian Knapweed, Unapproved Agents

Puccinia acroptili P. Syd. & Syd.

(Pucciniomycetes: Pucciniales)

DESCRIPTION AND LIFE CYCLE: 

Develops on upper and lower leaf 

surfaces. Basidiospores germinate 

in spring, developing club-shaped 

structures in summer. After pollination, 

single-celled yellow-brown urediospores 

are produced. There are multiple 

generations per season. Thick-walled 

and medium-brown teliospores 

overwinter. Spores are wind dispersed.

HISTORY AND CURRENT STATUS: First recorded in BC (CAN) in 1970 

as an adventive agent likely originating in South-central Asia. It is currently 

widespread in AB, BC, SK. At all sites, some plants appear resistant with no 

negative impact while others adjacent have heavy infection and collapse. In 

combination with Subanguina picridis galls, severely stunted and dying plants 

have been recorded. Not approved for release in the USA.

© Province of British Columbia. All rights 

reserved. Reproduced with permission of the 

Province of British Columbia
Biological Control OF WEEDS in the Northwest 83R.KNAPWEED
84 Biological Control OF WEEDS in the Northwest Loosestrife SYNONYMS: purple lythrum

ORIGIN: Native to Europe, northern Africa, Asia; introduced to North America 

in the early 1800s in ship ballast, wool, and most likely also as an ornamental 

or medicinal herb.

DESCRIPTION: Herbaceous, upright perennial typically growing numerous 

stems 5-9 ft tall (11⁄2-23⁄4 m) from a spreading, robust taproot. Stems are squarish 

in cross-section with 4-6 sides. Leaves are lance-shaped, smooth-margined, 

stalkless, and are 2-5 in long (5-12 cm). Leaves are opposite up the stem, and 

whorled closer to the base. Flowers are less than 1 in across (21⁄2 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 wetlands, can be found along streams, rivers, and 

b

Purple loosestrife

Lythrum salicaria L.

a) plant (K. George Beck & James Sebastian, Colorado State University), b) infestation (Eric Coombs, 

Oregon Department of Agriculture) (both www.bugwood.org)

a
Biological Control OF WEEDS in the Northwest 85Loosestrife

c) leaves, e) flowers (both Richard Old, XID Services, Inc, www.xidservices.comd), d) stem e) flowers 

(K. George Beck & James Sebastian, Colorado State University,) (all www.bugwood.org

irrigation canals, in swamps and freshwater tidal flats, and along lakes and ponds.

ECOLOGY: Spreads primarily by seeds that are easily carried by water, people, 

and animals, but can also reproduce from root fragments and cut stems. Seeds 

may remain viable for a few years following dissemination. Seedlings germinate 

in late spring, and plants may flower the first year. Flowers occur in spiked 

clusters in late summer to early fall. Plants die back in winter temperatures, with 

dead stems forming a thick mat persistent for many years. 

APPROVED BIOLOGICAL CONTROL AGENTS: USA and CAN: 

Galerucella calmariensis, G. pusilla, Hylobius transversovittatus and Nanophyes 

marmoratus.

Family Lythraceae

c d e

Lythr

salica
86 Biological Control OF WEEDS in the Northwest Loosestrife HISTORY IN THE NORTHWEST: European exploration for potential 

biological control agents began in 1986. Following the testing of six species, 

four were introduced to North America from 1991: Galerucella calmariensis, G. 

pusilla, Hylobius transversovittatus and Nanophyes marmoratus.

CURRENT STATUS: Both Galerucella species have established in the USA 

and CAN and are proving to be the most effective agents in both countries. 

High densities defoliate plants, reducing seed production, stunting growth, and 

providing excellent control at many sites. However, some sites in the USA remain 

unchanged despite high agent numbers. The Galerucella beetles often occur in 

mixed species populations. In both countries, G. calmariensis is generally more 

abundant than G. pusilla, but the reverse is true at some USA sites for unknown 

reasons. Extensive root feeding by H. transversovittatus can complement 

defoliation by Galerucella spp., sometimes resulting in plant death. However, H.

transversovittatus populations are believed to be limited throughout much of its 

range in USA and CAN. Its establishment and impact are both difficult to assess 

as larvae are hidden feeders and adults are nocturnal. Nanophyes marmoratus 

is not established in western CAN provinces. In the USA, populations remain 

limited at many sites due to competition with Galerucella spp. N. marmoratus, a 

flower feeder, can help reduce weed population spread at small infestations, but 

doesn’t damage existing plants.

RECOMMENDATIONS: Galerucella spp. have the highest priority for 

redistribution as high populations of these beetles have proven the most effective. 

G. calmariensis appears to be the most important at the majority of sites, though 

both species often occur in a mix, so should be redistributed as such. They are 

best collected as adults in spring using sweep nets and aspirators. Alternatively, 

adults of the new generation can be collected in mid-summer. Though H. 

transversovittatus can be cryptic, if populations can be found or obtained from 

rearing facilities, its known complementary action with Galerucella spp. makes 

this a medium to high priority agent for redistribution, especially at sites where 

Galerucella spp. do not appear to be abundant or effective. N. marmoratus may 

have the lowest impact of the established species (and thus the lowest priority for 

redistribution), but it may prove useful at sites with small loosestrife populations 

or where Galerucella spp. are absent or are ineffective. 

Purple Loosestrife Biological Control
Biological Control OF WEEDS in the Northwest 87Loosestrife

Galerucella calmariensis: David Cappaert, Michigan State University, www.bugwood.org, G. pusilla: 

Agriculture and Agri-Food Canada Archive, www.bugwood.org, Hylobius: Jennifer Andreas, 

Washington State University Extension, Nanophyes: Laura Parsons & Mark Schwarzländer, University 

of Idaho, www.bugwood.org

Agent Adult Impact Recommendation

Galerucella 

calmariensis

Defoliation by both 

Galerucella spp. can decimate 

weed populations at many 

sites. Highest abundance and 

impact of established agents. 

Should be redistributed as 

adults (collected via sweep 

netting) to new sites or where 

existing populations have 

decreased in boom/bust cycles.

Galerucella 

pusilla

Defoliation by both 

Galerucella spp. can decimate 

weed populations at many 

sites. Highest abundance and 

impact of established agents. 

Should be redistributed as 

adults (collected via sweep 

netting) to new sites or where 

existing populations have 

decreased in boom/bust cycles.

Hylobius 

tranversovittatus

Root-feeding can at high 

densities result in plant 

death. Cryptic nature 

make assessment difficult. 

Populations appear limited.

Should be redistributed when 

populations can be found; 

transfer infested plants. May 

complement Galerucella spp. 

impact.

Nanophyes 

marmoratus

Causes flower abortions that 

do not kill plants, but reduce 

population spread. Hindered 

by competition from 

Galerucella spp.

Low impact and poor 

competitive ability mean 

this agent should only be 

redistributed to small infestations 

or with low Galerucella spp.
88 Biological Control OF WEEDS in the Northwest Loosestrife DESCRIPTION: Larvae of both species are up to 5 mm long. They are greenishyellow with darkened head capsules and black spots down their back. Galerucella

secies cannot be distinguished in the egg or larval stage. Adults of both species 

can be 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 head.

Adult G. pusilla are light gold to orange-brown with dark antenna from the 

middle to the tips. Females of both species are slightly larger than males.

Galerucella calmariensis (L.) & G. pusilla (Duftschmidt)

Black-margined loosestrife beetle & Golden loosestrife beetle

a) Galerucella calmariensis adult (David Cappaert, Michigan State University), b) G. pusilla adult 

(Agriculture and Agri-Food Canada Archive) (both www.bugwood.org)

LIFE CYCLE: Overwintering adults feed on leaves and young shoot buds in 

early spring when purple loosestrife is bolting or resuming growth. 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. There 

are three larval instars. Pupation occurs in soil litter or stem tissue if stems are in 

standing water. Adults emerge in late summer, resume feeding, then overwinter 

in soil litter. There is usually one generation per year (two in warm climates).

DAMAGE: Larval feeding strips the photosynthetic tissue off leaves, creating a 

“window-pane” effect. Adult feeding causes a characteristic “shothole” defoliation 

pattern. Larval and adult feeding stunt growth, reduce seed production, and 

may kill plants outright over several years and at high agent densities.

PREFERRED HABITAT: Both species are established in numerous states and 

provinces, spanning a wide variety of climatic conditions. Both prefer sites 

without winter flooding and regular water fluctuations (such as via tide or dams). 

HISTORY: Both species were introduced from Germany and released (often as a 

a b
Biological Control OF WEEDS in the Northwest 89Loosestrife

mix) in the USA from 1992 (CA, CO, ID, MT, OR, UT, WA, WY) and also in 

Canada from 1992 (AB, BC from 1993 onwards). 

CURRENT STATUS: Both species are established in the same states and 

provinces of northwestern North America. In the USA, they 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 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. Boom-bust cycles 

are common for this system: as agent populations build, greater dispersal results 

in increases in weed population, followed by increases in 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 majority 

of purple loosestrife’s range. Both Galerucella species were initially widespread, 

but more recent surveys indicate most populations at many sites now consist 

primarily or wholly of G. calmariensis.

REDISTRIBUTION: Best collected in the adult stage in spring using sweep nets 

and aspirators, though new generation adults can be collected as well in mid- to 

late summer. Should be transferred to uninfested sites in groups 

of 100-200. Establishment can be monitored the following year 

by observing the 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: Peak dispersal of overwintered adults is during the first few 

weeks of spring. Predation may limit some populations. 

Coleoptera: Chrysomelidae

Galerucella spp.: a) eggs and larva (Bernd Blossey, Cornell University), b) larval window-pane feeding, 

c) adult shot-hole feeding (Eric Coombs, Oregon Department of Agriculture) (all www.bugwood.org)

a b c

Galeruc

spp.
90 Biological Control OF WEEDS in the Northwest Loosestrife 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 back which are comprised of 

white hairs. They are thick insects and up to 12 mm long.

Hylobius transversovittatus (Goeze)

Loosestrife root weevil

LIFE CYCLE: This species often requires two years to complete one generation. 

Overwintering larvae become active in early spring, feeding on roots and filling 

feeding tunnels with frass. They develop through three instars and can be 

present for up to two years. Pupation occurs in the root crown in early summer. 

Emerging adults feed on leaves. Females lay eggs singly (though up to 300 over 

two years) in the soil or stems near soil. Larvae emerge in late summer, feed, and 

overwinter in roots. Adults sometimes overwinter, and can live up to three years.

DAMAGE: Adult feeding is not significant. Roots attacked by larvae have 

reduced reserve capacity leading to reduced plant vigor, reproductive output, 

and even death. Large roots can withstand substantial feeding pressure, however, 

and several larval generations will be necessary before significant impacts are 

observed.

PREFERRED HABITAT: 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.

HISTORY: Introduced from Germany and released in the USA from 1991 (from 

1992 for western states CA, CO, ID, MT, OR, UT, WA). Introduced from 

Germany and Finland and released in Canada from 1992 (AB, BC from 1994). 

Hylobius transversovittatus: a) eggs, b) larva and root damage (a,b Gary Piper, Washington State 

University, www.bugwood.org), c) adult (Jennifer Andreas, Washington State University Extension)

a b c
Biological Control OF WEEDS in the Northwest 91Loosestrife

CURRENT STATUS: In the USA it is slower to disperse and reproduce than 

the other established agents. It is believed to have well established populations 

in OR and perhaps WA and ID, but is largely limited elsewhere. Extensive 

root feeding by this agent can complement defoliation by Galerucella spp., 

sometimes 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: Adults can be swept or hand-picked from purple loosestrife 

foliage 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, infested 

roots can also be collected and stored in a laboratory setting under conditions 

simulating the field. Emerging adults can be distributed to uninfested sites in 

groups of 50-100. Due to the great difficulty of field collections, the majority 

of released individuals are obtained from laboratory populations. 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 rootstock.

Coleoptera: Curculionidae

Hylobius

transversov
92 Biological Control OF WEEDS in the Northwest Loosestrife DESCRIPTION: 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. They are up to 21⁄2 mm long and have 

a long snout and wide body.

Nanophyes marmoratus (Goeze)

Loosestrife flower-feeding weevil

Nanophyes marmoratus: a) egg, b) larva in flower bud (a,b Gary Piper, Washington State University, 

www.bugwood.org)

LIFE CYCLE: Overwintering adults emerge in late spring and feed on shoot 

tips, producing a shot-hole appearance in upper leaves. Adults then feed on 

developing flowering buds. Females lay 60-100 eggs singly inside immature 

flower buds throughout summer. Hatching larvae develop through three instars 

and feed on floral parts (one larva per bud). Pupation occurs within the attacked 

buds, with adults emerging in late summer to overwinter in soil litter. There is 

one generation per year.

DAMAGE: Adult and larval feeding cause flower-bud abortion, reducing the seed 

output of purple loosestrife. This does not kill existing plants, but helps reduce 

the rate of spread.

PREFERRED HABITAT: Well adapted to a variety of environmental conditions 

throughout the range of the weed in North America. Does not do as well at sites 

with prolonged flooding or with high populations of Galerucella spp. as heavy 

defoliation by the leaf-feeders reduces food availability.

HISTORY: Introduced from France and Germany and released in the USA from 

1994 in CA, CO, ID, OR, WA. Introduced from Germany into Canada in 

1997, but not in the west (MB only). 

a b
Biological Control OF WEEDS in the Northwest 93Loosestrife

CURRENT STATUS: In the USA, feeding on floral buds often results in abortion 

which helps reduce weed spread. However, weevil populations are typically 

limited due to interspecific competition with Galerucella spp. (defoliated purple 

loosestrife plants often do not flower, removing N. marmoratus’ food supply). 

N. marmoratus may be an important agent at sites with decreasing loosestrife 

and smaller populations of the other agents. Though established in Canada, N. 

marmoratus only occurs in Manitoba, not in the western provinces.

REDISTRIBUTION: During summer, use sweep nets and aspirators to collect 

adults from loosestrife foliage. A stout beating stick can also be used to dislodge 

adults from flower spikes before catching them in trays. They 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: Has successfully overwintered on exposed islands in an estuary with 

high tidal exchange where multiple releases of Galerucella spp. have failed. The 

weevils can also persist where plants are scattered at low densities.

Coleoptera: Nanophyidae

c d

Nanophyes marmoratus: c) adult (Laura Parsons & Mark Schwarzländer, University of Idaho), d) 

damage to lower bud (Gary Piper, Washington State University) (both www.bugwood.org)

Nanoph

marmor
94 Biological Control OF WEEDS in the Northwest saltcedars

a) plant (Eric Coombs, Oregon Department of Agriculture), b) infestation (Steve Dewey, Utah State 

University) (both www.bugwood.org)

SYNONYMS: five-stamen tamarisk 

ORIGIN: Both species are geographically isolated in their native Asia (T. chinensis 

in the East, T. ramosissima in western Asia), but overlap and hybridize in North 

America. They were introduced to North America in the 1800s for erosion 

control and as shade plants. 

DESCRIPTION: Both species are very similar in appearance, differing only 

slightly in the shape of floral parts. In North America, extensive hybridization 

between these two species has occurred, making separation by appearance 

difficult to impossible. Both species and their hybrids are perennial shrubs or 

small trees growing up to 26 ft tall (8 m). Their root system is extensive, with 

a primary root that grows with little branching until it reaches the water table, 

at which point secondary root branching becomes substantial. Roots of mature 

plants are rhizomatous, giving rise to new plants. Leaves are scale-like with saltsecreting glands, and are up to 0.12 in long (3 mm). The foliage is deciduous. 

b

Saltcedar

Tamarix chinensis Willd., Tamarix ramosissima Ledeb. & hybrids

a
Biological Control OF WEEDS in the Northwest 95saltcedars

Stems are green and flexible when young, becoming brown and woody with age. 

Stem fragments can develop adventitious roots and produce new plants if the 

stem pieces are kept in moist soil. Some plants begin to flower their first year, but 

most flower in their third. Flowers occur in tight clusters 0.8-3 in long (2-8 cm) 

on branch ends. Each flower has 5 pink petals ~2 mm long. Fruits are capsules 

that contain many tiny brown seeds. A large plant may produce several hundred 

thousand seeds in a single growing season.

 

HABITAT: Readily invades moist habitats of arid regions, especially in saline soils. 

ECOLOGY: Spreads by seed, rhizomes, and sprouting from stem fragments. Seeds 

are readily transported by wind and water, but are viable for less than 6 months 

so do not form persistent seed banks. Seedlings germinate rapidly after seeds have 

direct contact with water. Germination can occur throughout the year. Flowers 

appear after foliage and are present from spring to fall, decreasing by fall.

APPROVED BIOLOGICAL CONTROL 

AGENTS: USA and CAN: None of the species 

established on Tamarix spp. in the USA are 

currently approved for use. 

NOTES: Both saltcedar parent species and their 

hybrids are the most invasive Tamarix species in 

North America. They differ from smallflower 

tamarisk with their flowers appearing after 

foliage in spring, having 5 petals, and flowering 

through fall. Smallflower tamarisk flowers have 

4 petals, appear before foliage in spring, and are 

present only in spring.

Family Tamaricaceae

c) leaves and stem (Bonnie Million, National Park Service), d) flowers (Leslie J. Mehrhoff, University 

of Connecticut)(both www.bugwood.org)

c d

Tamarix 

and T. ra
96 Biological Control OF WEEDS in the Northwest saltcedars

a) plant, b) infestation (both John M. Randall, The Nature Conservancy, www.bugwood.org)

SYNONYMS: N/A

ORIGIN: Native to southeastern Europe. Introduced to North America in the 

1800s for erosion control and as a shade plant. 

DESCRIPTION: Perennial shrub or small tree growing up to 16 ft tall (5 m). 

The root system is extensive, with a primary root that grows with little branching 

until it reaches the water table, at which point secondary root branching 

becomes substantial. Roots of mature plants are rhizomatous, giving rise to new 

plants. Leaves are scale-like with salt-secreting glands, and are up to 0.10 in long 

(21⁄2 mm). The foliage is deciduous. Stems are green and flexible when young, 

becoming brown and woody with age. Stem fragments can develop adventitious 

roots and produce new plants if the stem pieces are kept in moist soil. Some 

plants begin to flower their first year, but most flower in their third. Flowers 

occur in tight clusters 0.4 to 0.8 in long (1-2 cm) on branch ends. Each flower 

has 4 pink petals ~2 mm long. Fruits are capsules that contain many tiny brown 

seeds. A large plant may produce several hundred thousand seeds in a single 

b

Smallflower tamarisk

Tamarix parviflora DC.

a
Biological Control OF WEEDS in the Northwest 97saltcedars

growing season.

 

HABITAT: Readily invades moist habitats of arid regions, especially in saline soils. 

ECOLOGY: Spreads by seed, rhizomes, and sprouting from stem fragments. 

Seeds are readily transported by wind and water, but are viable for less than 6 

months so do not form persistent seed banks. Seedlings germinate rapidly after 

seeds have direct contact with water. Germination can occur throughout the 

year. Flowering occurs in spring; flowers appear before foliage.

APPROVED BIOLOGICAL CONTROL AGENTS: USA and CAN: None 

of the species established on Tamarix spp. in the USA are currently approved 

for use. 

NOTES: Smallflower tamarisk is the primary 

invader in CA, USA. Smallflower differs from 

saltcedar in that its flowers have 4 petals, appear 

before foliage in spring, and are only persistent 

through spring. Saltcedar flowers have 5 petals, 

appear after foliage in spring, and are present 

from spring through fall.

Family Tamaricaceae

c) resprouting from stem fragment (Joseph M. DiTomaso, University of California-Davis), d) flowers 

(Barry Rice) (both www.bugwood.org)

c d

Tamarix 
98 Biological Control OF WEEDS in the Northwest saltcedars 8-12 species of Tamarix were intentionally introduced to the USA. Of these, five 

saltcedar species have become invasive, including T. parviflora, T. canariensis, T. 

gallica, and the morphoically similar T. chinensis and T. ramosissima. The largest 

invasions in the West consist of T. chinensis, T. ramosissima and their hybrids. 

Tamarix parviflora is the primary invader in CA. The biocontrol agents thus far 

established in the USA primarily attack T. chinensis and T. ramosissima (and their 

hybrids) and T. parviflora. Consequently only these species are described in this 

field guide. 

HISTORY IN THE NORTHWEST: Numerous populations of the defoliating 

Diorhabda elongata were intentionally released in the USA from 2001. D. 

elongata has since been split into 5 species, 4 of which have been released in 

the USA from 7 different locations, corresponding to 7 different ecotypes. 

Two ecotypes (Turpan and Posidi Beach) failed to establish. The southwestern 

willow flycatcher, an endangered bird in the USA, utilizes Tamarix spp. in areas 

where its natural habitat has been encroached by this weed. Redistributions 

of Diorhabda spp. have been discontinued and are not approved until the 

legalities of this issue are resolved. Coniatus splendidulus was initially part of a 

genus of interest for Tamarix biocontrol in the USA but which has never been 

approved for release. The species was found established in AZ by 2006. 

CURRENT STATUS: Of the 5 Diorhabda spp. ecotypes that established prior 

to the moratorium, the Chilik and Fukang ecotypes originally required long 

daylight hours in order to avoid premature diapause, which initially prevented 

them from establishing south of the 38th parallel. They have since evolved, with 

changing photoperiod requirements now allowing them to persist well below the 

38th parallel. Throughout their range, both species are increasing and spreading, 

providing significant control locally to Tamarix populations. The remaining 

three ecotypes were not ever limited by long daylight hours. The Karshi and 

Tunisian ecotypes are established and increasing, but are to date restricted to 

TX and other parts of the Midwest. The Crete ecotype does well on T. parviflora

in CA. It did well on the widespread saltcedar (T. chinensis, T. ramosissima and 

hybrids) in TX but dispersal was limited. Recent hybridization with Diorhabda 

carinata has led to rapid expansion in TX and other Midwestern states. Flooding 

and predation limit population growth of all ecotypes. C. splendidulus is 

spreading rapidly in the Northwest and appears to complement Diorhabda by 

attacking foliage before and after Diorhabda is active.

RECOMMENDATIONS: C. splendidulus and Diorhabda spp. are not 

approved for redistribution in the USA. Saltcedar does not occur in Canada. 

Saltcedar Biological Control
Biological Control OF WEEDS in the Northwest 99saltcedars

Coniatus: Zeynep Özsoy, Colorado Mesa 

University, Diorhabda: Robert D. Richard, 

USDA APHIS PPQ, www.bugwood.org

Saltcedars, Unapproved Agents

Coniatus splendidulus (Fabricius)

(Coleoptera: Curculionidae)

DESCRIPTION AND LIFE CYCLE: Little is known 

about the biology of this species, and additional molecular 

work is required to help sort out the identification and 

taxonomy of the entire genus. Larvae are highly cryptic, 

closely resembling the scale-like leaves of Tamarix spp., 

albeit with black head capsules. Larvae pupate within 

woven baskets attached to Tamarix leaves. Adults are ~3 

mm long with robust bodies, large eyes, thick legs, and 

thick snouts pointing strongly downward. The elytra 

have distinct grooves. Adults vary from mottled brown 

to iridescent green and everything in between. Because 

larvae and adults can be so difficult to find, searching 

for the presence of pupal baskets is often the best way to 

confirm the insect’s presence. 

HISTORY AND CURRENT STATUS:Initially a genus 

of interest for Tamarix biocontrol in the USA, though it 

was never approved or officially released. The species was 

first recorded in AZ in 2006 and spread naturally to: CA, 

NV and UT by 2010, CO by 2011, and TX by 2012. Its 

mode of introduction to the USA is unknown. Overall 

abundance and impact are unknown as populations have 

only recently been reported established throughout southwestern USA, and 

individuals are cryptic in behavior. In CO, large populations have been observed 

emerging prior to Diorhabda emergence and attacking regrowth of Tamarix spp. 

after Diorhabda are in diapause. Not approved for redistribution in the USA.

Coniatus splendidulus: a) 

pupal basket, b) adult 

(both Zeynep Özsoy, 

Colorado Mesa University)

a

b

Coniatus 

splendidulus

Diorhabda 

spp.
100 Biological Control OF WEEDS in the Northwest saltcedars Diorhabda spp. (Coleoptera: Chrysomelidae)

DESCRIPTION AND LIFE CYCLE: 

What was released in the USA as 

Diorhabda elongata (Brullé) has since 

been split into five species, four of 

which were intentionally released in the 

USA. All are very similar in appearance, 

separated out morphologically by 

differences in genitalia. Eggs of all 

species are tan, spherical, and laid in 

masses on Tamarix foliage. Hatching 

larvae develop through three instars. Third instar larvae are up to 9 mm long, 

black and with distinct yellow longitudinal stripes. Adults are 51⁄2-6 mm long 

with yellowish tan bodies. Two dark stripes on each elytron are obvious on 

some species and less distinct on others. Both larvae and adults feed on foliage 

throughout the growing season. The four species released in the USA originated 

from seven different habitats, corresponding to seven different ecotypes. The 

Chilik and Fukang ecotypes (described below) originally required long daylight 

hours in order to avoid premature diapause. They have since evolved, with 

changing photoperiod requirements now allowing them to persist further south. 

These two ecotypes have two generations per year above the 38th parallel. The 

remaining five ecotypes (Karshi, Turpan, Crete, Posidi Beach, and Tunisian) can 

produce 3-4 generations per year. Adults of all ecotypes overwinter and emerge 

in early spring to lay eggs.

HISTORY AND CURRENT STATUS: The southwestern willow flycatcher, 

an endangered bird in the USA, utilizes Tamarix spp. in areas where its natural 

habitat has been encroached by this weed. In 2009, a lawsuit was filed against 

USDA APHIS due to the possible negative impacts this biocontrol program could 

have on the bird by destroying some of its adventive habitat. Redistributions 

of Diorhabda spp. have been discontinued and are not approved until this 

is resolved.

Chilik Ecotype of Diorhabda carinulata (Desbrochers): Introduced from 

Kazakhstan and released in UT from 2001. Successfully established and spread 

rapidly to AZ, CO and NV. Populations are high but experience heavy bird 

predation, though they have still increased sufficiently to exert significant control 

of Tamarix. This is especially true along the Colorado River near Moab where 

Robert D. Richard, USDA APHIS PPQ, 

www.bugwood.org

Saltcedars, Unapproved Agents
Biological Control OF WEEDS in the Northwest 101saltcedars

extensive defoliation had occurred for at least 18 river miles by 2006, and Delta 

where 30 ha had been defoliated by 2003. Recent evolution in photoperiod 

requirements has allowed them to spread south of the 38th parallel. Flooding 

limits agent populations. 

Fukang Ecotype of Diorhabda carinulata: Introduced from Fukang, China 

and released in CA CO NV WY from 2001 (ID MT OR WA subsequently). 

Established in CA CO ID NV NM OR SD UT WY with heavy defoliation 

at most release sites, however spread from release sites varies by location. Very 

successful throughout NV where thousands of ha defoliated by 2006. Repeated 

defoliation led to death of 70% of plants within 5 years. Also highly defoliating 

regionally in WY and CO. Populations limited in ID and OR where heavy 

defoliation only occurs locally. Recent evolution in photoperiod requirements 

has allowed them to spread south of the 38th parallel. Flooding and heavy 

predation limit agent populations. 

Turpan Ecotype of Diorhabda carinulata: Introduced from Turpan, China and 

released in CO in 2005 but is believed to have failed establishment.

Crete Ecotype of Diorhabda elongata: Introduced from Crete, Greece and 

released in CA and parts of the Midwest from 2003. Does well in CA on 

smallflower tamarisk, Tamarix parviflora, the dominant species in northern 

and central CA. In general, has had a lower rate of success on the widespread 

saltcedar (T. chinensis, T. ramosissima and hybrids) in CA. Did quite well in TX, 

though had lower rates of dispersal than that of the Fukang/Chilik ecotypes 

established in northern regions. Recent hybridization with Diorhabda carinata

has led to rapid expansion in TX and other Midwestern states. Flooding and 

predation limit population growth.

Posidi Beach Ecotype of Diorhabda elongata: Introduced from mainland 

Greece and released in the Midwest from 2005 but eventually died out.

Karshi Ecotype of Diorhabda carinata (Faldermann): Introduced from 

Uzbekistan and released in the Midwest from 2006 where it was localized 

initially. Hybridization with D. elongata (Crete ecotype) has led to rapid 

expansion in the Midwest. Flooding and predation limit population growth.

Tunisian Ecotype of Diorhabda sublineata (Lucas): Introduced from Tunisia 

and released in the Midwest (TX) from 2006. The dominant species at the 

original release location was a hybrid between Tamarix canariensis, T. gallica, 

T. ramosissima or T. chinensis, to which the beetles were not strongly attracted 

in outdoor cage tests. Once liberated they immediately dispersed in search of a 

better host, thus not establishing. Subsequent releases resulted in populations 

that expanded rapidly. Still restricted to TX by the end of 2012, but populations 

are high. Flooding and predation limit population growth.
102 Biological Control OF WEEDS in the Northwest thistlesThistle species comparison

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’ (11⁄2 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 11⁄2” (33⁄4 cm) 1⁄2” (11⁄4 cm) 3” (7 cm) 1⁄2” (11⁄4 cm) 

Bracts Spiny; Tipped in 

yellow Not spiny

End in small 

spines; Wide, 

triangular; Purple 

at maturity

Not spiny; 

Purplish

Capitulum

Bull, Canada and musk thistle are the primary targets of thistle biological control 

efforts in North America. Below is a comparison of these three species, as well as six 

others that are occasional hosts to thistle biocontrol agents. 
Biological Control OF WEEDS in the Northwest 103thistles

Credits: Bull: Jennifer Andreas, Washington State University Extension; Canada: Richard Old, XID 

Services, Inc, www.xidservices.com; Musk & Italian: Mary Ellen (Mel) Harte, www.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) 31⁄2’ (1 m) 31⁄2’ (1 m) 5’ (11⁄2 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” (21⁄2 cm) ≤ 1” (21⁄2 cm) <1” (21⁄2 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
104 Biological Control OF WEEDS in the Northwest thistles

Bull 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 lobe. Stems are stout, hairy, and have spiny wings. 

Capitula are 11⁄2-2 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: Grows best on neutral soils rich in nitrogen and with moderate 

b

a) plant (Marianna Szucs, University of Idaho), b) infestation (Forest and Kim Starr, Starr 

Environmental, www.bugwood.org)

a
Biological Control OF WEEDS in the Northwest 105thistles

c) leaf (Dan Tenaglia, Missouriplants.com, www.bugwood.org), d,e) stem, flower head (Jennifer 

Andreas, Washington State University Extension)

moisture. It is not typically found in sand, pure clay, or in soils with high humus 

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: 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).

APPROVED BIOLOGICAL CONTROL AGENTS: USA: Cheilosia grossa, 

Trichosirocalus horridus (which is no longer permitted for interstate transport), 

and Urophora stylata. Also attacked by Rhinocyllus conicus which was introduced 

intentionally but is no longer approved for use; CAN: R. conicus and U. stylata.

NOTES: Phenolic acids produced by the thistle 

have allelopathic effects against competing 

plants and (along with spines) serve as a defense 

against herbivory.

Family Asteraceae

d

Cirsiu

vulga

c e
106 Biological Control OF WEEDS in the Northwest thistles

Canada thistle

Cirsium arvense (L.) Scop.

a) plant, b) infestation (both Steve Dewey, Utah State University, www.bugwood.org)

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 (1⁄3-1.2 m) in height with rhizomatous roots. 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 (1⁄2 in or 11⁄4 cm diameter) capitula producing numerous tufted 

seeds. Receptacle bracts are not spiny. Florets vary in color from white to deep 

lavender.

 

HABITAT: Rapidly colonizes disturbed moist sites including prairies, meadows, 

ditches, stream banks, lawns, and agricultural fields. 

a b
Biological Control OF WEEDS in the Northwest 107thistles

ECOLOGY: 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 and form rosettes 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.

APPROVED BIOLOGICAL CONTROL AGENTS: USA: Altica carduorum,

Hadroplontus litura (=Ceutorhynchus litura), and Urophora cardui. Also attacked 

by Rhinocyllus conicus which was introduced intentionally but is no longer 

approved for use; CAN: A. carduorum, H. litura, Larinus carlinae (=Larinus 

planus), R. conicus, and U. cardui.

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.

Family Asteraceae

d

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 www.bugwood.

org)

Cirsiu

arven

c e
108 Biological Control OF WEEDS in the Northwest thistles

Musk thistle

Carduus nutans L.

a) plant (Mary Ellen (Mel) Harte, www.bugwood.org), b) infestation (Marianna Szucs, Colorado 

State University)

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 (11⁄2 

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 the 

ends of stems, 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
Biological Control OF WEEDS in the Northwest 109thistles

HABITAT: Readily invades pastures, roadsides, ditches, and meadows. Grows best 

in disturbed, neutral to acidic soils with moist conditions. 

ECOLOGY: 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.

APPROVED BIOLOGICAL CONTROL AGENTS: USA: Cheilosia grossa, 

Psylliodes chalcomera, Puccinia carduorum, Trichosirocalus horridus (which is no 

longer permitted for interstate transport), and Urophora solstitialis. Also attacked 

by Rhinocyllus conicus which was introduced intentionally but is no longer 

approved for use; CAN: R. conicus, T. horridus, and U. solstitialis.

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 North and South American 

specimens cannot be reliably assigned. In the 

USA, subspecies include nutans, leiophyllus, 

(which is synonymous with Carduus thoermeri) 

and macrocephalus.

Family Asteraceae

d

c) leaf (Rachel Winston, MIA Consulting), d) stem, e) flower head (d,e Mary Ellen (Mel) Harte, 

www.bugwood.org)

Cardu

nutan

c e
110 Biological Control OF WEEDS in the Northwest thistles HISTORY IN THE NORTHWEST: Nine thistle species are highly problematic 

in North America, though musk, Canada, and bull are typically the most 

problematic and common. Thistle biological control began in North America 

in 1969 with the importation of the thistle seed head weevil, Rhinocyllus conicus.

This agent has since been discovered attacking several species native to North 

America. Consequently, its USA interstate transport permits were revoked. To aid 

the thistle biocontrol program, an additional 9 insect species have subsequently 

been intentionally introduced to North America as classical biological control 

agents of thistle. Of those currently established, musk, Canada and bull thistle 

are the primary targets, though other thistle species serve as occasional hosts. An 

additional six adventive species are present on thistles in North America.

CURRENT STATUS: Six of the 10 intentionally introduced insects have 

established in North America. The three seed-feeding agents reduce seed 

production. This does not kill existing plants, but does help reduce the rate of 

spread of weed populations. This has proven effective for bull and musk thistle 

when infestations are also subjected to high plant competition. However, the 

most effective seed-feeder, R. conicus, is no longer approved for any use 

in the USA. Seed-feeding is ineffective against Canada thistle as it does not 

disrupt root reproduction. Both stem-mining species are largely ineffective due 

to the attacked plant’s ability to recover from feeding. The root crown-feeding 

T. horridus is effective on musk and plumeless thistle growing with high plant 

competition; however, due to observed nontarget attack, interstate transport 

of T. horridus is no longer permitted in the USA.

RECOMMENDATIONS: USA: R. conicus is no longer approved for any 

use. T. horridus is no longer approved for interstate transport, and some 

intrastate redistribution is banned as well. T. horridus is not overly effective 

against musk or plumeless thistle alone, but can work well in conjunction with 

the stresses from high competing plant vegetation. Redistributions should only 

be made in approved locations where nontarget species do not co-occur. The 

agents currently established are generally not effective against Canada thistle. 

Hadroplontus litura and Urophora cardui could be utilized as a last resort in shady 

or riparian environments where other control methods are not feasible. U. stylata

is effective against bull thistle stressed by high plant competition, although large 

populations are difficult to maintain and should be regularly supplemented. 

Gall-infested capitula can be transferred in fall or spring. CAN: The same 

combinations of insects are also the most effective against thistles in Canada. 

In addition, T. horridus is approved for use in Canada, as is R. conicus. Adult R. 

conicus should be redistributed to new musk infestations in spring using nets.

Thistle Biological Control
Biological Control OF WEEDS in the Northwest 111thistles

Approved, Non-Established Agents

Established Agents

Altica: André Gassmann, CABI-Switzerland, Lema: Alec McClay, 

McClay Ecoscience, Psilliodes: USDA ARS European Biological 

Control Laboratory, Urophora: Eric Coombs, Oregon Department 

of Agriculture

Cheilosia: Eric Coombs, Oregon Department of Agriculture, Hadroplontus, Rhinocyllus, Trichosirocalus, 

and Urophora cardui: Laura Parsons, University of Idaho, U. stylata: Peter Harris Agriculture and AgriFood Canada, www.bugwood.org

Agent Adult Impact Recommendation

Cheilosia 

grossa

Established only in OR, USA. 

Mines large plants of Italian 

and slenderflower (rarely 

plumeless), impact minor.

Not released in CAN.

Abundance and impact low 

in USA. Not high priority for 

redistribution.

Hadroplontus 

litura

Well established in USA 

and CAN. Typically only 

mines non-essential tissue of 

Canada; impact limited.

Effective in select settings, 

but typically low impact 

overall. Not high priority for 

redistribution.

Rhinocyllus 

conicus

Seed-feeding reduces musk 

density in combination with 

plant competition. Low impact 

on late flowering species.

No longer approved in USA; 

attacks natives. In CAN, can 

be redistributed to musk 

infestations with competition.

Trichosirocalus 

horridus

Best on musk and plumeless 

in USA, CAN. Root crownmining complements plant 

competition, but weak alone.

Interstate transport no longer 

legal in USA. In CAN, low 

priority; only for areas with 

high competing vegetation.

Urophora 

cardui

Attacks Canada in USA, 

CAN. Galls can stunt plants 

and reduce seed production. 

Impact typically limited. 

Could be redistributed to 

shady, protected areas with 

other agents. Low priority for 

redistribution elsewhere.

Urophora 

stylata

Established on bull in USA, 

CAN. Seed-feeding reduces 

production up to 60%. Okay 

in combination.

Widespread but variable 

abundance in USA, CAN. 

Regular redistributions 

recommended.

Altica 

carduorum

Lema 

cyanella

Psilliodes 

chalcomera

Urophora 

solstitialis
112 Biological Control OF WEEDS in the Northwest thistles SYNONYMS: Cheilosia corydon (Harris)

DESCRIPTION: Larvae are tan in color and grub-like, 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.

Cheilosia grossa (Fallén)

Thistle stem hover fly

Cheilosia grossa: a) adult, b) larval mining damage, c) capitula death due to mining (all Eric Coombs, 

Oregon Department of Agriculture, www.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, they mine into roots and continue feeding, developing 

through three instars. Pupae overwinter in roots or in soil litter. There is one 

generation per year.

DAMAGE: Larval mining interferes with plant function and ultimately results in 

a decrease of seed production, sometimes even death.

PREFERRED HABITAT: 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.

HISTORY: Introduced from Italy and released on musk and slenderflower thistle 

in the USA in 1990 (MT, NV, OR) and Italian thistle in OR in 1993. Found 

feeding on bull thistle in OR by 2001.

CURRENT STATUS: Established on Italian and slenderflower thistle in OR, 

USA, though it is not very abundant on either species. Rarely found on plumeless 

thistle. Where established on any of the above species, plants with large stem 

diameters (>10 mm) are often attacked, though overall impact is typically 

minor. Establishment failed on musk thistle. Occasionally found attacking large 

a b c
Biological Control OF WEEDS in the Northwest 113thistles

rosettes of bull thistle in OR, decreasing plant function and seed production. 

However, Carduus species are preferred over Cirsium.

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 the host plants die 

back with lower temperatures. The infested roots can then be transferred to new 

infestations. Or they may be stored overwinter 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 adults emerge, flies can be 

transferred to new thistle infestations in groups of 50-100. Damage similar to 

that caused by this agent 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 agent is not approved for release in Canada.

Diptera: Syrphidae

Canada musk

Cheilosia

grossa,

Canada a

musk

Cheilosia

grossa,

Canada and

musk

bull

Cheilosia

grossa, bull
114 Biological Control OF WEEDS in the Northwest thistles SYNONYMS: Ceutorhynchus litura (Fabricius)

DESCRIPTION: Larvae are white, grub-like, 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.

Hadroplontus litura (Fabricius)

Canada thistle stem weevil

Hadroplontus litura: a) larvae in stem, b) adult (Laura Parsons, University of Idaho), c) stem mining 

damage (a,c Norman E. Rees, USDA ARS) (all www.bugwood.org)

LIFE CYCLE: Overwintering adults emerge from soil litter and feed on leaf 

and stem tissue in early spring. Eggs are laid in spring in the mid-vein 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 

soil 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 

the stems of target plants via holes made by exiting larvae.

PREFERRED HABITAT: Does well in moist, disturbed areas where target 

thistles are dense and not stressed by drought, grazing, or other control methods. 

HISTORY: Introduced from Germany and released on Canada thistle in the 

USA from 1971 (CA, CO, ID, MT, OR, WA, WY). Introduced from France, 

Germany, Italy and Switzerland and released in Canada from 1965 (AB, BC 

from 1975).

a b c
Biological Control OF WEEDS in the Northwest 115thistles

CURRENT STATUS: On Canada thistle in the USA, some reports indicate 

the agent 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 established at most release sites on Canada thistle in Canada, the weevil 

has low reproductive and dispersal ability so populations are typically limited. 

Mining over multiple years decreases root biomass, when in conjunction with 

other stresses. Even in combination with other 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 individuals should be 

made on patches of at least 2,000 m2 (1⁄2 acre). 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.

Coleoptera: Curculionidae

Canada musk

Hadroplo

litura, m

Hadroplontus

litura, Canada

bull

Hadroplontus

litura, bull
116 Biological Control OF WEEDS in the Northwest thistles 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.

Rhinocyllus conicus (Frölich)

Thistle seedhead weevil

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 the 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 spread of thistle populations. 

PREFERRED HABITAT: Does best in meadows and moist areas with moderate 

temperatures. In areas where summer arrives quickly, weevils are unable to utilize 

later-developing capitula. 

HISTORY: Three strains have been collected for use against exotic thistles in the 

USA, originating from three host species in France and Italy and released from 

1969 on musk, plumeless, Scotch (failed), Italian, slenderflower, and milk thistle. 

The weevil spread naturally to bull and Canada thistle. Introduced from France 

Rhinocyllus conicus: a) eggs (Whitney Cranshaw, Colorado State University), b) larvae and damage in 

capitula (Mark Schwarzländer, University of Idaho, c) adult (Laura Parsons, University of Idaho) (a,b 

www.bugwood.org)

a b c
Biological Control OF WEEDS in the Northwest 117thistles

and released on and redistributed to numerous exotic thistle species throughout 

Canada from 1968.

CURRENT STATUS: Typically prefers Carduus spp. (musk, plumeless, Italian, 

slenderflower) over other thistles. In the USA, it is abundant on musk thistle 

on which it is effective when combined with Trichosirocalus horridus and plant 

competition. Abundant on Italian thistle in CA, ID, OR and slenderflower in 

OR. On both species it can be effective on early-blooming plants but only in 

combination with plant competition. Established on plumeless thistle in ID, 

OR, WA though impact is typically low as only early capitula are attacked. It is 

largely ineffective on Canada thistle (though widely distributed), because seed 

reduction doesn’t hinder the plant’s spread via roots. Attacks bull thistle in OR 

and milk thistle in CA and OR, but overall impact is minimal. Attacks 22 of 90 

Cirsium spp. native to the USA. Interstate shipment permits were revoked 

in 2000, and it is (strongly) not recommended for redistribution within 

each state. In Canada, it attacks over 90% of musk thistle capitula, reducing 

seed production by ~50%. It has been credited with controlling this species 

when plant competition is present. Established on bull, marsh and plumeless 

thistle in BC. Reduces seed production of plumeless thistle by 10% as only the 

early capitula are attacked. Attack to Cirsium thistles is even more minor.

REDISTRIBUTION: This species is no longer approved for redistribution in 

the USA. 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.

Coleoptera: Curculionidae

Canada musk

Rhinocyll

conicus, m

Rhinocyllus

conicus,

Canada

bull

Rhinocyllus

conicus, bull
118 Biological Control OF WEEDS in the Northwest thistles 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.

Trichosirocalus horridus (Panzer)

Musk thistle crown weevil

LIFE CYCLE: Overwintering adults emerge in spring and feed on rosettes of 

host plants. Eggs are deposited on the undersides of leaves along the midrib 

and primary veins of young plants. Hatching larvae move down and feed on 

the tissue at the root-stem 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 soil 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: Does best in open infestations of the target weed and 

on the perimeter where stems do not grow as tall. It is widely distributed but 

does not do as well at high elevations or under marshy conditions. 

HISTORY: Introduced from Italy and released on onto plumeless and musk thistle 

from 1974. Spread naturally to bull and slenderflower thistle. Redistributed to 

Italian and Scotch thistle from 1994. Introduced from Germany and released 

in Canada on musk and plumeless thistle from 1975. Later released on and 

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)

a b c
Biological Control OF WEEDS in the Northwest 119thistles

redistributed to bull, Scotch and marsh thistle. 

CURRENT STATUS: In the USA, it prefers musk over plumeless thistle 

(established on the latter in CO, MT, WA). On both it can be effective when 

in combination with plant competition and other agents, but is ineffective at 

many sites. Moderately effective on Italian and slenderflower thistle in OR. 

Found in limited amounts on bull thistle in WY where impact is minimal. 

Failed to establish on Scotch thistle in the USA. Established on plumeless thistle 

in BC, Canada and musk thistle in BC and AB. On both species damage is 

limited; attacked rosettes frequently survive to produce seed later in the season. 

Established on bull, marsh, and Scotch thistle in BC with unknown impact.

REDISTRIBUTION: Adults can be hand collected in spring from rosettes of 

host plants. 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 can be released at new sites. 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 USA, and some states have prohibited 

its redistribution within their borders. Where this agent is approved for 

redistribution, it is imperative to refrain from making releases at sites where 

known related or susceptible species co-occur.

NOTES: A 2002 revision of Trichosirocalus horridus concluded this species was in 

fact a complex of three species, with distinct host plant preferences: T. horridus, T. 

mortadelo, and T. briesei with preferences for Cirsium, Carduus and Onopordum

thistles, respectively. Because there is a disagreement for the morphological 

parameters selected by taxonomists for this separation, molecular studies are 

currently underway to determine if the species complex is truly a complex, and 

to what level. For now we refer to all Trichosirocalus in North America as T. 

horridus.

Coleoptera: Curculionidae

bull

Trichosirocalus

horridus, bull

Canada musk

Trichosiro

horridus, m

Trichosirocalus

horridus,

Canada
120 Biological Control OF WEEDS in the Northwest thistles 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.

Urophora cardui (L.)

Canada thistle stem gall fly

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 the 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: 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. 

HISTORY: Introduced from Austria and France and released on Canada thistle 

in the USA from 1977 (CA, CO, ID, MT, NV, OR, UT, WA, WY). Introduced 

from Austria, France and Germany and released on Canada thistle in Canada 

(AB, BC) from 1974. An additional strain from Finland was released in BC 

from 1987.

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)

a b c
Biological Control OF WEEDS in the Northwest 121thistles

CURRENT STATUS: Moderately abundant on Canada thistle in the USA. 

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 species 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 it can reduce density and stature of Canada thistle. 

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, 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 the 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.

Diptera: Tephritidae

Canada musk

Urophora

cardui, m

Urophora

cardui, Canada

bull

Urophora

cardui, bull
122 Biological Control OF WEEDS in the Northwest thistles 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.

Urophora stylata (L.)

Bull thistle seedhead gall fly

Urophora stylata: a) larvae in seed head, b) adult (a,b Peter Harris Agriculture and Agri-Food Canada, 

www.bugwood.org)

LIFE CYCLE: Overwintering larvae pupate in galls in spring when new plants 

are bolting. Adults emerge throughout the early summer and deposit eggs on 

maturing 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) instar larvae overwinter within galls. There is one 

generation per year.

DAMAGE: Larval feeding reduces seed production which can help reduce the 

rate of spread of thistle populations. 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: 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. 

HISTORY: Introduced from Germany and Switzerland and released on bull 

thistle in BC, Canada from 1973. Redistributed from Canada to bull thistle in 

the USA from 1983 (CA, CO, MT, OR, WA).

a b
Biological Control OF WEEDS in the Northwest 123thistles

CURRENT STATUS: Abundance and impact on bull thistle vary in the USA. 

Populations are cyclical in OR, and limited in CA, CO and WA. 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, it 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 Urophora 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 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: Bull thistle is short-lived and populations follow disturbance patterns, 

typically not lasting long in the same locations. Consequently, it is difficult to 

maintain large populations of U. stylata.

Diptera: Tephritidae

bull

Urophora

stylata, bull

Canada musk

Urophora

stylata, m

Urophora

stylata,

Canada
124 Biological Control OF WEEDS in the Northwest thistles 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 leaves. When mature, they 

drop to the soil for overwintering.

HISTORY: Introduced from Switzerland and released on Canada thistle in the 

USA from 1966 (CA, CO, ID, MT, NV, OR, WA). Establishment failed at all 

sites. Additional strains from France and Italy subsequently released in eastern 

states also failed to establish, possibly influenced by predation. Introduced from 

France and Switzerland and released in Canada from 1963 (AB, BC). Failed to 

establish as low development in cool summers exposed larvae to high predation. 

Lema cyanella (L.)

(Coleoptera: Chrysomelidae)

DESCRIPTION AND LIFE CYCLE: 

Overwintering adults emerge in spring 

and oviposit on leaf undersurfaces and 

stems. Larvae feed on 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 foam 

cocoons they secrete. Adults emerge in 

late summer and feed on foliage prior to overwintering in soil. 

HISTORY: Introduced from Switzerland and released on Canada thistle in more 

eastern provinces of Canada from 1983. After establishment failed, a population 

sourced from Switzerland and France obtained via New Zealand was released 

in AB from 1993. One population initially established at low densities, but 

concerns over nontarget attack led to its eradication. It is no longer considered 

established. Not approved for release in the USA.

André Gassmann, CABI-Switzerland

Thistles, Non-Established Agents

Alec McClay, McClay Ecoscience
Biological Control OF WEEDS in the Northwest 125thistles

Psylliodes chalcomera (Illiger)

(Coleoptera: Chrysomelidae)

DESCRIPTION AND LIFE CYCLE: 

Overwintering adults emerge in spring 

and oviposit at the bases of plants. They 

are shiny and dark with a metallic bluegreen 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 throughout the 

growing season. Pupation occurs in the soil litter. There is one generation per year.

HISTORY: Introduced from Italy and released on musk thistle in the USA in 1997 

(KS, MD, TX) but failed to establish. It is not widespread in its native range; as 

a result, it has been difficult to collect large enough populations for release and 

establishment in North America. Not approved for release in Canada.

Urophora solstitialis (Illiger)

(Diptera: Tephritidae)

LIFE CYCLE: Overwintering larvae are 

white, barrel-shaped with dark brown 

anal plates, and can be up to 4 mm 

long. Adults emerge in later spring and 

can be 5 mm long. They are brownish 

black with a yellow head and legs and 

two black “VII”-shaped markings on 

wings. Eggs are deposited in developing 

capitula. Hatching larvae feed on seeds and receptacles, forming hardened galls. 

Most larvae overwinter in galls, but early maturing larvae may pupate in early 

summer as a second generation. There are up to two generations per year.

HISTORY: Introduced from Italy and released on plumeless and musk thistle in 

the USA in 1993 (northwestern releases on musk only and from 1996). USA 

establishment failed. Introduced from Germany and Austria and released on 

plumeless and musk thistle in BC from 1990. Established only on plumeless 

thistle and only in more eastern provinces where overall impact is limited.

USDA ARS European Biological Control 

Laboratory (www.bugwood.org)

Thistles, Non-Established Agents

Eric Coombs, Oregon Department of 

Agriculture
126 Biological Control OF WEEDS in the Northwest thistles

Thistles, Unapproved Agents

Aceria: Eric Erbe, USDA ARS, www.bugwood.org, Cassida: Laura Parsons, University of Idaho, 

Cleonis: Ivo Tosevski, CABI-Switzerland, Larinus: Alec McClay, McClay Ecoscience, Puccinia: USDA 

ARS, www.bugwood.org, Terellia: Peter Harris, Agriculture and Agri-Food Canada

Six accidentally introduced species are established on thistles in North America. 

Though some of these 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 USA. Care should be taken when transferring approved agents to 

ensure that these unapproved species are not also included in transferred material.

In addition to the above sprecies, 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 use in the USA, there is recent 

interest in gaining authorization to utilize it intentionally.

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 urediospores form densely 

packed yellow-brown pustules on upper leaf surfaces that are easily blown to 

uninfected plants to repeat the cycle. There are many generations per year. When 

host plants die back in the fall, teliospores are produced to overwinter.

HISTORY AND CURRENT STATUS: Believed to have been accidentally 

introduced to North America by 1890, it is now widespread throughout the 

USA and Canada. Systemic infection can be lethal but is dependent on suitable 

conditions. Superficial foliar infections are more common in Canada thistle 

patches but have little impact on the plant, stunting growth and flowering but not 

reducing populations. Not yet approved for redistribution in the USA.

© Malcolm Storey, www.bioimages.org.uk

Aceria 

anthocoptes

Cassida 

rubiginosa

Cleonis 

pigra

Larinus 

carlinae

Puccinia 

carduorum

Terellia 

ruficauda
Biological Control OF WEEDS in the Northwest 127

Thistles, Unapproved Agents

thistles

Aceria anthocoptes (Nalepa)

(Acari: Eriophyidae)

DESCRIPTION AND LIFE CYCLE: 

Mites appear on foliage in spring as 

plants bolt. Nymphs and adults are 

white, tan, pink, or yellow, depending 

on the developmental stage. They 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: Accidental introduction discovered 

on Canada thistle in the USA in 1998; now established in CO, MT, WY (USA) 

and AB (Canada). Can cause thinning and leaf deformation in the lab, but has 

not been properly evaluated in the field where it appears impact is minimal. Has 

been collected from numerous thistles native to North America. Not approved 

for redistribution in the USA.

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 71⁄2 mm long. 

Eggs are laid in spring and summer; 

emerging larvae feeding 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 soil litter. There is one generation per year.

HISTORY AND CURRENT STATUS: Accidental introduction recorded on 

Canada thistle in North America in 1901; intentionally redistributed in the USA 

in the 1970s. Established in OR, WA, WY (USA) and AB, BC (Canada). In some 

areas, can significantly reduce biomass and survival; overall impact is typically 

minimal, likely hindered by predation and parasitism. Feeds on numerous thistle 

species, including many natives. Not approved for redistribution in the USA.

Eric Erbe, USDA ARS, www.bugwood.org

Laura Parsons, University of Idaho
128 Biological Control OF WEEDS in the Northwest thistles

Thistles, Unapproved Agents

Cleonis pigra (Scopoli) 

(Coleoptera: Curculionidae)

DESCRIPTION AND LIFE CYCLE: 

Adults emerge in spring and feed on 

young leaves. They are mottled brown 

with many shiny black lumps and 

can be up to 7 mm long. Their wide 

snouts appear grooved. Larvae hatch 

throughout summer and bore to the stem base where they feed internally. They 

are white with a brown head, grub-like, and are up to 3 mm long. Pupation 

occurs in soil litter. Adults emerge throughout fall and overwinter in soil litter. 

There is one generation per year.

HISTORY AND CURRENT STATUS: Accidental introduction recorded on 

Canada thistle in the USA by 1919 and in Canada by 1933. Only established in 

eastern states and provinces. Larval root mining may kill plants, but regeneration 

typically observed. Feeds on a wide array of important species; overall impact to 

exotic thistles is minimal. Not approved for redistribution in the USA.

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 or yellow hairs, 

and long snouts. Eggs are laid inside developing capitula. Larvae feed on developing 

seeds and receptacle tissue throughout summer. Larvae are white, grub-like, and 

can be up to 5 mm long. Pupation occurs within capitula; adults emerge in late 

summer and early fall and overwinter in soil litter. There is one generation per year.

HISTORY AND CURRENT STATUS: Accidental introduction recorded in 

the USA by 1968 and Canada by 1988. Intentionally redistributed within the 

USA. Established MT, OR, WA (USA) and AB, BC (Canada). Attacks numerous 

native thistle species; damage to natives often exceeds damage to exotics. Not 

approved for redistribution in the USA.

Ivo Tosevski, CABI-Switzerland

Alec McClay, McClay Ecoscience
Biological Control OF WEEDS in the Northwest 129thistles

Puccinia carduorum Jacky

(Pucciniomycetes: Pucciniales)

DESCRIPTION AND LIFE CYCLE: 

Overwintering teliospores germinate in 

spring. Basidiospores infect rosettes and 

bolting plants. Urediospores are the most 

characteristic, being gold brown, covered 

in short spines, round and tiny (25 μ). 

Spores occur in mass clusters (pustules) on infected leaves. Pustules are reddish 

brown and powdery. Urediospores are easily blown 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, USA by 1951. It is specific to that 

species and established in CA and OR, though its overall impact is unknown. A 

new strain was introduced on musk thistle in VA in 1987 for experimental field 

release but quickly spread and is now present and widespread in CA, MT and 

WY. It is specific to C. nutans subsp. leiophyllus on which it reduces seed set and 

quality. Neither strain is approved for redistribution in the USA.

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, grub-like, and up to 6 mm long. Pupa overwinter in capitula; there is one 

generation per year. 

HISTORY AND CURRENT STATUS: Accidental introduction discovered 

on Canada thistle in the USA and Canada by 1873. Populations are generally 

limited. Larvae destroy some seeds, but overall impact is minimal. Not approved 

for redistribution in the USA.

Thistles, Unapproved Agents

USDA ARS, www.bugwood.org

Peter Harris, Agriculture and Agri-Food 

Canada
130 Biological Control OF WEEDS in the Northwest BroomSYNONYMS: broom; Cytisus scoparius (L.) Link subsp. scoparius, Sarothamnus 

scoparius (L.) Wimm. ex W. D. J. Koch

ORIGIN: Introduced as an ornamental from Europe to North America prior to 

1850.

DESCRIPTION: Woody shrub typically growing from 3-10 ft tall (1-3 m) 

from a forked taproot. It can be prostrate or erect, and has numerous slender, 

dark green branches that are capable of photosynthesis. Stems are hairy when 

young and less so as the plant ages. Leaves are alternate and three-parted, and 

are deciduous early in the season and in times of stress. Flowers are yellow, in 

clusters of two, and are characteristic of the pea family by having petals form 

a banner and keel (similar to a boat). Seed pods can grow up to 3 in long (71⁄2 

cm); they are flattened and have hair on the margins, turning brown at maturity.

 

HABITAT: Widespread along the Pacific coast. It is particularly problematic in 

b

Scotch broom

Cytisus scoparius (L.) Link

a) plant, b) infestation (both Jennifer Andreas, Washington State University Extension)

a
Biological Control OF WEEDS in the Northwest 131Broom

c) leaves (Tom Heutte, Forest Service, www.bugwood.org), d) flower (Jennifer Andreas, Washington 

State University Extension), e) seed pods (Wendy DesCamp, Washington State Noxious Weed 

Control Board)

pastures, forests, and wastelands with moister soils. Favors full sunlight.

ECOLOGY: Spreads by seed only, but can also regenerate from the root crown 

after cutting the stem. Seedlings begin flowering at two years and continue 

to grow for 25-30 years. Flowering usually occurs in early spring though an 

occasional plant may bloom in late summer. When seed pods mature and dry, 

their opening event may scatter seeds great distances. Pods with seeds are also 

easily transported by humans, birds, and other animals. Seeds may remain viable 

for more than 60 years. 

APPROVED BIOLOGICAL CONTROL AGENTS: USA: Bruchidius 

villosus, Exapion fuscirostre and Leucoptera spartifoliella.

NOTES: Fire may encourage resprouting from 

root crowns.

Family Fabaceae

c d e

Cytis

scopa
132 Biological Control OF WEEDS in the Northwest BroomHISTORY IN THE NORTHWEST: Leucoptera spartifoliella was the first 

biological control agent utilized against Scotch broom in North America. Though 

released in the USA in 1960, it was found to have already been inadvertently 

established in the Pacific Northwest. Exapion fuscirostre was subsequently 

released in the USA in 1964. An adventive species, Bruchidius villosus, was 

subsequently approved through the proper channels and redistributed in the 

Pacific Northwest from 1998. Both E. fuscirostre and B. villosus spread naturally 

from the USA to Canada. 

CURRENT STATUS: USA: Success has not been achieved in the broom 

biocontrol program to date. All three agents established in the Northwest. 

E. fuscirostre is moderately abundant on Scotch broom however its impact is 

typically minor, and it appears to be outcompeted by B. villosus where both cooccur. Populations of B. villosus are increasing on Scotch broom in the Pacific 

Northwest. Seed destruction can be high at times, which limits the rate of spread 

of weed populations. It remains unclear whether this will be sufficient to affect 

stand density in the long term, but studies are underway to measure impact. 

Leucoptera spartifoliella is hindered by heavy parasitism. Where high densities 

exist, the agent can cause stem dieback, though existing weed stands are not 

decreased. Furthermore, plants often re-grow below the sites of damage. CAN: 

No species were intentionally released in Canada for the control of Scotch 

broom. The two broom seed-feeders spread naturally from the USA, though 

their impact and abundance remain unknown.

RECOMMENDATIONS: USA: Neither E. fuscirostre or L. spartifoliella 

cause sufficient damage to Scotch broom populations to warrant widespread 

redistribution. In addition, the high parasitism rates plaguing L. spartifoliella 

preclude its movement. It is too early to determine if B. villosus will have lasting 

impact, though populations are increasing and efficacy studies are currently 

underway. In the meantime, redistributions are recommended by collecting 

adults in early spring for releases at sites with no other control programs in effect. 

CAN: Broom biological agents established in Canada were not originally 

introduced via the proper channels.

Broom Biological Control
Biological Control OF WEEDS in the Northwest 133Broom

Bruchidius: Jennifer Andreas, Washington State University Extension, Exapion: Laura Parsons, 

University of Idaho, Leucoptera: Eric Coombs, Oregon Department of Agriculture, www.bugwood.

org

Agent Adult Impact Recommendation

Bruchidius 

villosus

Seed-feeding may help reduce 

rate of spread of population 

but doesn’t affect existing 

stands. Overall impact 

unknown.

Populations increasing and 

impact studies underway. 

Recommended for 

redistribution. Not intentional 

in CAN. 

Exapion 

fuscirostre

Seed-feeding may help reduce 

rate of spread of population 

but doesn’t affect existing 

stands. Overall impact 

limited.

Low impact makes low priority. 

May be more effective with 

complementary control methods 

and high plant competition. 

Not intentional in CAN. 

Leucoptera 

spartifoliella

Stem-mining can cause stem 

dieback, but plants often 

recover. Many populations 

heavily parasitized.

Already widely distributed. Not 

recommended for continued 

extensive use due to low impact; 

populations heavily parasitized. 

Not released in CAN.
134 Biological Control OF WEEDS in the Northwest BroomDESCRIPTION: Eggs are tiny, white, and oval-shaped. Larvae are an off-white 

color with brown head capsules. and can reach up to 2 mm in length. Adults can 

also be up to 2 mm long. They have gray-black bodies, antennae, and legs. Both 

their elytra and snouts are short.

Bruchidius villosus (Goeze)

Broom seed beetle

Bruchidius villosus: a) four eggs on a Scotch broom seed pod, b) larva feeding completely within the 

middle seed, c) adult (all Jennifer Andreas, Washington State University Extension)

LIFE CYCLE: Adults emerge from overwintering (away from the host plant) in 

spring when broom begins to flower. Eggs are laid on the pod, with hatching 

larvae burrowing in and feeding on developing seeds. A single larva will develop 

through four instars completely within an individual seed and then pupate 

within the seed coat. New adults emerge in late summer, leaving behind round 

emergence holes in seeds. Adults do not chew their way out of the pod, instead 

relying on the pod to split naturally at maturity (in order to spread its seeds). 

There is one generation per year.

DAMAGE: Larval feeding on developing seeds reduces viable seed production, 

leading to possible decreases in the rate of weed spread.

PREFERRED HABITAT: Does best in meadows or on hillsides with southern 

exposure. May perform poorly in heavily shaded, cold, high elevation, and/or 

damp sites.

HISTORY: Native to Europe and unintentionally introduced to the eastern USA. 

First recorded in MA in 1918 but spread along the east coast. Unintentional 

populations were tested for host specificity following USDA-APHIS TAG 

protocols and then deliberately transferred from NC to OR, WA onto Scotch 

broom beginning in 1998. Spread naturally from there to BC, Canada by 2001.

a b c
Biological Control OF WEEDS in the Northwest 135Broom

CURRENT STATUS: Widespread on Scotch broom in northwestern USA. 

Abundance is increasing but variable; 10-90% of pods are attacked, and 20-

80% of seeds are destroyed within attacked pods. Studies are continuing, but 

it is unclear if densities and attack rates are high enough yet to decrease plant 

populations. Parasitism is typically low but may limit populations in some 

regions. This species appears to outcompete E. fuscirostre at sites where they both 

occur. In Canada, abundance and impact are unknown, though it is more active 

than the other adventive Scotch broom agent, E. fuscirostre.

REDISTRIBUTION: Best collected in the adult stage using a beat net and 

racket with an aspirator during early spring when plants start flowering and 

producing seed pods. Can then be transferred to uninfested sites in groups of 

100-200. Establishment can be monitored the following growing season by 

observing adults on foliage and flowers or by dissecting seed pods to find larvae 

feeding within seeds. Note that first instar larvae can be difficult to differentiate 

from E. fuscirostre.

NOTES: Late instar larvae of B. villosus can be differentiated from E. fuscirostre 

in that B. villosus larvae feed completely within broom seeds, to 

the extent their presence can be difficult to detect unless seeds 

are dissected. Contrary to this, E. fuscirostre larvae cause external 

feeding damage to seeds that is obvious when the pod is first 

opened. B. villosus was observed attacking French broom in OR, 

USA by 2001 and appears to be spreading, though its impact 

has not been determined. This agent was not an intentional 

introduction in Canada.

Coleoptera: Chrysomelidae

Bruchidius villosus: d) emerged adult and feeding damage, e) adult (right) compared to an adult 

Exapion fuscirostre (left) (both Jennifer Andreas, Washington State University Extension)

d e

Bruchid

villosus,

broom
136 Biological Control OF WEEDS in the Northwest BroomSYNONYMS: Apion fuscirostre Fabricius

DESCRIPTION: Eggs are small, white to yellowish, and round. Larvae are an 

off-white color with brown head capsules. They can be up to 21⁄2 mm in length 

while adults can be up to 3 mm. Adults have brown bodies with two long, dark 

gray bands that run down either side of their bodies (one on each side). Their 

snouts are long and curved, and they have light brown legs.

Exapion fuscirostre (Fabricius)

Scotch broom seed weevil

Exapion fuscirostre: a) larvae in seeds (Eric Coombs, Oregon Department of Agriculture), b) adult 

(Laura Parsons, University of Idaho) (both www.bugwood.org)

LIFE CYCLE: Adults emerge from overwintering in soil litter in early spring 

when broom begins to flower. Females must feed on broom flowers in order 

to produce eggs. Eggs are laid inside the pod, with hatching larvae feeding on 

developing seeds. Larvae feed half in and half out of attacked seeds, developing 

through four instars and pupating within the seed pod. New adults emerge in 

late summer. Adults do not chew their way out of the pod, instead relying on 

the pod to split naturally at maturity (in order to spread its seeds). There is 

one generation per year, though generations sometimes overlap as adults are 

frequently active year-round.

DAMAGE: Larval feeding on developing seeds reduces viable seed production, 

leading to decreases in the rate of spread of Scotch broom, though the overall 

efficacy of this species is questionable. Adult feeding causes terminal shoot 

dieback, but does not kill the plant.

PREFERRED HABITAT: Does best in meadows or on hillsides with southern 

exposure. Performs poorly in heavily shaded, cold, high elevation, and/or damp 

sites.

a b
Biological Control OF WEEDS in the Northwest 137Broom

HISTORY: Introduced from Italy and released on Scotch broom in the USA (CA, 

ID, OR, WA) from 1964. Spread naturally to BC, Canada by 2007.

CURRENT STATUS: Though moderately abundant on Scotch broom in the 

USA, impact is generally low. Observed seed reduction rates between 20-60% 

are insufficient to impart significant control of plant populations alone, but 

may contribute to a slowed rate of spread. Parasitism is typically low but may 

limit populations in some regions. This species appears to be outcompeted by 

B. villosus at sites where they both occur. In Canada, abundance and impact are 

unknown, though it is less active than the other adventive Scotch broom agent, 

B. villosus.

REDISTRIBUTION: This species is a lower priority for redistribution than B. 

villosus. Regardless, it is best collected in the adult stage using a beat net and 

racket with an aspirator during early spring when plants start flowering. Adults 

can then be transferred to uninfested sites in groups of 100-200. Establishment 

can be monitored the following growing season by observing adults on foliage 

and flowers or by dissecting seed pods to find larvae feeding within. Note that 

first instar larvae can be difficult to differentiate from B. villosus.

NOTES: Late instar larvae of E. fuscirostre can be differentiated from 

B. villosus in that E. fuscirostre larval feeding damage to seeds is 

obvious once pods are opened. B. villosus larvae feed completely 

within seeds so individual seeds must be dissected to confirm the 

species is present. This agent was not an intentional introduction 

in Canada.

Coleoptera: Brentidae

Exapion fuscirostre: c) adult feeding damage (Eric Coombs, Oregon Department of Agriculture), d) 

emerged adult and feeding damage (Jennifer Andreas, Washington State University Extension)

c d

Exapion

fuscirost

broom
138 Biological Control OF WEEDS in the Northwest BroomDESCRIPTION: Larvae are green-brown, appear somewhat flattened, and can 

reach 3-4 mm in length. Adults are small (5 mm long) and are seldom seen. 

They are white with white antennae, feathered wing tips, and have pale gold 

markings.

Leucoptera spartifoliella (Hübner)

Scotch broom twig miner

Leucoptera spartifoliella: a) pupa, b) adult (both Eric Coombs, Oregon Department of Agriculture, 

www.bugwood.org)

LIFE CYCLE: Adults lay eggs in late summer when broom is in the late-flowering 

stage. Larvae hatch and tunnel into young shoots to feed. Larvae develop through 

six instars over several months and overwinter in the stems of broom. Pupation 

occurs in spring, with adults emerging in late spring and early summer as broom 

flowers. There is one generation per year.

DAMAGE: Larval mining causes stem dieback, however, plants often re-sprout 

below sites of damage. 

PREFERRED HABITAT: Does best at low-elevation infestations with moderate 

temperature and ample moisture. 

HISTORY: Introduced from France and released on Scotch broom from 1960 

in the USA (CA, OR), but was found to have already been present in CA, 

OR and WA. It was likely imported on ornamental plants prior to 1940. Both 

populations have since intermixed and are no longer differentiated. 

CURRENT STATUS: Widespread in on Scotch broom in CA and OR (USA), 

but present at only limited sites in WA. High numbers can deform plants and 

cause stem dieback, but plant density is not affected. Because plants often regrow below sites of damage, overall impact is negligible. Populations are also 

a b
Biological Control OF WEEDS in the Northwest 139Broom

heavily parasitized and do not fare well in hot, dry sites.

REDISTRIBUTION: This species is a very low priority for redistribution. 

Because larvae are heavily parasitized, it is best to collect adults using light traps 

in spring as plants start flowering. These can be transferred in groups of 50-100 

to new infestations. The species is already widely distributed throughout the 

Northwest, however, so infestations should be checked for its presence prior to 

redistribution attempts. Established of transferred individuals can be monitored 

the following growing season by dissecting stems in search of feeding larvae. 

Adults are cryptic and rarely seen.

NOTES: This agent is not approved for release in Canada.

Lepidoptera: Lyonetiidae

Leucopt

spartifo

broom
140 Biological Control OF WEEDS in the Northwest Broom

Broom, Unapproved Agents

Three accidentally introduced species are established on broom in North America. 

It is illegal to intentionally move these species to new areas in the USA. Care 

should be taken when transferring approved agents to ensure that these unapproved 

species are not also included in transferred material.

Aceria genistae (Nalepa) 

(Acari: Eriophyidae)

DESCRIPTION AND LIFE CYCLE: 

All stages are tiny and best viewed with 

a microscope. Larvae and nymphs are 

pinkish-white and 0.10-0.12 mm long. 

Adults are light pink and have a wormlike appearance. They have two pairs of 

developed legs near their heads and can 

be 0.16-0.225 mm long. All stages feed 

on stem bud tissue by extracting sap from 

plant cells. This induces the development of galls 5-30 mm in diameter that 

serve as protective housing to hundreds of mites. Galls are the best indication 

of mite presence. As galls grow, they become more hairy until they senesce, at 

which time mites migrate to new buds to form new galls. Galls may develop 

faster and have greater impact at hot, dry sites. There can be several generations 

per year. Mite numbers appear to be greatly reduced during overwintering. All 

stages are capable of overwintering within new buds.

HISTORY AND CURRENT STATUS: Accidental introduction recorded 

on Scotch broom in OR and WA (USA) by 2005. Possibly established in CA. 

Abundant in WA where overall impact is medium as it reduces flowering and 

plant biomass and in some cases may cause stem and plant mortality. Widespread 

in OR but only abundant locally with slight impact. Currently undergoing host 

specificity testing in WA with the intent of future intentional redistribution, if 

approved. Identified only recently in BC, Canada (2010) where impact thus far 

is minor. Currently not approved for redistribution in the USA.

Galls: Jennifer Andreas, Washington State 

University Extension
Biological Control OF WEEDS in the Northwest 141Broom

Broom, Unapproved Agents

Agonopterix nervosa (Haworth)

(Lepidoptera: Oecophoridae)

DESCRIPTION AND LIFE CYCLE: 

Larvae emerge in early spring and feed on 

feed in lightly spun tubes of plant material 

on shoot tips of broom and gorse. Larvae 

vary in color from yellowish-gray to brown 

and can be up to 15 mm long. Adults are 

typically 10-15 mm long with variable 

coloring. Typical adults have white or yellowish wings with gray to brown small 

mottling, sometimes appearing as stripes on wing veins. Adults appear in early 

summer and are present throughout the growing season, sometimes overwintering. 

There is one generation per year.

HISTORY AND CURRENT STATUS: Accidental introduction recorded on 

gorse in BC, Canada by 1915. Spread to the USA in the 1920s. Attacks both 

Scotch broom and gorse in CA, NV, OR, WA (USA), though is more effective 

on gorse. May stunt shoots and reduce seed production, but overall impact is 

limited. Populations are heavily parasitized. Abundance and impact on gorse in 

BC are unknown. Not approved for redistribution in the USA.

Arytainilla spartiophila (Förster)

(Hemiptera: Psyllidae)

DESCRIPTION AND LIFE CYCLE: 

Overwintering eggs are embedded in 

broom stems beneath a waxy cap. Tiny, 

orangey-brown nymphs (<2 mm long) 

hatch in spring and crawl into new growth 

buds to feed. Nymphs grow through five 

instars before developing into pale brown 

aphid-like adults (2–3 mm long) with clear wings. Adults feed on new growth, 

lay eggs, and die before winter. There is one generation per year.

HISTORY AND CURRENT STATUS: Accidental introduction recorded on 

Scotch broom in WA, USA in 1935. Now widespread in CA, OR, WA. High 

densities may weaken plants stressed from competition, making them vulnerable 

to pathogens. Overall impact likely limited. Their honeyew interferes with lateseason collections of other agents. Not approved for redistribution in the USA.

© Donald Hobern, Canberra, Australia

Landcare Research Ltd., New Zealand
142 Biological Control OF WEEDS in the Northwest Gorse

a) plant, b) infestation (both Wendy DesCamp, Washington State Noxious Weed Control Board)

SYNONYMS: furze

ORIGIN: Native to western Europe; introduced in the late 1800s as an ornamental 

or hedge plant to contain livestock, but soon escaped cultivation

DESCRIPTION: Woody shrub that typically grows 3-13 ft tall (1-4 m) from 

a woody, multi-branched root system. It can be prostrate or erect, and has 

numerous angular branches that end in spines. Stems are hairy when young and 

less so as the plant ages. Leaves are alternate and three-parted when the plant 

is young and are reduced to scales or thick spines as the plant ages. Flowers are 

yellow and occur either singly in leaf axils or in numerous clusters on the ends of 

older branches. Flowers are characteristic of the pea family by having petals form 

a banner and keel (similar to a boat). Seed pods are hairy, turning black with age. 

They grow to 0.8 in long (2 cm).

 

b

Gorse

Ulex europaeus L.

a
Biological Control OF WEEDS in the Northwest 143Gorse

HABITAT: Widespread along the Pacific coast. It is particularly problematic in 

open or disturbed places, especially roads, abandoned or overgrazed pastures, 

old agricultural fields, and sand dunes.

ECOLOGY: Spreads by seed only, but can also regenerate from the root crown 

after cutting the stem. Seedlings begin flowering at two years and continue to 

grow for 25-30 years. Flowering occurs in early spring with a smaller secondary 

bloom in late fall in some locations. When seed pods mature, they dry out and 

open rapidly, which may scatter seeds great distances. Pods with seeds are also 

easily transported by humans, birds, and other animals. Seeds may remain viable 

for 20 years. 

APPROVED BIOLOGICAL CONTROL 

AGENTS: USA: Exapion ulicis and Tetranychus 

lintearius

NOTES: Highly flammable with an oil content 

of 2 to 4%.

Family Fabaceae

c d e

c) leaves (Jennifer Andreas, Washington State Univrsity Extension), d) open flower (Wendy 

DesCamp, Washington State Noxious Weed Control Board), e) seed pods (Forest & Kim Starr, Starr 

Environmental GROUP www.bugwood.org)

Ulex

europ
144 Biological Control OF WEEDS in the Northwest GorseHISTORY IN THE NORTHWEST: Two agents have been released against 

gorse in the USA since 1953 (E. ulicis 1953 and Tetranychus lintearius 1994). 

Neither was released in Canada.

CURRENT STATUS: USA: Success has not been achieved in the gorse 

biocontrol program. Both of the agents released established in the Northwest. 

Exapion ulicis is moderately abundant on gorse, however its impact is typically 

minor. While seed destruction can be high at times, this at best limits the rate of 

spread of weed populations, but does not affect existing stand density. At many 

sites, seed predation is too low to have any noticeable impact, and gorse seed 

maturing in autumn/winter escapes attack completely. The gorse spider mite 

was initially widely distributed, causing a significant reduction of flowering. 

Populations have since been hindered by heavy predation such that it is now 

considered an ineffective agent. CAN: No species were intentionally released 

in Canada for the control of gorse.

RECOMMENDATIONS: USA: None of the agents currently established have 

provided significant long-term impact to gorse. Due to the high predation 

rates plaguing T. lintearius on gorse, it is not a high priority for redistribution. 

Exapion ulicis could be redistributed to uninfested sites, but due to its low 

efficacy, this should likely only occur at sites where additional control methods 

will be employed or high plant competition exists. Keep in mind alternative 

control methods damaging gorse seed pods will also damage E. ulicis. CAN: 

Gorse biological agents have not been released in Canada, and neither are 

currently established there.

Gorse Biological Control
Biological Control OF WEEDS in the Northwest 145Gorse

Exapion: Forest and Kim Starr, Starr Environmental, www.bugwood.org, Tetranychus: Rich Lee, San 

Juan County Noxious Weed Board

Agent Adult Impact Recommendation

Exapion 

ulicis

Seed-feeding may help reduce 

rate of spread of population 

but doesn’t affect existing 

stands. Late seeds escape 

attack. Overall impact limited.

Low impact, so low priority of 

redistribution. Should only be 

used with other control methods 

and/or high competition. Not 

released in CAN. 

Tetranychus 

lintearius

Stem- and foliage-feeding 

reduces flowering, decreasing 

weed rate of spread Severely 

attacked plants killed. Mites 

now heavily preyed upon.

Not recommended for 

continued extensive use as 

populations heavily preyed 

upon. Not released in CAN.
146 Biological Control OF WEEDS in the Northwest GorseSYNONYMS: Apion ulicis (Forster)

DESCRIPTION: Eggs are round, small, and translucent yellow. Larvae are cream 

colored, C-shaped, and can reach 3 mm in length. Adults are gray with very 

long, curved snouts and brownish gray legs. Faint stripes are sometimes apparent 

on their elytra, and they are typically 2-3 mm long.

Exapion ulicis (Forster)

Gorse seed weevil

Exapion ulicis: a) larvae and damage (George Markin, USDA Forest Service) b) adult (Forest and Kim 

Starr, Starr Environmental) (both www.bugwood.org)

LIFE CYCLE: Adults emerge from overwintering during early spring and deposit 

eggs into young seed pods. Larvae hatch in late spring and early summer and 

feed on developing seeds. They develop through four instars. Pupation occurs in 

seed pods, with adults emerging in late summer. Adults feed on spines and stems 

of gorse and then overwinter. There is one generation per year.

DAMAGE: Larval seed-feeding may reduce the rate of spread of gorse. Adult 

feeding leads to destruction of stem tissue but without significantly harming the 

plant.

PREFERRED HABITAT: Does best in open, sunny sites with dense plants. 

Distribution is limited in regions with cold winters, shade, only scattered host 

plants, and in salt spray zones along the coast.

HISTORY: Introduced from England and released on gorse in CA, OR, WA 

(USA) from 1953. 

CURRENT STATUS: Widespread and abundant on gorse in northwestern 

USA, though overall impact is limited. From 30-95% of seed pods are attacked. 

a b
Biological Control OF WEEDS in the Northwest 147Gorse

This does not reduce established stand density. It may at best slow the rate of 

spread of the weed, however it is ineffective on seed maturing in autumn/winter.

REDISTRIBUTION: Best collected in the adult stage using a beat net and 

racket with an aspirator during early spring when plants start flowering. Can 

then be transferred to uninfested sites in groups of 100-200. Establishment can 

be monitored the following growing season by observing adults on foliage and 

flowers or by dissecting seed pods to find larvae feeding within. 

NOTES: This agent is not approved for release in Canada.

Coleoptera: Brentidae

Exapion 

gorse
148 Biological Control OF WEEDS in the Northwest GorseDESCRIPTION: Eggs are tiny, round, and largely transparent. First stage (or 

larval mites) are light in color and have six legs. Second to fourth stage (nymphal) 

mites have eight legs, are brown, and resemble small adults. Adults also have 

eight legs, are brick red in color, and are up to 2 mm long.

Tetranychus lintearius (Dufour)

Gorse spider mite

LIFE CYCLE: Adults form a colony with large amounts of webbing on the 

terminal branches of gorse. Females lay eggs year-round on infested shoots. 

Hatching mites complete four immature stages, with larvae and nymphs feeding 

on plant tissue. Adults feed on stems and spines and live up to four weeks. There 

are up to six generations per year, with all stages capable of overwintering.

DAMAGE: Larval, nymphal, and adult feeding stunts branch growth and reduces 

flowering, thus contributing to a reduction in the spread of gorse. Heavily 

infested plants are killed by the extensive feeding.

PREFERRED HABITAT: Does best in warm, open gorse patches and away from 

the ocean. Damp, ocean-side infestations or heavily shaded forest patches are 

seldom attacked. Can be somewhat cold hardy, but severe winter temperatures 

limit populations. 

HISTORY: Introduced from England, Portugal, and Spain via New Zealand and 

released on gorse in CA, OR and WA (USA) from 1994. 

CURRENT STATUS: Initially widely distributed on gorse in the western USA, 

even leading to an 80% reduction in flowering in OR. Was most effective in 

open patches in inland areas susceptible to severe winters. Populations have since 

decreased significantly due to heavy predation by beetles and predatory mites. It 

Tetranychus lintearius: a) adults, b) webbing with mass of adults (a,b Rich Lee, San Juan County Noxious 

Weed Board), c) large infested gorse patch (Eric Coombs, Oregon Department of Agriculture)

a b c
Biological Control OF WEEDS in the Northwest 149Gorse

is now considered an ineffective agent.

REDISTRIBUTION: Best redistributed by clipping infested branches and 

transferring them to uninfested gorse. This can be done throughout the growing 

season. Establishment can be monitored the same season or in following years 

by observing new tent webbing on infected plants.

NOTES: This agent is not approved for release in Canada.

Acari: Tetranychidae

Tetranyc

linteariu

gorse
150 Biological Control OF WEEDS in the Northwest Gorse

Gorse, Unapproved Agents

Agonopterix nervosa (Haworth)

(Lepidoptera: Oecophoridae)

DESCRIPTION AND LIFE CYCLE: 

Larvae emerge in early spring and feed 

on feed in lightly spun tubes of plant 

material on shoot tips of gorse and 

Scotch broom. Larvae vary in color from 

yellowish-gray to brown and can be 

up to 15 mm long. Adults are typically 

10-15 mm long with variable coloring. 

Typical adults have white or yellowish wings with gray to brown small mottling, 

sometimes appearing as stripes on wing veins. Adults appear in early summer and 

are present throughout the growing season, sometimes overwintering. There is one 

generation per year.

HISTORY AND CURRENT STATUS: Accidental introduction recorded on 

gorse in BC, Canada by 1915. Spread to the USA in the 1920s. Attacks both 

Scotch broom and gorse in CA, NV, OR, WA (USA), though is more effective 

on gorse. May stunt shoots and reduce seed production, but overall impact is 

limited. Populations are heavily parasitized. Abundance and impact on gorse in 

BC are unknown. Not approved for redistribution in the USA.

© Donald Hobern, Canberra, Australia
Biological Control OF WEEDS in the Northwest 151Gorse
152 Biological Control OF WEEDS in the Northwest hawkweeds SYNONYMS: Grim the Collier, devil’s paintbrush; Hieracium aurantiacum L.

ORIGIN: Native to Europe. Introduced to North America by 1875 as a garden 

ornamental.

DESCRIPTION: An upright perennial typically growing 10-24 in (25-60 cm) 

tall from a fibrous root system. Plants produce short rhizomes as well as stolons 

that extend 4-12 in (10-30 cm) and form the next generation of plants. Stems 

are largely unbranched until the tips, which end in 5-30 capitula. Leaves (up to 

5 in or 13 cm long) typically occur only in a basal rosette, though 1 or 2 smaller 

leaves may occur on the plant stem. Stems and leaves are covered with stiff hairs 

that can be simple, glandular, and/or star-shaped. The entire plant contains a 

milky latex. Capitula are 1⁄2-1 in (1-21⁄2 cm) in diameter and contain reddishorange florets (all ray). Seed head bracts are covered in glandular hairs. Seeds 

(achenes) are topped by tufts of pappus, resembling dandelion seeds. 

 

b

Orange hawkweed

Pilosella aurantiaca (L.) F. W. Schultz & Sch. Bip.

a) plant (Howard F. Schwartz, Colorado State University), b) infestation (Forest and Kim Starr, Starr 

Environmental) (both www.bugwood.org)

a
Biological Control OF WEEDS in the Northwest 153hawkweeds

c) leaves (with leaflets), d) flower (Steve Dewey, Utah State University), e) mature seeds (© Keir 

Morse, www.keiriosity.com)

HABITAT: Prefers full sun or partial shade and soils that are well drained and 

coarse-textured. Dense infestations often occur in moist meadows, pastures, hay 

fields, roadsides, gravel pits, forested areas, tree plantations and riparian areas.

ECOLOGY: Reproduces by seed, stolons, and short rhizomes. Plants germinate 

in spring and flower from mid- to late summer. Seeds are transported by wind, 

water, or adhering to clothing or fur, and are often moved in contaminated soil 

associated with transplanting new plants into gardens and flower beds. Seeds 

remain viable in soil for up to 7 years. Stolons elongate throughout summer, 

forming daughter rosettes at their tips. Once daughter plants root, the stolons 

die, and the new plant becomes independent. After flowering, the supporting 

rosette dies. New plants sprout each year from rhizomes.

APPROVED BIOLOGICAL CONTROL AGENTS: USA and CAN: 

Aulacidea subterminalis

NOTES: Several studies suggest the plant may 

have allelopathic properties, inhibiting the 

growth or function of competing species.

Family Asteraceae

c d e

Pilosella 
154 Biological Control OF WEEDS in the Northwest hawkweeds SYNONYMS: Hieracium flagellare Willd., Hieracium ×flagellare Willd. (pro sp.) 

[caespitosum × pilosella]

ORIGIN: Native to Europe. Year of first introduction to North America unknown.

DESCRIPTION: Due to the current confusion and taxonomic flux of hawkweeds 

in North America (see following pages), the following description may only 

apply to some populations of whiplash hawkweed: An upright perennial 

typically growing 21⁄2-8 in (6-20 cm) tall from a fibrous root system. Plants 

produce rhizomes as well as long, leafy stolons which form the next generation 

of plants. Stems are largely unbranched until the tips, which end in 2-6 capitula. 

Leaves typically only occur in a basal rosette. The green leaves are slightly narrow 

at their bases and more broad toward their tips, usually growing 1-2 in (21⁄2-5 

cm) long. Leaves have dense hairs (both simple and star-shaped) along their 

margins and underside midveins. Stem hairs are simple and star-shaped near 

b

Whiplash hawkweed

Pilosella flagellaris (Willd.) Arv.-Touv.

a) plants from side view, b) infestation from above (both Rosemarie De Clerck-Floate, Agriculture 

and Agri-Food Canada)

a
Biological Control OF WEEDS in the Northwest 155hawkweeds

c) leaves, d) flower heads, e) underside of flower heads (all Rosemarie De Clerck-Floate, Agriculture 

and Agri-Food Canada)

the base, becoming glandular near the capitulum. The entire plant contains a 

milky latex. Capitula are typically 1⁄2-1 in (1.3-21⁄2 cm) in diameter and contain 

yellow florets (all ray). Florets often have a red stripe on their undersides. Seed 

head bracts are covered in star-shaped and/or glandular hairs. Seeds (achenes) 

are topped by tufts of pappus, resembling dandelion seeds. 

 

HABITAT: Does well in full sun or partial shade. Can be found in dense 

infestations in disturbed sites, roadsides, and forest edges.

ECOLOGY: Reproduces by seed, stolons, and short rhizomes. Plants germinate in 

spring and flower in late spring or early summer. Seeds are transported by wind, 

water, or adhering to clothing or fur, and are often moved in contaminated 

soil associated with transplanting new plants into gardens and flower beds. 

Stolons elongate throughout summer, forming daughter rosettes at their tips. 

Once daughter plants root, the stolons die, 

and the new plant becomes independent. After 

flowering, the supporting rosette dies. New 

plants sprout each year from rhizomes.

APPROVED BIOLOGICAL CONTROL 

AGENTS: USA and CAN: Aulacidea subterminalis

NOTES: This species likely resulted from a cross 

between plants of Pilosella caespitosa (meadow 

hawkweed) and P. officinarum (mouse-ear 

hawkweed). It is part of the P. flagellaris 

collective, which also includes P. macrostolona 

and P. prussica.

Family Asteraceae

c d e

Pilosella 
156 Biological Control OF WEEDS in the Northwest hawkweeds There are several hawkweeds presently established in North America, including 

both native and introduced species as well as hybrids. Identification can be 

difficult, which is compounded by the current state of taxonomic flux for members 

of this group. Morphometric and molecular studies are underway. To date only 

one biocontrol agent has been approved for use in North America, Aulacidea 

subterminalis. Though this species is approved for use against orange, whiplash, 

mouse-ear and king devil hawkweed, to date (April 2014) it has only been released 

against orange and whiplash hawkweed in North America. Consequently only 

these two hawkweed species are described in this field guide.

HISTORY IN THE NORTHWEST: Biological control of hawkweeds began 

in New Zealand where five biocontrol agents have been intentionally introduced 

since 1997. The early work conducted in New Zealand paved the way for testing 

undertaken later for North America. However, because North America has 

several native species related to exotic hawkweeds (unlike New Zealand), many 

of the previously tested agents were found unsafe for introduction to North 

America. The gall wasp Aulacidea subterminalis has thus far been the only species 

found safe to introduce. It was imported from Switzerland and released in both 

the USA (MT) and Canada (BC) on orange hawkweed from 2011. It was also 

released on whiplash hawkweed in BC repeatedly since 2011. 

CURRENT STATUS: Establishment has yet to be officially confirmed in the 

USA or Canada, but release and monitoring programs in both countries remain 

active. Orange hawkweed is not its preferred host, so Canadian releases after 

2011 have been and will continue to be focused on whiplash hawkweed.

RECOMMENDATIONS: USA and CAN: Additional releases should be made 

utilizing laboratory populations to increase the chance of establishment. Contact 

local biocontrol or weed authorities for information on agent availability.

Hawkweed Biological Control
Biological Control OF WEEDS in the Northwest 157hawkweeds

Aulacidea subterminalis photo Ghislaine Cortat, CABI-Switzerland

Agent Adult Impact Recommendation

Aulacidea 

subterminalis

Establishment yet to be 

officially confirmed in USA 

or CAN. In native range, 

galling reduces vegetative 

reproduction.

Additional releases from lab 

populations recommended 

to increase chance of 

establishment.
158 Biological Control OF WEEDS in the Northwest hawkweeds DESCRIPTION: Eggs are tiny and milky-white. Larvae are creamy white and 

are typically 2-3 mm long. Adults are small (2-3 mm long) with bulbous bodies. 

They have a brown abdomen and legs, while the thorax and head are typically 

brownish-black. Antennae are long and brown, and the wings are transparent 

with darker veins.

Aulacidea subterminalis Niblett

Hawkweed gall wasp

Aulacidea subterminalis: a) larvae in galls, b) adult (Ghislaine Cortat, CABI-Switzerland), c) adult 

ovipositing (a, b Gitta Grosskopf, CABI-Switzerland)

LIFE CYCLE: Overwintering larvae pupate within galls in early spring. Emerging 

adults lay eggs inside hawkweed stolon tips. This species of wasp is able to lay 

eggs without fertilization, so there are no males. Hatching larvae feed within 

the stolons throughout summer. Larval feeding induces the formation of fleshy 

green galls. Larvae remain in galls through autumn and winter. By spring, the 

galls dry out and turn brown, and larvae pupate within them. There is one 

generation per year.

DAMAGE: Galling reduces stolon growth, which reduces the vegetative 

reproduction of the plant by decreasing the number of daughter plants. 

PREFERRED HABITAT: Specific habitat requirements for this species are 

unknown.

HISTORY: Introduced from Switzerland and released on orange hawkweed 

in both the USA (MT) and Canada (BC) from 2011. It was also released on 

whiplash hawkweed in BC, Canada repeatedly from 2011.

CURRENT STATUS: Establishment has yet to be officially confirmed in the 

USA or Canada, but release and monitoring programs in both countries remain 

active. Orange hawkweed is not its preferred host, so Canadaian releases after 

2011 have been and will continue to be focused on whiplash hawkweed.

a b c
Biological Control OF WEEDS in the Northwest 159hawkweeds

REDISTRIBUTION: New releases should be made in both the USA and 

Canada, utilizing laboratory material where possible. When field populations 

are confirmed established and increase sufficiently to warrant redistribution, 

galls can be collected in late fall and transferred to sheltered positions in new 

hawkweed infestations. Galls are best transferred in groups of 100 or more. 

Establishment can be monitored the following growing season by observing galls 

on new hawkweed stolon growth. 

NOTES: In addition to orange and whiplash hawkweed, Aulacidea subterminalis 

is also approved for use against king devil (Pilosella ×floribunda) and mouse-ear 

hawkweed (Pilosella officinarum) in North America. To date (April 2014), neither 

of these hawkweed species has been targeted for release. A. subterminalis does not 

occur naturally on king devil hawkweed in its native Europe so is not believed to 

be an ideal host in North America. Though the wasp readily attacks mouse-ear 

hawkweed, this weed presently only occurs in small, isolated patches in BC so is 

being targeted with other control methods. Whiplash and mouse-ear hawkweed 

are also not overly abundant in the Northwest of the USA, but infestations of 

both (and especially mouse-ear) may be targeted for A. subterminalis release in 

the near future. 

? ? Hymeoptera: Cynipidae

orange whiplash

Aulacidea

subterminalis,

Orange

hawkweed

Aulacidea

subtermin

Whiplash

hawkweed
160 Biological Control OF WEEDS in the Northwest puncturevine SYNONYMS: caltrop, goat head

ORIGIN: Native to the Mediterranean, western Asia and Africa. Introduced to 

North America accidentally along with livestock by 1900.

DESCRIPTION: A prostrate annual plant growing from a taproot. The stems 

radiate from the crown, typically growing 2-7 ft (60-200 cm) in diameter to 

form a mat along the ground. Stems vary from green to reddish-brown and 

are somewhat hairy. The leaves are opposite and compound with 4-8 pairs of 

elliptical leaflets. The leaflets are typically dark green and hairy along margins. 

Leaflets are often 1⁄4-1⁄2 in (5-12 mm) long. Flowers appear in leaf axils, where 

leaves attach to stem branches. They have 5 lemon-yellow petals and are typically 

less than 1⁄2 in (12 mm) in diameter. Mature fruits break apart into 5 burs, each 

containing 1-4 seeds. Burs are bony and each armed with 2-4 rigid spines.

 

HABITAT: Often occurs in dense mats along areas of disturbance, including crop 

b

Puncturevine

Tribulus terrestris L.

a) plant, b) infestation (both Jennifer Andreas, Washington State University Extension)

a
Biological Control OF WEEDS in the Northwest 161puncturevine

c) leaves (with leaflets), d) flower (c,d Jennifer Andreas, Washington State University Extension), e) 

fruits (Steve Hurst, USDA NRCS PLANTS Database, www.bugwood.org)

margins, pastures, corrals, roadways, sidewalks and vacant lots. Seems to prefer 

semi-arid and Mediterranean-like climates.

ECOLOGY: Reproduces by seed only. Plants germinate in spring and summer 

with sufficient soil moisture and warm temperatures. The plant quickly grows a 

deep taproot that enables it to tolerate dry soils after establishment. Flowering 

occurs as quickly as 3 weeks after germination, and continues throughout 

summer. The sharp spines of burs readily puncture and adhere to tires, clothing, 

feet and fur, transporting seeds great distances. Seeds typically stay viable for 5 

years, though some reports claim up to 20 years.

APPROVED BIOLOGICAL CONTROL AGENTS: USA and CAN: 

Microlarinus lareynii, Microlarinus lypriformis

NOTES: The sharp spines on fruits are injurious 

to humans and livestock, interfere with 

agricultural harvesting, and lower the quality of 

seed, feed, and wool.

Family Zygophyllaceae

c d e

Tribulus 
162 Biological Control OF WEEDS in the Northwest puncturevine HISTORY IN THE NORTHWEST: Both the weed weevil, Microlarinus 

lareynii, and the stem miner, M. lypriformis, were introduced from Italy and 

released throughout the USA from 1961. Several redistributions followed, often 

involving a mixture of the two species. After initial releases failed to establish 

in some cold climates, a second introduction was made using a population of 

both species from the Abruzzi Mountains, Italy. These individuals were released 

in more northern areas of CA, but failed to establish. A population containing 

both species was collected from CO (USA) and redistributed to CAN (BC) in 

1986, but failed to establish. 

CURRENT STATUS: Both species are established with variable densities on 

puncturevine in the USA. In combination, they have successfully reduced 

puncturevine cover and seed production up to 80% in warmer areas of the 

southwest USA. They are generally ineffective at higher elevations and higher 

latitudes where cold winter temperatures reduce weevil abundance and impact. 

Recent redistribution efforts within CA successfully established a population 

of both species at one high elevation site, indicating establishment is possible 

when sites have overwintering shelter and limited disturbance. M. lareynii is 

much more successful at high elevation sites compared to M. lypriformis, and 

is established in limited amounts in WA and OR whereas M. lypriformis is not, 

indicating a higher cold tolerance by M. lareynii. Populations of both species 

are limited by parasites and predators at some sites. Both species have been 

observed attacking the native Kallstroemia californica, K. grandiflora, and 

one additional native Kallstroemia species. Adults have been found on 

numerous exotic species (some of economic importance), though impact is 

typically negligible.

RECOMMENDATIONS: USA: Redistribution of both species is recommended 

for warmer climate sites where they are not already established. Adults of both 

can be collected in fall or spring from the soil litter beneath plants using a 

vacuum or aspirator. They should be transferred in groups of 100-200. They are 

less recommended for release at cold sites where they are unlikely to establish 

or have great impact. If other control options are not feasible at cold climate 

sites, M. lareynii is more highly recommended than M. lypriformis, and emphasis 

should be placed on choosing sites with sufficient overwintering shelter and 

limited disturbance. Both weevil species should not be released where native 

Kallstroemia species occur. 

Puncturevine Biological Control
Biological Control OF WEEDS in the Northwest 163puncturevine

Microlarinus lareynii: Jennifer Andreas, Washington State University Extension, M. lypriformis: USDA 

ARS European Biological Control Laboratory, USDA ARS-European Biological Control Laboratory 

(both www.bugwood.org)

Agent Adult Impact Recommendation

Microlarinus 

lareynii

Established USA only. 

Larval feeding destroys 

seeds, reducing puncturevine 

population spread. Largely 

limited by cold climates

Recommended in warm 

climates; low priority for cold.

Should not be used near native 

Kallstroemia species.

Microlarinus 

lypriformis

Established USA only. Stemmining weakens plant vigor, 

causes stem breakage, reduces 

seed production. Largely 

limited by cold climates

Recommended in warm 

climates; not recommended for 

cold. Should not be used near 

native Kallstroemia species.
164 Biological Control OF WEEDS in the Northwest puncturevine DESCRIPTION: This species is very similar to Microlarinus lypriformis. Eggs are 

dark yellow and cylindrical. Larvae are C-shaped with white to yellow-brown 

bodies and dark brown head capsules. Pupae are creamy white and up to 41⁄2 

mm long. Adults are a mottled brown and covered with erect grayish hairs that 

make them appear shaggy. Adults are typically 4-5 mm long and have short, 

broad snouts. 

Microlarinus lareynii (Jacquelin du Val)

Puncturevine seed weevil

LIFE CYCLE: Adults emerge in spring and feed on puncturevine stems, leaves, 

and flowers. Females chew pits in young fruits and lay eggs before sealing the pit 

with a dark cement. Hatching larvae feed on seeds and fruit tissue, developing 

through four instars. They pupate within their feeding cell inside attacked 

fruits. New adults typically emerge within five days; the period from egg to 

adult frequently takes 25-30 days. In warm climates, many generations can be 

produced throughout a growing season, typically one generation per month.

DAMAGE: Larval feeding destroys seeds and may induce seed abortion, though 

the damaging spines of fruits still develop. Adult feeding is usually insignificant.

PREFERRED HABITAT: Distribution and abundance are limited by cold weather.

HISTORY: Introduced from Italy and released on puncturevine in the USA 

from 1961 (CA, CO, ID, MT, NV, OR, UT, WA, WY). After initial releases 

failed to establish in some cold climates, a second population from the Abruzzi 

Mountains, Italy, was released in more northern areas of CA but failed to 

establish. A population from CO (USA) was redistributed to CAN (BC) in 

1986, but failed to establish. 

CURRENT STATUS: Established with variable densities on puncturevine in the 

Microlarinus lareynii: a) larva in fruit (L.L. Berry, www.bugwood.org), b) adult (Jennifer Andreas, 

Washington State University Extension)

a b
Biological Control OF WEEDS in the Northwest 165puncturevine

USA. In combination with Microlarinus lypriformis, it successfully reduced weed 

cover and seed production up to 80% in warmer areas of the southwest USA, 

especially CA. It is generally ineffective at higher elevations and latitudes where 

cold winter temperatures reduce weevil populations. Recent redistribution 

efforts within CA successfully established a population at one high elevation 

site, indicating establishment is possible if sites have overwintering shelter and 

low disturbance. Populations are limited by parasites and predators at some sites.

REDISTRIBUTION: Adults can be collected in fall or spring in the heat of the 

day from the soil litter beneath plants using a vacuum or aspirator. Alternatively, 

infested plants and soil litter can be collected in paper bags or cardboard boxes 

and left in the sun for a short period of time. Any adults present will climb 

the walls of the container, allowing for easier collection. Adults (without plant 

material) should be transferred in groups of 100-200 to warm climates or sites 

with sufficient overwintering shelter and limited disturbance. They should 

not be released where native Kallstroemia species occur. Establishment 

can be monitored the following growing season by observing adults beneath 

puncturevine foliage during the heat of the day, or finding signs of attack.

NOTES: Microlarinus lareynii is slightly larger and has a more tear-shaped body 

than the similar M. lypriformis. M. lareynii is much more successful 

at high elevation sites compared to M. lypriformis, and is established 

in limited amounts in WA and OR whereas M. lypriformis is not, 

indicating a higher cold tolerance by M. lareynii. Also attacks 

the native Kallstroemia californica, K. grandiflora, and one 

additional native Kallstroemia species. Adults have been found 

on numerous exotic species (some of economic importance), 

though impact is typically negligible.

Coleoptera: Curculionidae

Microlarinus lareynii: c) adult feeding scars (Jennifer Andreas, Washington State University Extension), 

d) adult inside attacked fruit (Eric Coombs, Oregon Department of Agriculture, www.bugwood.org)

c d

Microlarin

lareynii
166 Biological Control OF WEEDS in the Northwest puncturevine DESCRIPTION: This species is very similar to Microlarinus lareynii. Eggs are 

dark yellow and cylindrical. Larvae are C-shaped with white to yellow-brown 

bodies and dark brown head capsules. Pupae are creamy white and up to 4 mm 

long. Adults are a mottled brown and covered with erect grayish hairs that make 

them appear slightly shaggy. Adults are typically 4-5 mm long and have short, 

broad snouts. 

Microlarinus lypriformis (Wollaston)

Puncturevine stem weevil

LIFE CYCLE: Adults emerge in spring and feed on puncturevine stems and leaves. 

Females chew pits into the root crown or on undersides of stems and lay eggs 

inside. Hatching larvae mine the stems and root crowns, developing through 

four instars. They pupate within the stem mines. New adults typically emerge 

within five days from exit holes in the stems or root crown. The period from egg 

to adult frequently takes 25-30 days. In warm climates, multiple generations can 

be produced throughout a growing season, typically one generation per month.

DAMAGE: Larval mining consumes vascular tissue, weakening the plant and 

often causing stem breakage. This, in turn, reduces the vigor and reproductive 

output of attacked plants. Adult feeding is usually insignificant.

PREFERRED HABITAT: Its distribution and abundance are limited by cold 

weather.

HISTORY: Introduced from Italy and released on puncturevine in the USA 

from 1961 (CA, CO, ID, MT, NV, OR, UT, WA, WY). After initial releases 

failed to establish in some cold climates, a second population from the Abruzzi 

Mountains, Italy, was released in more northern areas of CA but failed to 

establish. A population from CO (USA) was redistributed to CAN (BC) in 

1986, but failed to establish. 

Microlarinus lypriformis: a) larva in puncturevine stem, b) adult (both USDA ARS European Biological 

Control Laboratory, USDA ARS - European Biological Control Laboratory, www.bugwood.org)

a b
Biological Control OF WEEDS in the Northwest 167puncturevine

CURRENT STATUS: Established with variable densities on puncturevine in the 

USA. In combination with Microlarinus lareynii, it successfully reduced weed 

cover and seed production up to 80% in warmer areas of the southwest USA, 

especially CA. It is generally ineffective at higher elevations and latitudes where 

cold winter temperatures reduce weevil populations. Recent redistribution 

efforts within CA successfully established a population at one high elevation 

site, indicating establishment is possible if sites have overwintering shelter and 

low disturbance. Populations are limited by parasites and predators at some sites.

REDISTRIBUTION: Adults can be collected in fall or spring from the soil 

litter beneath plants using a vacuum or aspirator. Alternatively, infested plants 

and soil litter can be collected in paper bags or cardboard boxes and left in the 

sun for a short period of time. Any adults present will climb the walls of the 

container, allowing for easier collection. Adults (without plant material) should 

be transferred in groups of 100-200 to warm climates or sites with sufficient 

overwintering shelter and limited disturbance. They should not be released 

where native Kallstroemia species occur. Establishment can be monitored 

the following growing season by observing adults beneath puncturevine foliage 

during the heat of the day, or by dissecting stems and root crowns to find mining 

larvae.

NOTES: Microlarinus lypriformis is slightly smaller and has a less tear-shaped body 

(more symmetrical) than the similar M. lareynii. M. lypriformis is much less 

abundant at high elevation sites compared to M. lareynii, and is not established 

in WA and OR whereas M. lareynii is, indicating M. lypriformis has a lower cold 

tolerance. Also attacks the native Kallstroemia californica, K. grandiflora, 

and one additional native Kallstroemia species. Adults have been found on 

numerous exotic species (some of economic importance), though impact is 

typically negligible.

Coleoptera: Curculionidae

Microlarin

lypriform
168 Biological Control OF WEEDS in the Northwest RagwortTansy ragwort

Jacobaea vulgaris Gaertn.

a) plant (Jennifer Andreas, Washington State University Extension), b) infestation (Marianna Szucs, 

Colorado State University)

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 (1⁄3-1 m) from 

one to several soft, fleshy roots. Leaves are deeply lobed to pinnately toothed, 

alternate, and 3-8 in long (71⁄2-20 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 1⁄3-3⁄4 in long (8-20 mm) long. Seeds are topped by a fine pappus.

HABITAT: Especially problematic in open and/or disturbed rangeland, generally 

with moist soils.

a b
Biological Control OF WEEDS in the Northwest 169Ragwort

ECOLOGY: Spreads only by seed, which can be dispersed short distances by wind 

and longer distances by humans, other animals, and water. Seeds produced from 

both types of florets may remain viable in the soil for up to eight years. The life history 

varies depending on climatic conditions, with two life cycles predominant in western 

North America. In the Pacific Northwest, the plant typically acts as a biennial. 

Rosettes develop and put on considerable growth during the winter with bolting 

occurring early the following spring. Flowering may occasionally occur the first 

year, but is usually delayed until the second. Flowering occurs from July to 

September. In the shorter growing seasons of the Intermountain West, the plant 

may behave as a short-lived perennial. Seed germination typically begins in 

spring. Seedlings increase in size throughout the summer, and only the largest 

successfully overwinter. Bolting typically occurs early the following summer, 

and flowering takes place from July to October. Cutting or mowing the plant 

in the either climate may cause it to grow as a 

perennaial.

APPROVED BIOLOGICAL CONTROL 

AGENTS: USA: Botanophila seneciella, 

Longitarsus jacobaeae, and Tyria jacobaeae (which 

is no longer permitted for interstate transport); 

CAN: B. seneciella, Cochylis atricapitana, L. 

jacobaeae, and Tyria jacobaeae

NOTES: The entire plant is toxic to livestock, 

causing irreversible liver damage. 

Family Asteraceae

c) rosette (Jennifer Andreas, Washington State University Extension), d) stem leaf (Marianna Szucs, 

Colorado State University), e) flower head (Strobilomyces)

c d e

Jacob

vulga
170 Biological Control OF WEEDS in the Northwest Ragwort HISTORY IN THE NORTHWEST: Following a series of lengthy and involved 

host specificity testing, in 1959 the cinnabar moth, Tyria jacobaeae, became the 

first agent approved and released in North America against tansy ragwort. Though 

this defoliating moth proved effective at reducing tansy ragwort stands at some 

locations in the Northwest, the tansy ragwort biocontrol program continued to 

expand. By 1969, two additional species had been approved for release in both 

the USA and Canada: Botanophila seneciella and Longitarsus jacobaeae. In 1990, 

Cochylis atricapitana was approved and released only in Canada. 

CURRENT STATUS: B. seneciella is moderately abundant in CA, ID, MT, 

OR, WA (USA), and limited in abundance in BC (CAN). In both countries, 

it is susceptible to resource competition with the other established agents so is 

often restricted to small relic populations of tansy ragwort that are less desired 

by the other agents. It attacks 5-10% of early seed heads; later-developing 

capitula generally escape attack. B. seneciella is unable to control the weed alone. 

C. atricapitana has only established in coastal BC where populations remain 

limited. Though mining can suppress flower production and plant growth, the 

low populations likely make overall impact minor. The Italian CPNW strain 

of L. jacobaeae is well established in low-elevation coastal sites in CA, OR, WA 

and BC where it has proven highly effective in controlling tansy ragwort. The 

Italian CAD strain is established at colder high elevation sites in OR and MT 

where it provides local control. The Swiss strain is rapidly increasing in ID 

and MT at cold sites with heavy snowpack where it provides local control. It 

remains unknown if recent attempts to redistribute the Swiss strain to BC were 

successful. T. jacobaeae larvae often cause extreme defoliation to tansy ragwort 

in CA, MT, OR, WA and BC where populations are typically abundant. In 

mild climates, plants often recover. At sites with harsh, early winters, frost kills 

regrowth so plants never fully recover and impact can be high. Due to observed 

nontarget attack, interstate transport of T. jacobaeae is not permitted in the 

USA, and some states have prohibited its redistribution within their borders. 

RECOMMENDATIONS: USA: B. seneciella has overall low attack rates and 

is hindered by competition with other agents. Can be utilized as low priority 

for small, remote populations not desired by other agents and where alternative 

control methods are difficult to apply. T. jacobaeae is no longer approved for 

interstate transport, and some intrastate redistribution is banned as well.

Redistributions in approved locations should only be done in areas with cold, 

early winters, and where nontarget species do not co-occur. In such places, larvae 

can be transferred during the growing season. L. jacobaeae is the most effective 

of established agents, providing excellent control of tansy ragwort at many 

Tansy Ragwort Biological Control
Biological Control OF WEEDS in the Northwest 171Ragwort

Botanophila: © Malcolm Storey, www.bioimages.org.uk, Cochylis: © Geoff Riley, Longitarsus: Marianna 

Szucs, Colorado State University, Tyria: Mark Schwarzländer, University of Idaho

sites throughout its invaded range in the Northwest. Three strains are present 

in the USA with each preferring different climatic conditions. Additional 

redistributions of adults are recommended throughout the growing season, with 

emphasis placed on distributing the different strains to the appropriate habitats. 

C. atricapitana is not approved for release in the USA. CAN: B. seneciella 

and C. atricapitana are both limited in abundance and overall impact and are a 

low priority for redistribution. Similar to the USA, B. seneciella can be utilized 

in small, remote infestations without other agents present. Plants infested with 

C. atricapitana can be transferred in spring to provide small, localized impact 

in coastal habitats. T. jacobaeae has to date had only minor overall impact in 

Canada so is also a low priority. Larvae should only be redistributed to areas 

with harsh, early winters. L. jacobaeae is the most effective agent established in 

Canada and a high priority for continued redistribution. The strain currently 

established is effective at low-elevation, coastal sites. It is unknown if the Swiss 

strain successfully established, but additional emphasis should be given to 

moving this strain to colder, high-elevation sites of the interior. Adults can be 

transferred throughout the growing season. 

Agent Adult Impact Recommendation

Botanophila 

seneciella

Attacks 5-10% of early 

capitula only. Due to resource 

competition, restricted to 

small weed populations less 

desired by other agents.

Low impact alone and poor 

competitor. Low priority for 

redistribution, except remote 

populations where difficult to 

employ other methods.

Cochylis 

atricapitana

Stem-mining stunts growth, 

reduces flower production. 

Populations small and only 

coastal. Overall impact 

unknown, likely limited.

Not released in USA. In 

CAN, not high priority, but 

can contribute to control 

in coastal habitats. Transfer 

infested plants in spring.

Longitarsus 

jacobaeae

Foliage-feeding, root-mining 

weaken and kill plants. 3 

strains cause heavy impact 

in different habitats. Most 

effective agent established.

High priority for 

redistributing different strains 

to most appropriate habitats 

to optimize control. Transfer 

adults throughout season.

Tyria 

jacobaeae

Larvae cause extreme 

defoliation. Plants can recover 

in mild climates. At cold, 

harsh sites, frost prevents 

recovery, killing plants.

Interstate transport no longer 

legal in USA. In CAN, larvae 

should be redistributed only 

to sites with harsh, early 

winters.
172 Biological Control OF WEEDS in the Northwest Ragwort 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 instar larvae 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. 

Botanophila seneciella (Meade)

Ragwort seedhead fly

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) instar larvae 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 

spread of ragwort populations.

PREFERRED HABITAT: Does well in meadows and forest clearings. Where 

it is established alongside the cinnabar moth, the ragwort seed head 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).

HISTORY: Introduced from France and released in the USA (CA, OR, WA) from 

1966. Redistributed from CA to BC (CAN) from 1968. 

Botanophila seneciella: a) larva, b) pupae, c) adult (a-c © Malcolm Storey, www.bioimages.org.uk)

a b c
Biological Control OF WEEDS in the Northwest 173Ragwort

CURRENT STATUS: Moderately abundant in the USA. 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 seed head fly is the 

most widely distributed, it is usually the least abundant and least effective of 

the three agents established in the USA. Widely distributed in Canada though 

abundance is low. Populations are often restricted to small relic populations of 

weed less desired by other biocontrol agents. Unable to control the weed alone, 

but contributes to partial control in combination with Longitarsus spp. and 

Cochylis atricapitana. 

REDISTRIBUTION: Sweeping adult flies is possible, though may be damaging. 

Moving bouquets of fly-infested seed heads into uninfested patches is effective, 

but this may inadvertently spread new tansy ragwort seeds (from potentially 

different genotypes) and make the tansy ragwort problem worse. 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 very 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.

Botanophila seneciella: d) infested seed head, e) spittle on infested seed head (d,e Jennifer Andreas, 

Washington State University Extension), f) exit hole (Marianna Szücs, University of Idaho)

Diptera: Anthomyiidae

d e f

Botanoph

seneciella
174 Biological Control OF WEEDS in the Northwest Ragwort 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.

Cochylis atricapitana (Stephens)

Ragwort stem and crown boring moth

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 soil litter. Adults 

emerge in late spring as tansy ragwort is bolting and lay creamy-white eggs on 

the crown or on the underside of tansy ragwort leaves. Hatching larvae mine 

leaves and petioles while older larvae mine stems and roots crowns. Pupation 

of the new generation occurs in 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: Adapted to a wide variety of habitats where tansy 

ragwort grows, including high elevations and sites with early winters, but is to 

date established best in more mild coastal zones. 

HISTORY: Introduced from Spain via Australia and released in Canada from 

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)

a b c
Biological Control OF WEEDS in the Northwest 175Ragwort

1990 (BC from 1991). 

CURRENT STATUS: Established in BC (CAN), but populations are small and 

restricted to coastal regions; introductions into interior climates failed. Though 

this moth likely contributes to partial control with Longitarsus spp., formal 

evaluation of its impact is lacking.

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 the 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 instar larvae feeding in the root crown may be easily confused with 

Longitarsus jacobaeae larvae.

NOTES: This agent is not approved for release in the USA.

Lepidoptera: Tortricidae

Cochylis

atricapit
176 Biological Control OF WEEDS in the Northwest Ragwort DESCRIPTION: There are three strains of L. jacobaeae presently established in 

the USA: two Italian and one Swiss. All strains 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 instar larvae have 

brown head capsules. Pupae are white and 2-4 mm long. Adults are golden 

brown, 2-4 mm long, and have enlarged hindlegs.

Longitarsus jacobaeae (Waterhouse)

Tansy ragwort flea beetle

LIFE CYCLE: The three strains established in the USA differ genetically and in 

the timing of various stages in their life cycles. All strains have one generation 

per year, and larvae develop through three instars. Populations established in 

Canada are aligned with the Italian CPNW strain.

Italian CPNW strain: At low elevations in the Coastal Pacific Northwest (CPNW), 

adult beetles emerge in late spring and feed briefly on tansy ragwort rosettes 

before becoming dormant for the summer. Adult beetles become active again 

and feed on tansy ragwort foliage in the cooler/wetter fall. After 2-3 weeks of 

feeding, adults mate and females lay eggs around the bases of ragwort rosettes, 

sometimes laying eggs until early spring. Larvae hatch a couple weeks after eggs 

are laid and mine the leaf petioles and then root crowns of rosettes throughout 

winter and early spring. In spring, larvae leave root crowns to pupate in the soil.

Italian CAD strain: A cold-adapted strain of the Italian beetle (CAD) is established 

in lower numbers at high elevation sites in OR (USA) and the Intermountain 

West of the North America. At these locations, larvae do not aestivate; they 

continue feeding throughout summer. Pupation occurs in the soil in summer, 

and adults emerge soon after, laying eggs by late summer/early autumn. Eggs 

and larvae overwinter.

Swiss strain: Adult beetles emerge in mid- to late summer and feed on tansy 

ragwort foliage for 2-3 weeks prior to laying eggs around the bases of rosettes. 

Longitarsus jacobaeae: a) eggs and hatching larva (Ken Puliafico, Montana State University), b) late 

instar larva (Eric Coombs, Oregon Department of Agriculture), c) pupa (Laura Parsons, University 

of Idaho)

a b c
Biological Control OF WEEDS in the Northwest 177Ragwort

Egg laying may extend into early fall. Eggs overwinter, requiring at least 60 days 

(80 is optimal) before hatching in the spring. Larvae feed at first in tansy ragwort 

leaf petioles prior to moving into the root crown. Pupation occurs in the soil in 

late spring or early summer.

DAMAGE: Adult feeding results in characteristic shot-holes in leaves (typically 

rosette leaves rather than those of bolting plants). This interferes with 

photosynthesis and plant metabolism and may decrease the size of tansy ragwort 

plants. When beetle populations are high and plants are water-stressed, adult 

feeding can cause plant death, especially to seedlings and rosettes. The larval stage 

is generally the most destructive. Larval mining of the root crown depletes energy 

reserves, can reduce plant reproductive output, or cause death.

PREFERRED HABITAT: All strains do better in dense, unshaded tansy ragwort 

infestations. Flooding interferes with the larval and pupal stages so tansy ragwort 

infestations in floodplains are less amenable to biological control by this agent. 

The Italian CPNW 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. The Italian CAD strain is hardier than CPNW populations and can 

survive at higher elevations (1,000-1,600 m or 3,200-5,200 ft). The Swiss strain 

does well at elevations higher than 400 m (1,300 ft) characterized by warm 

summers and cold winters with hard frosts and snow cover. It may be found up 

to 1,675 m (5,500 ft).

HISTORY: Introduced from Italy and released in the USA from 1968 (CA, MT, 

OR, WA) where it established at low-elevation coastal sites. A cold-adapted 

strain of this release was later identified by University of Idaho researchers 

and determined to occur at high elevation sites in OR and the Intermountain 

Coleoptera: Chrysomelidae

Longitarsus jacobaeae: d) adult (Marianna Szucs, Colorado State University), e) adult feeding damage, 

f) larvae in roots (e,f Jeff Littlefield, Montana State University)

d e f
178 Biological Control OF WEEDS in the Northwest RagwortLongitarsus jacobaeae continued

West. A population from Switzerland was released in CA in 1969, but failed 

to establish. A second Swiss strain was successfully introduced to ID, MT, OR 

from 2002 to increase establishment in infestations with colder climates. Italian 

CPNW beetles CA and OR, USA were redistributed to BC, Canada from 1971 

and 1976, respectively. A small population from England was also released in 

BC in 1972. The three different release populations were later not differentiated 

and redistributed (likely as a mix) throughout BC and to other provinces. A 

strain from Switzerland was released in BC in 1973 but failed to establish. The 

Swiss strain that successfully established in the USA in 2002 was redistributed to 

BC in 2011 in an attempt to increase efficacy in cold habitats.

CURRENT STATUS: The Italian CPNW strain is established in high numbers 

at low-elevation, coastal locations characterized by warm, dry summers and 

mild, wet winters. There it has reduced tansy ragwort densities by over 90% at 

numerous sites. The Italian CAD strain is established in low numbers at highelevation sites at Mt. Hood OR and in MT where it has heavy impact. The Swiss 

strain is better suited to climates where the Italian CPNW strain does poorly 

(inland, colder regions with heavy snowpack). It is rapidly increasing at release 

sites in the USA though populations are still limited. The strain established in 

Canada is abundant in 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. It remains unknown 

whether the recent attempted release of the Swiss strain successfully established 

in Canada.

REDISTRIBUTION: Best collected in the adult stage either via sweeping 

(with or without an aspirator) or with an insect-collecting vacuum. Utilizing 

a sieve to sift beetles from debris helps make sorting easier. The Italian CPNW 

strain is best collected in the fall, while both the Italian CAD strain and the 

Swiss strain can be collected in late summer. All can be transferred to new 

infestations in groups of 200. Four non-approved Longitarsus species have 

been identified in mixed populations of L. jacobaeae in Canada, and one of 

these in the northwestern USA. Care should be taken in redistributing this 

species to ensure only L. jacobaeae is collected. (See page 182 for additional 

information.) Establishment can be monitored the following year by observing 

adults on ragwort foliage along with the characteristic shot-hole feeding. Adults 

of the Italian CPNW strain can be observed in early summer and the fall/early 

winter. Adults of the Italian CAD strain can be observed in fall. Adults of the 

Swiss strain can be observed throughout summer. Alternatively, plants can be 

dissected for evidence of larval feeding. Italian CPNW larvae can be found from 
Biological Control OF WEEDS in the Northwest 179Ragwort

fall through spring. Italian CAD larvae can be found from fall through the next 

summer, and the Swiss strain larvae can be found in spring and early summer. 

Note that larvae feeding within root crowns may be confused with early instar 

larvae of Cochylis atricapitana. 

NOTES: Works well in conjunction with Tyria jacobaeae.

Italian CAD Swiss

Longitarsu

jacobaeae

Swiss

Longitarsus

jacobaeae,

Italian CAD

Italian CPNW

Longitarsus

jacobaeae,

Italian CPNW
180 Biological Control OF WEEDS in the Northwest Ragwort DESCRIPTION: Eggs are small (1 mm) and bright yellow when new, but turn 

black with age. First instar larvae are light brown or orange, while 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 4 cm, and coloring often fades with moth age.

Tyria jacobaeae (L.)

Cinnabar moth

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 bolts, 

later instar larvae feed on stem leaves and developing buds, often in groups 

of 10-30. Final (sixth) instar larvae 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.

HISTORY: Introduced from France and released in the USA (CA, MT, OR, 

WA) from 1959. Introduced from Switzerland and released in BC (CAN) from 

1962. A second introduction was made in Canada in 1966 (BC in 1967) using 

material from the USA, though this failed to establish.

Tyria jacobaeae: a) eggs (Jeff Littlefield, Montana State University), b) early instar larvae (George 

Markin, U.S. Forest Service), c) late instar larva (Mark Schwarzländer, University of Idaho)

a b c
Biological Control OF WEEDS in the Northwest 181Ragwort

CURRENT STATUS: Populations fluctuate in the USA. High densities often 

completely defoliate plants. In mild regions of CA, OR, WA the weed often 

re-grows and recovers sufficiently to successfully overwinter and reproduce. 

In the colder, harsher Intermountain West, frosts usually kill regrowth before 

plants fully recover so the moth is more effective at reducing weed populations. 

Widespread in Canada (BC) though 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: 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 USA, and some 

states have prohibited its redistribution within their borders. Where this 

agent is approved for redistribution, it is imperative to refrain from making 

releases at sites where known related or susceptible species cooccur.

NOTES: T. 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.

Lepidoptera: Erebidae

Tyria jacobaeae: d) pupa (George Markin, U.S. Forest Service), e) adult (Mark Schwarzländer, 

University of Idaho), f) larvae feeding gregariously (Jeff Littlefield, Montana State University)

d e f

Tyria

jacobaea
182 Biological Control OF WEEDS in the Northwest Ragwort

Tansy Ragwort, Unapproved Agents

Longitarsus spp. (Acari: Eriophyidae)

DESCRIPTION AND LIFE CYCLE: 

The 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 11⁄2-4 

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 21⁄2-31⁄2 mm long. They 

have fully developed wings and are capable of flight, though they more often 

utilize their enlarged hindlegs 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 mixed 

populations with L. jacobaeae where it reportedly had limited impact on the weed. 

Additional evaluation is needed to confirm its presence. Longitarsus ganglbaueri

is only present in limited numbers in MB and NS, Canada, but has reportedly 

been documented at some point in the USA in CA, OR, WA. Its current status 

remains unknown. Longitarsus gracilis was identified in NS, Canada, 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. 

The species is considered well-established at one site in the Okanagan Valley in 

Adult L. flavicornis: (Mark Schwarzländer, 

University of Idaho)
Biological Control OF WEEDS in the Northwest 183Ragwort

BC. Longitarsus succineus is established only in NL, Canada. These four flea 

beetles are not recommended for redistribution in Canada or the USA 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.
184 Biological Control OF WEEDS in the Northwest skeletonweed SYNONYMS: skeleton weed, hogbite, nakedweed, gum succory 

ORIGIN: Inadvertently introduced into the eastern United States in the 1870s.

DESCRIPTION: Herbaceous perennial usually growing 1-4 ft tall (1⁄3-1.2 m) 

and having a rhizomatous root system. Rosettes have deeply lobed leaves. Plants 

produce multiple stems that are wiry and rigid with alternate, very narrow 

leaves. The plant has an overall skeleton appearance. Bottom portions of stems 

are covered with stiff, golden-reddish and downward pointing hairs. Flower 

heads are 1⁄2 in across (1 cm) and consist of 9-12 yellow florets that produce seeds 

without fertilization. Seeds are small, brown, and topped by tufts of pappus. All 

parts of the plant exude a milky latex when damaged. 

HABITAT: A serious weed of roadsides, rangeland, abandoned cropland, and 

b

Rush skeletonweed

Chondrilla juncea L.

a) plant (Rachel Winston, MIA Consulting), b) infestation (Laura Parsons, University of Idaho)

a
Biological Control OF WEEDS in the Northwest 185skeletonweed

disturbed places. It does best in semiarid conditions with cool, moist winters 

and warm summers without extensive drought, and in well-drained soils.

ECOLOGY: Spreads by seed and rhizomes. Seeds are readily carried by wind, 

water, wildlife and human activity. Root pieces less than 1⁄2 in long (1 cm) can 

develop into new plants. Rosettes develop from fall through spring; plants bolt 

in spring. Flower heads bloom in late summer.

APPROVED BIOLOGICAL CONTROL AGENTS: USA: Aceria chondrillae, 

Bradyrrhoa gilveolella, Cystiphora schmidti, and Puccinia chondrillina; CAN: B. 

gilveolella.

NOTES: Seven genotypes of this weed are recognized in North America; five in 

the West and two on the East Coast. Two of the 

genotypes occurring in the West also occur in 

Midwestern and Eastern North America. Some 

biocontrol agents behave differently depending 

on the genotype of the attacked weed. See 

the following pages for a map of known rush 

skeletonweed genotypes in western North 

America.

Family Asteraceae

d

c) rosette leaves (Richard Old, XID Services, Inc, www.xidservices.com, www.bugwood.org) d) stem 

hairs, e) flower head (both Rachel Winston, MIA Consulting,) 

Chon

junce

c e
186 Biological Control OF WEEDS in the Northwest skeletonweed HISTORY IN THE NORTHWEST: Rush skeletonweed is a problematic 

weed in numerous parts of the world. The call for biological control of this 

weed first began in Australia in 1936, though the first biocontrol agent was not 

released there until 1971. To date, a total of one rust fungus, two insects, and 

one mite species have been released in Australia. The same species were also 

released in the USA: Cystiphora schmidti in 1975, Puccinia chondrillina in 1976, 

Aceria chondrillae in 1977, and Bradyrrhoa gilveolella in 2002. B. gilveolella was 

intentionally redistributed from the USA to BC (CAN) from 2007 onwards. A. 

chondrillae and P. chondrillina spread naturally from the USA to BC.

CURRENT STATUS: A. chondrillae is established in CA, ID, MT, OR, WA, 

WY (USA) where abundance and impact are variable. It reduces flowering and 

seed production up to 90% in OR and WA, but efficacy is limited in CA due to 

predation and in ID due to high overwintering mortality. Though it is widespread 

in BC (CAN), populations are limited and the weed continues to thrive. B. 

gilveolella is confirmed established only in OR and ID (USA) where numbers 

are increasing at the original release sites. B. gilveolella has not officially been 

confirmed as established in BC (CAN); however, early results look promising 

and monitoring continues. Additional time is needed in both countries before 

overall establishment, impact and abundance can be evaluated. C. schmidti is 

established in CA, ID, OR, WA, WY (USA) where infested plants are stunted 

and produce fewer seeds. Though widespread, populations are limited in 

abundance due to heavy parasitism and predation. P. chondrillina is established 

in CA, ID, OR, WA, WY (USA) where efficacy varies by weed genotype and 

site conditions. It is the most effective in WA and CA where it decreases plant 

size and reproductive output, but is less effective elsewhere, especially hot and 

dry sites. Though widespread in BC (CAN), overall impact is limited as rush 

skeletonweed populations are persisting.

RECOMMENDATIONS: USA: High predation and parasitism make C. 

schmidti a low priority for redistribution. B. gilveolella is only recently established 

and additional releases are warranted to help increase populations. These 

should likely be made from lab colonies as field populations are still limited. A. 

chondrillae and P. chondrillina have variable success depending on site conditions 

and rush skeletonweed genotype. Redistributions of both species should occur 

at mesic sites (moist for P. chondrillina) with mild winters. CAN: Abundance 

and impact of A. chondrillae remain limited. B. gilveolella is not yet officially 

confirmed as established, and additional releases from lab colonies are warranted 

to increase populations.

Rush Skeletonweed Biological Control
Biological Control OF WEEDS in the Northwest 187skeletonweed

Credits for photos in table above: Aceria, 

Cystiphora: Charles Turner, USDA ARS, www.

bugwood.org, Bradyrrhoa: Laura Parsons & 

Mark Schwarzländer, University of Idaho, 

Puccinia: Jennifer Andreas, Washington State 

University Extension 

99

98

97

96

95

94

93

92

91

90

89

88

87

85

84

83

82

81

80

78

77

76

75

74

73

72

71

70

69

68

67

66

65

64

154

153

152

151

146

149

148

147

145

142

140 141

139

138

137

136

134

132

130

129

128

127

126

125

124

118

117

112

111

110

109

108

107 105 106

104

103

102

133

144

143

131

86

101

100

123

60

61

62

63

Genotype 1a

Genotype 3a

59

Genotype 3

Genotype 2

150 79

Genotype 1

145

NV

CA

OR

WA

BC

MT

ID

CANADA

USA

Fig. 2

Rush skeletonweed genotypes in western North 

America (reprinted with permission from 

Gaskin, J.F., M. Schwarzländer, C.L. Kinter, J.F. 

Smith, and S.J. Novak. 2013. Propagule pressure, 

genetic structure, and geographic origins of 

Chondrilla juncea (Asteraceae): an apomictic 

invader on three continents. American Journal 

of Botany 100(9): 1871-1882.) 

Agent Adult Impact Recommendation

Aceria 

chondrillae

Galling reduces flowering, seed 

production. Effective at some 

USA sites. Suffers predation, 

overwintering mortality 

elsewhere. Limited in CAN.

Average reduced efficacy 

makes this only a medium 

priority for redistribution to 

mesic sites with mild winters. 

Not intentional in CAN. 

Bradyrrhoa 

gilveolella

Root- feeding decreases plant 

vigor, root reserves; kills 

above-ground portions. Too 

early to determine impact in 

USA or establishment in CAN

Additional releases warranted 

in both USA and CAN. 

Likely should be sourced 

from lab colonies as field 

populations still limited.

Cystiphora 

schmidti

Galling stunts plants, 

decreases seed production. 

Populations typically limited 

by parasitism, predation.

Due to high levels of 

parasitism and predation, very 

low priority for redistribution 

efforts. Not released in CAN.

Puccinia 

chondrillina

Rust infection decreases 

plant size, seed output. Most 

effective in moist, mesic 

areas and on certain weed 

genotypes. 

Redistribute in USA to moist 

sites where genotypes match. 

Not intentional in CAN 

where impact low overall.
188 Biological Control OF WEEDS in the Northwest skeletonweed SYNONYMS: Eriophyes chondrillae (Canestrini)

DESCRIPTION: All stages are tiny and best viewed with a microscope. Nymphs 

are pale yellow and 0.10 mm long in the first stage. Second stage nymphs are 

humpbacked, orange, have four legs, and reach 0.17 mm. Adults are worm-like, 

yellow-orange, and have two pairs of legs. Males are up to 0.18 mm long while 

females are 0.26 mm.

Aceria chondrillae (Canestrini)

Rush skeletonweed gall mite

LIFE CYCLE: There are multiple generations per year. Overwintering adults 

attack shoot buds when rush skeletonweed bolts in spring. Feeding leads to 

the formation of contorted galls; each gall may contain several hundred mites. 

Females lay 60-100 eggs within the gall they occupy. One generation can be 

completed in 10-12 days. Mites may spread with wind-dispersed seeds in the 

fall. Mite populations and galls increase until skeletonweed dies back in the 

winter.

DAMAGE: Galls induced by mite feeding stunt shoot growth, reduce rosette and 

seed production, reduce root carbohydrate reserves, and often result in seedling 

death.

PREFERRED HABITAT: Well adapted to a variety of environmental conditions 

throughout the Northwest. Rapidly colonizes plants growing in undisturbed, 

well-drained soils on south- or west-facing slopes. Mite populations do not 

persist in sites subjected to repetitive soil disturbance, such as cropland. High 

overwintering mortality occurs in areas with harsh winters and without winter 

rosettes of rush skeletonweed.

Aceria chondrillae: a) adult (Charles Turner, USDA ARS), b, c) damage (b Richard Old, XID Services, 

INC, c Biotechnology and Biological Control Agency) (a,b www.bugwood.org)

a b c
Biological Control OF WEEDS in the Northwest 189skeletonweed

HISTORY: Introduced from Italy and released in CA, ID, OR, WA (USA) from 

1977. Spread naturally from the USA to Canada.

CURRENT STATUS: Abundance and impact in the USA are variable. It is 

widespread in OR and WA where it reduces flowering and seed production by 

50-90%, depending on plant size and environmental conditions. Efficacy is 

limited in CA due to predation and in ID due to high overwintering mortality. 

Though it is established at multiple locations in BC (CAN), weed populations 

are persisting. Mite abundance is low and overall abundance is limited.

REDISTRIBUTION: Stems infested with galls can be gathered from late 

summer through fall. Stems should be placed in direct contact with uninfested 

stems at new sites (taking care not to spread skeletonweed seeds to new sites as 

this may introduce new genotypes). As galls dry, mites will relocate to uninfested 

stems. Establishment can be monitored the following season by observing new 

galls on growing plants.

NOTES: Different biotypes of the mite show close associations with certain 

genotypes of rush skeletonweed. This agent was not an intentional introduction 

in Canada.

Acari: Eriophyidae

Aceria

chondrill
190 Biological Control OF WEEDS in the Northwest skeletonweed DESCRIPTION: Larvae are 20-25 mm long, off-white, and have brown head 

capsules. Adults are creamy buff colored and have three brown, horizontal bands 

on their front wings. They have wingspans up to 28 mm.

Bradyrrhoa gilveolella (Treitschke)

Rush skeletonweed root moth

LIFE CYCLE: There are two generations per year in Europe, where adults emerge 

in spring as rush skeletonweed bolts. Females lay eggs (up to 250 each) on stems 

or soil near plants. Once in contact with the plant, larvae feed into the stem 

base, and move downward to attach themselves to the root, feeding on root 

cortex and spinning feeding tubes made of silk, sand, and frass as they travel. 

Tubes may be up to 60 mm long and extend to the soil surface as exit chimneys. 

Pupation occurs in tubes. Adults emerge in late summer and lay eggs. Emerging 

larvae overwinter in feeding tubes.

DAMAGE: Heavy larval feeding results in death of aboveground plant parts, 

diminished root reserves, and decreased vigor.

PREFERRED HABITAT: Does best on plants growing in sandy, granitic, or 

loose-textured soils.

HISTORY: Introduced from Greece and released in CA, ID, OR, WA (USA) 

from 2002. Redistributed from the USA to BC (CAN) from 2007 onwards.

CURRENT STATUS: In the USA, populations are becoming locally abundant 

at the original release sites. It is too soon following establishment to determine 

overall impact. Establishment has not been officially confirmed in Canada, 

though early results are promising and monitoring continues.

Bradyrrhoa gilveolella: a) larva, b) root tunnel, c) adult (all Laura Parsons & Mark Schwarzländer, 

University of Idaho)

a b c
Biological Control OF WEEDS in the Northwest 191skeletonweed

REDISTRIBUTION: Once field populations become larger, adults can be swept 

from vegetation during the evening in spring and late summer when either 

generation is peaking. Take care to collect prior to the majority of egg-laying, 

or redistribution will be fruitless. Also be aware that sweeping can damage 

these fragile moths. Alternatively, harvest the roots of infected skeletonweed in 

the fall and store them 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 

sites in groups of 25-25. The latter method is only plausible if precise attack 

symptoms can be recognized. Establishment can be monitored the following 

year by dissecting stems and roots to observe larvae feeding.

NOTES: Several larvae may feed on the same root simultaneously.

? Lepidoptera: Pyralidae

Bradyrrh

gilveolel
192 Biological Control OF WEEDS in the Northwest skeletonweed DESCRIPTION: Larvae are flattened, 1-21⁄2 mm long, and are pink or orange. 

Adults are light brown and very small, usually 1 to 11⁄2 mm long. Legs are long 

and delicate. Female abdomens end in a bulbous enlargement.

Cystiphora schmidti (Rübsaamen)

Rush skeletonweed gall midge

Cystiphora schmidti: a) larvae (top Eric Coombs, Oregon Department of Agriculture, bottom Gary Piper, 

Washington State University), b) adult (Charles Turner, USDA ARS) (all www.bugwood.org)

LIFE CYCLE: Adults emerge in spring, and females deposit 60–180 eggs in leaves 

of rush skeletonweed rosettes. Larvae feed on stem and leaf tissue, inducing the 

formation of purplish galls. Leaf galls are circular, 3 mm in diameter, and slightly 

raised, whereas stem galls are elongated and usually more elevated. Pupation 

occurs within galls with each larva spinning a silky cocoon around itself prior 

to pupation. Adults emerge from cocoons and galls using pupal head spines, 

destroying plant tissue in the process. New eggs are laid in stems and stem leaves. 

There are 4 or 5 generations per year. Larvae or pupae overwinter in galls or soil.

DAMAGE: Attacked tissue is injured or destroyed, leading to fewer branches and 

flower heads and less viable seeds.

PREFERRED HABITAT: Does best in warm, dry areas and on plants growing 

in open locations in well-drained soil. 

HISTORY: Introduced from Greece via Australia and released in the USA from 

1975 (CA, ID, OR, WA). 

CURRENT STATUS: In the USA, infested plants are stunted and have decreased 

seed production. Midge populations are generally small, however, being greatly 

hindered by parasitism and predation.

a b
Biological Control OF WEEDS in the Northwest 193skeletonweed

REDISTRIBUTION: Stems infested with Cystiphora schmidti galls can be 

gathered from midsummer through early fall. Stems should be placed in direct 

contact with uninfested stems at new sites. Many emerging midges will attack 

the new plants upon emergence. Transferring infested galls may also transfer 

unwanted parasitoids, other insects, or rush skeletonweed seed from different 

genotypes. To avoid this, 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 rush skeletonweed infestations in groups of 50-100. Establishment can be 

monitored by observing galls on new foliage throughout the following growing 

season. 

NOTES: Attacks all genotypes of rush skeletonweed present in the northwestern 

USA. This agent is not approved for release in Canada.

Diptera: Cecidomyiidae

Cystiphora schmidti: c,d) damage (Gary Piper, Washington State University, www.bugwood.org)

c d

Cystipho

schmidt
194 Biological Control OF WEEDS in the Northwest skeletonweed DESCRIPTION and LIFE CYCLE: During fall, lesions form at the bases of 

flowering rush skeletonweed shoots. These form teliospores that overwinter in 

dormancy. In spring, spores germinate in rosette leaves in clusters of pycnia 

that yield pycniospores. These lead to aecia and aeciospores on leaves, which 

germinate to produce uredia and urediospores. Urediospores are the most 

abundant during the growing season, and are the most distinctive spore. They 

are round, dark brown, dry and powdery. Urediospores are easily dispersed by 

both wind and rain, spreading rapidly from plant to plant. Multiple generations 

are produced per year.

Puccinia chondrillina (Bubák & Syd.)

Rush skeletonweed rust fungus

DAMAGE: Pustules reduce rush skeletonweed photosynthetic capabilities and 

deplete root nutrient storage, leading to plant weakening and even death. Small 

rosettes and seedlings are often destroyed by heavy rust infestations. If larger 

plants are infected sufficiently early in the season, flowering stems are stunted 

and deformed and produce few viable seeds.

PREFERRED HABITAT: Does best in mesic climates with regular dew periods. 

Hindered by overly harsh winters that kill infected hosts.

HISTORY: Introduced from Italy and released in CA, ID, OR, WA (USA) from 

1976. A different strain was introduced along with its rush skeletonweed host 

in eastern USA (MD) in an unknown year. The intentionally introduced strain 

spread naturally from the USA to BC (CAN) by 1976.

CURRENT STATUS: In the USA, efficacy varies by weed genotype and site 

conditions. It is considered the most effective agent in WA and CA where it 

Puccinia chondrillina: a,b) spores on infected leaves (Jennifer Andreas, Washington State University 

Extension), b) infected rosette (Wendy DesCamp, Washington State Noxious Weed Control Board), 

c) infected stems (Eric Coombs, Oregon Department of Agriculture, www.bugwood.org)

a b c
Biological Control OF WEEDS in the Northwest 195skeletonweed

decreases plant size and reproductive output. It is less effective in ID and OR. 

The rust fares poorly on hot and dry sites. One strain is parasitized. Widespread 

in BC (CAN) where it has been observed stunting and reducing the density of 

young plants. It is most effective in high moisture areas and in regions where 

infected overwintering rosettes are not killed by harsh temperatures. Despite 

being abundant in BC overall impact is considered limited as rush skeletonweed 

populations are persisting.

REDISTRIBUTION: Should be collected by vacuuming urediospores from 

infected leaves throughout the growing season, suspending the spores in water, 

and spraying them on new foliage prior to a dew period. Alternatively, transfer 

infected stems to new sites in the evening during summer, and spray uninfested 

plants with water. In fall and spring, whole infected plants can be transplanted 

to new sites. Take care not to spread rush skeletonweed seeds to new sites as this 

may introduce new genotypes. Establishment can be monitored by observing 

pustules on new rush skeletonweed foliage throughout the following growing 

season.

NOTES: This agent was not an intentional introduction in Canada. The three 

most prevalent genotypes of rush skeletonweed in the western USA differ in 

their susceptibility to the two different rust strains. Genotype 2 is resistant to 

both strains, genotype 1 is resistant to one strain but not the other, and genotype 

3 is susceptible to both strains.

Pucciniomycetes: Pucciniales

Puccinia

chondri
196 Biological Control OF WEEDS in the Northwest starthistleYellow starthistle

Centaurea solstitialis L.

SYNONYMS: St. Barnaby’s thistle 

ORIGIN: Introduced from the Mediterranean in the mid-1800s as a contaminant 

in hay and imported seed.

DESCRIPTION: Winter annual usually growing between 1⁄2-6 ft tall (15 cm -1.8 

m) and having a deep taproot. Rosettes have deeply lobed leaves. Stems are rigid 

with alternate, narrow leaves. Stem leaf bases extend down the stem, giving a 

winged appearance. Both stems and leaves are covered with dense hair, resulting 

in their characteristic gray-green color. Flower heads consist of numerous bright 

yellow florets that bloom in midsummer. The base of the flower head is covered 

with bracts ending in long (up to 3⁄4 in or 2 cm), sharp spines. Two types of 

seeds are produced: tan-colored plumed seeds from the center, and dark brown 

unplumed seeds from the periphery.

 

b

a) plant (Laura Parsons, University of Idaho), b) infestation (Rachel Winston, MIA Consulting)

a
Biological Control OF WEEDS in the Northwest 197starthistle

c) rosette (Steve Dewey, Utah State University), d) winged stems (Rachel Winston, MIA Consulting), 

e) flower head (Peggy Greb, USDA ARS) (c,e www.bugwood.org)

HABITAT: A serious weed of roadsides, rangeland, abandoned cropland, and 

disturbed places. It occurs in a variety of soils and conditions but is most 

common below 4000 ft (1200 m) on south-facing slopes in areas with more 

than 6 in (15 cm) of rain annually. 

ECOLOGY: Spreads only by seed. In Mediterranean climates, germination occurs 

in fall following autumn rains. Spring germination occurs elsewhere in North 

America. Rosettes develop from fall through spring; stems bolt in spring and 

throughout the summer. Seeds are readily transported by water, wildlife and 

human activity and may remain viable in the soil for up to 10 years.

APPROVED BIOLOGICAL CONTROL AGENTS: USA: Bangasternus 

orientalis, Chaetorellia australis, Eustenopus 

villosus, Larinus curtus, Puccinia jaceae var. 

solstitialis, and Urophora sirunaseva.

NOTES: Horses feeding on yellow starthistle 

can develop a fatal nervous disorder called 

chewing disease. The PLANTS database and 

other data distribution sources indicate the species 

is established in AB (CAN). While populations 

have been found in the past, none have persisted.

Family Asteraceae

d

Centa

solstit

c e
198 Biological Control OF WEEDS in the Northwest starthistle HISTORY IN THE NORTHWEST: The USA biocontrol program for yellow 

starthistle began with the introduction of a fly believed to Urophora sirunaseva

in 1969. After introductions failed, it was determined the species was indeed 

U. jaculata, one that is specific to yellow starthistle biotypes growing only in 

Italy. The true U. sirunaseva was released in 1984. Four additional species were 

released subsequently (one fly and three weevils). A contaminant fly species 

was accidentally introduced to the USA along with the approved fly in 1991 

shipments. A rust fungus was introduced in 2003 to supplement the action of 

the established seed-feeding insects. 

CURRENT STATUS: All intentionally introduced insect species successfully 

established in the USA, though the abundance of each species has changed 

dramatically over time and with the introduction of additional species. 

Bangasternus orientalis, Larinus curtus, and Urophora sirunaseva were all more 

abundant in the few years following their release. These are since being replaced 

by higher populations of Eustenopus villosus and the unapproved fly, Chaetorellia 

succinea to the point of being considered insignificant agents. The approved C. 

australis often relies on the presence of the exotic weed bachelor’s button early 

in the spring, so is restricted in distribution and also has low attack rates on 

yellow starthistle. In combination, E. villosus and C. succinea reduce overall seed 

production by >70%. However, only at low initial plant densities can this impact 

yellow starthistle population growth; at many study sites plants compensate for 

decreased seedling density by growing larger and producing more seeds. The rust 

Puccinia jacea var. solstitialis has proven difficult to establish, being ill-suited to 

the dry climate found throughout much of yellow starthistle’s invaded range. 

Populations remain very small and with low impact in CA.

RECOMMENDATIONS: USA: The low impact and continuously decreasing 

population size of B. orientalis, C. australis, L. curtus, and U. sirunaseva make 

these agents a low priority for redistribution. C. australis is also considered a 

low priority due to its resemblance and often co-ccurrence with the unapproved 

C. succinea. P. jacea var. solstitialis is also a low priority due to its low impact 

and limitations for establishment. It should only be redistributed to moist 

areas and where the other agents are limited. It is illegal to redistribute C. 

succinea, though this agent is already widespread. E. villosus is also already 

widely distributed and likely abundant at most infestations, demonstrating that 

seed-feeding agents are often insufficient to control yellow starthistle alone, and 

releases of additional agents attacking non-reproductive tissue are warranted. 

Such agents are currently under study. In the meantime, E. villosus would be the 

highest priority for redistribution. Adults can be collected in midsummer with a 

Yellow Starthistle Biological Control
Biological Control OF WEEDS in the Northwest 199starthistle

Bangasternus, C. succinea, Eustenopus, Larinus, Urophora: Laura Parsons & Mark Schwarzländer, 

University of Idaho, C. australis: Charles Turner, USDA ARS, www.bugwood.org, Puccinia: Stephen 

Ausmus, USDA ARS, www.bugwood.org

sweep net and aspirator. CAN: Canada does not have an official yellow starthistle 

biocontrol program. None of the agents described herein are approved for 

release in Canada; yellow starthistle currently does not occur in Canada.

Agent Adult Impact Recommendation

Bangasternus 

orientalis

Seed-feeding reduces up 

to 60% seeds in attacked 

capitula. Attack rates low and 

continue to decrease from 

competition, parasitism.

Low efficacy and decreasing 

abundance makes low priority 

for redistribution. Not released 

in CAN.

Chaetorellia 

australis

Seed-feeding reduces up 

to 90% seeds in attacked 

capitula. Attack rates low. 

Often requires bachelor’s 

button for spring generation.

Low efficacy, need for bachelor’s 

button, difficulty differentiating 

from C. succinea make low 

priority for redistribution. Not 

released in CAN.

Chaetorellia 

succinea

Seed-feeding reduces overall 

seed production >70% with 

E. villosus.

Accidental introduction not 

approved for redistribution in 

USA. Not released in CAN.

Eustenopus 

villosus

Seed-feeding and adult-caused 

capitula abortion reduce 

overall seed production >70% 

with C. succinea. 

Most effective of approved 

agents. Recommended for 

redistribution wherever not 

established. Not released in 

CAN.

Larinus 

curtus

Seed-feeding reduces up 

to 100% seeds in attacked 

capitula. Attack rates 

decreasing from parasitism, 

perhaps competition.

Low attack rates/efficacy and 

decreasing abundance makes 

low priority for redistribution. 

Not released in CAN.

Puccinia 

jacea var.

solstitialis

Rust infection stunts plants, 

reduces seed production.

Abundance, distribution very 

low. Ill suited to climatic 

conditions at most infestations. 

Recommended only for moist 

areas. Not released in CAN.

Urophora 

sirunaseva

Galls reduce seed production 

in attacked capitula. Many 

seeds still produced, and 

attack rates decreasing, 

possibly from competition.

Low efficacy and decreasing 

abundance makes low priority 

for redistribution. Not released 

in CAN.
200 Biological Control OF WEEDS in the Northwest starthistle DESCRIPTION: Larvae are up to 6 mm long with white, C-shaped bodies and 

brown head capsules. Adults are 4-6 mm long with short snouts and brown 

bodies with yellow-white hairs that give them a mottled appearance.

Bangasternus orientalis (Capiomont)

Yellow starthistle bud weevil

Bangasternus orientalis: a) egg (University of Idaho Archive), b) adult (Laura Parsons & Mark 

Schwarzländer, University of Idaho) (both www.bugwood.org)

LIFE CYCLE: Adults overwinter in soil litter and resume activity in spring when 

yellow starthistle is bolting. Females lay eggs singly just below flower heads. They 

may lay up to 470 eggs in a lifetime. Eggs are covered with a dark, protective 

substance. Hatching larvae tunnel through the stem to reach the flower head 

where they feed on bracts, receptacle tissue, and developing seeds through three 

instars. Pupation occurs in chambers made of damaged seed and receptacle 

tissue. Adults emerge in late summer. There is one generation per year.

DAMAGE: Larvae feed on flower head tissue and developing seeds. Seed 

consumption does not kill existing plants, but does help reduce the rate of 

spread of starthistle populations. 

PREFERRED HABITAT: Specific habitat requirements are unknown, but can 

be found throughout most yellow starthistle infestations in the western USA.

HISTORY: Introduced from Greece and released on yellow starthistle in the USA 

from 1985 (CA, ID, OR, WA). A redistribution was attempted from to the 

related Iberian starthistle in CA in 1994, but this failed to establish. 

CURRENT STATUS: In the USA, larval feeding typically destroys 60% of seeds 

within attacked seed heads. It was initially the most widespread of established 

agents. However, densities of the weevil have been declining since their peak 

a b
Biological Control OF WEEDS in the Northwest 201starthistle

a few years after their original release. The current attack rate is only 1% of 

available capitula. Predation, parasitism, and displacement by other established 

agents limit populations in many areas.

REDISTRIBUTION: Though populations are increasingly low in the USA, 

some populations are reportedly large enough for redistribution. Adults can be 

collected with a sweep net (with or without an aspirator) in early summer as 

yellow starthistle is in the early bud stage. Releases of 200 individuals should 

be made on patches of at least 2,000 m2 (1/2 acre). Establishment can be 

monitored the following summer by checking for adults and/or feeding larvae 

within capitula. Note that feeding larvae can be very difficult to distinguish from 

other starthistle weevil species.

NOTES: This species has a shorter snout than both Eustenopus villosus and Larinus 

curtus and is becoming the least abundant (consequently also becoming the least 

effective). This agent is not approved for release in Canada.

Coleoptera: Curculionidae

Bangast

oriental
202 Biological Control OF WEEDS in the Northwest starthistle DESCRIPTION: Larvae are up to 5 mm long, barrel-shaped, and whitish with no 

head capsules. Adults are tan with black spots (8 on the thorax of C. australis while 

C. succinea has 10). Eyes are multi-colored and metallic. Wings are clear with thick 

brown bands. Males are 3-4 mm long; females are 4-6 mm, including ovipositors.

Chaetorellia australis (Treitschke) & C. succinea (Costa)

Yellow starthistle peacock fly & False yellow starthistle peacock fly

Chaetorellia: a) larva in seed head (Gary Piper, Washington State University, www.bugwood.org), b,c) 

adult thorax comparison: b) C. australis, c) C. succinea with extra dot (J. Johnson, University of Idaho)

LIFE CYCLE: Adults of both species emerge in early spring as yellow starthistle 

bolts. Females lay eggs singly beneath bracts of closed buds. Hatching larvae 

tunnel into capitula, feeding on receptacle tissue and developing seeds through 

three instars. Pupation occurs in flower heads inside chambers made of pappus 

and chewed seeds. Adults emerge in early summer, mate, and lay eggs on more 

starthistle buds. Larvae of this generation overwinter within flower heads. There 

are two, sometimes three, generations per year. First generation C. australis adults 

emerge earlier than C. succinea, often too early to utilize starthistle. Consequently 

they frequently use buds of the earlier-flowering invasive weed bachelor’s button 

(Centaurea cyanus). The second generation utilizes yellow starthistle.

DAMAGE: Larvae feed on developing seeds. Seed consumption does not kill 

existing plants, but does help reduce the rate of spread of starthistle populations. 

PREFERRED HABITAT: C. australis does best where bachelor’s button co-occurs 

with yellow starthistle. Both fly species do better in warm, low-elevation sites.

HISTORY: C. australis was introduced from Greece and released on yellow 

starthistle in the USA from 1988 (CA, ID, OR, WA), but quickly established 

on bachelor’s button as well. A release made in OR in 1991 believed to be just C. 

australis was contaminated with C. succinea. The contaminant was unknowingly 

redistributed with C. australis throughout CA, OR, WA from 1994. 

a

b

c
Biological Control OF WEEDS in the Northwest 203starthistle

CURRENT STATUS: C. australis is established on both bachelor’s button and 

yellow starthistle. Its abundance varies, often in relation to bachelor’s button 

presence. Attack rates are often higher on bachelor’s button, on which it can 

reduce seed production by up to 70% in WA. It can destroy up to 90% of seeds 

in attacked yellow starthistle capitula. However, attack rates have typically not 

exceeded 10% of available capitula, likely due to poor synchrony in spring. C. 

succinea is considered the more effective control agent for yellow starthistle. 

Larval feeding destroys up to 80% of seeds within attacked yellow starthistle seed 

heads and decreases pollinator visitation. In conjunction with Eustenopus villosus,

it can reduce seed production by >70% overall. Only at low initial plant densities 

can this impact the population growth; at many study sites plants compensate for 

decreased seedling density by growing larger and producing more seeds. 

REDISTRIBUTION: C. succinea is not approved for redistribution in the 

USA. However it is already widespread and abundant. C. australis is approved, 

though its low overall impact on starthistle and its occasional reliance on bachelor’s 

button make it a low priority for redistribution. In addition, it is difficult to 

ensure only the approved C. australis is the one released. Establishment of either 

species can be confirmed by observing larvae in capitula throughout the growing 

season. Adults are needed in order to determine 

which species is present.

NOTES: Eustenopus villosus oviposition deters 

Chaetorellia succinea oviposition. C. succinea 

consumes a higher proportion of seeds when 

plants are not infected with Puccinia jacea var. 

solstitialis. Neither agent is approved for release 

in Canada.

Diptera: Tephritidae

Adults of d) Chaetorellia australis, (Charles Turner, USDA ARS), e) C. succinea (note extra dot on 

thorax, Laura Parsons & Mark Schwarzländer, University of Idaho) (both www.bugwood.org)

d e

C. australis C. succinea

Chaeto

succine

Chaetorellia

australis
204 Biological Control OF WEEDS in the Northwest starthistle

DESCRIPTION: Larvae are up to 6 mm long with white, C-shaped bodies 

and brown head capsules. Adults are 4-6 mm long and have brown bodies 

with white stripes. Their snouts are very long and slender, and they have long 

hairs on their back.

Eustenopus villosus (Boheman)

Yellow starthistle hairy weevil

Eustenopus villosus: a) pupa (University of Idaho, www.bugwood.org), b) adult (Laura Parsons & 

Mark Schwarzländer, University of Idaho)

LIFE CYCLE: Adults overwinter in soil litter and emerge in spring when yellow 

starthistle is bolting. They feed heavily on immature starthistle buds. Females 

chew holes in the sides of mature, closed buds in early to midsummer, lay 

eggs inside, and cap holes with a dark substance. Hatching larvae feed on 

developing seeds through three instars. Pupation occurs in chambers made of 

damaged seed and receptacle tissue. Adults emerge in late summer. There is 

one generation per year.

DAMAGE: Larvae feed on receptacle tissue and developing seeds. Adult feeding 

leads to a high percentage of seed head abortion. Both forms of feeding 

do not kill existing plants, but help reduce the rate of spread of starthistle 

populations. 

PREFERRED HABITAT: Does well throughout the majority of conditions 

yellow starthistle has invaded in the USA. 

HISTORY: Introduced from Greece and released on yellow starthistle in the 

USA from 1990 (CA, ID, NV, OR, WA).

CURRENT STATUS: Abundant and widespread in the USA where larval 

feeding destroys up to 100% of seeds within attacked seed heads. Adult 

a b
Biological Control OF WEEDS in the Northwest 205starthistle

feeding also causes abortion of attacked seed heads, having the largest total 

effect on the weed’s fecundity. However, bud herbivory reduces the plant’s 

attractiveness to ovipositing seed predators, reducing direct negative effects 

of bud herbivory. In conjunction with Chaetorellia succinea, this species can 

reduce seed production by >70% overall. Only at low initial plant densities 

can this impact population growth; at many study sites plants compensate 

for decreased seedling density by growing larger and producing more seeds. 

Parasitism and predation negate impact at some sites.

REDISTRIBUTION: Already widespread throughout the range of yellow 

starthistle. Wherever not currently established, adults can be collected with 

a sweep net (with or without an aspirator) in midsummer when yellow 

starthistle is in the late bud stage. Releases of 200 individuals should be made 

on patches of at least 2,000 m2 (1/2 acre). Establishment can be monitored 

the following summer by checking for adults and/or feeding larvae within 

capitula. Note that feeding larvae can be very difficult to distinguish from 

other starthistle weevil species.

NOTES: This species has a longer snout than both Bangasternus orientalis and 

Larinus curtus. E. villosus consumes a higher proportion of seeds when plants 

are not infected with Puccinia jacea var. solstitialis. This agent is not approved 

for release in Canada.

Coleoptera: Curculionidae

Eusteno

villosus
206 Biological Control OF WEEDS in the Northwest starthistle DESCRIPTION: Larvae are up to 6 mm long with white, C-shaped bodies and 

brown head capsules. Adults are 5-6 mm long and have medium-length snouts. 

Bodies are brown with white hairs that give them a mottled appearance. Hairs 

are often yellowish from pollen.

Larinus curtus Hochhut

Yellow starthistle flower weevil

Larinus curtus: a) larva in seed head (Charles Turner, USDA ARS, www.bugwood.org), b) adult 

(Laura Parsons & Mark Schwarzländer, University of Idaho)

LIFE CYCLE: Adults overwinter in soil litter and emerge in summer when yellow 

starthistle is in bud and flowering. They feed on florets and pollen through four 

larval instars. Females lay eggs singly at the base of florets. Hatching larvae feed 

on developing seeds. Pupation occurs in chambers made of damaged seed and 

receptacle tissue. Adults emerge in late summer. There is one generation per year.

DAMAGE: Larvae feed on flower head tissue and developing seeds. Seed 

consumption does not kill existing plants, but does help reduce the rate of 

spread of starthistle populations.

PREFERRED HABITAT: Specific habitat requirements are unknown, but can 

be found throughout most yellow starthistle infestations in the western USA.

HISTORY: Introduced from Greece and released on yellow starthistle in the USA 

from 1992 (CA, ID, OR, WA). 

CURRENT STATUS: In the USA, larval feeding destroys up to 100% of seeds 

within attacked seed heads; however, attack rates are typically low. Abundance 

plateaued within a few years of introduction and it varies from high in portions 

of OR, to moderate in WA, and becoming more limited in ID and CA. It is less 

abundant than the other seed-feeding agents which have been unable to impact 

yellow starthistle population trajectories. Some weevil populations are limited 

a b
Biological Control OF WEEDS in the Northwest 207starthistle

by Nosema sp. parasites.

REDISTRIBUTION: Only Nosema-free populations (lab-reared) are 

permitted for release in the USA. Releases of 200 individuals should be made 

on patches of at least 2,000 m2 (1/2 acre). Establishment can be monitored the 

following summer by checking for adults and/or feeding larvae within capitula. 

Note that feeding larvae can be very difficult to distinguish from other starthistle 

weevil species.

NOTES: This species has a longer snout than Bangasternus orientalis but shorter 

than Eustenopus villosus. This agent is not approved for release in Canada.

Coleoptera: Curculionidae

Larinus 
208 Biological Control OF WEEDS in the Northwest starthistle DESCRIPTION and LIFE CYCLE: This fungus has several stages in its life 

cycle. Teliospores can withstand freezing temperatures and are the overwintering 

stage. These germinate in spring and produce basidiospores which initiate the 

sexual process of rust development. Aeciospores are then produced, followed by 

urediospores. Urediospores are the most distinctive spore. They are flat, round, 

tiny (25 μ in diameter) and covered with short spines. Masses of urediospores 

occur in a pustule on an infected leaf. They appear reddish brown and powdery 

and are easily blown to uninfected plants. With suitable levels of moisture and 

temperature, spores germinate and repeat the cycle, producing more urediospores. 

This process can take two weeks to complete. When host starthistle plants die 

back in late summer, the fungus produces teliospores in preparation for winter.

Puccinia jacea var. solstitialis Savile

Yellow starthistle rust

Puccinia jacea var. solstitialis: a) dew on yellow starthistle leaf, b) infected leaf (a,b Stephen Ausmus, 

USDA ARS, www.bugwood.org)

DAMAGE: Infected plants can experience stunted growth, reduced seed 

production, and a higher susceptibility to interspecific competition and attack 

from additional biocontrol agents.

PREFERRED HABITAT: Requires climates with dew periods that result in 

moisture forming or collecting on starthistle foliage. 

HISTORY: Introduced from Turkey and released in the USA from 2003 (CA 

2003, OR 2008).

CURRENT STATUS: Established only in CA (USA). Under optimal conditions 

(moist, mild temperatures) the rust can reduce biomass and number of capitula, 

especially in conjunction with high plant competition. At drier sites, impact is 

decreased and likely to be of only minor biological significance. Across much of 

a b
Biological Control OF WEEDS in the Northwest 209starthistle

yellow starthistle’s range, suboptimal conditions prevent the rust’s persistence 

and/or significant impact. 

REDISTRIBUTION: Should be collected by vacuuming urediospores from 

infected leaves throughout the growing season, suspending the spores in water, 

and spraying them on new foliage prior to a dew period. Alternatively, transfer 

infected stems to new sites in the evening during summer, and spray uninfested 

plants with water. Take care not to spread yellow starthistle seeds to new sites 

as this may introduce new genetic material. Establishment can be monitored by 

observing pustules on new yellow starthistle foliage throughout the following 

growing season.

NOTES: Infection by this rust is sometimes additive with the effects of seed 

predators; under other conditions it indirectly causes a reduction of seed 

predation which can cancel out entirely the direct negative impact of the rust. 

This agent is not approved for release in Canada.

Pucciniomycetes: Pucciniales

Puccinia 

var. sols
210 Biological Control OF WEEDS in the Northwest starthistle DESCRIPTION: Larvae are up to 5 mm long and barrel-shaped. They are whitish 

and have no head capsules. Adults are black with a yellow spot on the bottom 

part of the thorax. Eyes are multi-colored and metallic. Wings are clear with 

dark crossbands. Males are 3-4 mm long while females are 4-6 mm, including 

ovipositors.

Urophora sirunaseva (Héring)

Yellow starthistle gall fly

LIFE CYCLE: Adults emerge in spring as yellow starthistle bolts. Females lay eggs 

(up to 270 in a lifetime) on top of immature, closed buds. Hatching larvae feed 

on florets. When they reach the receptacle, a woody gall is formed around each 

larva; multiple galls may occur in one flower head. There are three larval instars, 

prior to pupation within galls. Adults emerge in summer, mate, and lay eggs on 

more starthistle buds. Larvae of this generation overwinter within galls. There 

are two generations per year.

DAMAGE: Floret feeding and gall formation reduce seed production. Galls act as 

nutrient sinks, diverting plant resources from regular plant function.

PREFERRED HABITAT: Specific habitat requirements are unknown, but does 

not seem to do well at overly windy locations.

HISTORY: The first introductions occurred on yellow starthistle in CA, USA 

from 1969 utilizing flies collected in Italy. After these failed to establish, it was 

determined the species introduced was in fact Urophora jaculata, which is specific 

to yellow starthistle biotypes growing only in Italy. Two additional populations 

were subsequently introduced and released from 1984 (from Greece into CA, 

ID, OR, WA; from Turkey into ID). The Turkish introduction presumably did 

not survive. 

Urophora sirunaseva: a) larva in gall, b) adult (Laura Parsons & Mark Schwarzländer, University of 

Idaho), c) multiple galls in capitulum (a,c Charles Turner, USDA ARS, www.bugwood.org)

a b c
Biological Control OF WEEDS in the Northwest 211starthistle

CURRENT STATUS: In the USA, gall formation decreases seed production, 

though multiple galls are required per seed head before seed reduction is 

significant. High gall density per capitulum is not common. Though this species 

is widely distributed, abundance is low. Attack rates have decreased from peaks 

around 50% within the few years following successful establishment to usually 

around 10%. Overall impact is now limited. Populations at some sites are 

hindered by competition with other seed head agents.

REDISTRIBUTION: Sweeping adult flies is possible, though may be damaging. 

Instead, infested capitula 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, 

flies can be transferred to new yellow starthistle infestations in groups of 50-100. 

Prior to release, ensure that insect populations do not contain Chaetorellia 

succinea, which is not approved for redistribution, though it is already 

widespread in the USA. Establishment can be monitored by observing adults 

on starthistle foliage the following summer or by dissecting capitula for galls/

larvae from summer throughout the following spring. Note that feeding larvae 

can be difficult to distinguish from other starthistle seed head insects. Urophora 

can be distinguished by their presence within galls.

NOTES: This agent is not approved for release in Canada.

Diptera: Tephritidae

Uropho

sirunase
212 Biological Control OF WEEDS in the Northwest St. Johnswort 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 (1⁄3-1 m) 

with numerous stems 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 (21⁄2 cm). Leaves have numerous 

transparent dots as well as tiny black glands along their margins. Flowers are 

numerous, bright yellow, 3⁄4 in (11⁄2 cm) in diameter, have many stamens, and 

have petals with additional black glands along margins. Seed pods are sticky, 

3-celled, 1⁄4 in (2⁄3 cm) long, and filled with numerous seeds.

 

b

Common St. Johnswort

Hypericum perforatum L.

a) plant (Richard Old, XID Services, Inc, www.xidservices.com, www.bugwood.org), b) infestation 

(Marianna Szucs, Colorado State University)

a
Biological Control OF WEEDS in the Northwest 213St. Johnswort

c) leaves (Steve Dewey, Utah State University), d) mature plant (Norman Rees, USDA ARS) e) flowers 

(Marianna Szucs, Colorado State University) (c,d www.bugwood.org)

HABITAT: Found in diverse areas, often with open sunlight and disturbance, such 

as clear cuts, roadsides, and overgrazed land. Frequents sandy or gravelly soil.

ECOLOGY: 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, 

especially if buried more than 1 in deep (21⁄2 cm). Vegetative reproduction is 

responsible for much of the growth in a common St. Johnswort population.

APPROVED BIOLOGICAL CONTROL AGENTS: USA: Agrilus hyperici, 

Aplocera plagiata, Chrysolina hyperici, C. quadrigemina, C. varians, and

Zeuxidiplosis giardi; CAN: A. hyperici, Aphis 

chloris, A. plagiata, C. hyperici, C. quadrigemina, 

C. varians and Z. giardi.

NOTES: This plant is toxic to white-haired 

animals, though usually not resulting in death.

Family Hypericaceae

d

Hype

perfo

c e
214 Biological Control OF WEEDS in the Northwest St. Johnswort HISTORY IN THE NORTHWEST: The first approved biological control agents 

released against common St. Johnswort in North America were the klamathweed 

beetles Chrysolina hyperici and C. quadrigemina released in the USA in 1945 and 

1946, respectively. The introductions of these insects led to a marked decrease 

of common St. Johnswort throughout much of its invaded range, though some 

infestations continued to expand even with Chrysolina present. Consequently, 

the root borer Agrilus hyperici and the gall midge Zeuxidiplosis giardi were 

released in 1950; the defoliating inchworm Aplocera plagiata was released in 

1989. C. hyperici and C. quadrigemina were subsequently redistributed from the 

USA to Canada in 1951 and 1952, respectively, while A. hyperici and Z. giardi 

were redistributed from the USA to Canada in 1955 and 1995, respectively. 

A. plagiata was introduced directly from Europe prior to its release in Canada 

from 1967. The aphid Aphis chloris was introduced from Europe and released 

only in Canada. A third Chrysolina species, Chrysolina varians, was introduced 

from Europe and released on common St. Johnswort in the USA in 1950 and in 

Canada from 1957, but failed to establish in either country.

CURRENT STATUS: A. hyperici is established in both the USA and CAN 

and its root-boring initially demonstrated high control ability for common St. 

Johnswort. It has since been displaced by C. quadrigemina, and populations are 

limited in both countries. Defoliation by A. plagiata can be damaging locally, but 

populations are limited in both the USA and CAN. Z. giardi failed to establish in 

Canada. Heavy parasitism has limited populations to only select locations in CA, 

USA. A. chloris is established only in CAN where it can provide control locally, 

but populations fluctuate with the weather and due to interspecific competition 

with Chrysolina spp. The Chrysolina spp. have been the most effective common 

St. Johnswort agents to date. Within 10 years of the first release, most common 

St. Johnswort populations in open, sunny areas were reduced more than 97%. 

Chrysolina spp. frequently occur in mixed populations and often in boom/bust 

cycles. The plant still cyclically rebounds, especially where land management 

practices have not improved, but infestation levels are much lower than they 

were historically. C. hyperici is still considered widespread and abundant in some 

places, though C. quadrigemina has since become the main factor controlling 

the weed throughout much of the western USA and CAN. 

RECOMMENDATIONS: USA and CAN: The limited impact and decreased 

abundance of A. hyperici and A. plagiata make them a low priority for 

redistribution. Z. giardi is so heavily parasitized, it should not be redistributed 

in the USA or back to CAN where it failed to establish. A. chloris should be 

redistributed to cold sites in CAN where Chrysolina spp. are limited or absent. 

St. Johnswort Biological Control
Biological Control OF WEEDS in the Northwest 215St. Johnswort

Agrilus, Chrysolina hyperici: Laura Parsons & Mark Schwarzländer, University of Idaho, Aphis: © 

Province of British Columbia. All rights reserved. Reproduced with permission of the Province of 

British Columbia, Aplocera, C. quadrigemina: Eric Coombs, Oregon Department of Agriculture, 

Zeuxidiplosis: Norman Rees, USDA ARS, www.bugwood.org

Aphis chloris is not approved for release in the USA. Chrysolina spp. are 

typically widespread, but populations fluctuate. Where populations are in the 

bust stage, redistributions of adults should be made. In cold, moist climates, 

C. hyperici should be considered. Elsewhere, C. quadrigemina is the most 

recommended species. Mixed populations may increase the probability of a 

successful redistribution. In shady habitats, other agents and/or control methods 

should be utilized.

Agent Adult Impact Recommendation

Agrilus 

hyperici

Root-boring initially displayed 

ability to control the weed, 

but populations have since 

been largely displaced by C. 

quadrigemina. Now limited.

Decreased and limited 

abundance coupled with current 

low overall impact make this 

low priority for redistribution in 

USA and CAN.

Aphis 

chloris

Sap-sucking provides control 

at some sites. Populations 

fluctuate due to weather 

and abundance/impact of 

Chrysolina spp. 

Not released in USA.

Recommended for 

redistribution in CAN where 

Chrysolina spp. are limited or 

not established.

Aplocera 

plagiata

Defoliation can be damaging 

locally, but populations are 

typically low throughout 

range in USA and CAN.

Limited abundance coupled 

with current low overall impact 

make this low priority for 

redistribution in USA and 

CAN.

Chrysolina 

hyperici

Defoliation first considered 

high impact. Now less 

important than C. 

quadrigemina in most habitats; 

better suited to others.

Lower priority than 

C. quadrigemina, but 

recommended for colder, 

more moist habitats where C. 

quadrigemina is less suited.

Chrysolina 

quadrigemina

Defoliation has extremely 

high impact. Most important 

agent. Doesn’t thrive in all 

habitats. Populations follow 

boom/bust cycle with weed.

Already widespread 

throughout much of North 

America. Recommended 

for redistribution where 

populations currently limited.

Zeuxidiplosis 

giardi

Galls reduce growth of heavily 

infested plants. However 

populations highly parasitized so 

are very limited in abundance. 

Not established in CAN.

High parasitism rates and 

extremely low abundance 

make this a low priority for 

redistribution in the USA.
216 Biological Control OF WEEDS in the Northwest St. Johnswort DESCRIPTION: Larvae are white with brown mouthparts 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.

Agrilus hyperici (Creutzer)

St. Johnswort root borer

LIFE CYCLE: Larvae overwinter within roots, feeding again within the roots the 

following spring as plants bolt. After the fourth instar, pupation occurs in the 

roots. Adults emerge through early summer as the weed 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, with the attacked plant dying outright 

in some instances.

PREFERRED HABITAT: 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. 

HISTORY: Introduced from France and released on common St. Johnswort in the 

USA from 1950 (CA, ID, MT, NV, OR, WA). Populations established in CA 

were redistributed to BC, Canada in 1955, 1964, and 1977, but all shipments 

failed to establish. A population from Idaho was successfully redistributed to 

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)

a b c
Biological Control OF WEEDS in the Northwest 217St. Johnswort

BC in 1987.

CURRENT STATUS: Abundance and impact in the USA vary. It disperses 

widely, but populations are typically low until occasional explosions. This 

beetle initially displayed the ability to destroy common St. Johnswort in CA 

but was displaced by Chrysolina quadrigemina and persisted only in some areas. 

Infestation levels reached up to 87% in WA. It contributed significantly to 

common St. Johnswort suppression in ID where it is still abundant. Established 

Canada though it is typically uncommon. At only one site have populations 

been large enough to redistribute. Overall impact has been negligible.

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

an aspirator) during summer when plants are in flower and can be transferred to 

new infestations 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: Has been observed attacking Hypericum concinnum, a forb/small shrub 

endemic to California.

Coleoptera: Buprestidae

Agrilus

hyperici
218 Biological Control OF WEEDS in the Northwest St. Johnswort 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.

Aphis chloris Koch

St. Johnswort aphid

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 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 stems and leaves, feeding on plant fluids. 

Under high aphid densities this feeding can cause individual common St. 

Johnswort plants to wither and die. In field studies, healthy potted plants were 

killed in one month when attacked by this species.

PREFERRED HABITAT: Does best where summers are humid and temperatures 

are cool. Sufficient cold winter temperatures are required for egg development.

Does not do well in hot, dry locations where plants wither and burn from heat. 

HISTORY: Introduced from Austria, Germany, and Hungary and released in BC, 

Canada from 1979.

a b
Biological Control OF WEEDS in the Northwest 219St. Johnswort

CURRENT STATUS: Provides significant control at some sites in 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 new infestations 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 as this may introduce 

new genotypes). Establishment can be monitored throughout the same or 

following by observing adults or nymphs on foliage of common St. Johnswort. 

NOTES: This agent is not approved for release in the USA.

Hemiptera: Aphididae

Aphis ch
220 Biological Control OF WEEDS in the Northwest St. Johnswort DESCRIPTION: Eggs are small, pearly-white ovals. Larvae resemble twigs and 

are reddish brown with weak gray stripes. They are up to 21⁄2 cm long. Pupae are 

greenish-golden and slender. Adults are triangular in shape and have gray wings 

with dark gray bands. Wingspans reach 33⁄4 cm (11⁄2 inches).

Aplocera plagiata (L.)

St. Johnswort inchworm

Aplocera plagiata: a) eggs (Norman Rees, USDA ARS, www.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 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 defoliation only weakens common St. Johnswort plants. 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. 

HISTORY: Introduced from France, Germany, Switzerland and released in the 

USA (CA, MT, OR) from 1989. Introduced from Germany, Switzerland, and 

France and released in BC, Canada in 1967, 1977, and 1980, respectively. All 

a b
Biological Control OF WEEDS in the Northwest 221St. Johnswort

three populations established and subsequently intermixed.

CURRENT STATUS: In the USA where it is locally abundant, defoliation 

hinders and may kill plants outright. However, overall abundance is typically 

limited. It is most effective in warm, dry areas where the insect can complete two 

generations. In Canada, it disperses readily throughout southern interior BC. 

However, populations remain low and do minimal damage.

REDISTRIBUTION: Adults may be collected and transferred, however this 

stage is fragile and sweep netting often results in injury to the moths. 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 new 

infestations 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 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.

Lepidoptera: Geometridae

Aplocera plagiata: c) adult (Eric Coombs, Oregon Department of Agriculture), d) defoliation (Norman 

Rees, USDA ARS, www.bugwood.org)

c d

Aplocer

plagiata
222 Biological Control OF WEEDS in the Northwest St. Johnswort 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.

Chrysolina hyperici (Forster) & C. quadrigemina (Suffrian)

Klamathweed beetles

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 and 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 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.

HISTORY: C. hyperici and C. quadrigemina were introduced from England and 

France (respectively) via Australia. They were released on common St. Johnswort 

in the USA from 1945 and 1946, respectively, in CA, ID, MT, NV, OR, UT, 

Chrysolina spp. a) eggs (Norman Rees, USDA ARS, www.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, www.bugwood.org)

a b d

c
Biological Control OF WEEDS in the Northwest 223St. Johnswort

WA. Populations of C. hyperici and C. quadrigemina established in the USA 

were redistributed to BC (CAN) from 1951 and 1952, respectively. 

CURRENT STATUS: Within 10 years of the first Chrysolina release, the weed 

population was reduced more than 97% at most open, sunny sites. The beetles 

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 often crash, leading to 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 USA and Canada, though C. quadrigemina is now typically considered 

to be more abundat and effective throughout the western USA and Canada. 

REDISTRIBUTION: Adults can be collected with a sweep net during summer 

when plants are in flower and transferred to new infestations in groups of 200. 

Keep in mind that Chrysolina adults often rest in the soil during late summer 

(July and August). Establishment can be monitored by observing larvae on St. 

Johnswort foliage the following spring (larvae feed at night). Alternatively, adults 

can be observed throughout the following summer during the heat of the day. 

Attacked plants will appear stripped and wilty.

NOTES: In the USA, C. quadrigemina attacks the 

native Hypericum concinnum and the exotic H. 

calycinum. A third Chrysolina species, C. varians 

(Schaller), was introduced from Europe and 

released on common St. Johnswort in the USA 

(CA, ID) from 1950. It was also introduced from 

Sweden and released in CAN (BC) from 1957, 

but failed to establish in either country.

Coleoptera: Chrysomelidae

e, f) Chrysolina spp. adults and damage: (both Jennifer Andreas, Washington State University 

Extension)

e f

C. hyperici C. quadrigemina

Chrysolin

quadrige

Chrysolina

hyperici
224 Biological Control OF WEEDS in the Northwest St. Johnswort DESCRIPTION: Eggs are elongated and pale red in color. Larvae are orange and 

can reach up to 2 mm. 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.

Zeuxidiplosis giardi (Kieffer)

St. Johnswort gall midge

Zeuxidiplosis giardi: a) adult, b) gall damage (both Norman Rees, USDA ARS, www.bugwood.org)

LIFE CYCLE: Larvae emerge in early spring and feed on 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. 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: 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. Nor does it do well with heavy livestock grazing. 

HISTORY: Introduced from France and released in the USA from 1950 (CA, 

ID, MT, OR, WA). A second release attempt was made in 1992 utilizing a 

population from Hawaii reportedly doing much better than individuals in the 

USA. This second introduction failed to establish. Populations in CA (USA) 

were redistributed to BC (CAN) from 1995. 

a b
Biological Control OF WEEDS in the Northwest 225St. Johnswort

CURRENT STATUS: Established only in CA (USA) where it can reduce 

growth in heavily infested plants. However the species is heavily parasitized so 

populations are very limited. Not established in Canada. Populations thrived the 

first summer of release but were subsequently annihilated due to sudden subzero temperatures in mid-November.

REDISTRIBUTION: Sweeping adult flies 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 from different genotypes. 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 foliage.

NOTES: Capable of forming galls on Hypericum concinnum, a forb/small shrub 

endemic to California. However, damage to this plant is insignificant.

Diptera: Cecidomyiidae

Zeuxidip

giardi
226 Biological Control OF WEEDS in the Northwest toadflaxes SYNONYMS: broad-leaved toadflax; Linaria genistifolia (L.) Mill. ssp. dalmatica

(L.) Maire & Petitm., Linaria dalmatica (L.) Mill., Linaria genistifolia (L.) Mill.

ORIGIN: Likely introduced from Eurasia by 1900 in horticultural trials.

DESCRIPTION: Upright, herbaceous perennial typically growing numerous 

stems 1-4 ft tall (1⁄3-1.2 m) from a deep taproot with lateral roots. Leaves are 

alternate, thick, blue-green, and often waxy. Leaves are heart-shaped at the 

base, clasp the stem, and are typically 1-2 in long (2-5 cm) and nearly as wide. 

Flowers are bright yellow and snapdragon-like with two lips. Each has a bearded, 

yellowish-orange throat and a long spur. Flowers occur in spiked clusters 

emerging from leaf axils. Each flower produces a round capsule holding 60-300 

small, somewhat triangular seeds. 

 

HABITAT: A weed of wastelands, roadsides, abandoned pastures, slash piles, and 

rangeland. It does well in cool, semiarid climates and on coarse-textured soils. 

b

Dalmatian toadflax

Linaria dalmatica ssp. dalmatica (L.) Mill.

a) plant (K. George Beck & James Sebastian, Colorado State University, www.bugwood.org), b) 

infestation (Jennifer Andreas, Washington State University Extension)

a
Biological Control OF WEEDS in the Northwest 227toadflaxes

c) leaves, d) flower (c,d Bonnie Million, National Park Service), e) seeds (Steve Hurst, USDA NRCS 

PLANTS database) (all www.bugwood.org)

ECOLOGY: Reproduces both by seed and by its spreading root system. Seedlings 

germinate in fall or spring; bolting occurs in spring. Flowering occurs throughout 

the summer. Seeds may remain viable in the soil for up to 10 years. 

APPROVED BIOLOGICAL CONTROL AGENTS: USA: Brachypterolus 

pulicarius, Calophasia lunula, Eteobalea intermediella, E. serratella, Mecinus 

janthinus, M. janthiniformis, Rhinusa antirrhini, and R. linariae; CAN: C. 

lunula, E. intermediella, M. janthinus, M. janthiniformis, R. antirrhini, and R. 

linariae.

NOTES: May be toxic to grazing livestock. Dalmatian and yellow toadflax can 

both be highly variable in North America, which is compounded by their ability 

to hybridize. The taxonomic status of this group of species and their hybrids 

remains uncertain. The authors of this manual follow 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 one (L. 

dalmatica ssp. dalmatica) is invasive and weedy 

in North America. Two widely recognized 

forms of L. dalmatica subsp. dalmatica (narrowleaved and broad-leaved) could be hybrids or 

unique species. It is the broad-leaved form that 

has proven most problematic in North America.

Family Plantaginaceae

c d e

Linar

dalm
228 Biological Control OF WEEDS in the Northwest toadflaxes 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 (1⁄3-1 m) from a taproot with spreading rhizomatous roots. 

Leaves are alternate, pale green, pointed at both ends, and have small stalks. 

They are narrow and typically 2 in long (5 cm) with a large central vein on the 

underside. Flowers are bright yellow and snapdragon-like with two lips. Each 

has a bearded, bright orange throat and a long spur. Flowers occur in spiked 

clusters emerging from leaf axils Each flower produces a round capsule holding 

up to 250 round, winged seeds.

 

HABITAT: A weed of wastelands, roadsides, clear cuts, and field edges. It does 

b

Yellow toadflax

Linaria vulgaris Mill.

a) plant (Tiffany Wax, Washington State University Extension), b) infestation (Michael Shephard, 

Forest Service, www.bugwood.org)

a
Biological Control OF WEEDS in the Northwest 229toadflaxes

c, d) leaves, d) flowers (both Michael Shephard, Forest Service), e) seeds (Steve Hurst, USDA NRCS 

PLANTS database) (all www.bugwood.org)

well on coarse-textured soils in cool climates that are typically more moist than 

those preferred by Dalmatian toadflax.

ECOLOGY: Reproduces both by seed and by its spreading root system. Seedlings 

typically germinate and bolt in spring. Flowering occurs throughout the summer. 

Seeds generally have low viability, but some may remain viable in the soil for 

several years. 

APPROVED BIOLOGICAL CONTROL AGENTS: USA: Brachypterolus 

pulicarius, Calophasia lunula, Eteobalea intermediella, E. serratella, Mecinus 

janthinus, M. janthiniformis, and R. linariae; CAN: C. lunula, E. serratella, M. 

janthinus, M. janthiniformis, and R. linariae.

NOTES: This species is reportedly not sought after by grazing livestock. Yellow and 

Dalmatian toadflax can both be highly variable 

in North America, which is compounded by 

their ability to hybridize. The taxonomic status 

of this group of species and their hybrids remains 

uncertain.

Family Plantaginaceae

c d e

Linar

vulga
230 Biological Control OF WEEDS in the Northwest toadflaxes HISTORY IN THE NORTHWEST: The first biological control agents for 

control of toadflax in North America were accidentally introduced. A strain 

of R. antirrhini preferring yellow toadflax arrived by 1909 and was found on 

(or intentionally redistributed to Dalmatian) in the USA and CAN by 1957. 

A second strain of R. antirrhini was intentionally introduced on Dalmatian 

toadflax in the USA and CAN in 1996 and 1993, respectively. Brachypterolus 

pulicarius arrived to the USA by 1919 and CAN by 1953. One population 

was subsequently redistributed to both species in the USA from 1992. R. neta

arrived accidentally in the USA by 1937 and CAN by 1957. This agent has not 

been intentionally redistributed. A third Rhinusa species (R. linariae) was only 

intentionally introduced, and was released on both species in both the USA and 

CAN in 1996. Calophasia lunula was intentionally introduced in 1962 onto both 

toadflaxes in CAN, and redistributed to both species in the USA by 1968. What 

was believed to be Mecinus janthinus was released on both toadflaxes in CAN 

from 1991 and in the USA from 1996. It has since been revealed the cryptic 

M. janthiniformis was part of releases made in CAN in 1992. M. janthiniformis

has since been redistributed and spread naturally to the USA. The two Eteobalea

moths (E. intermediella and E. serratella) were intentionally released on both 

toadflaxes in both countries in 1992.

CURRENT STATUS: Both Eteobalea moths failed to establish in both the USA 

and CAN. R. linariae failed to establish in the USA, and is only established on 

yellow toadflax in BC where its populations and root-galling impact are both 

limited. B. pulicarius and R. antirrhini are both widespread on yellow toadflax 

in the USA and CAN. Impact and abundance are greater on this species than 

Dalmatian. However, even at high densities, the flower- and seed-feeding 

by both species has little overall impact. C. lunula occurs on both species in 

both countries, but populations are typically limited. Even at high densities, 

plants can typically recover from heavy defoliation. Mecinus janthiniformis has 

proven highly effective against Dalmatian toadflax in the USA and CAN. It 

has controlled the weed at numerous sites in both countries. M. janthinus is 

more limited by cold climates and by the confusion from the cryptic species 

identification, though populations are increasing now that the situation has 

been clarified. Additional time is needed to determine if populations will build 

on yellow toadflax, similar to M. janthiniformis on Dalmatian, though early 

results are encouraging.

RECOMMENDATIONS: USA and CAN: Due to their already widespread 

distribution and limited impact, redistributions of B. pulicarius and R. 

antirrhini are not recommended. The limited populations of R. linariae make 

Toadflax Biological Control
Biological Control OF WEEDS in the Northwest 231toadflaxes

Brachypterolus: Daniel K. MacKinnon, Colorado State University, Calophasia, Rhinusa antirrhini: 

Laura Parsons, University of Idaho, Mecinus, Rhinusa linariae: Bob Richard, USDA APHIS PPQ (all 

www.bugwood.org)

this species difficult to collect; its limited impact also makes it a low priority 

for redistribution. C. lunula is more available and its limited populations may 

warrant supplementation. However, this species is less damaging to toadflax over 

time as heavily attacked plants often recover. Consequently it is a low priority 

for redistribution. Concern for nontarget attack should dissuade intentional 

redistribution of C. lunula. M. janthiniformis is very effective on Dalmatian 

toadflax but is already quite widespread. Where this species is absent, adults 

should be redistributed in spring using nets and aspirators. The true M. janthinus

should also have a high priority for redistribution to yellow toadflax sites, when 

populations are sufficiently large for collection. Nets and aspirators can again be 

used to collect adults in spring. Emphasis should be placed on redistributions to 

sites with warmer climates and low elevations.

Agent Adult Impact Recommendation

Brachypterolus 

pulicarius

Prefers yellow on which 

delays flowering, reduces 

seed production. Though 

abundant, overall impact 

minimal.

Already widespread in USA and 

CAN with little overall impact 

to yellow so is a low priority for 

redistribution. Not intentional 

in CAN.

Calophasia 

lunula

Limited abundance on both 

yellow and Dalmatian in USA 

and CAN. High densities 

cause heavy defoliation, but 

plants usually recover.

Limited impact makes low 

priority for redistribution. 

Reports of nontarget attack; 

redistribute with caution.

Mecinus 

janthiniformis

Mecinus 

janthinus

Mining and adult feeding 

decrease Dalmatian 

significantly in USA and 

CAN. Populations still limited 

on yellow.

M. janthiniformis most effective 

agent on Dalmatian. Should be 

redistributed where not already 

present. M. janthinus should be 

redistributed to yellow.

Rhinusa 

antirrhini

Most abundant strain in USA 

and CAN prefers yellow. 

Floral feeding reduces seed 

production. Despite high 

abundance, impact limited.

Limited impact despite high 

abundance on yellow makes this 

a low priority for redistribution 

on either species.

Rhinusa 

linariae

Prefers yellow. Adult feeding, 

larval root-galling reduce 

plant nutrient reserves. In BC 

only; populations too low for 

significant impact.

Widely failed releases and 

low impact of established 

populations make this a low 

priority for redistribution.
232 Biological Control OF WEEDS in the Northwest toadflaxes DESCRIPTION: 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.

Brachypterolus pulicarius (L.)

Toadflax flower-feeding beetle

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. Hatching larvae feed on flower pollen, anthers, ovaries, and immature 

seeds. They develop through three instars and drop to the soil in fall to overwinter 

as pupae in soil litter. There is one generation per year.

DAMAGE: Adult feeding can delay flowering and reduce the number of healthy 

flowers (and thus seeds) produced. 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 spread for 

toadflax population spread.

PREFERRED HABITAT: Well adapted to a variety of environmental conditions 

and can be found throughout the majority of toadflax infestations in North 

America. 

HISTORY: Initially found as an unintentional introduction on yellow toadflax in 

NY (USA) in 1919 from where it spread throughout the USA on both yellow 

and Dalmatian toadflax. First recorded on Dalmatian and yellow toadflax as 

an accidental introduction in BC (CAN) in 1953. One population found 

feeding exclusively on Dalmatian in Canada was subsequently redistributed to 

Dalmatian in MT, ID, NV, and WY in 1992 and yellow toadflax in MT in 

1997. The different groups of B. pulicarius in the USA now overlap. Because 

they are not genetically different and are likely moving between the two weed 

Brachypterolus pulicarius: a) larva, b) adult (a,b Daniel K. MacKinnon, Colorado State University), c) 

adults (Susan Turner, British Columbia Ministry of Forests) (all www.bugwood.org)

a b c
Biological Control OF WEEDS in the Northwest 233toadflaxes

species on their own, they can no longer be differentiated.

CURRENT STATUS: It was initially believed different biotypes 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. B. pulicarius

prefers and performs better on yellow toadflax; the use of Dalmatian is incidental 

in both the USA and Canada. On Dalmatian toadflax in the USA, high densities 

(such as in ID, OR, WA) can stunt weed height and causes increased branching, 

though overall impact to flowering and seed production is minimal at most sites. 

It is abundant on yellow toadflax in the USA on which it can delay flowering 

and reduce seed production by 80-90% at some locations. However, overall 

impact is minimal. On yellow toadflax in Canada, it is abundant but 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). 

Found sporadically on Dalmatian toadflax in Canada but appears to be too rare 

to have any major impact on seed production. 

REDISTRIBUTION: Adults can be collected with a sweep net and aspirator 

during spring when plants are in bud or flowering and transferred to new 

infestations 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: This agent was not an intentional introduction in Canada. Though 

B. pulicarius was first an accidental introduction in the USA, it was subsequently 

intentionally redistributed and also later introduced intentionally from Canada. 

Competition between Rhinusa antirrhini and Brachypterolus pulicarius prevents 

additive impact in many locations.

Coleoptera: Kateridae

Dalmatian yellow

Brachypter

pulicarius,

yellow

Brachypterolus

pulicarius,

Dalmatian
234 Biological Control OF WEEDS in the Northwest toadflaxes DESCRIPTION: Eggs are pale yellow and strongly ribbed. Larvae are gray 

initially but have black and yellow stripes with white spots at the final instar. 

They can be up 40 cm long. Pupae are golden brown within green cocoons. 

Adults are a mottled gray-brown with light and dark markings on the wings. 

They are 1-11⁄2 cm long with a wingspan of 21⁄2-3 cm.

Calophasia lunula (Hufnagel)

Toadflax moth

LIFE CYCLE: Adults emerge in late spring and feed on nectar. Females lay 30-80 

eggs on toadflax foliage. Hatching larvae feed on young leaves, but will consume 

lower stem leaves as plants become increasingly defoliated. Upon maturation 

after the fifth instar, larvae move to the base of toadflax and spin cocoons of silk, 

chewed leaves, and soil. Adults emerge in mid-summer and repeat the process. 

There are 1-3 generations per year, the final one overwintering as pupae within 

cocoons.

DAMAGE: Larval defoliation can kill young toadflax plants.

PREFERRED HABITAT: Prefers dry with coarse-textured soils. Establishment 

can be limited in cold climates.

HISTORY: Introduced onto both Dalmatian and yellow toadflax in AB and BC 

(CAN) from populations sourced in Switzerland (1962) and former Yugoslavia 

(1989). The Switzerland population was redistributed from Canada to the USA 

from 1968 on both species of toadflax (CO, ID, MT, NV, OR, WA, WY).

CURRENT STATUS: Populations are limited on both Dalmatian and yellow 

toadflax throughout much of the USA, though some localized population 

explosions occur. At high densities it can lead to patch defoliation. Overall, larval 

feeding typically decreases leaf area but does not disrupt the photosynthetic 

Calophasia lunula: a) larva, b) cocoon (Gary Piper, Washington State University, www.bugwood.org), 

c) adult (a,c Laura Parsons & Mark Schwarzländer, University of Idaho)

a b c
Biological Control OF WEEDS in the Northwest 235toadflaxes

capacity sufficiently to have significant impact on attacked plants. The 

population from former Yugoslavia established on both yellow and Dalmatian 

toadflax in Canada where the impact is limited for the same reasons as in the 

USA. Parasitism may also limit populations in some parts of Canada.

REDISTRIBUTION: Adults are delicate and are easily damaged by sweep 

netting. They are also difficult to find. Consequently, this biocontrol agent is best 

transferred in the larval stage. Larvae can be gently picked from toadflax foliage 

using forceps in summer through fall. Later instar larvae 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 agent’s host 

specificity. Caution should be taken during its redistribution, especially in 

areas with desirable snapdragon species present.

Calophasia lunula: d) larvae and damage (Laura Parsons & Mark Schwarzländer, University of Idaho), e) 

larval damage (Susan Turner, British Columbia Ministry of Forests) (both www.bugwood.org)

Lepidoptera: Noctuidae

d e

Dalmatian yellow

Calophasi

lunula, ye

Calophasia

lunula,

Dalmatian
236 Biological Control OF WEEDS in the Northwest toadflaxes DESCRIPTION: Both species are morphologically very similar. Larvae are white 

with brown head capsules and are up to 5 mm long. Adults are bluish-black, 

elongate with long snouts, and are up to 5 mm long.

Mecinus janthiniformis Toševski & Caldara & M. janthinus Germar

Toadflax stem weevils

LIFE CYCLE: Overwintering adults emerge in early spring and feed on shoot 

tips, producing a shot hole pattern in upper leaves. 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. Hatching larvae feed in short 

tunnels chewed into toadflax stems. M. janthinus tends to mine lower in toadflax 

stems than does M. janthiniformis. Pupation occurs in late summer within the 

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: M. janthiniformis is well adapted to a variety of 

environmental conditions and can be found throughout much of Dalmatian 

toadflax infestations in the Northwest. M. janthinus prefers more mild, lowelevation sites in its native range. 

HISTORY: What was originally released in the USA and Canada as Mecinus 

janthinus was recently discovered to be a mixture of M. janthinus and the cryptic 

M. janthiniformis. The true M. janthinus was sourced from France and Germany 

and released in the USA on Dalmatian from 1996 (MT, WA, WY) and on yellow 

from 1997 (CO, ID, MT, OR, UT, WA, WY). The same France/Germany 

source was used for M. janthinus releases on both Dalmatian and yellow toadflax 

Mecinus spp. a) larva (Rosemarie De Clerck-Floate, Agriculture and Agri-Food Canada), b) pupa, c) 

adult (b,c Bob Richard, USDA APHIS PPQ) (all www.bugwood.org)

a b c
Biological Control OF WEEDS in the Northwest 237toadflaxes

in Canada from 1991 (AB, BC). M. janthiniformis was reportedly introduced 

from the Republic of Macedonia and released on Dalmatian toadflax in Canada 

from 1992 (AB, BC). It was redistributed from Dalmatian to yellow toadflax 

in AB, BC from 2000. Redistributions of M. janthiniformis were made from 

Canada to Dalmatian in the USA post 1996 (CA, CO, ID, MT, NV, OR, UT, 

WA, WY) and to yellow in MT post 1996 in mixes with the true M. janthinus.

CURRENT STATUS: M. janthiniformis usually prefers Dalmatian toadflax; M. 

janthinus usually prefers yellow. M. janthiniformis is abundant on Dalmatian in the 

USA and Canada where it has reduced the weed dramatically throughout much 

of its range. M. janthinus is established on yellow in the USA and Canada where 

densities and impact can be high locally but are typically low overall. Parasitism, 

cold climates, and incorrect host/agent matching with the janthinus/janthiniformis

complex are all contributors, though impact is now increasing at some sites.

REDISTRIBUTION: Adults can be swept from toadflax foliage from spring 

through mid-summer when plants are bolting to late flowering. Adults should 

be readily visible, mating and congregating on shoot tips and in leaf axils. 

They are most active during the warm time of day and in calm, sunny weather. 

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 the cryptic M. 

janthiniformis has only recently been made, 

sorting the release history and establishment 

status of both Mecinus species on both toadflax 

species is a work in progress in North America.

Coleoptera: Curculionidae

Mecinus spp. damage: (d,e,f) d) Jennifer Andreas, Washington State University Extension, e) (Gary 

Piper, Washington State University, www.bugwood.org), f) (Laura Parsons, University of Idaho)

d e f

M. janthiniformis 

on Dalmatian

M. janthinus 

on yellow

Mecinus

janthinus,

yellow

Mecinus

janthiniformis,

Dalmatian
238 Biological Control OF WEEDS in the Northwest toadflaxes SYNONYMS: Gymnetron antirrhini (Paykull)

DESCRIPTION: Larvae are creamy white with dark brown head capsules and 

are up to 4 mm long. Adults are gray to black and covered in dense, short hairs. 

They have a long, distinctly curved and pointed snout. Adults are typically 21⁄2 

mm long and have a wide body.

Rhinusa antirrhini (Paykull)

Toadflax seed capsule weevil

Rhinusa antirrhini: a) larvae in seeds, b) adult (Laura Parsons, University of Idaho), c) adults on 

flowers (a,c Eric Coombs, Oregon Department of Agriculture) (all www.bugwood.org)

LIFE CYCLE: Overwintering adults emerge in late spring and feed on shoot 

tips and young leaves. As toadflax flowers open, adults feed on pollen and 

flower tissue. Females lay 40-50 eggs singly inside flower ovaries, triggering the 

development of galls of enlarged seed tissue. Hatching larvae feed on seed tissue. 

Pupation occurs within seed capsules, with adults emerging in late summer or 

early fall to overwinter in soil litter. There is one generation per year.

DAMAGE: Galls and larval feeding reduce seed viability. Adult feeding is typically 

insignificant.

PREFERRED HABITAT: Overall habitat preferences are unknown but it is 

distributed throughout much of the toadflax habitats in North America.

HISTORY: An unintentional introduction referred to as the vulgaris biotype was 

found on yellow toadflax in the eastern USA in 1909 and on Dalmatian toadflax 

by 1957. This biotype was also intentionally redistributed from yellow to 

Dalmatian toadflax in WY in 1986. An additional strain (dalmatica biotype) was 

intentionally introduced from former Yugoslavia and released against Dalmatian 

toadflax from 1996 (MT, WY). An accidentally introduced population was 

first recorded in BC (CAN) in 1917. An additional strain was intentionally 

a b c
Biological Control OF WEEDS in the Northwest 239toadflaxes

introduced from former Yugoslavia and released on Dalmatian toadflax in AB 

and BC from 1993.

CURRENT STATUS: The vulgaris biotype is established on the narrow-leaved 

form of Dalmatian toadflax in the USA. Though attack rates on this form can be 

high locally, it is the least common and problematic form of Dalmatian toadflax 

so overall impact is minimal. It is unknown if the dalmatica biotype established 

on Dalmatian toadflax in the USA. Larval feeding of the vulgaris biotype 

on yellow toadflax destroys some seeds in attacked capsules. Seed reduction 

between 85 and 90% have been reported in WA, though it is typically much 

lower in other areas. Attack rates from 30-40% in OR had minimal impact on 

plant density, so it is believed that overall impact is limited. The unintentionally 

introduced strain of R. antirrhini is established on both Dalmatian and yellow 

toadflax in Canada. Populations of the new strain are confirmed established and 

increasing on Dalmatian. Though the impact of this intentional strain has yet to 

be studied in Canada, the yellow toadflax strain is widespread but still has yet to 

achieve satisfactory control.

REDISTRIBUTION: Already widespread on yellow toadflax in North America. 

Where redistributions may be required, adults can be collected with a sweep 

net and aspirator during late spring when plants are in bud or early flowering 

and can be transferred to new infestations in groups of 200. Establishment can 

be monitored by observing adults on toadflax flowers the following spring. 

Alternatively, seeds can be dissected to reveal larvae feeding within throughout 

the summer.

NOTES: Competition between R. antirrhini and Brachypterolus pulicarius prevents 

additive impact in many locations. R. antirrhini has a more pointed and curved 

snout than R. neta and is grayish-black while R. neta is gray to brown. R. 

antirrhini differs from R. linariae in its location of attack (adults attack flowers 

and larvae attack seeds while R. 

linariae adults attack stems and 

larvae attack roots).

Coleoptera: Curculionidae

vulgaris biotype 

Dalmatian

vulgaris biotype 

yellow

Rhinusa

antirrhini,

vulgaris

biotype, yellow

Rhinusa

antirrhini,

vulgaris

biotype,

Dalmatian

dalmatica biotype 

Dalmatian

Rhinusa

antirrhini,

dalmatica

biotype,

Dalmatian
240 Biological Control OF WEEDS in the Northwest toadflaxes SYNONYMS: Gymnetron linariae Panzer

DESCRIPTION: Larvae are creamy white with brown head capsules and are up 

to 4 mm long. Adults are small and black with pronounced, curved snouts. They 

are covered in dense, short hairs and up to 21⁄2 mm long.

Rhinusa linariae (Panzer)

Toadflax root-galling weevil

Rhinusa linariae: a) adult (Bob Richard, USDA APHIS PPQ), b) damage (Rosemarie De ClerckFloate, Agriculture and Agri-Food Canada) (both www.bugwood.org)

LIFE CYCLE: Overwintering adults emerge in spring and feed on toadflax 

stems. As flowers open, adults feed on pollen and flower tissue. Females lay eggs 

singly into pockets chewed into toadflax root crowns, triggering gall formation. 

Hatching larvae feed on galled root tissue. Pupation occurs in galls with adults 

emerging in mid- to late summer. Adults may feed briefly on toadflax stems, 

then overwinter in soil litter. There is one generation per year.

DAMAGE: Galls are a metabolic sink and disrupt nutrient transport. Adult and 

larval feeding reduces nutrient reserves which may stunt plants and reduce 

reproductive output.

PREFERRED HABITAT: Habitat preferences are unknown are populations are 

restricted to limited areas in only BC. In European literature, R. linariae does 

well in grassland habitats.

HISTORY: Introduced from Germany and released on Dalmatian toadflax in 

ID, MT, OR (USA) from 1996 as well as on yellow toadflax in MT from 1996. 

Introduced from central and southern Europe and southern Russia and released 

on both Dalmatian and yellow toadflax in AB and BC (CAN) from 1996. After 

USA introductions failed to establish, a population from BC was redistributed 

a b
Biological Control OF WEEDS in the Northwest 241toadflaxes

to CO (USA) in 2008.

CURRENT STATUS: Established only on yellow toadflax and only in Canada 

where populations are very limited. Because populations are slow to build, 

redistributions are made every 2-4 years when possible. Adult foliage feeding 

and larval galling reduce plant nutrient reserves. However, populations are too 

low for significant impact.

REDISTRIBUTION: Populations are restricted to 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 new infestations. 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: R. linariae has a more pointed and curved snout than R. neta and is black 

while R. neta is gray to brown. R. 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.)

Coleoptera: Curculionidae

Dalmatian yellow

Rhinusa

linariae, y

Rhinusa

linariae,

Dalmatian
242 Biological Control OF WEEDS in the Northwest toadflaxes Eteobalea intermediella Riedl &

E. serratella Treitschke

(Lepidoptera: Cosmopterigidae)

DESCRIPTION AND LIFE CYCLE: 

Both species are very similar, differing 

mainly in their egg-laying behavior and 

number of generations per year. Adults 

are slender, 8-10 mm long, and are black 

with white and yellow spots. They have a 

wingspan up to 18 mm. Adults emerge 

in late spring, and females lay up to 180 

eggs in small strings at the base of toadflax stems. Hatching larvae bore into the 

root crown where they feed on tissue inside tunnels they carve and line with silk. 

Larvae are off-white with brown heads. 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.

HISTORY: E. intermediella from former Yugoslavia and E. serratella from Italy 

were introduced against both Dalmatian and yellow toadflax in MT (USA) from 

1996. E. intermediella from Serbia was released on Dalmatian toadflax in AB 

and BC (CAN) in 1992. E. serratella from Italy was released on yellow toadflax 

in AB and BC in 1992. All introductions failed to permanently establish in both 

the USA and Canada.

Eteobalea intermediella: Bob Nowierski, 

Montana State University (www.bugwood.org)

Toadflaxes, Non-Established Agents
Biological Control OF WEEDS in the Northwest 243toadflaxes

Toadflaxes, Unapproved Agents

Rhinusa neta (Germar)

(Coleoptera: Curculionidae)

DESCRIPTION AND LIFE CYCLE: 

Overwintering adults emerge in late 

spring and feed on toadflax shoot tips and 

young leaves. Adults are gray or brown 

with a snout that is somewhat blunt and 

only slightly curved. They are covered 

in dense, short hairs and are typically 3 

mm long. As flowers open, adults feed on 

pollen and flower tissue. Females lay 40-

50 eggs singly inside flower ovaries. Hatching larvae feed on seed tissue through 

three instars. Larvae are 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 litter. There is one generation per year. 

HISTORY AND CURRENT STATUS: Accidental introduction discovered 

on both Dalmatian (narrow-leaved form) and yellow toadflax in eastern states 

of the USA in 1937 and in Canada by 1957. It is presently established on both 

species in at least WA and possibly other states in the Northwest, but occurs 

only in scattered populations. Established on both species in BC (CAN), but 

only on yellow toadflax in AB. It prefers yellow toadflax over Dalmatian in 

both countries. Larval feeding destroys a high proportion of seeds in attacked 

capsules, though overall attack rates to yellow toadflax are typically limited in the 

USA. Even in Canada, where yellow toadflax attack rates are higher, satisfactory 

control has yet to be achieved. Not approved for redistribution in the USA.

Gyorgy Csoka, Hungary Forest Research 

Institute (www.bugwood.org)
244 Biological Control OF WEEDS in the Northwest Leafy spurge SYNONYMS: N/A

ORIGIN: Native to Eurasia. Likely introduced to North America in contaminated 

ship’s ballast; 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 rhizomatous roots are brown 

and have pinkish buds. Leaves are alternate, narrow, and 1-3 in long (21⁄2-71⁄2 

cm). They have smooth margins and a deep midvein. Flowers are tiny, lime 

green, and enclosed by showy, yellow-green bracts. The are arranged in clusters 

at stem tips. Seed pods contain three smooth, elongated, gray-brown seeds. 

 

HABITAT: Occupies many different habitats and soil types and can be found from 

grasslands to forests to riparian areas. It is dominant in pastures, rangelands, 

waste areas, and along roadsides.

ECOLOGY: Reproduces both by seed and by its spreading root system. Root 

b

Leafy spurge

Euphorbia esula L.

a) plant (John M. Randall, The Nature Conservancy), b) infestation (William M. Ciesla, Forest 

Health Management International) (both www.bugwood.org)

a
Biological Control OF WEEDS in the Northwest 245Leafy 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) (all www.bugwood.org)

pieces as small as 1⁄2 in (1 cm) can develop into new plants. Peak 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.

APPROVED BIOLOGICAL CONTROL AGENTS: USA: Aphthona 

abdominalis, A. cyparissiae, A. czwalinai, A. flava, A. lacertosa, A. nigriscutis, 

Chamaesphecia crassicornis, C. hungarica, C. tenthrediniformis, Hyles euphorbiae, 

Oberea erythrocephala, Spurgia capitigena and S. esulae; CAN: Aphthona 

cyparissiae, A. czwalinai, A. flava, A. lacertosa, A. nigriscutis, Chamaesphecia 

astatiformis, C. crassicornis, C. hungarica, C. tenthrediniformis, H. euphorbiae, 

Lobesia euphorbiana, Minoa murinata, O. erythrocephala, Pegomya curticornis, P. 

euphorbiae, S. capitigena and S. esulae.

NOTES: Leafy spurge is a controversial and 

morphologically variable species considered 

to represent a complex of forms, species and 

hybrids. A toxic, milky latex oozes from damaged 

stems and leaves. Caution should be taken while 

handling this plant.

Family Euphorbiaceae

c d e

Euph

esula
246 Biological Control OF WEEDS in the Northwest Leafy spurge HISTORY IN THE NORTHWEST: Biological control of leafy spurge began 

in 1966 in North America with the release of Hyles euphorbiae in both the USA 

and Canada. Oberea erythrocephala was next released in Canada in 1979 and in 

the USA from 1980. Five Aphthona flea beetles were released in both countries 

throughout the 1980s, with an additional species (A. abdominalis) released in 

1993 only in the USA. Lobesia euphorbiana and Minoa murinata were released 

only in Canada in 1983 and 1988, respectively. Four Chamaesphecia species 

were released in North America from the 70s to the 90s. Pegomya and Spurgia 

agents were released as single species in the late 80s, though both have since been 

split into two species each. Pegomya spp. were approved in both the USA and 

Canada but released only in the USA.

CURRENT STATUS: All Chamaesphecia and Pegomya species failed to establish 

in North America, as did A. abdominalis and M. murinata. Spurgia capitigena 

is established only in more eastern states and provinces not covered in this field 

guide. S. esulae is established on leafy spurge in a few states in western USA where 

its density remains low and stem-galling impact is negligible. H. euphorbiana 

populations are hindered by disease and predation. Even at high densities, 

defoliation caused by H. euphorbiana does not kill plants. L. euphorbiana is 

established in BC, Canada where leaf tying causes moderate impact to leafy 

spurge. O. erythrocephala is widely distributed but typically at densities too 

low to cause significant impact. This species may be too host-specific to some 

leafy spurge biotypes. The five established Aphthona flea beetles have variable 

abundance and impact in North America. A. cyparissiae and A. czwalinai are 

believed to be of only limited abundance in western states and provinces, though 

this is currently under study. A. flava is of moderate abundance where its rootfeeding impact is likely limited alone, but may be significant in combination 

with other agents. A. lacertosa and A. nigriscutis are highly effective at reducing 

leafy spurge density in both the USA and Canada. A. lacertosa is suited to a 

variety of habitats while A. nigriscutis is typically only effective at dry, open sites.

RECOMMENDATIONS: USA: A. flava and H. euphorbiana have medium 

priority for redistribution. Though they likely do not provide control alone, they 

can be useful in combination with other agents at mesic, open sites. A. lacertosa

and A. nigriscutis have the highest priority for redistribution; A. lacertosa can be 

used under a variety of conditions while A. nigriscutis should be redistributed only 

to dry, open sites. Remaining species have the lowest priority for redistribution. 

L. euphorbiana is not approved for release in the USA. CAN: Similar to the 

USA, however L. euphorbiana is also of medium priority for redistribution to 

warm sites to complement other agents.

Leafy Spurge Biological Control
Biological Control OF WEEDS in the Northwest 247Leafy spurge

Credits for photos above: See individual agent pages

Approved, Non-Established Agents

Established Agents

Aphthona 

abdominalis

Chamaesphecia 

spp.

Minoa 

murinata

Pegomya 

spp.

Agent Adult Impact Recommendation

Aphthona 

cyparissiae

Limited abundance so rootfeeding ineffective alone. Best 

in combination with others.

Low priority but could be 

redistributed to dry, mesic sites 

to complement other agents.

Aphthona 

czwalinai

Root-feeding reduces plant 

density. Currently believed to 

be limited in abundance.

Tentative low priority in CAN 

and western USA due to 

decreasing abundance.

Aphthona 

flava

Limited-moderate abundance 

so root-feeding ineffective 

alone. Best in combination.

Medium priority but could be 

redistributed to dry, mesic sites 

to complement other agents.

Aphthona 

lacertosa

Abundant so root-feeding 

highly effective at most sites 

in USA and CAN.

Already widespread, but high 

priority for redistribution to sites 

with variable conditions.

Aphthona 

nigriscutis

Abundant so root-feeding 

highly effective at dry sites in 

USA and CAN.

Already widespread but high 

priority for redistribution to dry 

open sites.

Hyles 

euphorbiae

Defoliation at high densities 

does not kill plants. Hindered 

by disease and predation. 

Low priority alone but could 

be redistributed where it 

complements other agents.

Lobesia 

euphorbiana

Moderate abundance and 

impact in BC CAN. Leaf tying 

reduces reproduction.

Not released in USA. Medium 

priority for redistribution to 

warm sites as complement.

Oberea 

erythrocephala

Stem-mining kills large plants 

but abundance typically too 

low for high impact.

Low priority as populations 

remain limited. May be too 

host-specific for some spurge.

Spurgia 

capitigena &

S. esulae

Abundance low. Even at high 

densities, stem tip galling 

occurs too late for impact.

Low impact and continued 

limited abundance make low 

priority for redistribution.
248 Biological Control OF WEEDS in the Northwest Leafy spurge DESCRIPTION: Larvae are 1-5 mm long, have short legs, a white body and 

yellow head with thick head capsule. Adults are usually just over 3 mm long. 

They are a light reddish-brown color and oval in shape.

Aphthona cyparissiae (Koch)

Brown dot leafy spurge flea beetle

LIFE CYCLE: Overwintering larvae resume feeding on young roots in early 

spring as leafy spurge is resuming growth. Pupation occurs in the soil. Adults 

are active from early summer to late summer as leafy spurge bolts, flowers, and 

matures. Females lay numerous eggs in the soil throughout the growing season. 

Hatching larvae burrow into the soil to feed on roots, developing through three 

instars. There is one generation per year.

DAMAGE: Larvae feed on root hairs and young roots, inhibiting root function 

and stunting leafy spurge stem growth. Adults feed on leaves and flowers, 

decreasing photosynthesis and plants’ sugar-making ability for root reserves.

PREFERRED HABITAT: Does best in moderately-dense infestations of leafy 

spurge found on more dry, mesic sites. Does poorly in soils with too much sand 

or clay.

HISTORY: Introduced from Austria, Hungary, Italy, and Switzerland and released 

on leafy spurge in the USA from 1986 (CO, ID, MT, NV, OR, UT, WA, WY). 

Introduced from Austria, Hungary, and Switzerland and released on leafy spurge 

in Canada from 1982 (AB, BC).

CURRENT STATUS: Widespread on leafy spurge in the USA where it is well 

established at a few release sites but is overall much less abundant than other 

Aphthona cyparissiae: a) pupa (Neal Spencer, USDA ARS, www.bugwood.org), b) adult (R. Richard, 

USDA APHIS)

a b
Biological Control OF WEEDS in the Northwest 249Leafy spurge

Aphthona spp. Populations are highest at dry, mesic sites with sandy loam soils. 

Under these conditions, plant density may decrease quickly, but unattacked 

roots recover. Numerous years under the right conditions are required for this 

agent to decrease leafy spurge populations permanently. Damage is typically 

greatest in combination with other Aphthona spp. High populations in Canada 

effectively control the weed at dry, open sites, but insect densities are too low 

and ineffective elsewhere.

REDISTRIBUTION: 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 

leafy 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: A. 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 beetles are often unreliable. A. czwalinai and A. lacertosa are black 

beetles.

Coleoptera: Chrysomelidae

Aphthon

cypariss
250 Biological Control OF WEEDS in the Northwest Leafy spurge 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, 

while females are usually just over 3 mm.

Aphthona czwalinai (Weise)

Black leafy spurge flea beetle

Aphthona czwalinai: a) pupa (Neal Spencer, USDA ARS, www.bugwood.org), b) adult (R. Richard, 

USDA APHIS)

LIFE CYCLE: Overwintering larvae resume feeding on young roots in early 

spring as leafy spurge is resuming growth. Pupation occurs in the soil. Adults 

are active from early summer to late summer as leafy spurge bolts, flowers, and 

matures. Females lay numerous eggs in the soil throughout the growing season. 

Hatching larvae burrow into the soil to feed on roots, developing through three 

instars. There is one generation per year.

DAMAGE: Larvae feed on root hairs and young roots, inhibiting root function 

and stunting leafy spurge stem growth. Adults feed on leaves and flowers, 

decreasing photosynthesis and plants’ sugar-making ability for root reserves.

PREFERRED HABITAT: Does best in moderately-dense infestations of leafy 

spurge found on more mesic sites. Does poorly in soils with too much sand or 

clay.

HISTORY: Introduced from Austria and Hungary and released on leafy spurge 

in the USA from 1987 (CO, ID, MT, NV, OR, UT, WA, WY). A second 

population from Russia was released in MT in 1993. Introduced from Austria 

and released on leafy spurge in Canada from 1985 (AB). Populations initially 

from Austria and Hungary were redistributed from the USA and released in 

Canada from 1995 (AB, BC).

a b
Biological Control OF WEEDS in the Northwest 251Leafy spurge

CURRENT STATUS: The population from Austria and Hungary is established 

on leafy spurge in the USA. For many years it was believed that control of 

leafy spurge on the local level was achieved primarily by Aphthona nigriscutis, 

A. czwalinai and A. lacertosa. A. 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. It is unknown if the Russian population established 

in MT. A. czwalinai is established on leafy spurge in Canada though 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: 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 

leafy 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: A. czwalinai has solid dark hind femurs compared to the other black 

beetle, A. lacertosa. A. cyparissiae, A. flava, and A. nigriscutis are all brown beetles. 

Occasionally referred to as A. czwalinae.

Coleoptera: Chrysomelidae

Aphthon

czwalina
252 Biological Control OF WEEDS in the Northwest Leafy spurge 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 31⁄2 mm long. Females are slightly larger than males.

Aphthona flava Guillebeau

Copper leafy spurge flea beetle

LIFE CYCLE: Overwintering larvae resume feeding on root hairs in early spring 

as leafy spurge is resuming growth. Pupation occurs in the soil. Adults are active 

from early summer to early fall as leafy spurge bolts, flowers, and matures. 

Females lay numerous eggs in groups on leafy spurge stems at or just below the 

soil surface. Hatching larvae burrow into the soil to feed on roots, developing 

through three instars. There is one generation per year.

DAMAGE: Larvae feed on root hairs and young roots, inhibiting root function 

and stunting leafy spurge stem growth. Adults feed on leaves and flowers, 

decreasing photosynthesis and plants’ sugar-making ability for root reserves.

PREFERRED HABITAT: Does best in moderately-dense infestations of leafy 

spurge found on more mesic, dry sites in alluvial soils above flood lines and 

light shade (USA) and at mesic, dry sites with warm temperatures (CAN). Does 

poorly in soils with too much sand or clay. It is probably less likely to survive low 

temperatures than other Aphthona spp. 

HISTORY: Introduced from Hungary and Italy and released on leafy spurge in 

the USA from 1985 (CO, ID, MT, NV, OR, UT, WA, WY). Introduced from 

Hungary and Italy and released on leafy spurge in Canada from 1982 (AB, BC).

CURRENT STATUS: Widespread in the USA. In one area in MT its effect has 

been spectacular, but overall it is much less abundant than other Aphthona spp. It 

persists at fairly low levels with little noticeable impact on infestations. Moderately 

Aphthona flava: a) larva (Neal Spencer, USDA ARS), b) adult (USDA APHIS PPQ), c) adults and 

damage (Norman E. Rees, USDA ARS) (all www.bugwood.org)

a b c
Biological Control OF WEEDS in the Northwest 253Leafy spurge

abundant in Canada. Leafy spurge density has declined where populations of A. 

flava are high, however it’s not possible to attribute the reduction to A. flava alone 

as the site has been grazed by sheep, and A. nigriscutis is also present. 

REDISTRIBUTION: 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 leafy 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: A. flava is typically more orange than the other two brown beetles, A. 

cyparissiae and A. nigriscutis. A. flava also does not have the black spot on the back 

that A. nigriscutis has. However, coloration differences among brown beetles are 

often unreliable. A. czwalinai and A. lacertosa are black beetles.

Coleoptera: Chrysomelidae

Aphthon

flava
254 Biological Control OF WEEDS in the Northwest Leafy spurge 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.

Aphthona lacertosa Rosenhauer

Brown-legged leafy spurge flea beetle

Aphthona lacertosa: a) adult (Laura Parsons & Mark Schwarzländer, University of Idaho), b) adults 

and damage (Todd Pfeiffer, Klamath County Weed Control) (both www.bugwood.org)

LIFE CYCLE: Overwintering larvae resume feeding on young roots in early 

spring as leafy spurge is resuming growth. Pupation occurs in the soil. Adults are 

active from early to late summer as leafy spurge bolts, flowers, and matures. Each 

female lays 200-300 eggs in the soil throughout the growing season. Hatching 

larvae burrow into the soil to feed on roots, developing through three instars. 

There is one generation per year.

DAMAGE: Larvae feed on root hairs and young roots, inhibiting root function 

and stunting leafy spurge stem growth. Adults feed on leaves and flowers, 

decreasing photosynthesis and plants’ sugar-making ability for root reserves.

PREFERRED HABITAT: Does best in moderately-dense infestations of leafy 

spurge found growing in loamy soils. It can adapt locally to both dry and wet 

habitats in the USA but does better at mesic to moist sites in Canada. Does 

poorly in soils with too much sand or clay.

HISTORY: Introduced from Austria, Hungary, and former Yugoslavia and released 

on leafy spurge in the USA from 1993 (CA, CO, ID, MT, NV, OR, UT, WA, 

WY). Introduced from Hungary and former Yugoslavia in Canada from 1987 

(AB, BC from 1990). Populations from Hungary established in the USA were 

also redistributed to AB and BC from 1995.

a b
Biological Control OF WEEDS in the Northwest 255Leafy spurge

CURRENT STATUS: Widespread and abundant in the USA. Along with A. 

nigriscutis, it is significantly reducing leafy spurge density at the local level in 

most regions. Not effective at all sites. Abundant in Canada where it is reducing 

leafy spurge plant density at most sites. A. 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: 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 

leafy 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: A. lacertosa has lighter colored hind femurs than the other black beetle, 

A. czwalinai. A. cyparissiae, A. flava, and A. nigriscutis are all brown beetles.

Coleoptera: Chrysomelidae

Aphthon

lacertos
256 Biological Control OF WEEDS in the Northwest Leafy spurge 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.

Aphthona nigriscutis Foudras

Black dot leafy spurge flea beetle

LIFE CYCLE: Overwintering larvae resume feeding on root hairs in early spring 

as leafy spurge is resuming growth. Pupation occurs in the soil. Adults are active 

from early to late summer as leafy spurge bolts, flowers, and matures. Females lay 

numerous eggs in groups on leafy spurge stems at or just below the soil surface. 

Hatching larvae burrow into the soil to feed on roots, developing through three 

instars. There is one generation per year.

DAMAGE: Larvae feed on root hairs and young roots, inhibiting root function 

and stunting leafy spurge stem growth. Adults feed on leaves and flowers, 

decreasing photosynthesis and plants’ sugar-making ability for root reserves.

PREFERRED HABITAT: Prefers relatively sparse leafy spurge patches at dry 

sites with sandier soil. Does poorly in soils with too much clay.

HISTORY: Introduced from Hungary and released on leafy spurge in AB and BC 

(CAN) from 1983. Canadian populations were redistributed to leafy spurge in 

the USA from 1989 (CA, CO, ID, MT, NV, OR, UT, WA, WY).

CURRENT STATUS: Widespread and abundant on leafy spurge in the USA. 

Along with A. lacertosa, it is significantly reducing plant density at the local 

level in most regions. Not effective at all sites. Impact may be hindered by a 

bacterium which causes high mortality in males, resulting in female-biased 

Aphthona nigriscutis: a) larva (Neal Spencer, USDA ARS, www.bugwood.org), b) adult (R. Richard, 

USDA APHIS)

a b
Biological Control OF WEEDS in the Northwest 257Leafy spurge

populations. Abundance and impact are variable in Canada. 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: 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 

leafy 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 

leafy spurge Aphthona species. 

NOTES: The other brown beetles A. cyparissiae and A. flava typically do not have 

the black spot on the back. A. flava is also usually more orange in color than 

A. nigriscutis, though coloration differences among brown beetles are often 

unreliable. A. czwalinai and A. lacertosa are black beetles. Spillover feeding 

by A. nigriscutis has been observed on the native Euphorbia robusta; as leafy 

spurge density declined, so did feeding on E. robusta, and E. robusta populations 

increased.

Coleoptera: Chrysomelidae

Aphthon

nigriscut
258 Biological Control OF WEEDS in the Northwest Leafy spurge 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.

Hyles euphorbiae (L.)

Leafy spurge hawk moth

LIFE CYCLE: There are two generations per year. Adults emerge in early to midsummer when leafy spurge is bolting/flowering. Females lay 70-150 eggs in 

clumps on leaves and bracts. Hatching larvae feed on these parts as leafy spurge 

is 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 overwinter as pupae.

DAMAGE: Larval feeding defoliates leafy spurge plants, though this often does 

not kill the weed.

PREFERRED HABITAT: Does best in thick leafy spurge infestations growing 

in open areas near trees. Pupae are heavily preyed upon so sites with decreased 

amounts of rodents, ants, etc., are preferred. 

HISTORY: Introduced from France, Germany and Switzerland and released on 

leafy spurge in Canada from 1966 (AB, BC). This material was redistributed to 

the USA from 1966 (CO, ID, MT, NV, OR, WA, WY). A second population 

was introduced from Hungary and released in CO, ID, MT, OR, WA, WY from 

1980.

CURRENT STATUS: Both source populations established in the USA where 

Hyles euphorbiae: a) larva, b) pupa (Whitney Cranshaw, Colorado State University, www.bugwood.

org), c) adult (a,c R. Richard, USDA ARS)

a b c
Biological Control OF WEEDS in the Northwest 259Leafy spurge

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, abundance is typically only moderate due to predation. Even when 

populations are high, plants recover from defoliation. It has limited biocontrol 

value alone, but may stress the weed in combination with other 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 leafy spurge is beginning to flower, 

or late summer/fall as leafy spurge matures. Any instar can be collected, though 

the 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 the collector. They can be transferred in groups of 50-100 to new 

infestations. Establishment can be monitored by observing adults or larvae on 

leafy spurge foliage throughout the following growing season.

NOTES: This agent resembles native hawk moth species but is more active during 

daytime.

Lepidoptera: Sphingidae

Hyles

euphorb
260 Biological Control OF WEEDS in the Northwest Leafy spurge 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.

Lobesia euphorbiana (Freyer)

Spurge leaf tying moth

LIFE CYCLE: Adults emerge in spring as leafy 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 the soil litter within folded leaves. There are two generations 

per year, with three possible in suitable climates.

DAMAGE: Larval feeding of buds prevents flowering while repeated heavy attack 

may eventually kill plants. When larvae vacate leaf ties, the sites often receive 

secondary attack from thrips and aphids.

PREFERRED HABITAT: 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. Often inhabits riparian areas as 

well as fringe forested areas, so shade is tolerated. 

HISTORY: Introduced from Italy and released on leafy spurge in Canada from 

1983 (AB, BC from 1987).

Lobesia euphorbiana: a) larva, b) cocoon, c) pupa (all Laura Parsons, University of Idaho, www.

bugwood.org)

a b c
Biological Control OF WEEDS in the Northwest 261Leafy spurge

CURRENT STATUS: Established on leafy spurge in Canada where populations 

are dispersing well from release sites. Impact is moderate and fluctuates with 

leafy spurge density and vigor.

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; make sure 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 agent is not approved for release in the USA.

Lobesia euphorbiana: d) adult (CABI, previously IIBC), e) damage (Laura Parsons, University of 

Idaho, www.bugwood.org)

Lepidoptera: Tortricidae

d e

Lobesia

euphorb
262 Biological Control OF WEEDS in the Northwest Leafy spurge DESCRIPTION: Mature larvae are up to 20 mm long, slender, and white. Bodies 

are obviously segmented and the head is yellowish with a head capsule. 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. The legs are yellowish-brown.

Oberea erythrocephala (Schrank)

Red-headed leafy spurge stem borer

LIFE CYCLE: Adults emerge in early to mid-summer and feed on leafy spurge 

leaves and flowers. Females girdle a leafy 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: 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.

HISTORY: Introduced from Italy and released on leafy spurge in OR and WY 

(USA) from 1980. After these failed to establish, a different population was 

sourced from Austria, Hungary and Italy and released from 1982 in CA, CO, 

ID, MT, NV, OR, UT, WA, WY. Introduced from Switzerland and released in 

Canada from 1979 (AB 1980). 

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) (all www.

bugwood.org)

a b c
Biological Control OF WEEDS in the Northwest 263Leafy spurge

CURRENT STATUS: Established on leafy spurge in CA, CO, ID, MT, OR, 

WY (USA). 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. Established on leafy spurge in AB (CAN) but is considered rare. 

At high densities, small plants can be killed, however field populations are too 

low to have a significant impact.

REDISTRIBUTION: Adults should be collected in early summer as leafy 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 leafy 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.

Coleoptera: Cerambycidae

Oberea

erythoroce
264 Biological Control OF WEEDS in the Northwest Leafy spurge 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.

Spurgia capitigena (Bremi) & S. esulae Gagné

Leafy spurge tip gall midges

LIFE CYCLE: Adults emerge in spring when leafy spurge is resuming growth. 

They live only a number of hours. Eggs are laid in groups of 20+ among the leaves 

of 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 leafy spurge growing tips destroy the shoots’ ability 

to flower and produce seeds. The shoots eventually die and are replaced by new 

stems that are attacked by the next generation of midges.

PREFERRED HABITAT: Prefers dense leafy spurge infestations growing on 

south-facing slopes in cooler climates. It can reportedly tolerate some shading.

HISTORY: The two species were previously lumped together under the name 

Bayeria capitigena. It wasn’t until after their introduction that B. capitigena 

was transferred to Spurgia and split into the two species. Consequently, the 

release history is convoluted. What is now S. esulae was introduced from Italy 

and released on leafy spurge in the USA from 1985 (CO, ID, MT, NV, OR, 

Spurgia esulae: a) eggs (L.L. Berry), b) larvae and pupae in galls (Norman Rees, USDA ARS), c) adult 

(USDA APHIS PPQ Archive) (all www.bugwood.org)

a b c
Biological Control OF WEEDS in the Northwest 265Leafy spurge

UT, WA, WY). S. capitigena is believed to have been a contaminant of one 

population of S. esulae released in ND in 1986. Both species were redistributed 

to leafy spurge in Canada from 1987, though it is believed only S. esulae was 

released in western provinces (AB, BC) and only from 1989. A new population 

of S. capitigena was intentionally released in ND from 2001-2002 utilizing two 

different shipments from France.

CURRENT STATUS: S. esulae is established portions of the western USA. 

Densities are generally low, but even where it is most abundant, galls form 

following flowering so overall impact is insignificant. S. capitigena (from both 

sources) is established only in ND where impact is largely unknown but assumed 

to be negligible. Both species are only established on leafy spurge in more eastern 

provinces of Canada where their 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 

leafy spurge, so collect from mid-May to mid-June (depending on location) 

prior to leafy spurge flowering. Clip at least 6 in (15 cm) below galls, bunch 

clipped stems, and wrap the bottoms in damp paper towels. Transfer to new sites 

as soon as possible, and place upright to help avoid predation. Establishment can 

be monitored by observing galls on new leafy 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.

Diptera: Cecidomyiidae

S. capitigena S. esulae

Spurgia Spurgia esu

capitigena
266 Biological Control OF WEEDS in the Northwest Leafy spurge 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 the 

soil and feed on roots and root hairs 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.

HISTORY: Introduced from Italy and released on leafy spurge in the USA from 

1993 (CO, MT, OR) but failed to establish. Not released in Canada.

Chamaesphecia spp. (Lepidoptera: Sesiidae)

DESCRIPTION AND LIFE CYCLE: 

The four species all 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. 

HISTORY: C. crassicornis, C. hungarica and C. tenthrediniformis were introduced 

from Europe and released in the USA from 1975 (ID, MT, OR). C. astatiformis, 

C. crassicornis and C. hungarica from Europe were released in AB (CAN) from 

1991. All introductions failed. C. astatiformis was not released in the USA.

R. Richard, USDA APHIS (www.bugwood.

org)

Leafy Spurge, Non-Established Agents

Chamaesphecia crassicornis: R. Richard, USDA 

APHIS (www.bugwood.org)
Biological Control OF WEEDS in the Northwest 267Leafy spurge

Minoa murinata (Scopoli)

(Lepidoptera: Geometridae)

DESCRIPTION AND LIFE CYCLE: 

Pupa overwinter just beneath the soil. 

Adults emerge in late spring and lay 

eggs on 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. There can be two generations per year in suitable climates. Adults 

of the second generation emerge in late summer.

HISTORY: Introduced from Germany and Austria and released in Canada from 

1988 (AB, BC from 1991), but eventually died out. Not released in the USA.

Pegomya curticornis (Stein) &

P. euphorbiae (Kieffer)

(Diptera: Anthomyiidae)

LIFE CYCLE: Both species are virtually 

indistinguishable. Adults emerge in 

early spring and lay eggs in the leaf buds 

of new shoots. 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. Hatching larvae tunnel down young shoots, which have less toxic milky 

latex. Larvae are a light gray and grub-like. Larvae eventually tunnel into the 

roots where their vascular tissue feeding induces the formation of galls. They 

overwinter as pupae within the roots. There is one generation per year.

HISTORY: Both species were previously lumped under Pegomya argyrocephala.

Both were introduced from Hungary and released in AB (CAN) from 1988, 

though both eventually failed to establish. Due to taxonomic uncertainty, it is 

possible all material released was P. euphorbiae. Not released in the USA.

Siga

Leafy Spurge, Non-Established Agents

Pegomya euphorbiae: André Gassmann, CABISwitzerland
268 Biological Control OF WEEDS in the Northwest Bindweed SYNONYMS: morning glory

ORIGIN: Native to Eurasia. Likely introduced via contaminated crop seed; 

identified in North America as early as 1739.

DESCRIPTION: Twining and trailing perennial with prostrate stems typically 

growing 1-4 ft long (1⁄3-1.2 m). The fleshy roots can extend up to 20 ft in length 

(6 m). The plant also produces rhizomes which may root and send up additional 

above ground shoots. Leaves are alternate and shaped like arrowheads with lobes 

at their base. Flowers are bell-shaped, white to pinkish, and 1 in (21⁄2 cm) in 

diameter. Two small bracts are located 1⁄2 to 1 in (1-21⁄2 cm) below the flower. 

Fruit is small and circular, usually containing four wedge-shaped seeds.

 

HABITAT: Well-adapted to many different habitats, but is dominant on dry soils 

b

Field bindweed

Convolvulus arvensis L.

a) plant (Rachel Winston, MIA Consulting), b) infestation (Barry Rice, sarracenia.co, www.

bugwood.org)

a
Biological Control OF WEEDS in the Northwest 269Bindweed

c) leaf (Ohio State Weed Lab Archive, The Ohio State University, www.bugwood.org), d) flower, e) 

bracts (d,e Rachel Winston, MIA Consulting)

in open and disturbed areas including abandoned fields, roadsides, orchards, 

and gardens.

ECOLOGY: Reproduces both by seed and by its spreading root system. Small 

root pieces can develop into new plants. Stems sprout from vegetative roots 

throughout the growing season. Peak germination is from April through May. 

Flowers typically appear from June through late fall. Seeds are readily transported 

by water, birds, and other animals, and may stay viable up to 50 years.

APPROVED BIOLOGICAL CONTROL AGENTS: USA and CAN: Aceria 

malherbae and Tyta luctuosa.

NOTES: Mildly toxic to grazing animals.

Family Convolvulaceae

c d e

Conv

arven
270 Biological Control OF WEEDS in the Northwest Bindweed HISTORY IN THE NORTHWEST: The North American field bindweed 

biological program began in the 1960s and 70s in Canada with the redistribution 

of a number of native insects. These attempts largely failed. A classical biological 

control program was subsequently initiated, leading to the introduction of Tyta 

luctuosa in 1987 and Aceria malherbae in 1989 (releases in Pacific Northwest 

states and provinces occurred shortly thereafter). 

CURRENT STATUS: Both species established in the USA, though to date, 

populations of T. luctuosa are too limited to have any impact. Results with A. 

malherbae vary. The agent has proven effective at some sites, while having no 

impact at others. Reasons for this variability are not understood, but populations 

are known to be impacted by climate and possibly host plant resistance. Only 

A. malherbae established in Canada, and in such limited amounts that overall 

impact is considered minor.

RECOMMENDATIONS: USA and CAN: Additional research is needed to 

understand why both species have established poorly in North America and 

what is causing the variability of A. malherbae impact. Additional releases of 

both species are warranted with the intent of finding some sites and conditions 

where each species can thrive. A. malherbae galls can be transferred throughout 

the growing season. T. luctuosa field populations are likely too limited to be used 

for redistribution; lab colonies may be the best source for new populations. As 

noticeable impact by either species may take several years, additional control 

methods are also warranted.

Bindweed Biological Control
Biological Control OF WEEDS in the Northwest 271Bindweed

Aceria: Bob Nowierski, Montana State University, Tyta: USDA ARS, both www.bugwood.org

Agent Adult Impact Recommendation

Aceria 

malherbae

Galls stunt stem, reduce 

flowering. Helps control weed 

at some USA sites; ineffective 

at others for unknown 

reasons. Limited in CAN.

Continue redistributing galls 

throughout range of weed in 

attempt to find sites/conditions 

where agent thrives and has 

high impact.

Tyta 

luctuosa

Larval feeding defoliates plant. 

Populations too limited in 

USA to date to have impact. 

Not established in CAN.

Continue releasing species (with 

lab colonies) throughout range 

of weed in attempt to find sites/

conditions where agent thrives 

and has high impact.
272 Biological Control OF WEEDS in the Northwest Bindweed DESCRIPTION: Nymph and adult stages are similar except for the presence of 

external genitalia on adults. Both stages are worm-like with two pairs of legs on 

the joined head and thorax, and both have yellowish, translucent bodies. Mites 

are tiny and can be seen only through a microscope. Consequently, it is their 

damage that is more useful for identifying their presence.

Aceria malherbae Nuzzaci

Bindweed gall mite

LIFE CYCLE: Adults emerge in early spring and feed on new bindweed growth. 

They lay eggs within galls and produce multiple generations per year. There 

are two nymphal stages prior to the adult stage; their development can be 

completed in 10 days, depending on temperature. Overwintering occurs in both 

the nymphal and adult stage on root buds.

DAMAGE: Both nymphal and adult stages form galls on actively growing leaves, 

leaf stems, and stem tips of bindweed. Galls are characterized by the discolored 

folding and twisting of leaves along the midrib where mites feed. Attacked stem 

tips fail to elongate and form clusters of stunted leaves. Attacked plants also 

experience a reduction in flowering.

PREFERRED HABITAT: Largely unknown, but appears to do better under 

hot, dry conditions. 

HISTORY: Introduced from Greece and released on field bindweed in the USA 

and Canada from 1989 (CO, ID, MT, NV, OR, WA, WY from 1992; BC 1992, 

AB 1993). 

CURRENT STATUS: Established on field bindweed in the USA, though 

abundance, attack levels and impact vary dramatically across and within 

Aceria malherbae: a) adult (USDA-ARS), b) damage (Bob Nowierski, Montana State University), c) 

damage (Jennifer Andreas, Washington State University Extension) (a,b www.bugwood.org)

a b c
Biological Control OF WEEDS in the Northwest 273Bindweed

established states. There has been no impact at some sites, and >90% decrease 

in aboveground plant biomass at others. Reasons for this variability have not 

been studied explicitly, but populations are known to be impacted by climate 

and possibly host plant resistance. In Canada, its distribution and abundance 

are limited. Galling damage has been found up to 1.4 km from one site. Some 

plants are heavily galled and stunted, though impact has not been evaluated 

quantitatively. Field bindweed continues to be a problematic weed in many parts 

of Canada.

REDISTRIBUTION: Can be redistributed by collecting galls from attacked 

plants and placing these on uninfested bindweed plants in new locations. This can 

be done throughout the year when bindweed is actively growing. Establishment 

can be monitored the following season by observing galls on new bindweed 

growth. Once established, mite populations can be encouraged to multiply by 

mowing the bindweed infestation. 

NOTES: Also released on the similar hedge bindweed (Calystegia sepium) in 

MD, USA, where establishment is unknown and in WA (from 2010) where 

establishment has thus far failed.

Acari: Eriophyidae

Aceria

malherb
274 Biological Control OF WEEDS in the Northwest Bindweed DESCRIPTION: Larvae are a drab brown color with three dark-edged strips 

along their back and a dark brown line along the side with two wavy lines above 

it. Larvae also have four lines of black dots on their heads and can be up to 34 

mm long at maturity. Adults are dark brown with four large white spots, one on 

each wing. The white spots on the hind wings form a wide band that sometimes 

becomes narrowed. Adults are typically 11 mm long with wingspans up to 29 

mm.

Tyta luctuosa (Denis & Schiffermüller)

Bindweed moth

LIFE CYCLE: Adults emerge in late spring and lay eggs on elongating stems. 

Larvae feed on foliage, developing through five larval instars prior to pupation, 

which occurs in the soil or in plant litter. Second generation adults emerge 

in late summer on bindweed that is both elongating and flowering. There are 

usually two generations per year. Overwintering occurs in both the larval and 

adult stage.

DAMAGE: Larvae feed on flowers and leaves, sometimes defoliating whole plants. 

PREFERRED HABITAT: Still being determined in North America. The moth 

is reportedly not restricted to any certain habitat in its native range. 

HISTORY: Introduced from Italy and released on field bindweed in the USA in 

1987 (ID, MT, OR, WA from 1996) and Canada in 1989 (AB 1990). 

CURRENT STATUS: Established on field bindweed in the USA but at such 

small levels that impact of larval feeding on flowers and foliage is likely minor at 

best. Adults were found one year after release in AB (CAN). They possibly still 

remain, but permanent establishment has not been confirmed.

Tyta luctuosa: a) larva (Eric Coombs, Oregon Department of Agriculture), b) pupa, c) adult (b,c USDA 

ARS) (all www.bugwood.org)

a b c
Biological Control OF WEEDS in the Northwest 275Bindweed

REDISTRIBUTION: Populations are still very limited in the USA, so 

redistribution is likely not yet possible. In its native range, this moth is best 

redistributed by hand-collecting larvae from infested plants, or by using a tap 

& funnel. If larvae are abundant on the plant, infested plant material can be 

clipped and placed in gauze bags. Larvae can be found from spring to early fall 

on elongating bindweeds. Adult moths can be collected at night with the aid of 

light traps with black light bulbs. The adults can be found when bindweeds are 

actively growing from spring to early fall. Both adults and larvae can be transferred 

to new infestations in groups of 50-100. Establishment can be monitored the 

following year by observing adults or larvae on foliage throughout the growing 

season. Larvae can be cryptic and are often found feeding at night.

NOTES: Also released on the similar hedge bindweed (Calystegia sepium) in 

eastern regions of North America, but is believed to have failed establishment.

Lepidoptera: Noctuidae

Tyta luct
276 Biological Control OF WEEDS in the Northwest Chamomile SYNONYMS: scentless false mayweed, Matricaria perforata Mérat, 

Tripleurospermum maritimum (L.) W. D. J. Koch subsp. 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 

1⁄2-3.2 ft tall (15-100 cm) from a fibrous root system. Leaves are alternate and 

very finely divided, giving the plant an overall fern-like appearance. Flower heads 

are daisy-like with white outer ray florets and yellow inner disc florets. Flower 

heads are typically 11⁄4-15⁄8 in (30-40 mm) in diameter. Seeds are small (0.08 in 

or 2 mm long), elongate, brown, and ribbed, with no pappus. 

 

HABITAT: Well-adapted to many different habitats, thriving in disturbance 

b

Scentless chamomile

Tripleurospermum inodorum (L.) Sch. Bip.

a) plant (Robert Vidéki, Doronicum Kft., www.bugwood.org), b) infestation (Alec McClay, McClay 

Ecoscience)

a
Biological Control OF WEEDS in the Northwest 277Chamomile

c) leaves (Caleb Slemmons, University of Wisconsin, Stevens Point, www.bugwood.org), d) flower 

heads (Alec McClay, McClay Ecoscience)

typical of annual and perennial crops, pastures, wasteland, roadsides, and 

ditches. It germinates readily at sites with periodic flooding.

ECOLOGY: 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.

APPROVED BIOLOGICAL CONTROL AGENTS: USA: There are no 

approved biocontrol agents; CAN: Microplontus 

edentulus, Omphalapion hookerorum and 

Rhopalomyia tripleurospermi.

NOTES: Diploid and tetraploid forms occur in 

both Europe and North America.

Family Asteraceae

c d

Tripleuro

inodorum
278 Biological Control OF WEEDS in the Northwest Chamomile HISTORY IN THE NORTHWEST: The North American scentless 

chamomile biological program began in the 1980s in Canada. To date, releases 

have occurred only in Canada. The first agent approved for use, Omphalapion 

hookerorum, was released in AB and BC from 1992. An adventive population of 

O. hookerorum was discovered established in NS in 1990, but field observations 

indicated it was host specific as well. Both populations (intentional and 

adventive) of O. hookerorum were subsequently intermixed in the field and are 

no longer differentiated. Microplontus edentulus and Rhopalomyia tripleurospermi

were approved and released in 1997 and 1999, respectively. 

CURRENT STATUS: All three species established in AB, while O. hookerorum 

and R. tripleurospermi established in BC as well. To date, only one population 

of M. edentulus is established in AB and is too limited to have any impact. 

Populations of the other two species are abundant and widespread, though 

impact is only medium overall. Seed-feeding by O. hookerorum and galling by R. 

tripleurospermi lead to reduced seed production and stunted growth. 

RECOMMENDATIONS: USA: No species have been approved for use 

or released in the USA for the control of scentless chamomile. CAN: 

Microplontus edentulus is rare in the field with no documented impact, 

consequently it is not a recommended priority for redistribution efforts, though 

releases with laboratory colonies could be made if more suitable field conditions 

are determined. Omphalapion hookerorum and R. tripleurospermi are already 

widespread throughout much of AB and some of BC. Though they reduce 

seed production, scentless chamomile is a prolific seed producer and many 

seeds escape attack. Still, the additional stunting effect of R. tripleurospermi in 

combination with the seed reducing impact of both species make them useful in 

combination with other (complementary) control methods or at locations where 

some control methods are not feasible. O. hookerorum can be redistributed using 

adults collected from new growth of scentless chamomile in spring, or from 

mature seed heads in late summer. For R. tripleurospermi, gall-infested plants 

should be transplanted into field sites as the adults are too short-lived and 

delicate for field collection. To avoid transferring unwanted parasitoids, other 

insects, or scentless chamomile seeds, gall-infested plants can be collected and 

adults reared out indoors prior to release in spring and summer.

Chamomile Biological Control
Biological Control OF WEEDS in the Northwest 279Chamomile

Microplontus, Omphalapion, Rhopalomyia: all Alec McClay, McClay Ecoscience

Agent Adult Impact Recommendation

Microplontus 

edentulus

Stem-mining weakens stems, 

may reduce seed production. 

Only one population 

established thus far in CAN. 

No measurable impact.

Low establishment rates and 

impact make low priority for 

redistribution in CAN. Not 

approved for use in USA.

Omphalapion 

hookerorum

Seed-feeding reduces seed 

output and possible rate of 

population spread in CAN. 

Plant is prolific seed producer; 

many seeds escape attack.

Already widespread; should be 

redistributed to any uninfested 

sites to complement other 

control methods. Not approved 

for use in USA.

Rhopalomyia 

tripleurospermi

Galling stunts growth, delays 

flowering, decreases seed 

production in CAN. Plant is 

prolific seed producer; many 

seeds escape attack.

Already widespread; should be 

redistributed to any uninfested 

sites to complement other 

control methods. Not approved 

for use in USA.
280 Biological Control OF WEEDS in the Northwest Chamomile SYNONYMS: Ceutorhynchus edentulus Schultze

DESCRIPTION: Larvae are white, C-shaped grubs with 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. 

Microplontus edentulus (Schultze)

Scentless chamomile stem-mining weevil

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.

HISTORY: Introduced from Austria and released on scentless chamomile in 

Canada from 1997 (AB, BC). 

CURRENT STATUS: Established on scentless chamomile only at one site in AB 

Canada. To date there has been no evidence of impact in the field. Larval mining 

in stems occurs too late to impact plant fitness, and mining in receptacles does 

Microplontus edentulus: a) larva in flower head, b) adult (both Alec McClay, McClay Ecoscience)

a b
Biological Control OF WEEDS in the Northwest 281Chamomile

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 agent be further 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 agent has not been released in the USA.

Coleoptera: Curculionidae

Microplontus edentulus: c) larvae and mining damage in stem (Hariet Hinz, CABI-Switzerland), d) 

emergence hole in plant stem (Alec McClay, McClay Ecoscience)

c d

Microplo

edentulu
282 Biological Control OF WEEDS in the Northwest Chamomile SYNONYMS: Apion hookeri Kirby

DESCRIPTION: Eggs are small and round, changing from white to brown with 

age. Larvae are white, C-shaped grubs typically up to 2 mm long. Adult males 

are black and 11⁄2-2 mm long. Females have a metallic sheen in shades of blue, 

turquoise or purple and are typically 2-21⁄2 mm long. Both males and females 

have rounded bodies and curved snouts with bulging eyes.

Omphalapion hookerorum (Kirby)

Scentless chamomile seed weevil

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 spread of scentless chamomile 

populations. 

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.

HISTORY: The population used for screening and the initial releases was 

introduced from Germany and released in Canada from 1992 (AB, BC). 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.

Omphalapion hookerorum: a) larva in damaged flower head, b) adult, c) adults on a flower head (all Alec 

McClay, McClay Ecoscience)

a b c
Biological Control OF WEEDS in the Northwest 283Chamomile

CURRENT STATUS: Established on scentless chamomile in AB and BC 

(CAN). Abundance is high and overall impact is medium. Up to 78% of 

scentless chamomile seed heads are attacked by O. hookerorum and up to 32% 

by Rhopalomyia tripleurospermi. Estimated 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: Already widespread throughout much of the range of 

scentless chamomile in Canada, though less widespread in BC than in other 

provinces. 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 (1/2 acre). 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 agent has not been released in the USA.

Coleoptera: Brentidae

Omphala

hookeror
284 Biological Control OF WEEDS in the Northwest Chamomile 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 21⁄2 mm long with a brown head and thorax and gray abdomen. 

Male legs are long and slender. Adult females are typically 21⁄2-3 mm long with 

a bright red abdomen and shorter, thicker legs. Females contain fully developed 

eggs; larger females contain more eggs.

Rhopalomyia tripleurospermi Skuhravá & Hinz

Scentless chamomile gall midge

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 the 

plant, reducing flowering. High attack rates can kill overwintering rosettes.

PREFERRED HABITAT: The midge appears to thrive in all habitats where 

scentless chamomile occurs.

HISTORY: Introduced from Austria and released in Canada from 1999 (AB, BC).

CURRENT STATUS: Established on scentless chamomile in AB and BC (CAN). 

Abundance is high and overall impact is medium. Up to 78% of seed heads 

are attacked by Omphalapion hookerorum and up to 32% by R. tripleurospermi. 

Rhopalomyia tripleurospermi: a) eggs, b) male pupa, c) female adult (all Alec McClay, McClay Ecoscience)

a b c
Biological Control OF WEEDS in the Northwest 285Chamomile

Estimated 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 

with heavy attack. Dispersing 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 mid summer. 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 agent has not 

been released in the USA.

Diptera: Cecidomyiidae

Rhopalomyia tripleurospermi: d) gall on rosette, e) gall on shoot tip (both Alec McClay, McClay 

Ecoscience)

d e

Rhopalomy

tripleurosp
286 Biological Control OF WEEDS in the Northwest Hemlock SYNONYMS: N/A

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 an overall 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: Often occurs in dense stands at shady or moist sites. Is frequently 

b

Poison hemlock

Conium maculatum L.

a) plant (Steve Dewey, Utah State University), b) infestation (Joe DiTomaso, University of California) 

(both www.bugwood.org)

a
Biological Control OF WEEDS in the Northwest 287Hemlock

c) leaf, d) stem (Jan Samanek, State Phytosanitary Administration), e) inflorescence (c,e Pedro 

Tenorio-Lezama) (all www.bugwood.org)

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. 

ECOLOGY: 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.

APPROVED BIOLOGICAL CONTROL AGENTS: USA: Agonopterix 

alstroemeriana

NOTES: All parts of the plant contain alkaloids 

that are highly toxic to livestock and humans.

Family Apiaceae

c d e

Conium 
288 Biological Control OF WEEDS in the Northwest Hemlock HISTORY IN THE NORTHWEST: There have been no intentional 

introductions of classical biocontrol agents to North America. Agonopterix 

alstroemeriana is an adventive agent first recorded in the USA (NY) in 1973, 

from where it spread rapidly throughout the northwestern states. It has since 

been granted redistribution permits by the USDA APHIS for use on poison 

hemlock and has been moved around extensively. 

CURRENT STATUS: Agonopterix alstroemeriana is widespread and abundant 

in all western states. High populations cause severe defoliation at some sites. 

Though this can decrease seed production and cause plant mortality, many 

plants typically recover and resume growth after larvae pupate in mid-summer. 

Changes in poison hemlock stand density have not been documented, so the 

overall impact is believed to be limited.

RECOMMENDATIONS: USA: Agonopterix alstroemeriana is already 

widespread throughout the northwest. Its high abundance and typically low 

impact overall make it a low priority for redistribution. In areas where other 

control options are not available and/or where A. alstroemeriana is not already 

present, supplemental releases can be made. Larvae should be hand collected 

along with poison hemlock foliage in spring and transferred to new sites in 

groups of 50-100. Rubber gloves and protective clothing should be worn at all 

times during the cutting and handling of poison hemlock to help protect against 

the plant’s high toxicity. CAN: No species are approved for release in Canada 

for the control of poison hemlock. 

Poison hemlock Biological Control
Biological Control OF WEEDS in the Northwest 289Hemlock

Agonopterix alstroemeriana photo Eric Coombs, Oregon Department of Agriculture, www.bugwood.org

Agent Adult Impact Recommendation

Agonopterix 

alstroemeriana

Larval feeding causes severe 

defoliation; reduces seed 

production, may kill plants 

outright; many plants recover; 

stand density not decreased

Already widespread; should be 

redistributed to any uninfested 

sites to complement other 

control methods. Not released 

in CAN.
290 Biological Control OF WEEDS in the Northwest Hemlock DESCRIPTION: Eggs are pale yellow and cylindrical. Early instar larvae are 

predominantly yellow with black head capsules. Later instar larvae 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 about 10 mm long with 18 

mm wingspans. Adults are speckled brownish-gray and have a distinctive dark 

brown spot on each wing. 

Agonopterix alstroemeriana (Clerck)

Defoliating hemlock moth

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-instar larvae incorporate flower tissue into their tubes. They pupate 

in the soil with new adults emerging in mid-summer. 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.

HISTORY: Accidental introduction first documented in the USA (NY) in 1973. 

It spread rapidly to many additional states including CA, OR and UT by 1983. 

Despite being introduced accidentally, the USDA APHIS has granted permits 

for its redistribution, and it is currently commercially available.

CURRENT STATUS: Established at high densities on poison hemlock 

Agonopterix alstroemeriana: a) eggs, b) larva, c) adult (all Eric Coombs, Oregon Department of 

Agriculture, all www.bugwood.org)

a b c
Biological Control OF WEEDS in the Northwest 291Hemlock

throughout the western USA. It can reduce seed production and cause severe 

defoliation, 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: Populations are already widespread throughout the 

western USA. Where Agonopterix alstroemeriana appears to be missing, 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 warn 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 away during the day. This agent is not 

approved for release in Canada.

Lepidoptera: Oecophoridae

Agonopterix alstroemeriana: d) defoliated leaves, e) defoliated stand (both Eric Coombs, Oregon 

Department of Agriculture, www.bugwood.org)

d e

Agonopte

alstroeme
292 Biological Control in the Northwest GlossaryGlossary

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, but is not self-sustaining 

and whose numbers are only increased through nonreproductive means, unlike a naturalized species

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 gasoline- or battery-powered 

vacuum aspirator

basal Located at the base of a plant or plant part

biennial A plant that flowers and dies between its first and 

second years and does not flower in its first year

biological control The reduction in the abundance of a pest 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
Biological Control in the Northwest 293Glossary

capitulum (pl. capitula) Seed head of a plant in the sunflower family

complete metamorphosis A 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

deciduous Sheds its leaves annually

density Number of individuals per unit area

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 an insect

exotic Not native 

floret One of the small, closely clustered flowers forming 

the head of a composite flower in the sunflower 

family
294 Biological Control in the Northwest Glossary 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)

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

gradual metamorphosis A life cycle with three distinct stages (egg, nymph, 

adult)

grub A soft, thick-bodied, C-shaped beetle larva

head Insect segment 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 insect and its host (i.e. weed). A highly 

host-specific insect feeds only on its host and on no 

other species

inflorescence The flowering part of a plant

instar The phase of an insect’s nymphal or larval 

development between molts

involucre A circle of bracts under an inflorescence
Biological Control in the Northwest 295Glossary

larva (pl. larvae) Immature insect 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 a the leaf stalk

lobed A leaf with shallow or deep, rounded segments, as in 

a thistle rosette leaf

membranous Thin and transparent

molting Process of insect development that involves shedding 

its exoskeleton and producing another for the next 

instar

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 that undergo gradual 

metamorphosis. Resembles adults

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
296 Biological Control in the Northwest Glossary 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 insect stage between larva and 

adult

qualitative Measurement of descriptive elements (e.g., age class, 

distribution)

quantitative Measurement of quantity; the number or amount 

(e.g., seeds per capitula)

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 Final stage in a plant’s life cycle

species A fundamental category of taxonomic classification, 

ranking below a genus or subgenus and consisting of 

related organisms capable of interbreeding
Biological Control in the Northwest 297Glossary

stolon Stem which grows at the soil surface or just below 

ground that forms adventitious roots at the nodes, 

and new plants from the 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

transect A straight line of varying length along which plants 

are periodically sampled individually or in quadrants

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
references

298 Biological Control in the Northwest

Selected References

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Knapweeds

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