A Misplaced Sense of Risk: 

Variation in U.S. Standards for Management of Risks

Posed by New Species Introduced for Different Purposes

Roy G. Van Driesche, Robert M. Nowierski, and Richard C. Reardon

LEVEL OF REGULATION

LEAST REGULATED

Fish & Fur-bearing animals

nutria

Pets

Burmese python

Horticulture

kudzu

Animals vectoring disease

fire belly toad

Biocontrol agents

thistle-feeding weevil

MOST REGULATED

LEVEL OF RISK

MOST DANGEROUS

Horticulture

kudzu smothering trees

Animals vectoring disease

native frog killed by chytrid fungus

Fish & fur-bearing animals

trees being killed by nutria

Pets

python eating deer

Biocontrol agents

thistle seedhead destroyed by weevil

LEAST DANGEROUS

United States Department of Agriculture

Forest Health Assessment

and Applied Sciences Team

FHAAST-2019-02

July 2020
a b c d e

f g h i j

Cover Photos: (a) nutria (Philippe Amelant, Wikipedia.org); (b) Burmese python (Roy Wood, National Park Service, 

Bugwood.org); (c) kudzu (Marco Schmidt, iNaturalist.org); (d) fire belly toad (Kim, Hyun-tae, iNaturalist.org); (e) thistlefeeding weevil (Eric Coombs, Oregon Department of Agriculture, Bugwood.org); (f) kudzu blanketing trees (Kerry 

Britton, USDA Forest Service, Bugwood.org); (g) native frog killed by chytrid fungus (Brian Gratwicke, iNaturalist.

org); (h) trees being killed by nutria (Gerald J. Lenhard, Louisiana State University, Bugwood.org); (i) python eating 

a deer (Alex Griffiths, Wikipedia.org); (j) thistle seedhead destroyed by weevil (Eric Coombs, Oregon Department of 

Agriculture, Bugwood.org)

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. FHTET became Forest Health Assessment and Applied Sciences 

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https://www.fs.fed.us/foresthealth/applied-sciences/index.shtml

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A Misplaced Sense of Risk: 

Variation in U.S. Standards for Management of Risks

Posed by New Species Introduced for Different Purposes

Roy G. Van Driesche 

Department of Environmental Conservation, University of Massachusetts, Amherst, MA; vandries@umass.edu

Robert M. Nowierski

USDA /NIFA, Kansas City, MO; robert.nowierski@usda.gov

Richard C. Reardon

FHAAST (retired), USDA Forest Service, Morgantown, WV; richard.c.reardon@usda.gov

FHAAST-2019-02

July 2020
Variation in U.S. Standards for Introducing New Species

Acknowledgments

We thank Joseph Milan (BLM), Susan Jewell and Dolores Savignano (USFWS), Robert Pfannenstiel (USDA, APHIS), Dan 

Simberloff (University of Tennessee), Howard Frank (University of Florida), Norm Leppla (University of Florida), Mark Wright 

(University of Hawaii), and Lynn LeBeck (University of California) for their helpful reviews, which improved this publication. We 

extend our gratitude to all of the photographers who granted permission for the use of photos. 

This publication was produced by Richard Reardon (FHAAST), and the layout was designed by Rachel Winston (MIA Consulting). 

During his career, Richard Reardon produced over 100 outreach publications in the FHTET/FHAAST Technical Series to improve 

communication and information transfer between scientists, land managers, and the public. The authors here join the biocontrol 

community in thanking Dr. Reardon for his long-term support. Roy Van Driesche thanks Rachel Winston for her editing diligence 

and detailed development and improvement of this publication.

For additional copies of this publication, contact: 

Denise Binion FHAAST, USDA Forest Service, 180 Canfield Street, Morgantown, WV 26505; 304.285.1552;

denise.binion@usda.gov

This publication is available online at: 

https://www.fs.fed.us/foresthealth/technology/pdfs/FHAAST-2019-02_Misplaced_Sense_Risk.pdf

How to cite this publication:

Van Driesche, R.G., R.M. Nowierski, and R.C. Reardon. 2020. A Misplaced Sense of Risk: Variation in U.S. Standards for 

Management of Risks Posed by New Species Introduced for Different Purposes. FHAAST-2019-02. USDA Forest Service, 

Morgantown, West Virginia, USA. https://www.fs.fed.us/foresthealth/technology/pdfs/FHAAST-2019-02_Misplaced_Sense_

Risk.pdf.
Variation in U.S. Standards for Introducing New Species

TABLE OF CONTENTS

INTRODUCTION ........................................................................................................................................... 1

GROUP #1: FORESTRY, FORAGE, AND FODDER PLANTS........................................................................ 12

History of U.S. Introductions of Forestry, Forage, or Fodder Plants............................................................12

Regulation of Risks: What were the Perceived Problems?...........................................................................13

Risk-Regulation Profile for Forestry, Forage, and Fodder Plants................................................................ 14

Risk 1: Direct attack on non-target species .............................................................................................................. 14

Risk 2: Potential to harbor pest insects, mites, or nematodes ............................................................................... 14

Risk 3: Potential to vector pathogens to non-target plants..................................................................................... 14

Risk 4: Potential to become pests in crops................................................................................................................. 14

Risk 5: Potential to degrade native habitats or ecosystems.................................................................................... 15

Risk 6: Potential to reduce density of native species by changing food webs...................................................... 15

Summary of Risk Regulation for Forestry, Forage, or Fodder Plants .........................................................15

GROUP #2: ORNAMENTAL PLANTS.......................................................................................................... 16

History of U.S. Introductions of Ornamental Plants...................................................................................... 16

Regulation of Risks: What were the Perceived Problems?.......................................................................... 16

Summary of Risk Regulation for Ornamentals ...............................................................................................17

GROUP #3: CROP PLANTS ...................................................................................................................... 18

History of U.S. Introductions of Crop Plants ..................................................................................................18

Regulation of Risks: What were the Perceived Problems?...........................................................................18

Summary of Risk Regulation for Crops ...........................................................................................................18

GROUP #4: TERRESTRIAL MAMMALS FOR RANCHING OR VIEWING ................................................... 20

History of U.S. Introductions of Terrestrial Mammals for Ranching or Viewing...................................... 20

Category B: Summary of California Law ...................................................................................................................... 20

Categories B* and L: Summary of Florida Law............................................................................................................ 20

Category N: Summary of North Carolina Law.............................................................................................................. 21

Regulation of Risks: What were the Perceived Problems?...........................................................................21

Summary of Risk Regulation for Terrestrial Mammals Used for Ranching or Viewing ..........................22

GROUP #5: FISH USED FOR AQUACULTURE .......................................................................................... 23

History of U.S. Introductions of Fish used for Aquaculture .........................................................................23

Regulation of Risks: What Were the Perceived Problems?.......................................................................... 24

Risk-Regulation Profile for Fish Used for Aquaculture ................................................................................ 24

Risk 1: Direct attack on non-target species............................................................................................................... 24

Risk 2: Potential to vector pest insects, mites, ticks, or nematodes..................................................................... 25

Risk 3: Potential to vector parasites or pathogens to non-target fish................................................................... 25

Risk 4: Potential to become pests in crops................................................................................................................. 25

Risk 5: Potential to degrade native habitats or ecosystems.................................................................................... 25

Risk 6: Potential to reduce density of native species by changing food webs...................................................... 25

Summary of Risk Regulation for Fish for Aquaculture ................................................................................ 26

GROUP #6: COMMERCIALLY PRODUCED INVERTEBRATES .................................................................. 27

History of U.S. Introductions of Commercially Produced Invertebrates ...................................................27

Regulation of Risks: What were the Perceived Problems?...........................................................................27

Damage to commercial crops or horticultural plants (land snails) .........................................................................27
Variation in U.S. Standards for Introducing New Species

Transmission of pathogens to native congeners in natural habitats (pathogens of oysters)..............................27

Introduction of associated undesirable species (e.g., oyster predators)............................................................... 28

Displacement of similar native species from their habitats (in Europe, oysters and crayfish) ......................... 28

Spread of vertebrate animal disease (earthworms or pathogens able to attack native insects)...................... 29

Risk-Regulation Profile for Commercially-reared Invertebrates................................................................ 29

Risk 1: Direct attack on non-target species............................................................................................................... 29

Risk 2: Potential to vector pest insects, mites, ticks, or nematodes..................................................................... 29

Risk 3: Potential to vector predators or pathogens................................................................................................... 29

Risk 4: Potential to become pests in crops................................................................................................................. 29

Risk 5: Potential to degrade native habitats or ecosystems.................................................................................... 30

Risk 6: Potential to reduce density of native species by changing food webs...................................................... 30

Summary of Risk Regulation for Commercially Produced Invertebrates .................................................30

GROUP #7: PREDATORY MAMMALS FARMED FOR FUR ........................................................................ 31

History of U.S. Introductions of Predatory Mammals Farmed for Fur.........................................................31

Regulation of Risks: What were the Perceived Problems?...........................................................................32

Risk-Regulation Profile for Predators Farmed for Fur...................................................................................32

Risk 1: Direct attack on non-target species............................................................................................................... 32

Risk 2: Potential to vector pest insects, mites, ticks, or nematodes..................................................................... 32

Risk 3: Potential to vector pathogens to non-target animals.................................................................................. 32

Risk 4: Potential to become pests in crops................................................................................................................. 32

Risk 5: Potential to degrade native habitats or ecosystems.................................................................................... 32

Risk 6: Potential to reduce density of native species by changing food webs...................................................... 33

Summary of Risk Regulation for Predatory Furbearers ...............................................................................33

GROUP #8: HERBIVOROUS MAMMALS FARMED FOR FUR.................................................................... 34

History of U.S. Introductions of Herbivorous Mammals Farmed for Fur.....................................................34

Nutria.................................................................................................................................................................................. 35

Chinchilla........................................................................................................................................................................... 35

Capybara ............................................................................................................................................................................ 35

Regulation of Risks: What were the Perceived Problems?...........................................................................35

Risk-Regulation Profile for Herbivorous Mammals Farmed for Fur ...........................................................36

Risk 1: Direct attack on non-target species............................................................................................................... 36

Risk 2: Potential to vector pest insects, mites, ticks, or nematodes..................................................................... 36

Risk 3: Potential to vector pathogens to non-target animals.................................................................................. 36

Risk 4: Potential to become pests in crops................................................................................................................. 36

Risk 5: Potential to degrade native habitats or ecosystems.................................................................................... 36

Risk 6: Potential to reduce density of native species by changing food webs...................................................... 36

Summary of Risk Regulation for Herbivorous Mammals Farmed for Fur...................................................36

GROUP #9: BIRDS AND MAMMALS FOR HUNTING ............................................................................... 37

History of U.S. Introductions of Birds and Mammals for Hunting ...............................................................37

Birds.....................................................................................................................................................................................37

Mammals............................................................................................................................................................................ 38

(1) Release of new species into the wild................................................................................................................ 38

(2) Creating fenced populations of exotic mammals subject to hunting ......................................................... 38

Regulation of Risks: What were the Perceived Problems?...........................................................................39

Risk of pathogen introduction ....................................................................................................................................... 39

Species protected under CITES...................................................................................................................................... 39

Risk-Regulation Profile for Birds and Mammals for Hunting.......................................................................39

Risk 1: Direct attack on non-target species............................................................................................................... 39

Risk 2: Potential to vector pest insects, mites, ticks, or nematodes..................................................................... 39
Variation in U.S. Standards for Introducing New Species

Risk 3: Potential to vector pathogens to non-target animals.................................................................................. 39

Risk 4: Potential to become pests in crops................................................................................................................. 39

Risk 5: Potential to degrade native habitats or ecosystems.................................................................................... 39

Risk 6: Potential to reduce density of native species by changing food webs...................................................... 39

Summary of Risk Regulation for Birds and Mammals for Hunting ........................................................... 40

GROUP #10: EXOTIC FISH FOR SPORT OR COMMERCIAL FISHING ..................................................... 41

History of U.S. Introductions of Fish for Sport or Commercial Fishing ..................................................... 41

Regulation of Risks: What were the Perceived Problems?.......................................................................... 42

Risk-Regulation Profile for Fish Released for Sport or Commercial Fishing.............................................43

Risk 1: Direct attack on non-target species............................................................................................................... 43

Risk 2: Potential to vector pest insects, mites, ticks, or nematodes..................................................................... 43

Risk 3: Potential to vector pathogens to non-target fish ......................................................................................... 43

Risk 4: Potential to become pests in crops................................................................................................................. 43

Risk 5: Potential to degrade native habitats or ecosystems.................................................................................... 43

Risk 6: Potential to reduce density of native species by changing food webs...................................................... 43

Summary of Risk Regulation for Fish Released for Fishing .........................................................................43

GROUP #11: ANIMALS SOLD AS PETS ................................................................................................... 45

History of U.S. Introductions of Animals Sold as Pets.................................................................................. 45

Regulation of Risks: What were the Perceived Problems?.......................................................................... 45

(1) Pathogens.................................................................................................................................................................... 45

(2) Crop pests.................................................................................................................................................................... 45

(3) Environmental pests..................................................................................................................................................46

Risk-Regulation Profile for Exotic Species Sold as Pets.............................................................................. 46

Risk 1: Direct attack on non-target species...............................................................................................................46

Risk 2: Potential to vector pest insects, mites, ticks, or nematodes..................................................................... 46

Risk 3: Potential to vector pathogens to humans or wildlife................................................................................... 46

Risk 4: Potential to become pests in crops.................................................................................................................46

Risk 5: Potential to degrade native habitats or ecosystems.................................................................................... 46

Risk 6: Potential to reduce density of native species by changing food webs...................................................... 46

Summary of Risk Regulation for Animals Sold as Pets ................................................................................47

GROUP #12: ANIMALS INTRODUCED FOR MEDICAL USES.................................................................... 48

History of U.S. Introductions of Animals for Medical Uses.......................................................................... 48

Regulation of Risks: What were the Perceived Problems?.......................................................................... 48

Risk-Regulation Profile for Animals Introduced for Medical Uses............................................................. 49

Risk 1: Direct attack on non-target species...............................................................................................................49

Risk 2: Potential to vector pest insects, mites, ticks, or nematodes..................................................................... 49

Risk 3: Potential to vector pathogens to non-target species.................................................................................. 49

Risk 4: Potential to become pests in crops.................................................................................................................49

Risk 5: Potential to degrade native habitats or ecosystems.................................................................................... 49

Risk 6: Potential to reduce density of native species by changing food webs...................................................... 50

Summary of Risk Regulation for Animals Introduced for Medical Uses.................................................... 50

GROUP #13: VERTEBRATES FOR PEST CONTROL .................................................................................. 51

History of U.S. Introductions of Vertebrates for Pest Control .....................................................................51

Regulation of Risks: What were the Perceived Problems?...........................................................................52

Risk-Regulation Profile for Vertebrates used for Biocontrol.......................................................................52

Risk 1: Direct attack on non-target species............................................................................................................... 52

Risk 2: Potential to vector pest insects, mites, ticks, or nematodes..................................................................... 52

Risk 3: Potential to vector pathogens to non-target animals.................................................................................. 53
Variation in U.S. Standards for Introducing New Species

Risk 4: Potential to become pests in crops................................................................................................................. 53

Risk 5: Potential to degrade native habitats or ecosystems.................................................................................... 53

Risk 6: Potential to reduce density of native species by changing food webs...................................................... 53

Summary of Risk Regulation for Vertebrates Used for Pest Control..........................................................53

GROUP #14: PARASITOIDS FOR INSECT BIOLOGICAL CONTROL ......................................................... 54

History of U.S. Introductions of Parasitoids for Insect Biological Control ............................................... 54

Regulation of Risks: What were the Perceived Problems?.......................................................................... 56

Risk-Regulation Profile for Parasitoids used for Insect Biological control...............................................57

Risk 1: Direct attack on non-target species................................................................................................................57

Risk 2: Potential to vector pest insects, mites, ticks, or nematodes......................................................................57

Risk 3: Potential to vector pathogens to non-target plants......................................................................................57

Risk 4: Potential to become pests in crops..................................................................................................................57

Risk 5: Potential to degrade native habitats or ecosystems.....................................................................................57

Risk 6: Potential to reduce density of native species by changing food webs.......................................................57

Summary of Risk Regulation for Parasitoids for Insect Biological Control...............................................58

GROUP #15: PREDATORY INSECTS AND MITES FOR BIOLOGICAL CONTROL ..................................... 59

History of U.S. Introductions of Predatory Insects and Mites for Biological control.............................. 59

Regulation of Risks: What were the Perceived Problems?.......................................................................... 59

Risk-Regulation Profile for Predatory Insects and Mites used for Biological control............................ 60

Risk 1: Direct attack on non-target species...............................................................................................................60

Risk 2: Potential to vector pest insects, mites, ticks, or nematodes..................................................................... 60

Risk 3: Potential to vector pathogens to non-target plants..................................................................................... 61

Risk 4: Potential to become pests in crops................................................................................................................. 61

Risk 5: Potential to degrade native habitats or ecosystems.................................................................................... 61

Risk 6: Potential to reduce density of native species by changing food webs...................................................... 61

Summary of Risk Regulation for Predatory Insects and Mites for Biological Control............................ 61

GROUP #16: INSECTS AND MITES FOR WEED BIOLOGICAL CONTROL ................................................ 62

History of U.S. Introductions of Insects and Mites for Weed Biological control...................................... 62

Regulation of Risks: What were the Perceived Problems?...........................................................................63

Risk-Regulation Profile for Insects and Mites for Weed Biological Control .............................................63

Risk 1: Direct attack on non-target species............................................................................................................... 63

Risk 2: Potential to vector pest insects, mites, ticks, or nematodes..................................................................... 63

Risk 3: Potential to vector pathogens to non-target plants..................................................................................... 64

Risk 4: Potential to become pests in crops.................................................................................................................64

Risk 5: Potential to degrade native habitats or ecosystems.................................................................................... 64

Risk 6: Potential to reduce density of native species by changing food webs...................................................... 64

Summary of Risk Regulation for Insects and Mites for Weed Biological Control .................................. 65

GROUP #17: PATHOGENS FOR WEED OR INSECT BIOLOGICAL CONTROL............................................ 66

History of U.S. Introductions of Pathogens for Weed or Insect Biological Control ..................................... 66

Against weeds...................................................................................................................................................................66

Against insects..................................................................................................................................................................66

Regulation of Risks: What were the Perceived Problems?...........................................................................67

Plant pathogens.................................................................................................................................................................67

Insect pathogens...............................................................................................................................................................67

Risk-Regulation Profile for Pathogens USED for Weed or Insect Biocontrol ............................................67

Risk 1: Direct attack on non-target species................................................................................................................67

Risk 2: Potential to vector pest insects, mites, ticks, or nematodes..................................................................... 68

Risk 3: Potential to vector pathogens to non-target plants..................................................................................... 68
Variation in U.S. Standards for Introducing New Species

Risk 4: Potential to become pests in crops................................................................................................................. 68

Risk 5: Potential to degrade native habitats or ecosystems.................................................................................... 68

Risk 6: Potential to reduce density of native species by changing food webs...................................................... 68

Summary of Risk Regulation for Pathogens USED for Weed or Insect Biocontrol .................................. 68

Plant pathogens................................................................................................................................................................ 68

CREATING A UNIFORM, RISK-BASED SYSTEM FOR ALL GROUPS OF ORGANISMS.............................. 69

The past: An Ad Hoc Collection of Narrowly Focused Regulations............................................................. 69

Arguments for Retaining the Present U.S. System (special rules for special groups) ............................72

Argument #1. Some groups do not cause invasions and hence can be lightly regulated. ..................................72

Argument #2. Some groups are too economically important to restrict their importation. ..............................73

Argument #3. Public support does not exist for a new system. ..............................................................................73

Arguments for Creating a New, Risk-based System, Applied Evenly to All Species Groups...................73

REFERENCES.............................................................................................................................................. 74
Variation in U.S. Standards for Introducing New Species
Variation in U.S. Standards for Introducing New Species

INTRODUCTION

Biological control introductions, seen as a “green” technology that should be encouraged as a substitute 

for pesticides that were demonstrably polluting the environment when the authors were young graduate 

students (1970s), morphed in the public mind though the 1980s and 1990s into a potentially dangerous 

activity that should be more highly regulated than any other type of new species introductions. This change 

in public perception was facilitated by publications that overstated the risks and received disproportionate 

media attention. The purpose of this review is to consider that change in the public’s view of our science. If 

biological control introductions are characterized as highly dangerous, the question that comes first to mind 

is “compared to what?” and the logical comparison would seem to be to introductions of new species made 

for other purposes. That is what we have attempted to discuss here—how the risks of biological control agent 

introductions compare to those of introductions made by other sectors, such as the horticultural trade, the 

pet industry, aquaculture, state fish and game department sport introductions, and others. 

Over the previous 500+ years since European colonization of North America, new species of many 

sorts have arrived (Crosby, 2003). While some of the new species were accidental invasions, many others 

were deliberate introductions. Such intentional introductions were made for various reasons, but most were 

made because people were looking for economic advantage in some sector (agriculture, forestry, fisheries, 

etc.) or were motivated by nostalgia for familiar species left behind in the countries the colonists had come 

from. Views of the safety and benefits of such introductions were strongly influenced by people’s assumptions 

rooted in the pleasure or value associated with the use of the species in question. So, beautiful plants and tasty 

fish, to name a few, were good things to have and thus were good to import if they were not already present. 

Early in the history of introductions, risks were either unrecognized or disregarded until resultant damage 

began to be recognized. Also determining the legal policies of countries in relation to the importation of 

new organisms was the presence of commercial groups with economic reasons to import species (such as 

the horticultural industry or the pet industry, both of which are heavily dependent on having new species to 

sell). Finally, another factor driving importations has been the activities of state agencies—departments of 

fish and game, agriculture, forestry, or those in charge of management of public grazing lands, etc.—either 

promoting or opposing species importations, according to the beliefs prevalent at the time. 

In this review, we have organized the purposes behind intentional introductions into 17 groups: (#1) 

forestry, forage, and fodder plants, (#2) ornamental plants, (#3) crop plants, (#4) terrestrial mammals for 

ranching or viewing, (#5) fish used for aquaculture, (#6) commercially produced invertebrates, (#7) predatory 

mammals farmed for fur, (#8) herbivorous mammals farmed for fur, (#9) birds and mammals for hunting, 

(#10) non-native fish for sport or commercial fishing, (#11) animals sold as pets, (#12) animals introduced for 

medical uses, (#13) vertebrates for pest control, (#14) parasitoids for insect biocontrol, (#15) predatory insects 

and mites for insect biocontrol, (#16) insects or mites for weed biocontrol, and (#17) pathogens introduced 

for weed or insect biocontrol (Table 1). Note that these groups are defined with more attention as to why the 

species were introduced than to their taxonomy. Also, while most importations seem to fit into this scheme, 

very likely some examples exist that do not, and some species were introduced for multiple purposes.

Introduction 1
Variation in U.S. Standards for Introducing New Species Table 1. Types of potential risks posed by new species introductions and degree of regulation for species group x risk. For each group, each risk is classified as (1) regulated, (2) partly regulated, (3) not regulated, (4) degree of risk unknown, and (5) not applicable. Examples are worldwide for various time periods. Risk analysis is for the United States, at present.

G

r

o

u

p

/

u.s. example

RISK 1.attack nontarget species

RISK 2.vector insects or mites

RISK 3.vector pathogens

RISK 4.damage crops

RISK 5.degrade habitats

RISK 6.change food webs

#1 FORESTRY, FORAGE, OR FODDER PLANTSExamples: forage grasses (buffel grass, Cenchrus 

ciliaris L.; Lehmann lovegrass, 

Eragrostis lehmanniana Nees) 

and kudzu, Pueraria montana

var. lobata (Willd.) Maesen 

& S.M. Almeida ex Sanjappa & Predeep, introduced for forage and soil erosion control; 

Melaleuca quinquenervia

(Cav.) S.T. Blake, introduced for timber and landscape potential, soil stabilization, and as a wind break

NOT APPLICABLE Most plants lack potential for direct trophic effects (other than parasitic species such as dodder and broomrape).

REGULATED Plant shipments inspected at port of entry.

PARTIALLY REGULATED Importation of plants that are known hosts of known pathogens are prohibited or screened before importation (NAPPRA, 2019a). Unrecognized pathogens capable of host range expansion to native plants are per force uncontrolled.

PARTIALLY REGULATED Introductions of a few known crop weeds are prohibited (NAPPRA, 2019b). Most plant species have not been evaluated for their weed potential.

PARTIALLY REGULATED A few plants known to be invasive in natural habitats are prohibited (NAPPRA-listed species). Most plant species have not been evaluated for invasiveness potential. In the U.S., grasses have more frequently become invasive than forestry trees.

NOT REGULATED Effects of invasive plants on food webs are known to be important, but this is not evaluated before introduction.

#2 ORNAMENTAL PLANTSExamples: waterhyacinth, Pontederia (formerly Eichhornia) crassipes (Mart.) 

Solms (Center et al., 2002); purple loosestrife, Lythrum 

salicaria L.

NOT APPLICABLE Most plants lack potential for direct trophic effects.

REGULATED Shipped plants must be found to be insect-free via partial inspection at port of entry (or be shipped as seed), and some plant 

x country importations that might 

vector pest insects are prohibited (NAPPRA, 2019A). However, multiple shipments periodically cause pest introductions, e.g., sweet potato whitefly, Bemisia 

tabaci (Gennadius), on poinsettia 

(Euphorbia pulcherrima Willd. ex 

Klotzsch) to Florida (Hamon and Salguero, 1987) or cycad scale, 

Aulacaspis yasumatsui Takagi, 

which destroyed native cycads on Guam (Marler and Lawrence, 2012).

PARTIALLY REGULATED Importation of plants that are hosts of known pathogens are prohibited or screened before importation (NAPPRA, 2019A). Unrecognized pathogens capable of host range expansion to native plants are uncontrolled (e.g., at the time of invasion, 

Phytophthora ramorum

Werres et al., the causal agent of sudden oak death). 

PARTIALLY REGULATED

A few known crop weeds are prohibited (NAPPRA, 2019b). Most plant species have not been evaluated for weed potential. 

PARTIALLY REGULATED A few plants known to be invasive in natural habitats are prohibited (NAPPRA, 2019b). Most plant species have not been evaluated for invasiveness potential. Many introduced ornamentals have become invasive and damaging to natural habitats. The USDA Noxious Weed List (USDA NRCS, 2020) is comprised of species already established in the U.S. and is useful only for slowing spread to new regions within the county.

NOT REGULATED Some introduced plants that become invasive may change food webs in ways that harm native species (e.g., Burghardt et al., 2010; Carvalheiro et al., 2010; Hladyz et al., 2011; Wang et al., 2013), but this risk is not regulated.

2   Introduction
Variation in U.S. Standards for Introducing New Species

Table 1 (continued). Types of potential risks posed by new species introductions and degree of regulation for species group x risk. For each group, each risk is classified as (1) regulated, (2) partly regulated, (3) not regulated, (4) degree of risk unknown, and (5) not applicable. Examples are worldwide for various time periods. Risk analysis is for the United States, at present.

G

r

o

u

p

/

u.s. example

RISK 1.attack non-targetspecies

RISK 2.vector insects ormites

RISK 3.vector pathogens

RISK 4.damage crops

RISK 5.degrade habitats

RISK 6.change foodwebs

#3 CROP PLANTS Example: water spinach, Ipomoea aquatica Forssk. 

(Austin, 2007)

NOT APPLICABLE Most plants lack potential for direct trophic effects.

REGULATED Shipped plants must be found to be insect-free via partial inspection at port of entry (or, as is common for many crops, be shipped as seed). Also, some plants that have potential to vector insects are listed under NAPPRA (2019a) and their importation is controlled as to the permitted plant parts and countries of origin so as to reduce risk of pest vectoring by crop introductions. 

PARTIALLY REGULATED Importation of plants that are hosts of known pathogens are prohibited or screened before importation (NAPPRA, 2019a). Unrecognized pathogens capable of host range expansion to native plants are uncontrolled. Whether crop plants pose such risks needs consideration, especially as a wider range of crop plants is desired by new ethic communities.

PARTIALLY REGULATED Some herbs and minor crop plants have potential to become weeds themselves, e.g., water spinach. Some invasive grasses are prohibited from importation (NAPPRA, 2019b). Invasive plants already in the country are prohibited from interstate distribution if placed on the USDA Noxious Weed List (USDA NRCS, 2020).

PARTIALLY REGULATED Most crop plants probably lack the potential to damage natural habitats. However, water spinach can degrade aquatic habitats (Austin, 2007; USDA NRCS, 2015); the blackberry Rubus niveus Thunb. 

is an environmental pest in the Galapagos (Rentería et al., 2012); and strawberry guava (Psidium cattleianum Sabine) 

is a key environmental pest of forests in Hawaii (Patel, 2012). No crops not already present in the U.S. are prohibited from importation because of their potential to become environmental weeds.

NOT REGULATED Some introduced crop plants that become invasive may change food webs in ways that harm native species (e.g., Austin, 2007; Rentería et al., 2012; Patel, 2012; USDA NRCS, 2015).

#4 TERRESTRIAL MAMMALS FOR RANCHING OR VIEWING Example: goats in Hawaii

NOT REGULATED Escaped or released populations of farmed or otherwise imported mammals (e.g., deer, rabbits, goats, cattle, pigs, goats, foxes) have a high potential to destroy plant populations in natural areas (Fraser et al., 2003), or, for predatory species, to prey on native animals (e.g., for foxes: [Drummond and Leonard, 2010; Bytheway and Banks, 2019]), especially on islands.

REGULATED Introduction of exotic mammals (domesticated or wild species to be farmed) has the potential to spread ticks, e.g., Asian longhorned tick, 

Haemaphysalis longicornis

Neumann, that can affect native mammals. This risk is controlled by animal inspection at the time of importation.

REGULATED Exotic mammals have significant potential to introduce microbial 

pathogens that can affect wildlife. Known risks are regulated via animal inspections at the time of importation.

NOT REGULATEDIntroduced herbivorous or omnivorous mammals have potential to become crops pests. For example, wild boar in the U.S. damage crops (USDA APHIS, 2019a). This risk is being mitigated by a special program, but the risk itself was not considered before introduction of wild boar.

NOT REGULATEDEscaped or released populations of mammals (deer, rabbits, goats, cattle, pigs, goats) have extraordinarily high potential to destroy habitats, especially on islands. 

NOT REGULATEDPopulations of domestic animals that destroy natural vegetation through grazing in natural habitats inevitably degrade and rearrange food webs.

Introduction 3
Variation in U.S. Standards for Introducing New Species Table 1 (continued). Types of potential risks posed by new species introductions and degree of regulation for species group x risk. For each group, each risk is classified as (1) regulated, (2) partly regulated, (3) not regulated, (4) degree of risk unknown, and (5) not applicable.

G

r

o

u

p

/

u.s. example

RISK 1.attack non-targetspecies

RISK 2.vectorinsects ormites

RISK 3.vector pathogens

RISK 4.damage crops

RISK 5.degrade habitats

RISK 6.change foodwebs

#5 FISH USED FOR AQUACULTURE Example: European common carp

PARTIALLY REGULATED Trophic effects of fish introduced for use in aquaculture are possible if fish escape from pens, are farmed in natural water bodies, or are transported from pens or farm ponds to wild areas. This risk overlaps with use of such fish for sport (i.e., unconfined fish populations in natural waters). In general, this risk is not assessed. However, a few species of fish on the list of “injurious wildlife” (USFWS, 2019a) are listed because they are harmful to fish or other aquatic wildlife (e.g., snakehead fish [Love and Newhard, 2012]). 

NOT APPLICABLE

REGULATED The U.S. Fish and Wildlife Service can, under the Lacey Act, list species of fish as “injurious wildlife” whose introduction is prohibited or at least controlled. Of 408 species of fish listed in this way, 228 are species of Salmonidae that can vector pathogens to other fish. Fish pathogens can infect fish reared for aquaculture, and this process can accidentally move pathogens into wild populations if rearing water is connected to wild water or infected fish are released (e.g., whirling disease associated with trout in hatcheries reached wild trout in rivers in Colorado and Montana [Bartholomew and Reno, 2002]).

NOT APPLICABLE NOT REGULATED 

Fish escaped from rearing ponds may establish in wild waters, and some species can affect habitat quality. For example, carp from Europe were introduced for pond aquaculture, but escaped and damaged habitats by increasing turbidity and algal levels (Tapia and Zambrano, 2003; Badiou and Goldsborough, 2015). 

NOT REGULATED Fish introduced to rear as food in wild waters can affect food webs (e.g., Nile perch [Lates 

niloticus (L.)] 

in Lake Victoria [Goldschmidt, 1996; Welz, 2017]).

#6 COMMERCIALLY PRODUCED INVERTEBRATES Example: Introduction of new species of oysters 

NOT APPLICABLE Direct trophic impacts of introduced mollusks or crustaceans seem unlikely unless escape leads to established populations.

NOT APPLICABLE

PARTIALLY REGULATEDHistorically, farmed oysters introduced at least two highly destructive pathogens into Chesapeake Bay, greatly damaging wild oysters. Also, abalone farming in California introduced a parasitic worm affecting mollusks into coastal water in California (Moore et al., 2007). For prevention of such introductions, pathogens associated with reared mollusks have been identified to reduce inadvertent spread due to aquaculture (Carnegie et al., 2016). While crayfish introductions to the U.S. have not yet brought in new pathogens, European introductions of U.S. crayfish did introduce new strains of the pathogen Aphanomyces astaci, 

which devastated local crayfish species (Jussila et al., 2016).

PARTIALLY REGULATEDLand snails of the species consumed by people are generalist herbivores that eat many crop and horticultural plants. The brown garden snail, Cornu aspersum

(Müller) (= Helix 

aspersa) has become 

established in the wild in California, where it is now a garden and horticulture pest (Stearns, 1900; UCANR, 2019).

PARTIALLY REGULATEDBecause oysters make their own habitat, the decline of oyster densities in Chesapeake Bay also degraded oyster reefs, a required structure for new oyster growth. Also, introduction of red swamp crawfish, Procambarus clarkii

(Girard), in Spain contributed 

to the conversion of macrophyte-dominated water bodies to algal and planktondominated ones due to heavy grazing by exotic crawfish (Geiger et al., 2005).

NOT REGULATEDSharp drops (>90%) in oyster densities in Chesapeake Bay (at least substantially due to introduced pathogens spread by moving exotic oysters) led to dramatically lower levels of water filtration, leading to algal blooms and food web effects on other species. 

4   Introduction
Variation in U.S. Standards for Introducing New Species

Table 1 (continued). Types of potential risks posed by new species introductions and degree of regulation for species group x risk. For each group, each risk is classified as (1) regulated, (2) partly regulated, 

(3) not regulated, (4) degree of risk unknown, and (5) not applicable.

G

r

o

u

p

/

u.s. example

RISK 1.attack non-target species

RISK 2.vector insectsor mites

RISK 3.vector pathogens

RISK 4.damage crops

RISK 5.degrade habitats

RISK 6.change foodwebs

#7 PREDATORY MAMMALS FARMED FOR FUR Example: American mink in Europe

NOT REGULATED Trophic impacts can be severe if exotic farmed animals escape (or are released) and establish, as occurred in the U.K. with American mink (Rushton et al., 2000; Macdonald and Harrington, 2003). Risk in the U.S. is unregulated because animals are assumed to remain in cages, and exotic species have not been used. 

REGULATED Introduction of predatory mammals has the potential to spread ectoparasites that can affect native mammals. This risk is controlled by animal inspection at the time of importation.

REGULATEDMost predators reared for fur in the U.S. are native. Exotic species, if used in this way in the future, would be screened by a veterinarian before introduction to exclude sick individuals.

NOT APPLICABLE NOT REGULATED

Potential exists for impacts on habitats if key herbivore species’ densities were depressed by the predator. There are no known examples in the U.S. 

NOT REGULATEDIn theory, this risk may occur, but there are no examples in the United States.

#8 HERBIVOROUS MAMMALS FARMED FOR FURExample: Nutria, Myocastor 

coypus (Molina), in California, 

Maryland, and Louisiana

NOT REGULATED Herbivorous mammals farmed for fur are unlikely to be plant specialists, so the feeding impacts of populations of such animals would likely be born by many plant species. Rare plant species might be damaged incidentally, but the impacts of this group are treated as habitat destruction in cases such as nutria in the U.S. and brushtail possum, Trichosurus vulpecula

(Kerr), in New Zealand.

REGULATED Introduction of exotic herbivorous mammals has the potential to spread ectoparasites that can affect native mammals. This risk is controlled by animal inspection at the time of importation.

REGULATEDExotic herbivores would be screened by a veterinarian before introduction to exclude sick individuals. 

NOT REGULATEDNutria are indirect pests of agriculture due to their damage to irrigation and canal systems. Crop impact would depend on the specific biology of the imported species.

NOT REGULATEDMarsh habitat destruction occurred in the U.S. from nutria (Taylor and Grace, 1995; CDFW, 2019), which is the precedent species for the U.S. In New Zealand, brushtail possum, imported to be reared for fur, is highly destructive to native forest habitats (Atkinson and Cameron, 1993); its importation to the U.S. is prohibited under the Lacey Act (USFWS, 2019a).

NOT REGULATEDIn theory, this risk may occur, but there are no examples in the United States.

#9 BIRDS AND MAMMALS FOR HUNTINGExample: European boar 

NOT REGULATEDTrophic impacts of new sport animals are not calculated before their introduction.

REGULATEDIntroduction of exotic animals to be hunted have the potential to spread ectoparasites that can affect native 

mammals. This risk is controlled by animal inspection during the importation process.

REGULATEDAnimals would be screened by a veterinarian before introduction to exclude introduction of sick individuals.

NOT REGULATEDSome introductions of birds and mammals for sport hunting have potential to become crop pests. Wild boar in the U.S. can damage crops (USDA APHIS, 2019a). This risk is being mitigated by a special program, but the risk itself was not considered before introduction of boar.

NOT REGULATEDIn Hawaii, wild hogs maintained as feral animals for hunting degrade native forests and ecosystem processes (Bruland et al., 2010; Wehr et al., 2018).

NOT REGULATEDThis risk is of considerable concern, but has not been studied in the United States.

Introduction 5
Variation in U.S. Standards for Introducing New Species Table 1 (continued). Types of potential risks posed by new species introductions and degree of regulation for species group x risk. For each group, each risk is classified as (1) regulated, (2) partly regulated, (3) not regulated, (4) degree of risk unknown, and (5) not applicable. Examples are worldwide for various time periods. Risk analysis is for the United States, at present.

G

r

o

u

p

/

u.s. example

RISK 1.attack non-targetspecies

RISK 2.vector insects ormites

RISK 3.vector pathogens

RISK 4.damage crops

RISK 5.degrade habitats

RISK 6.change food webs

#10 FISH FOR SPORT OR COMMERCIAL FISHINGExample: releases of trout where they are not native have damaged populations of native fish (Dowling and Childs, 1992; Ward and MortonStarner, 2015), insects (Englund and Polhemus, 2001), and amphibians (Nyström et al., 2001; Pilliod, and Peterson, 2001).

PARTIALLY REGULATEDTrophic impacts on native fish, insects, and amphibians were not considered in the past before fish were introduced into new regions (Dowling and Childs, 1992; Englund and Polhemus, 2001; Nyström et al., 2001; Pilliod and Peterson, 2001; Ward and Morton-Starner, 2015). Few regulations currently control such fish introductions at the national level.

NOT APPLICABLEIntroduced fish do not have the biological potential to vector insects or ticks.

PARTIALLY REGULATEDUnder the Lacey Act (18 U.S.C 42), the U.S. Fish and Wildlife Service can list species of fish as “injurious wildlife” whose introduction is prohibited with permit exceptions. Of 408 species of fish listed in this way, 228 are species of Salmonidae that can vector pathogens to other fish. Fish pathogens can infect fish reared for sport release, and this process can move pathogens into wild populations, e.g., Myxobolus 

cerebralis Hofer in Alaska (Arsan 

and Bartholomew, 2008).

NOT APPLICABLEIntroduced fish do not have the biological potential to become crop pests.

NOT REGULATEDSome fish, such as carp, can damage aquatic habitats, but the type of predatory fish introduced for sport or commercial fishing do not seem to pose such a risk.

NOT REGULATEDIntroduced fish causing harm that is indirectly mediated through food webs (rather than via direct predation) are not commonly documented, but Pope et al. (2008) show that trout introductions can facilitate snake predation on amphibians by acting as alternate prey (“apparent competition”).

#11 ANIMALS SOLD AS PETSExamples: Burmese python, 

Python bivittatus (Kuhl), 

in Florida and red lionfish, 

Pterois volitans (L.), in Atlantic 

coastal waters of Florida.

NOT REGULATEDTrophic impacts can be severe, as shown in both marine (red lion fish)(Albins and Hixon, 2008) and terrestrial (Burmese pythons) (Dorcas et al.,2012; Sovie et al., 2016) systems. 

REGULATEDIntroduction of exotic pets have the potential to spread ectoparasites that can affect native animals. This risk is controlled by animal inspection during the importation process.

PARTIALLY REGULATEDRisks of introducing lethal pathogens are demonstrated in Europe by the crayfish plague vectored by red swamp crayfish, 

Procambarus clarkii (Cammà et al., 

2010; Aquiloni et al., 2011) and by the chytrid amphibian pathogen 

Batrachochytrium dendrobatidis

Longcore, Pessier & D.K. Nichols, vectored by sale of live Asian toads (O’Hanlon et al., 2018). This risk has been partly regulated under the Lacey Act (USFWS, 2019a) by listing risky groups as “injurious wildlife”—in particular, the salamander genera whose species act as vectors of a related pathogen (Martel et al., 2014). 

PARTIALLY REGULATEDThe risk of crop damage is generally less applicable to species 

introduced as pets, but it would depend on the species being sold. For example, some aquatic snails sold in the aquarium trade have the potential to become pests of rice or other paddy crops, such as Pomacea canaliculata

(Lamarck) on taro, 

Colocasia esculenta (L.) 

Schott, plantations in Hawaii (Tamaru et al., 2006).

PARTIALLY REGULATEDA few species have been listed as “injurious wildlife” because they pose risk to native habitats, but this risk is not consistently evaluated before new species are introduced in the United States.

NOT REGULATEDThe potential for invasive species brought in by the pet trade to damage native species’ food webs is real, as illustrated by the effects of red lion fish on reef communities (Bumbeer et al., 2018; Sancho et al., 2018). This risk is not assessed before introduction.

6   Introduction
Variation in U.S. Standards for Introducing New Species

Table 1 (continued). Types of potential risks posed by new species introductions and degree of regulation for species group x risk. For each group, each risk is classified as (1) regulated, (2) partly regulated, 

(3) not regulated, (4) degree of risk unknown, and (5) not applicable. Examples are worldwide for various time periods. Risk analysis is for the United States, at present.

G

r

o

u

p

/

u.s. 

example

RISK 1.attack non-targetspecies

RISK 2.vector insectsor mites

RISK 3.vector pathogens

RISK 4.damagecrops

RISK 5.degrade habitats

RISK 6.change foodwebs

#12 ANIMALS INTRODUCED FOR MEDICAL USESExample: African clawed frog, Xenopus laevis Daudin, in California (Somma, 2019).

NOT REGULATEDThe African clawed frog, 

Xenopus laevis Daudin, has had 

direct impacts on non-target species in California (Somma, 2019).

NOT APPLICABLE REGULATED

Introduction of medical animals have the potential to spread ectoparasites that can affect native animals. This risk is controlled by animal inspection during the importation process.

NOT APPLICABLE

NOT REGULATEDIn theory, this risk may occur, but there are no examples in the United States.

NOT REGULATEDIn theory, this risk may occur, but there are no examples in the United States.

#13 VERTEBRATES USED FOR PEST CONTROLExample: mongoose in Hawaii; grass carp for aquatic weed suppression.

REGULATEDRisks of direct predation on nontarget wildlife due to historical introductions of terrestrial predatory mammals for biocontrol are well documented, but such species have not been introduced into the United States in more than 100 years (Pimentel, 1955; Seaman and Randall, 1962). Use of fish for pest control has continued, with further use of three previouslyintroduced species for mosquito or aquatic weed control.

REGULATEDNo examples are known of vertebrates introduced for biocontrol vectoring ticks or insects. Theoretically, such a risk could exist, but modern introductions would be screened for such parasites, as are other vertebrate introductions, effectively controlling the risk.

REGULATEDNo examples are known of vertebrates introduced for biocontrol vectoring pathogens. Theoretically, such a risk could exist, but modern introductions would be screened for pathogens, as are other vertebrate introductions, effectively controlling the risk.

NOT APPLICABLEHerbivorous fish used for weed biocontrol might pose risks to some aquatic crop species. However, since no new fish are being introduced for this purpose, the risk is moot.

REGULATEDCarp used for weed biocontrol pose risks to aquatic habitats. However, these risks are regulated and would be considered prior to any introduction.

REGULATEDThe potential for introduced vertebrates to affect food webs certainly exists, e.g., the cane toad in Australia (Jolly et al., 2015). But, these risks are regulated, and no new vertebrate species are being introduced for biocontrol.

#14 PARASITOIDS FOR INSECT BIOLOGICAL CONTROLExample: Compsilura 

concinnata (Meigen) 

for gypsy moth, 

Lymantria dispar (L.) 

(Boettner et al., 2000).

REGULATEDSince the 1990s, the standard applied has been that newly introduced parasitoids must not harm populations of non-target native insects (Plant Protection Act, 2000). Laboratory host range testing is required before introduction to minimize this risk. 

REGULATEDSince before 1900, introduced 

parasitoids have been screened to prevent the introduction of hyperparasitoids, the only undesirable insects conceivably associated with parasitoids.

REGULATEDParasitoids may sometimes vector insect pathogens, but typically if insect pathogens exist in shipments of parasitoids, and if they do not affect the health of the parasitoid, they are pathogens of the target pest (e.g., the NPV virus of spruce sawfly, Gilpinia 

hercyniae (Hartig) [Balch, 1943]). 

Pathogens that do affect the health of the parasitoids, such as microsporidia, would be observed (as sick parasitoids) during quarantine and destroyed.

NOT APPLICABLEParasitoids have no biological potential to become plant pests.

REGULATED This risk is regulated, but difficult to foresee. Parasitoids may indirectly improve or harm habitats. If they control pests of native plants (e.g., scales in Queensland rain forest [Waterhouse and Sands, 2001; Van Driesche et al., 2010]), it is positive, but if they control pests of invasive plants, it would be negative (e.g., exotic scales attacking ice plants in California dunes [Tassan et al., 1982; Magnoli et al., 2013]).

REGULATEDThis risk is regulated, but interactions in food webs may be difficult to predict. Some cases, both positive and negative have been recognized (negative: Benson et al., 2003; positive: Herlihy et al., 2014).

Introduction 7
Variation in U.S. Standards for Introducing New Species Table 1 (continued). Types of potential risks posed by new species introductions and degree of regulation for species group x risk. For each group, each risk is classified as (1) regulated, (2) partly regulated, (3) not regulated, (4) degree of risk unknown, and (5) not applicable. Examples are worldwide for various time periods. Risk analysis is for the United States, at present.

G

r

o

u

p

/

u.s. example

RISK 1.attack non-targetspecies

RISK 2.vector insects ormites

RISK 3.vector pathogens

RISK 4.damage crops

RISK 5.degrade habitats

RISK 6.change food webs

#15 PREDATORY INSECTS AND MITES FOR BIOLOGICAL CONTROLExample: Harmonia 

axyridis (Pallas), Coccinella 

septempunctata L. (Harmon 

et al., 2007; Losey et al., 2007)

REGULATEDSince the 1990s, the standard applied has been that newly introduced predatory insects must not harm populations of non-target native insects (Plant Protection Act, 2000). Laboratory prey range testing is required before introduction to minimize this risk. 

REGULATEDSince before 1900, introduced predators have been screened to prevent the introduction of their own parasitoids, the only undesirable insects conceivably associated with predatory insects.

REGULATEDPopulations for introductions are screened for fungal or microsporidian pathogens, and laboratory colonies are cleared of pathogens before introduction.

REGULATEDIntroduced predatory insects must not damage crops or cause economic losses. Plant-feeding predaceous mirid bugs feed on crops as well as greenhouse pests (Moerkens et al., 2016), and decisions as to whether or not to introduce such zoophytophagous predators may differ between countries. Harmonia 

axyridis can cause irregular 

flavors in wine if adults contaminate the grapes (Pickering et al., 2004).

REGULATEDThis risk is now regulated. In some cases, predatory insects improve habitats if they control invasive pests that damage the habitat (e.g., cycad forests on Guam [Van Driesche and Reardon, 2017]).

REGULATEDThis risk is now regulated in principle, but it is difficult to predict. Impacts by two introduced coccinellids, 

H. axyridis and C. 

septempunctata, illustrate 

food web impacts and can be used as a model to avoid future similar events. 

#16 INSECTS AND MITES FOR WEED BIOLOGICAL CONTROLExample: Rhinocyllus conicus

(Frölich) (Louda, 1998; Louda et al., 2005) and Cactoblastis 

cactorum Berg (Stiling et al., 

2004; Pemberton and Liu, 2007)

REGULATEDWeed biocontrol agents undergo preintroduction host range evaluation (Wapshere, 1974), and they must not have the potential to significantly damage non-target plants or reduce their populations. 

REGULATEDParasitic insects or nematodes attacking candidate weed biocontrol agents internally, if present, are eliminated during quarantine.

REGULATEDInsects and mites in systems with such concerns can be screened for pathogen DNA, and groups of agents rejected if pathogen DNA is detected. For an example of such pathogen DNA-screening (for a parasitoid), see Hoy et al., 2001.

REGULATEDCrop species that are 

potentially suitable for agent feeding are included in tests for evaluation of host range, and agents are rejected if they have the potential to feed on crops (e.g., Cristofaro et al., 2013).

REGULATEDHabitats produced by native plants are not affected because feeding on native plants by biocontrol agents is nil to incidental. However, habitats created by invasive plants may be affected if the target invasive weed is successfully suppressed. Benefits from such weeds would have to be determined and weighed against the weed’s ecological damage before initiating a project.

REGULATEDNo real examples are known of harm to native food webs from successful weed biocontrol. However, if the potential for impacts is suspected, they could be evaluated in the review of particular agents. In the case of melaleuca (Melaleuca quinquenervia) in 

Florida, the melaleuca sawfly, 

Lophyrotoma zonalis (Rohwer), 

produces toxins potentially poisonous to song birds eating the sawfly’s larvae. To protect against this risk, this sawfly was not pursued for release as a biocontrol agent (Purcell and Goolsby, 2005).

8   Introduction
Variation in U.S. Standard

s forIntroducingNew Species

Table 1 (continued). Types of potential risks posed by new species introductions and degree of regulation for species group x risk. For each group, each risk is classified as (1) regulated, (2) partly regulated, 

(3) not regulated, (4) degree of risk unknown, and (5) not applicable. Examples are worldwide for various time periods. Risk analysis is for the United States, at present.

Group/u.s. example RISK 1. attack non-target

species

RISK 2.vector insects ormites

RISK 3.vector pathogens

RISK 4.damage crops

RISK 5.degrade habitats

RISK 6.change food webs

#17 PATHOGENS FOR WEED OR INSECT BIOLOGICAL CONTROLExamples: a) weed pathogensThe rust Maravalia 

cryptostegiae (Cummins) Y. 

Ono, a pathogen of rubber vine, Cryptostegia grandiflora

(Roxb.) R.Br., in Australia (Vogler and Lindsay, 2002)b) insect pathogens

Entomophaga maimaiga

Humber, Shimazu, & R.S. Soper, a pathogen of gypsy moth in North America (Hajek et al., 2007)

REGULATEDa) weed pathogensPlant pathogens used for weed biocontrol must not significantly affect nontarget plants or reduce their populations.b) insect pathogensRisks to non-target insects would have to be evaluated at the time of introduction.

NOT APPLICABLEBoth weed and insect pathogens lack potential to vector pest insects.

NOT APPLICABLEBoth weed and insect pathogens lack potential to vector other pathogens.

REGULATEDa) weed pathogensPathogens used as weed biocontrol agents must not infect crops, including horticultural plants. For this reason, the pathogen causing rose rosette disease cannot be used for control of multiflora rose, 

Rosa multiflora Thunb. 

(Al-Rwahnih et al., 2019)b) insect pathogensInsect pathogens lack the potential to harm crops.

REGULATEDa) weed pathogensNative plant populations must not be harmed by pathogens used for weed biocontrol. Therefore, native habitats will not be harmed. However, habitats created by invasive plants may be affected if the target invasive weed is successfully suppressed. Benefits from such weeds would have to be determined and weighed against the weed’s ecological damage before initiating a project.b) insect pathogensIf a pest insect damages native habitats (e.g., gypsy moth) then pathogen introduction, if successful, would benefit native habitats.

REGULATED a) weed pathogensNo examples are known of harm to native food webs from successful weed biocontrol by a pathogen. However, if the potential for impacts is suspected, this risk could be evaluated in the review of particular agents. b) Insect pathogensNo examples are known of harm to native food webs from successful insect biocontrol by a pathogen. However, if the potential for impacts is suspected, this risk could be evaluated in the review of particular agents.

Introduction 9
Variation in U.S. Standards for Introducing New Species

Risks associated with deliberate introductions, unlike those from accidental invasions, were not 

immediately recognized by most people or government agencies. Rather, attention was focused on the 

expected benefits from the introductions. Because many benefits were associated with new kinds of plants 

(used as crops, timber, forage, or ornamentals), one of the earliest forms of risk recognized in the United 

States was that such plant introductions might not attain their full social benefits (or might harm other 

plants) if importations were not restricted to clean stock, free of damaging insects and plant pathogens. 

Consequently, plant quarantine acts were enacted early on to reduce such risks (Plant Quarantine Act, 1912). 

Importantly, however, the new plant species themselves were not considered to pose any risks that needed to 

be evaluated. The goal was merely to ensure the plants were vigorous, healthy, and free of pests. In contrast to 

our views of plants, deliberate introductions of mammals and birds (non-caged) were recognized very early 

as potentially damaging and were prohibited from 1900 to 1948, at which time the law was changed and this 

blanket prohibition was replaced with a black list of injurious wildlife.

As with plant importations, it has long been recognized that movement of livestock or other mammals 

had the potential to move pathogens or parasites to new areas. This again led quite early to regulatory efforts 

to ensure that livestock and live poultry entering the United States were free of pathogens and parasites. The 

U.S. Animal Industry Act of 1884 created the Bureau of Animal Industry, which was charged with enforcing 

animal importation regulations. Currently, the Veterinary Services, Organisms and Vectors Permitting Unit 

of the Animal and Plant Health Inspection Service (APHIS) regulates the importation into the United States 

and interstate transportation of organisms and vectors of pathogens of livestock and poultry. Given the 

importance of animal production industries to the U.S. economy, potential vectors of pathogens of livestock 

and poultry are extensively regulated. Imported wildlife (principally mammals), for hunting, display, or 

other uses, also pose similar risks of introducing new pathogens to domestic livestock (Pavlin et al., 2009), a 

risk that has been recognized and is regulated, at least as far as known pathogens are concerned. 

Risks to wildlife from animal introductions were recognized somewhat later. While most attention in this 

area has also been focused on pathogens associated with fish, mammals, and birds, the accidental movement 

of pathogens in imported frogs (Muths et al., 2003; Adams et al., 2017), salamanders (Martel et al., 2014), and 

crawfish (Cammà et al., 2010; Aquiloni et al., 2011) illustrates the potential harm to native biodiversity of 

introduced pathogens of other groups. Currently, this risk is partly regulated through listing of some species 

as “injurious wildlife” under certain provisions of the Lacey Act (discussed in Group 5). For a summary of 

the intent, powers and process of listing non-native species as “injurious wildlife” under the Lacey Act and 

associated statutes, see USFWS (2020a), and for the criteria for listing see USFWS (2020b). These acts provide 

the agency with the ability to list as “injurious wildlife” vertebrate species and some groups of invertebrates 

(mollusks and crustaceans, but not insects), but do not provide any authority over plant introductions.

Risks of deliberately imported herbivorous insects were not considered before the 1920s because, for 

the most part, there were none. But about 1920, in Australia, damage from invasive cacti was so severe that 

such herbivorous insect importations were systematically pursued. While not the first effort to use insects 

to reduce invasive plant densities, the control of invasive Opuntia cacti in New South Wales, Australia, was 

the first large, state-sponsored, successful effort (Wilson, 1960). During the implementation of this project, 

concern that the deliberately imported plant-feeding insects might damage crops or other economically 

important plants led to the creation of legal controls on such importations. Regulations were adopted under 

plant protection acts (such as the Plant Quarantine Act, 1912 in the United States) requiring laboratory 

testing to show that the insects being imported would not harm economically important plants. While the 

regulatory mandate begun in the 1920s was to ensure that crops and economic plants would not be affected 

by deliberately imported plant-feeding insects, by the late 1960s that goal had been broadened to include 

assessment of potential risks to non-economic, native plants. This larger task was done by estimating the 

fundamental host range of the proposed agents, rather than just checking lists of economically important 

species for possible feeding (Julien and White, 1997). 

A main theme of this review is the gradual expansion of social recognition of different types of risks 

and the uneven application of regulatory processes to control them. Here, we define six risk categories that 

10   Introduction
Variation in U.S. Standards for Introducing New Species

should be considered before approving the introduction of any new species (Table 1): (1) direct attack on 

non-target species*; (2) potential of an imported species (usually a plant) to vector pest insects or mites, 

or, for imported animals, ticks; (3) potential of an imported species to vector pathogens able to infect nontarget plants or animals; (4) potential for imported plants or animals to damage crops; (5) potential for an 

imported plant or animal to change native habitats or ecosystems; and (6) potential for a new species to 

reduce the density of native species by changing food webs. 

While the above risks now seem reasonable and fairly comprehensive, they were recognized gradually 

over time as experience with damage caused by various types of imported species accrued. As awareness 

grew, additional regulations or programs were adopted to prevent recurrence of newly recognized risks.

However, regulations to reduce these risks were not applied comprehensively across species imported 

for different purposes, but rather were frequently developed to apply only to a particular type of species 

importation, to control the risk in one specific context. The contention of this review is, therefore, that 

a uniform, defined risk-review process should be developed and used in the future for assessment of all 

species use-groups as discussed here, rather than the ad hoc, historical patchwork that now exists. In a 

U.S. context, this is sometimes referred to as having an “Organic Act” covering an issue as a whole, rather 

than many separate acts addressing pieces of the problem. Currently in the United States, we have no such 

Organic Act addressing the risks potentially posed by new species importations. 

In this review, first we show that different species use-groups (species imported for a particular 

purpose) have historically been, and still are, regulated in the United States with strikingly different levels of 

rigor. Second, we show that this difference in regulatory rigor is not justified, which in theory it might be if 

some species “use-groups” were intrinsically free of certain types of risks, but which we show is not the case. 

We review the 17 purposes we have recognized for novel species introductions (“species-use groups”) and 

consider, for each species use-group, if the six risks we have identified above are regulated, partly regulated, 

not regulated, or not applicable.

*Throughout this publication, “non-target species” refers to species native to the United States as well as species not native to the United States that were 

introduced intentionally and are still considered desirable.

Introduction 11
Variation in U.S. Standards for Introducing New Species

Banner Photos. Plants intentionally introduced to the U.S. and used for forestry, fodder, or forage that have since caused ecological damage include (from 

left to right) Tasmanian blue gum, Eucalyptus globulus Labill. (Forest & Kim Starr, Starr Environmental); timothy, Phleum pratense L. (John M. Randall, The 

Nature Conservancy, Bugood.org); kudzu, Pueraria montana (Lour.) Merr. (Scott Ehardt, Wikipedia.org); white leadtree, Leucaena leucocephala (Lam.) de Wit 

(William M. Ciesla, Forest Health Management International, Bugwood.org); Lehmann lovegrass, Eragrostis lehmanniana Nees (John Ruter, University of Georgia,

Bugwood.org); and hairy vetch, Vicia villosa Roth (John D. Byrd, Mississippi State University, Bugwood.org).

12   GROUP #1: Forestry, Forage, and Fodder Plants

GROUP #1: FORESTRY, FORAGE, AND FODDER PLANTS

HISTORY OF U.S. INTRODUCTIONS OF FORESTRY, FORAGE, OR FODDER PLANTS

This group includes plants used in forestry, or for forage or fodder, or for certain other economic reasons such 

as erosion control or stabilization of areas of sand or mud. In North America, the abundance of desirable soft 

woods for lumber and hardwood trees suitable for many purposes led to domination of the forestry sector 

by native species, with few non-native trees being imported for production in plantations (and those that 

were, being of only limited acreage). Hawaii, in contrast, made extensive use of exotic trees for reforestation 

of denuded, eroding lands, including plantations of pines and eucalyptus (Woodcock, 2003; Fischer et al., 

2009). In the Southern Hemisphere, a similar paucity of native softwoods suitable for use as building lumber 

led to large-scale planting of exotic trees (often Pinus spp.), especially in Australia, New Zealand, Chile, and 

South Africa (Gilmour, 1946; Scott, 1960). In many warmer regions of the world (e.g., central Africa), exotic 

eucalyptus species have been widely grown in plantations (e.g., in the Congo [Istas, 1954]). Due to a lower 

need for exotic forestry plantations, the United States has had relatively few problems with exotic forestry 

tree species invading and naturalizing in native forests. Most pest trees in natural areas in the United States, 

such as tree of heaven (Ailanthus altissima [Mill.] Swingle) and Norway maple (Acer platanoides L.), were 

introduced not for forestry, but rather as ornamentals. 

In contrast to problems with novel species used for forestry, the United States has a significant history 

of introduction of exotic forage grasses (e.g., buffel grass [Cenchrus ciliaris L.] and Lehmann lovegrass 

[Eragrostis lehmanniana Nees]) in attempts to improve grazing, especially in several western states, where 

introduced grasses now dominate large areas and have had dramatic ecological consequences (buffel grass 

[Fig. 1; Sands et al., 2009; Olsson et al., 2012; Lyons et al., 2013] and Lehmann lovegrass [McDonald and 

McPherson, 2011; Lindsay et al., 2011]). Similarly, in Hawaii, exotic pasture grasses were deliberately 

introduced (Whitney et al., 1939), and some exotic grasses have had large effects on native grasslands, often 

changing the fire cycle to the detriment of native species (e.g., Paspalum conjugatum P.J. Bergius [Ainsworth 

and Kauffman, 2010]). In contrast, relatively few woody plants have been introduced in the continental 

United States for use as fodder for cattle or goats, although exotic species of mesquite (Prosopis spp.) and the 

nitrogen-fixing shrub Leucaena leucocephala (Lam.) de Wit, both excellent sources of high-protein cattle 

fodder in dry tropical areas, are examples of damaging introductions made for this purpose in areas such as 

Hawaii and Guam (Egler, 1947; Cronk and Fuller, 1995; Gallaher and Merlin, 2010). Finally, several plants 

introduced to vegetate mud flats (e.g., Spartina alterniflora Loisel. in San Francisco Bay, California [Ayres et 
Variation in U.S. Standards for Introducing New Species

a b c

Figure 1. Buffel grass, Cenchrus ciliaris L. (a), was intentionally planted to improve grazing, but quickly spread in many western states (b), dramatically 

altering ecosystems and promoting hot, rapidly-moving fires (c). (Photos: Forest & Kim Starr, Starr Environmental)

GROUP #1: Forestry, Forage, and Fodder Plants 13

al., 2004]) or to reduce soil erosion (e.g., kudzu, Pueraria montana (Lour.) Merr. [Rowalt, 1937]) have had 

damaging effects over large or ecologically important areas (Van Driesche et al., 2002). 

REGULATION OF RISKS: WHAT WERE THE PERCEIVED PROBLEMS?

Historically, unrestricted movement of plants, timber, and other plant-products from overseas locations 

into the eastern United States and Canada led to the accidental introduction of a great many plant pests. 

Some accidentally introduced pest insects and plant pathogens were highly destructive of native trees, such 

as the browntail moth, Euproctis chrysorrhoea (L.); winter moth, Operophtera brumata (L.); chestnut blight, 

Cryphonectria parasitica (Murrill) Barr; and beech scale, Cryptococcus fagisuga Lindinger (Van Driesche 

and Reardon, 2014). Simultaneously, introduced species of scales, mealybugs, whiteflies, and other insects 

affected crops (Nechols et al., 1995). Therefore, the Plant Quarantine Act of 1912 was passed, regulating the 

importation and movement of nursery stock and other plants and plant products within the United States 

to control the dissemination of injurious plant pests and diseases. The goal of this Act was to deal with this 

influx of plant pests, newly recognized in this period. Plants themselves were not viewed under this Act as 

potential pests in this period, merely potential vectors of plant pests. The mechanism created to reduce this 

risk was the use of inspections of plants entering the United States, to detect and exclude infested or infected 

plants vectoring such pests. To date, the regulatory mission concerning imported plants has remained largely 

unchanged from its original purpose. Under U.S. law, nearly all plant species themselves are assumed to be 

benign and acceptable for importation. Relatively recently, a small number of plants have been identified 

whose importation is prohibited without a prior risk review, a process called NAPPRA (“not authorized 

pending pest risk analysis”). There are two types of NAPPRA lists. The goal of the first is the prevention of 

the introduction of pests attacking plants (NAPPRA, 2019a). The list consists of species (or genera) of plants 

that may not be imported from various countries because their movement would pose a risk of importing 

a known pest insect or pathogen. The second NAPPRA list addresses a new risk: the plants themselves. The 

plants on list two (for first three rounds, 79 species out of the quarter million species of existing plants) have 

been identified as likely weeds of crops, forests, or other natural areas (NAPPRA, 2019b). The burden of risk 

identification remains with the government rather than the person or group making the importation. Thus, 

the current posture of the U.S. government with regard to plant importations is that “For taxa of plants for 

planting whose importation is not specifically restricted or prohibited in the regulations [NAPPRA listing 

as mentioned above], the only risk mitigation requirements are that the shipments enter the United States 

through a Federal plant inspection station, be accompanied by a phytosanitary certificate and a permit, and 
Variation in U.S. Standards for Introducing New Species

be sampled and visually inspected for quarantine pests.” That is, any plant not on the NAPPRA lists may 

legally be imported for planting, provided it is not obviously diseased or infested with insects. 

RISK-REGULATION PROFILE FOR FORESTRY, FORAGE, AND FODDER PLANTS

Risk 1: Direct attack on non-target species 

Direct attack on non-target plants is not applicable for most groups of imported plants, excepting only a few 

parasitic species. 

Risk 2: Potential to harbor pest insects, mites, or nematodes 

Extensive measures are in place to prevent the inadvertent introduction of pest insects, mites, or nematodes 

in or on imported plants. Risk reduction activities include (1) inspections of imported material at U.S. ports of 

entry, (2) inspections of plants at foreign production sites, and (3) prohibition of importation of certain plants 

from countries where pests occur that might accompany imported plants of the prohibited genus or species 

(NAPPRA, 2019a). For example, to forestall the importation of the citrus longhorned borer, Anoplophora 

chinensis (Forster) (Cerambycidae), it is forbidden to import Acacia species, except as seeds, cut flowers, or 

“greenery” (parts incapable of concealing live stages of the insect in question), from any country except for 

Canada. Similarly, to forestall the accidental importation of the plant-parasitic nematode Bursaphelenchus 

cocophilus (Cobb) Baujard, the importation of plants in eight genera (Acrocomia, Astrocaryum, Attalea, 

Bactris, Euterpe, Mauritia, Oenocarpus, and Roystonea) is prohibited from all countries, except as seeds, 

cut flowers, or greenery (plant parts incapable of vectoring live stages of the nematode). New specific 

prohibitions are published periodically by the U.S. Animal and Plant Health Inspection Service (APHIS) 

under NAPPRA. The same process is used to reduce the risk of introduction of plant pathogens (see Risk 3 

below). Note, however, that while NAPPRA-listed species have been flagged as requiring review, they may 

still be imported after a risk analysis if the agency chooses. Also, this black-listing approach has been applied 

to only a tiny fraction of existing plant species, leaving most plants unreviewed. 

Risk 3: Potential to vector pathogens to non-target plants

To make the accidental introduction of plant pathogens on imported plants less likely (through partial 

regulation), a similar approach is used to restrict movement of plants likely to harbor such pathogens. Detection 

of diseased plants at points of entry would result in rejection of a plant shipment. However, plants may either 

be infected but not yet show symptoms or may harbor organisms to which they are tolerant (and relatively 

symptom-free) but which can undergo host range expansion onto susceptible hosts in new regions of the world 

following importation of their host plants. For example, Phytophthora ramorum Werres et al., the causal agent 

of sudden oak death, kills several tree species but was introduced by the nursery industry on three genera of 

shrubs that are not themselves strongly affected by the pathogen (Hüberli et al., 2008; Poucke et al., 2012). 

To lower the risk of introducing pathogens, importation of some plants is prohibited from countries 

where specific pathogens are known to occur and be associated with particular groups of plants (NAPPRA, 

2019a). NAPPRA lists are of prohibited plant species (or genera) x plant part(s) x country combinations, 

whose prohibition is intended to forestall importation of certain plant pests or pathogens. For example, to 

reduce the risk of importation of the alder pathogen Phytophthora alni Brasier & S.A. Kirk, the importation of 

any species of Alnus (excepting only the importation of seed) is prohibited from all countries except Canada.

Risk 4: Potential to become pests in crops

Some plant species have been identified by APHIS in the United States as having the potential to become weeds 

in U.S. crops or natural areas, based not on testing, but rather on literature records. These species are on a short 

14   GROUP #1: Forestry, Forage, and Fodder Plants
Variation in U.S. Standards for Introducing New Species

NAPPRA black list (31 species in 2013 and 22 more in 2017), and their introduction is prohibited pending 

review (therefore, this risk is partly regulated; NAPPRA, 2019b). These species are pests of crops or natural 

areas (or both) in their native ranges, or in previously invaded areas. However, many plants not on such lists 

still have an undetermined potential to become invasive pests of agriculture, forestry, or natural areas. 

Risk 5: Potential to degrade native habitats or ecosystems

Many deliberately imported plant species have become pests of natural areas (Foxcroft et al., 2013). New plant 

importations in the United States are not routinely tested for this risk, nor is their importation prohibited unless 

the species happens to be one of the few species whose literature records have been reviewed and placed on the 

prohibited lists (79 species) mentioned above as posing a risk of becoming crop weeds (NAPPRA, 2019b). These 

species are black-listed based on literature records that show the species are pests of crops or natural areas (or both) 

in their native ranges, or in previously invaded areas. For example, the grass Acroceras zizanioides (Kunth) Dandy 

is one such NAPPRA-listed species that is recorded as “flourishing in semi-aquatic and forest environments in 

Africa, Asia, and tropical America. It occurs in both disturbed and undisturbed soils, in forests and throughout 

the interior and coastal savannas, and would seem well adapted to be a significant threat to wetlands and forest 

in any tropical regions of the United States.” Another such example is silky hakea, Hakea sericea Schrad. & J.C. 

Wendl., an introduced tree in South Africa that is now widely invasive there in dry natural areas (Fugler, 1982).

The NAPPRA listing process has two shortcomings. First, the number of species placed on the list is 

less than 0.1% of all plant taxa, leaving 99.9% of plant species unreviewed, even based solely on literature. 

Second, the listing process is triggered by plants being weeds in either their native ranges or previously 

invaded areas. However, many plants that are not weeds in their native ranges have potential to increase in 

density and become pests in new regions either due to separation from the natural enemies that suppress 

their densities in their native range (Blossey and Kamil, 1996) or other mechanisms (Enders and Jeschke, 

2018). The whole field of plant management through natural enemy importation (weed biocontrol) is based 

on the repeated occurrence of such introduction-induced plant explosions (Van Driesche et al., 2008). 

Currently in the United States, the burden of proof concerning the potential risk of importation 

of particular plants rests on the government, which must show that the importation of a particular plant 

is not safe, rather than requiring the importer to show that it is safe. This situation is reminiscent of the 

commercialization of chemicals for use as pesticides before the 1947 Federal Insecticide, Fungicide, 

and Rodenticide Act, whose passage inverted a similar presumption of safety, placing the burden on the 

manufacturer to prove safety before being permitted to sell a chemical as a pesticide product (implemented 

through a new requirement for product registration [Aspelin, 2003]).

Risk 6: Potential to reduce density of native species by changing food webs

Invasive plants that dominate habitats or change them structurally are very likely to also affect non-target 

species through changes to native food webs (e.g., Pritekel et al., 2006; Lowe et al., 2008). However, it is 

difficult to predict the direction (harmful versus beneficial) and intensity of such effects, and this risk is not 

assessed for new plant introductions in the United States. 

SUMMARY OF RISK REGULATION FOR FORESTRY, FORAGE, OR FODDER PLANTS 

For forestry, forage, and fodder plants, Risk 1 (direct attack) is not relevant, while Risks 2 and 3 (vectoring 

pests or pathogens) have been the core regulatory focus of concern since the beginning of controls on plant 

importations in the United States more than a century ago. Insect invasions, however, are much easier to detect 

than invasions of previously unrecognized pathogens in asymptomatic hosts, making Risk 3 only partially 

regulated. Regulation of Risks 4 and 5 (plants being weeds or damaging natural habitats) has begun, but only 

for a few NAPPRA-listed species. Risk 6 (impacts of plants on food webs) remains unregulated. Overall, the 

burden of proof to show a proposed plant introduction is unsafe remains with the government, not the importer.

GROUP #1: Forestry, Forage, and Fodder Plants 15
Variation in U.S. Standards for Introducing New Species

16   GROUP #2: Ornamental Plants

Banner Photos. Plants intentionally introduced to the U.S. as ornamentals that have since caused ecological damage include (from left to right) chocolate 

vine, Akebia quinata (Houtt.) Decne. (Chris Evans, University of Illinois); Norway maple, Acer platanoides L. (Leslie J. Mehrhoff, University of Connecticut); 

butterfly bush, Buddleja davidii Franch. (Leslie J. Mehrhoff, University of Connecticut); pampas grass, Cortaderia selloana (Schult. & Schult.f.) Asch. & Graebn. 

(John Ruter, University of Georgia); Japanese honeysuckle, Lonicera japonica Thunb. (Chris Evans, University of Illinois); and Scotch broom, Cytisus scoparius

(L.) Link (Eric Coombs, Oregon Department of Agriculture) (all images from Bugwood.org).

GROUP #2: ORNAMENTAL PLANTS

HISTORY OF U.S. INTRODUCTIONS OF ORNAMENTAL PLANTS

In North America, as in Europe, the importation of ornamental plants for their beauty or other desired 

qualities has long been a popular and commercially important activity (Cunningham, 1990; Wulf, 2010), 

and such importations have been the source of most plant invasions (Reichard and White, 2001). The desire 

of people to have new and unusual plants in their private estates (Fig. 2) has long created a market demand, 

which led to the development of a nursery industry to satisfy such interest. Before approximately 1400, 

plants were moved slowly over land between areas, which forced many introductions to be based on the 

use of seed. As European ships began to more thoroughly explore the world in the 15th century, transit 

times were greatly reduced, and trade routes were used to import goods, including live plants. European 

interest in plants from China was especially strong in the 18th and 19th centuries (Cox, 1961). Once new 

plant species entered the nursery trade in Europe, they were moved widely among countries with suitable 

climates, especially to regions of the world that Europeans had colonized (Crosby, 2003). In many regards, 

the importation of plants as ornamentals was very similar to the introduction of plants for forestry, forage, 

or fodder. But two differences are worth mentioning. First, the number of plants potentially considered 

desirable for importation as ornamentals is greater by orders of magnitude. Secondly, the development of a 

worldwide commercial industry centered on making such plant translocations created a large and effective 

mechanism for plant movement, with a strong and sustained motive for doing so on a continuing basis. 

This industry then provided a political constituency for plant importations, lobbying for lenient terms of 

importation. 

REGULATION OF RISKS: WHAT WERE THE PERCEIVED PROBLEMS?

Historically, unrestricted movement of imported plants, including ornamentals from overseas locations into 

the eastern United States, led to the accidental introduction of many plant pests. Some of these introduced 

insects and plant pathogens became forest or garden pests (e.g., for pests in U.S. forests, see Van Driesche 

and Reardon, 2014). This risk was reduced by the same act (Plant Quarantine Act, 1912) mentioned above, 

which restricted the introduction of plants, including ornamentals, into the United States by requiring plant 

inspections. The regulatory status of this group of novel species is the same as described above for Forestry, 
Variation in U.S. Standards for Introducing New Species

GROUP #2: Ornamental Plants 17

Forage, and Fodder plants. The most significant difference between ornamentals as a group and those 

plants imported for use in forestry or as forage or fodder, is that ornamentals provide a much larger pool of 

new plant species for importation and an industry (horticulture) eager to obtain and sell them to private, 

individual users at millions of locations, which provide many points of introduction into natural habitats.

SUMMARY OF RISK REGULATION FOR ORNAMENTALS 

For plants sold as ornamentals, Risk 1 (direct attack) is not relevant. Risks 2 and 3 (vectoring pests or 

pathogens) have been the core regulatory focus since the beginning of control a century ago and, in principle, 

are regulated. However, the sheer diversity of the taxa involved makes it difficult to recognize and control 

these risks effectively through inspection. Furthermore, insect invasions are much easier to detect than 

invasions of previously unrecognized pathogens in asymptomatic hosts, making Risk 3 only partially regulated. 

Risks 4 and 5 (plants being weeds or damaging natural habitats) have begun to be regulated, but only for a 

few NAPPRA species, with risk evaluation remaining the obligation of the government, not the importer. 

Many ornamental plants imported for use in gardens are not invasive due to lack of competitiveness, being 

dependent on weeding and fertilization by homeowners. However, some groups of plants (vines [Gordon et 

al., 2017], ground covers, and grasses [Overholt and Franck, 2017]) may have higher potential for invasion 

and cause greater damage to natural ecosystems than other growth forms (Phillips et al., 2010). Risk 6 

(impacts of ornamental plants on food webs) remains unregulated, but clearly exists (e.g., Burghardt et al., 

2010; Carvalheiro et al., 2010; Hladyz et al., 2011; Wang et al., 2013). 

a b c

Figure 2. Water hyacinth, Pontederia (formerly Eichhornia) crassipes (Mart.) Solms (a), was intentionally introduced as an aquatic ornamental (b), but 

escaped ponds and was also intentionally dumped with aquaria contents. It has since become one of the worst aquatic invaders in the world (c). (Photos: 

a. Shaun Winterton, California Department of Food and Agriculture; b. Leslie J. Mehrhoff, University of Connecticut; c. James R. Holland) (all images from 

Bugwood.org)
Variation in U.S. Standards for Introducing New Species

Banner Photos. Crop species introduced to the U.S. that have since become invasive, causing ecological damage include (from left to right) species of 

blackberry, Rubus spp. (Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org); watercress, Nasturtium officinale W.T. 

Aiton (Zack Abbey, iNaturalist.org); water spinach, Ipomoea aquatica Forssk. (Eric in SF); common St. Johnswort, Hypericum perforatum L. (Ohio State 

University Weed Lab, Bugwood.org); hardy kiwi, Actinidia arguta (Siebold & Zucc.) Planch. ex Miq. (Onidiras, iNaturalist.org); and spearmint, Mentha spicata

L. (Modestcowboy, iNaturalist.org).

18   GROUP #3: Crop Plants

GROUP #3: CROP PLANTS 

HISTORY OF U.S. INTRODUCTIONS OF CROP PLANTS 

Plants grown as crops in agricultural fields are often less competitive than wild plants due to human-selection 

for traits desired by farmers. Some crops species, however, can be invasive (Pasiecznik and Jaenicke, 2009; 

Quinn et al., 2015). Examples of crops that have become invasive include (1) watercress (Nasturtium officinale

W.T. Aiton) in Massachusetts (U.S.) (Van Driesche, pers. obs.), (2) water spinach (Ipomoea aquatica Forssk.) 

in Florida, California, and Hawaii (U.S.) (Austin, 2007; USDA NRCS, 2015); (3) blackberries (Rubus niveus

Thunb.) in the Galápagos (Rentería et al., 2012); and (4) strawberry guava (Psidium cattleianum Sabine) in 

Hawaii (Fig. 3; Patel, 2012) and Lord Howe Island (Australia) (Bower, 2016). Our intent here is not to review 

crops as invasive plants, but only to make the point that it can happen, and therefore that the potential risks 

of new crops should be reviewed before introduction of new species not already in the country. 

REGULATION OF RISKS: WHAT WERE THE PERCEIVED PROBLEMS?

In general, the importation and growing of exotic plants as food crops has been seen as having few risks 

(except as vectors of pests or pathogens), and such plant introductions have not been prevented or restricted, 

with only a few exceptions where the plant was perceived to have potential to become a weed (i.e., water 

spinach in rice in Texas, where personal cultivation is banned at the state level).

SUMMARY OF RISK REGULATION FOR CROPS 

For plants grown as food crops, Risk 1 (direct attack on non-target species) is not relevant. Risks 2 and 3 

(vectoring pests or pathogens) are regulated under the Plant Quarantine Act, 1912, as is true for all plant 

introductions. Insect invasions, however, are much easier to detect than invasions of previously unrecognized 

pathogens in asymptomatic hosts, making Risk 3 only partially regulated. Compared to ornamentals, the 

numbers of plants used as food crops is small, well established, and stable. Risks 4 and 5 (plants being 

agricultural weeds or damaging to natural habitats) in theory might be regulated by designating a species 

as a NAPPRA species, but this has never been done for a crop plant. Risk 6 (impacts of crop plants on food 
Variation in U.S. Standards for Introducing New Species

a b c

Figure 3. Strawberry guava, Psidium cattleianum Sabine (a), was intentionally introduced to Hawaii for its fruit, but quickly escaped. It readily forms dense, 

impenetrable thickets (b) and large monocultures (as seen from above, c) that displace native species and serve as refuges for fruits flies that are serious 

pests to agriculture. (Photos: Forest & Kim Starr, Starr Environmental)

GROUP #3: Crop Plants 19

webs) could occur (as surely must be the case for strawberry guava in Hawaii) but no requirements exist to 

forecast and consider such risks when new crop plants are first imported. 
Variation in U.S. Standards for Introducing New Species

Banner Photos. Exotic species introduced for ranching and viewing in North America sometimes escape and cause ecological and economical damage, 

including (from left to right) cows, Bos taurus L. (Johnny N. Dell, Bugwood.org); donkeys, Equus africanus asinus L. (Tony Rebelo, iNaturalist.org); domestic 

sheep, Ovis aries L. (Keith Weller, Wikipedia.org); zebras, Equus spp. (Howard F. Schwartz, Colorado State University, Bugwood.org); domestic goats, Capra 

hircus aegagrus Erxleben (Jakob Fahr, iNaturalist.org); and horses, Equus ferus caballus L. (Terry Spivey, USDA Forest Service, Bugwood.org).

20   GROUP #4: Terrestrial Mammals for Ranching or Viewing

GROUP #4: TERRESTRIAL MAMMALS FOR RANCHING OR VIEWING 

HISTORY OF U.S. INTRODUCTIONS OF TERRESTRIAL MAMMALS FOR RANCHING OR VIEWING

There is overlap between the introduction of exotic vertebrates for ranching or viewing and for use as pets. 

The former tends to be larger species, dominated by mammals, while pets may be large or small and span 

a wider taxonomic range. Exotic vertebrate animals (usually mammals but also birds and reptiles) held on 

ranches may be used for trophy hunting or viewing by tourists (“wildlife parks”) in large fenced enclosures. 

The most common exotic mammals held on U.S. ranches are species of Bovidae (cattle and antelope), 

Cervidae (deer), or Equidae (horses and zebras) (Land.com, 2019). Ranches sell excess animals to other 

ranches or private individuals (Fernandez, 2017). Since fenced enclosures are not highly secure, animals 

can and do occasionally escape, leading in some cases to the establishment of populations of exotic animals 

in natural areas. Russian wild boar (Sus scrofa L.; Fig. 4), now widely established as feral animals in several 

states, were introduced through this mechanism (Waithman et al., 1999).

Legal restrictions on the possession of exotic vertebrates vary by state (for details for all 50 states see 

Born Free USA [2020]). Examples of some states’ requirements follow, with categories defined as (1) “B” = 

ban on private ownership of exotic animals; (2) “B*” = ban on private ownership of those exotic animals on 

a prohibited list; (3) “L” = requirement for the owner of the exotic animal to obtain a license or permit or to 

register the animal with state or local authorities to privately possess the animal; and (4) “N” = states that 

do not require a license or permit to possess the animal, but may regulate some aspects (i.e., entry permit, 

veterinary certificate, etc.). 

Category B: Summary of California Law 

It is unlawful for persons to possess wild animals unless the animal was in possession prior to January 1992. 

Wild animals include, but are not limited to “the following [groups]: Primates; Marsupialia; Insectivora 

(shrews); Chiroptera (bats); Carnivora (non-domestic dog and cats); Proboscidea (elephants); Perissodactyla 

(zebras, horses, rhinos); Reptilia (crocodiles, cobras, coral snakes, pit vipers, snapping turtles, alligators); 

etc.” (CAL. CODE REGS. Tit. 14, §671 and §671.1).

Categories B* and L: Summary of Florida Law

It is unlawful for a person to possess any Class I Wildlife unless the animal was in possession prior to 

August 1, 1980. Class I Wildlife includes, but is not limited, to the following: chimpanzees, gorillas, 
Variation in U.S. Standards for Introducing New Species

Figure 4. Russian wild boar, Sus scrofa L. (a), were intentionally introduced to North America as food animals and for hunting, but subsequently escaped. 

Feral populations do extensive damage to native vegetation and agricultural crops (b,c), reduce water quality, destroy nests of ground-nesting species, kill 

fawns and young livestock, and can transmit diseases to domestic pigs and humans. (Photos: a. Dushenkov, iNaturalist.org; b,c. Sasa Kunovac, Bugwood.org)

GROUP #4: Terrestrial Mammals for Ranching or Viewing 21

orangutans, baboons, leopards, jaguars, tigers, lions, bears, elephants, crocodiles, etc. Persons may possess 

Class II Wildlife if he or she obtains a permit from the Fish & Wildlife Conservation Commission. Class 

II Wildlife includes, but is not limited to, the following: howler and guereza monkeys, macaques, cougars, 

bobcats, cheetahs, ocelots, servals, coyotes, wolves, hyenas, alligators, etc. For all other wildlife in personal 

possession not defined as Class I or II Wildlife, owners must obtain a no-cost permit. In addition, Florida 

has promulgated regulations governing possession of Class II and III animals (caging requirements, 

etc.). In 2010, Florida passed state regulations prohibiting the importation, sale, use, and release of nonnative species. The regulations include a ban on capturing, keeping, possessing, transporting or exhibiting 

venomous reptiles or reptiles of concern, including listed python species; the green anaconda, Eunectes 

murinus (L.); the Nile monitor, Varanus niloticus (L.), and other reptiles designated by the commission as a 

conditional or prohibited species. Persons who hold pre-July 1, 2010 permits for these species may legally 

possess the species for the remainder of the reptile’s life. Traveling wildlife exhibitors who are licensed or 

registered under the United States Animal Welfare Act and licensed zoos are exempted (FLA. ADMIN. 

CODE ANN. r. §68A-6.002, §68A-6.0021, and §68A-6.0022. FL ST. §379.231-2 [nonnative animals]).

Category N: Summary of North Carolina Law

A county or city may by ordinance regulate, restrict, or prohibit the possession of dangerous animals. In 

addition, an entry permit from the State Veterinarian is required before importing into the state a skunk, fox, 

raccoon, ringtail, bobcat, North or South American feline, coyote, marten, or brushtail possum (N.C. SESS. 

LAWS §153A-131 and §160A-187; N.C. ADMIN. CODE tit. 2, r. 52B.0212).

REGULATION OF RISKS: WHAT WERE THE PERCEIVED PROBLEMS?

Three potential problems were recognized in relation to the keeping of wild animals, and in each case local 

(state, county, or city) regulations, rather than federal regulations, were deemed sufficient. (1) Greatest 

public awareness has focused on the potential for captive wild animals to harm people. Controls enacted in 

the regulations of many states have, therefore, often been drafted to prevent animals like bears or lions from 

hurting people who may accidentally come into contact with them where they are housed or should they 

escape. These regulations may apply to private menageries or animal collections, or to individuals keeping 

one or more such animals as pets. (2) A second problem of concern to some groups has been the potential 

a b c
Variation in U.S. Standards for Introducing New Species

for cruelty to animals kept under poor conditions. (3) A third and more ecological concern is that animal 

pathogens might be introduced through the importation of infected animals that could affect domestic 

animals or wildlife in the same general taxonomic group. To control this risk, veterinary certificates are 

required in some states (but not others) to prevent the introduction of known wildlife diseases, including 

rabies (a viral disease caused by Rabies lyssavirus) and other diseases that are transmissible to people. 

Unknown pathogens, however, are not controlled by this approach. Also, the lack of this being a requirement 

in all states allows opportunity for animals that are infected but not visibly ill to be imported to states 

where veterinary inspections are not required, with subsequent uncontrollable spread of the pathogen if it 

establishes in a wild population of a related species.

A fourth problem, the risk of exotic introduced animals themselves becoming pests in natural areas, 

has not been identified specifically as a risk. This risk is, however, controlled in some states (e.g., Alaska) 

if the state has a blanket prohibition against wildlife importations by private parties. In the lower 48 states, 

the patchwork of the presence and absence of such controls across different states leaves the country as a 

whole at risk of exotic animals establishing in the wild in one or more states with weak or no regulations, 

with the animal then spreading naturally or being spread by enthusiasts to other states. This is the scenario 

by which the Russian wild boar gained entrance and spread over a wide region in the United States (Le 

Stegeman, 1938; Wood and Lynn, 1977; Howe et al., 1981). More generally, on islands and in countries such 

as New Zealand, introductions of exotic animals such as deer for ranching or hunting have frequently led to 

establishment of damaging populations (e.g., New Zealand Department of Conservation, 2020).

SUMMARY OF RISK REGULATION FOR TERRESTRIAL MAMMALS USED FOR RANCHING OR 

VIEWING 

For exotic vertebrate animals introduced for ranching, enclosed hunting, or viewing, Risk 1 (direct attack 

on non-target species) is relevant for introduced herbivores, but not regulated. Examples include various 

species of deer that have become established in other countries (Fraser et al., 2003). For predatory animals, 

direct attack on native prey is also an unregulated risk (Drummond and Leonard, 2010; Bytheway and Banks, 

2019). Risks 2 and 3 (vectoring pests like ticks or bacterial or viral pathogens) are regulated in principle. 

However, this risk is addressed by states, and requirements for veterinary inspections of animals entering 

the country vary considerably among states. Risks 4 and 5 (the exotic animals damaging natural habitats or 

their component species) is unregulated. Risk 6 (impacts on native food webs by exotic animals established 

in natural areas) is unregulated, but the impacts of European boar populations have received some study 

(Wood and Lynn, 1977; Howe et al., 1981).

22   GROUP #4: Terrestrial Mammals for Ranching or Viewing
Variation in U.S. Standards for Introducing New Species

Banner Photos. Exotic fish species introduced for aquaculture in North America sometimes escape and cause ecological and economical damage, including (left 

to right) blue tilapia, Oreochromis aureus (Steindachner) (Enriqueperez, iNaturalist.org); common carp, Cyprinus carpio L. (Dezidor, Wikipedia.org); bighead carp, 

Hypophthalmichthys nobilis (J. Richardson) (South Dakota Game, Fish and Parks, Bugwood.org); walking catfish, Clarias batrachus (L.) (J.D. Willson, iNaturalist.

org); banded tilapia, Tilapia sparrmanii Smith (Rob Palmer, iNaturalist.org); and Asian swamp eel, Monopterus albus (Zuiew) (Maggiekuo, iNaturalist.org).

 GROUP #5: Fish Used for Aquaculture 23

GROUP #5: FISH USED FOR AQUACULTURE 

HISTORY OF U.S. INTRODUCTIONS OF FISH USED FOR AQUACULTURE 

At least 673 fish species have been introduced in the United States and its territories, including introductions 

that failed (Witmer and Fuller, 2011). A small number of these fish introductions were accidental (as ballast 

contaminants), but most were deliberate introductions. Intentional introductions were made either for sport 

(e.g., trout and salmon [Salmonidae spp.] and bass [Micropterus spp.]) or, the majority, were introduced 

for use as pets (tropical fish) or use as bait fish (Fuller, 2003; see also Groups 10 [sport] and 11 [pets] later 

in this publication). Only a few species were introduced as a food source (e.g., common carp [Cyprinus 

carpio L.] and tilapia [Oreochromis spp.]). The list of all introduced fishes is dominated by two orders, the 

Cypriniformes and Perciformes, which together make up some 400 introduced species (Fuller, 2003, as 

discussed in Witmer and Fuller, 2011). See also the list of introduced fish compiled by the U.S. Fish and 

Wildlife Service (USFWS) (USGS, 2019a). Many of these introduced fish species have provided important 

food and sport resources or economic gains for the pet trade, and many do not cause large adverse effects. 

However, others have become pests through spread of fish diseases, predation or competition with native 

fish, or by causing habitat degradation or food web changes. 

Intentional fish introductions have been a mixture of authorized and unauthorized actions, in varying 

proportions (e.g., in California, Moyle [1976]). For example, blue tilapia, Oreochromis aureus (Steindachner), 

and other species of tilapia native to Africa were introduced to the United States as a food source or as sport 

fish and escaped from aquaculture facilities. In natural waters, blue tilapia consume native aquatic vegetation 

and compete with native fish (Fuller et al., 1999). 

Aquaculture production in North America began with state and federal efforts to enhance sport 

fishing opportunities through rearing and release of reared fish into wild waters, including various species of 

native and introduced trout and catfish (FAO, 2019a). Rearing of trout in the United States has largely been 

done to restock depleted or degraded rivers, and only a small proportion of trout produced via aquaculture 

have been reared for sale to consumers. In the United States, aquaculture production of fish for consumption 

has been dominated by channel catfish, Ictalurus punctatus (Rafinesque), a native fish that is widely reared in 

ponds in the southeastern United States. In 2008, this species constituted 81% of the 287,132 tons of finfish 

produced in the United States. A second species, Atlantic salmon (Salmo salar L.), began to be produced 

in the 1970s in North America using ocean net pens in the Pacific Northwest, a region in which Atlantic 

salmon is not native. In 2008, 17,000 tons of Atlantic salmon were produced, valued at 45 million dollars. 

In general, five types of fish have dominated aquaculture in the United States (catfish, trout, salmon, tilapia, 
Variation in U.S. Standards for Introducing New Species

and hybrid striped bass). These fish are native in some parts of the United States where they are produced, 

but exotic in others. In addition, fish aquaculture facilities produce bait fish and ornamental fish. The latter 

is discussed in Group 11 (pets) (Centers for Epidemiology & Animal Health, 1995). 

The search for new species of fish to farm continues. For example, University of Florida researchers 

are examining the rearing of South American pirarucu (Arapaima spp.) in ponds in southern Florida (Hill 

and Lawson, 2015). It is known that these large fish (up to 200 lbs or 91 kg) can prey on other fish and would 

do so if they got into the wild waters (Buck, 2016).

REGULATION OF RISKS: WHAT WERE THE PERCEIVED PROBLEMS?

Two key risks have long been known to potentially be associated with fish introductions: (1) fish vectoring 

pathogens that cause disease in fish or humans (such as whirling disease and hemorrhagic septicemia), and 

(2) the potential for exotic fish to damage native fisheries through competition, hybridization, predation, 

or habitat degradation (USGS, 2019b). For example, whirling disease, which affects trout and salmon, is 

caused by the non-native pathogen Myxobolus cerebralis Hofer, a myxozoan parasite first introduced into 

the United States in 1958. This parasite can be spread to wild fish by stocking of infected fish (Fig. 5). By 

2008, this parasite had reached Alaska, where it now threatens native fish (Arsan and Bartholomew, 2008). 

Introduced fish can also pose health risks to humans. For example, Asian swamp eels, Monopterus albus

(Zuiew), are commonly eaten in Asia, either from wild-caught or farmed sources. However, this eel can 

vector parasitic nematodes (Gnathostoma spp.) that cause tissue damage or even death in people (Cole et 

al., 2014). Wild populations of this eel, introduced casually for human consumption, are now established in 

Florida, Georgia, New Jersey, and Hawaii (USGS, 2019b), and wild swamp eels are infected with the parasitic 

nematode (Cole et al., 2014). 

In response to risks posed by invasive and otherwise harmful wildlife, the USFWS, under the injurious 

wildlife provisions of the Lacey Act (18 U.S.C. 42 as amended), a law passed in 1900, has the authority to 

list animal species as “injurious” and to date has listed 408 species of fish. The entry of listed species into the 

United States is prohibited, except by permit for certain purposes. Of these listed species, over half (228) are 

salmonids that pose a risk of disease transmission to other salmon and trout populations, as well as other 

fish. Of these listed fish, 122 are walking catfish (Clariidae), and 44 are species of snakeheads (Channidae).

The other 14 species are not clustered in particular groups. This black list covers 1.3% of the world’s fish 

species (approximately 32,500), or 2.7% of its freshwater species (app. 15,000) (Nelson, 2006; IUCN, 2019). 

No regulatory prohibition on importation exists for the remaining 97–99% of fish species.

RISK-REGULATION PROFILE FOR FISH USED FOR AQUACULTURE

Risk 1: Direct attack on non-target species

It is well known and generally accepted that introduced predatory fish will prey on native invertebrates and 

fish. Similarly, introduced herbivorous fish will consume native plants. Fish introductions are not prohibited 

based on the potential for such ordinary direct effects on native species unless the impacts are severe or the 

affected species themselves are rare or endangered, or ecologically or economically important. The general 

prohibition of the introduction of snakehead fish (Channidae) is based on their ability to harm native or 

established fisheries, such as largemouth bass (Micropterus salmoides (Lacépède); Love and Newhard, 2012). 

New introductions, such as pirarucu (Arapaima spp.) for production in ponds in Florida, have the potential 

to harm populations of non-target native fish, but this risk is assumed to not exist, as fish are reared in ponds 

rather than wild waters. However, while it is known that many fish, previously introduced for rearing in 

outdoor ponds, later escaped or were deliberately moved into wild waters by individuals who valued the fish, 

this risk in not given credence when evaluating such introductions.

24   GROUP #5: Fish Used for Aquaculture
Variation in U.S. Standards for Introducing New Species

a b c

Figure 5. Whirling disease is caused by the non-native pathogen Myxobolus cerebralis Hofer (a). It is often carried by farmed salmon and trout (b) and can 

infect wild populations following the wild stocking of infected fish. This disease causes skeletal deformation (c) and neurological damage and has a juvenile 

mortality rate of up to 90% in infected populations. (Photos: a. USGS; b. aeafa17, iNaturalist.org; c. Dr. Thomas L. Wellborn, Jr. and USFWS)

 GROUP #5: Fish Used for Aquaculture 25

Risk 2: Potential to vector pest insects, mites, ticks, or nematodes

This risk is not applicable to fish introductions if nematodes are taken to mean plant-infesting species. Parasitic 

nematodes of animals are considered below. 

Risk 3: Potential to vector parasites or pathogens to non-target fish

The potential for new fish species to introduce parasites or pathogens able to infect native or economically 

important fish has been recognized, and some efforts have been made to limit spread of known pathogens 

by restricting further introductions or spread of problem species from infected sources of production. 

However, there is no requirement to investigate the potential of a first-time fish introduction to pose such 

a problem, provided that the fish is not on the list of prohibited species under the Lacey Act (18 U.S.C. 42). 

Risk 4: Potential to become pests in crops

This risk is generally not applicable to fish used in aquaculture. 

Risk 5: Potential to degrade native habitats or ecosystems

In Canada, studies have shown that the bottom-feeding habit of common carp can cause degradation of 

aquatic ecosystems, causing a shift from clear, macrophyte-dominated water to a turbid phytoplanktondominated state at levels of under 600 kg of carp per ha (Badiou and Goldsborough, 2015). In Mexico, carp 

aquaculture has been observed to reduce water quality and native species abundance (Tapia and Zambrano, 

2003).

Risk 6: Potential to reduce density of native species by changing food webs

The potential for new fish species to strongly affect native fish communities through changes in food webs has 

been amply demonstrated by the documented changes in Lake Victoria in East Africa following the deliberate 

introduction of Nile perch, Lates niloticus (L.), which led to the complete collapse and reorganization of the 

lake’s ecosystems and apparent extinctions of many endemic fish species (Goldschmidt, 1996; Welz, 2017). 

While the purpose of this particular introduction was to create a new fishery rather than for aquaculture, it 

establishes the point that new fish establishments can pose such risks. This, coupled with the fact that species 

reared in ponds frequently escape during flooding or through the action of people, highlights the risk from 

new-species aquaculture operations. 
Variation in U.S. Standards for Introducing New Species

SUMMARY OF RISK REGULATION FOR FISH FOR AQUACULTURE 

As with other vertebrates, the release of new species of fish potentially poses serious risk of direct attack 

on non-target species (Risk 1), which is only partially regulated, and spread of pathogens (Risk 3), which is 

more fully regulated. There is also risk of damage to aquatic habitats (Risk 5) and impacts on food webs (Risk 

6), but these concerns are not regulated. The approach used to minimize these risks in the United States has 

been to create a small (408 species) list of fish species whose introduction into the United States, or transport 

between listed jurisdictions, is prohibited (except by permit for certain purposes). For species not placed 

on the prohibited list, importation remains unrestricted. The risk most often regulated to date has been the 

possible spread of pathogens to native fish.

26   GROUP #5: Fish Used for Aquaculture
Variation in U.S. Standards for Introducing New Species

Banner Photos. Many commercially-produced invertebrates have established outside of containment and/or were introduced infected with parasites 

and other pest species, causing ecological and economical damage, including (from left to right) the red swamp crayfish, Procambarus clarkii (Girard) 

(Edoswalt, iNaturalist.org); the brown garden snail, Cornu aspersum (Müller) (Gerardo, iNaturalist.org); the oyster Magallana angulata (Lamarck) (Jan Johan 

ter Poorten, Wikipedia.org); the European nightcrawler, Dendrobaena veneta (Michaelsen) (Trevor Reid, Wikipedia.org); the giant African snail, Achatina 

fulica (Suzannevf, iNaturalist.org); and the common yabby, Cherax destructor (Adam Yates, iNaturalist.org).

GROUP #6: Commercially Produced Invertebrates 27

GROUP #6: COMMERCIALLY PRODUCED INVERTEBRATES 

HISTORY OF U.S. INTRODUCTIONS OF COMMERCIALLY PRODUCED INVERTEBRATES 

Non-native invertebrates commercially produced in the United States, or directly imported live from foreign 

sources, include species of oysters, mussels, clams, edible land snails, earthworms, and crayfish. In some 

cases, the species being produced may be grown in cages or isolated ponds (from which escape is sometimes 

possible), and in others, the species are reared in nets, cages or on surfaces in natural water bodies, from 

which dispersal is highly likely.

REGULATION OF RISKS: WHAT WERE THE PERCEIVED PROBLEMS?

Risks known to follow, or potentially follow, commercial rearing of invertebrates have included (1) damage 

to commercial crops or horticultural plants (e.g., land snails), (2) transmission of pathogens to native 

congeners in natural habitats (e.g., pathogens of oysters and, in Europe, crayfish), (3) introduction of 

associated undesirable species (e.g., oyster predators), (4) displacement of native species from their habitats 

(e.g., oysters and crayfish, both in Europe), and (5) spread of vertebrate animal disease (e.g., earthworms). 

Damage to commercial crops or horticultural plants (land snails)

Land snails of the species consumed by people are generalist herbivores that eat many crop and horticultural 

plants. Escaped populations of such land snails can and do become crop pests. The brown garden snail, Cornu 

aspersum (Müller) (= Helix aspersa), is being produced on Long Island, New York, at a private farm licensed to 

do so by the U.S. Department of Agriculture (Wilson, 2018). This same snail has become established in the wild 

in California, where it is now a garden and horticulture pest (Stearns, 1900; UCANR, 2019).

Transmission of pathogens to native congeners in natural habitats (pathogens of oysters)

Introduction of non-native oysters for aquaculture is a potential vectoring mechanism for pathogens affecting 

related native oysters (Ruesink et al., 2005). There are two confirmed such cases of pathogen transfer to wild 

oyster populations. The protozoan Haplosporidium nelsoni (MSX) was first noted on the East Coast of the 

United States in Delaware Bay in 1957, but it is now widespread along the Atlantic and Caribbean coasts, 
Variation in U.S. Standards for Introducing New Species

where it infects the U.S. native eastern oyster, Crassostrea virginica (Gmelin). MSX was likely introduced to 

the East Coast through importation of infected Pacific oysters (Crassostrea gigas Thunberg) from California, 

which themselves had become infected with this Asian protozoan due to an earlier importation of oysters 

from Japan to California (Burreson et al., 2000). Similarly, Bonamia ostreae Pichot et al. was moved from 

its native range in the United States into Europe, where it causes mortality in wild populations of the native 

European oyster Ostrea edulis L. (Chew, 1990). 

Introduction of associated undesirable species (e.g., oyster predators)

Movement of exotic oyster spat into the United States, before imposition of controls and domestic spat 

production, led to the introduction and establishment of predators and competitors of oysters and clams 

in native habitats in the United States. In the early to mid-1900s, transfers of C. virginica from the U.S. East 

Coast to the U.S. West Coast resulted in the introduction of the slipper shell Crepidula fornicata (L.) (an 

oyster competitor) and the predaceous oyster drill Urosalpinx cinerea (Say) (National Research Council, 

2004a) (Fig. 6). Also, in the early to mid-1900s, introduction of C. gigas to the U.S. and Canadian West Coast 

and to Western Europe resulted in the establishment of the Japanese oyster drill, Ocinebrellus inornatus 

(Récluz) (Barber, 1997; National Research Council, 2004a).

a b c

Figure 6. In the early to mid-1900s, transfers of Crassostrea virginica (Gmelin) (a) from the U.S. East Coast to the U.S. West Coast resulted in the 

introduction of Crepidula fornicata (L.) (b; an oyster competitor) and Urosalpinx cinerea (Say) (c top left; a predaceous oyster drill). (Photos: a. Andrew C, 

Wikipedia.org; b. Ken-ichi Ueda, iNaturalist.org; c. Sjplante, iNaturalist.org)

28   GROUP #6: Commercially Produced Invertebrates

Displacement of similar native species from their habitats (in Europe, oysters and crayfish)

There are no known examples in the United States of competitive displacement of native U.S. oysters or crayfish 

by introductions of exotic species in these groups. However, in principle, this can happen and has happened 

in other countries, as discussed here for illustration of the issue. In France, introduction of the exotic oyster 

Magallana angulata (Lamarck) in approximately 1868 displaced the native oyster O. edulis; by 1870, the native 

species was gone from some stretches of the French coast (Ruesink et al., 2005). In Europe, several species 

of North American crayfish have been introduced, with damaging effects on native crayfish due to direct 

competition and to the spread of an associated pathogen. In particular, the American species Procambarus 

clarkii (Girard) (the red swamp crayfish, which is the dominant crayfish used in aquaculture in the United 

States and which is also used in aquaculture in Italy [FAO, 2019b]) and Pacifastacus leniusculus (Dana) are 

responsible for a wide range of harmful impacts on native crayfish populations in Europe (Savini et al., 2010). 

Procambarus clarkii and the rusty crayfish, Faxonius rusticus (Girard), (both indigenous to parts of the United 

States) are being spread into parts of the United States where they are not native through use as bait (a form of 

aquaculture), with impacts on local native species (Kilian et al., 2009; O’Shaughnessey and Keller, 2019).
Variation in U.S. Standards for Introducing New Species

Spread of vertebrate animal disease (earthworms or pathogens able to attack native insects)

Because earthworms contain soil in their guts, worms raised and sold as live fish bait have the potential to 

transport vertebrate pathogens, including the pathogen causing foot and mouth disease, a critical disease 

of cattle and other livestock. Consequently, the importation of any species of earthworms from countries 

other than Canada requires submission to the U.S. Animal and Plant Health Inspection Service (APHIS) 

of a PPQ 526 permit application. The sole exception is for the European nightcrawler, Dendrobaena veneta

(Michaelsen) (also known as Eisenia hortensis), provided it is imported from a European country that APHIS 

agrees is free of foot-and-mouth disease (USDA APHIS, 2019b). If permits are issued for other species of 

earthworms or from other locations, rearing of worms on artificial diets is required to free their guts of soil 

contamination. It is important to note that this procedure is not aimed at preventing invasions of new species 

of earthworms, but rather the prevention of worms being a vector for foot and mouth disease. Because exotic 

earthworm change soil structure and processes, particularly in areas in North America naturally devoid of 

earthworms, their own ecological effects (not just their potential to vector pathogens) are important and 

should be considered in the regulation of the group (Hendrix and Bohlen, 2002). No regulations, however, 

currently address this issue.

Several insect species are commercially reared and sold for a mixed set of reasons, including 

pollination (Bombus spp.) and as pet food (Tenebrio spp. and Gryllus spp.), among others. These colonies 

have the potential to spread pathogens between countries and infect native insects in the same genus or 

family where they are introduced for use (e.g., Goulson, 2010) or become invasive themselves.

RISK-REGULATION PROFILE FOR COMMERCIALLY-REARED INVERTEBRATES

Risk 1: Direct attack on non-target species

Not applicable.

Risk 2: Potential to vector pest insects, mites, ticks, or nematodes

Not applicable.

Risk 3: Potential to vector predators or pathogens

Importation of spat of foreign species of oysters into the United States for rearing in wild waters led to the 

introduction of both predators (e.g., oyster drill) and pathogens (e.g., MSX). To prevent more such introductions, 

production of oyster spat in state-owned hatcheries replaced importation of foreign material. More recently, 

sterile triploid native oysters have been developed that grow faster and show some resistance to key pathogens. 

Triploid native oysters now dominate the aquaculture industry in Virginia (Kobell, 2015). However, the nonfarmed oyster population remains suppressed by pathogens and lack of suitable substrate for settling of spat. 

Risk 4: Potential to become pests in crops

To mitigate the risk of farmed snails escaping and establishing in the wild, snail farming is regulated by federal 

regulations and, in some areas, by state statutes. The U.S. Department of Agriculture (USDA) requires snailrearing facilities to conform to certain specifications. The USDA allows interstate shipment of live snails, 

provided the importing state approves the shipment. However, federal statutes prohibit interstate movement 

or importation into the United States of snails in the genus Achatina, e.g., Achatina fulica (Férussac), the 

giant African snail (USDA, 2019). Based on this regulatory position, it is likely that importation of other 

edible snails (apart from Achatina species) would not be prohibited, although rearing facilities would have 

to meet certain specifications to reduce the likelihood of escape.

GROUP #6: Commercially Produced Invertebrates 29
Variation in U.S. Standards for Introducing New Species

Risk 5: Potential to degrade native habitats or ecosystems

Under the injurious wildlife provisions of the Lacey Act, which has authority over mollusks and crustaceans 

(but not insects), eight species of invertebrates have been prohibited from importation, including some that 

can affect habitats: (1) mitten crabs (Eriocheir spp.), which pose human health risks and can damage banks 

and levees (Cohen and Weinstein, 2001; see the listing at 54 FR 22286, 23 May 23 1989), (2) quagga and 

zebra mussels (Dreissena bugensis Andrusov and Dreissena polymorpha (Pallas) (note: these two mussels 

are already established in the wild in the United States), and (3) the crayfish known as the common yabby 

(Cherax destructor Clark) (USFWS, 2019a).

Risk 6: Potential to reduce density of native species by changing food webs

While this risk certainly exists, it is not at this time reviewed or part of the regulatory process.

SUMMARY OF RISK REGULATION FOR COMMERCIALLY PRODUCED INVERTEBRATES 

This group covers a wide variety of organisms, although most are aquatic. The main risks that have been 

regulated to date relate to the spread of pathogens (by oysters, worms). Some attention under the Lacey Act 

has been given to protection of wildlife habitats through a short black list. Finally, the Plant Quarantine 

Act (1912) has been used to regulate land snails due to their status as direct plant pests. In general, this is a 

significantly under-regulated group, with actions currently being guided by a patchwork of laws at several 

levels (state, federal, and international) that influence introductions but do not act directly to review and 

control them (e.g., for oysters and other marine invertebrates, see National Research Council, 2004b). A tool 

for assessing the likely degree of risk for the introduction of new species for marine aquaculture has been 

developed that emphasizes four components of impact: probability of establishment, rate of spread, degree 

of direct impact on ecosystems, and ability to vector a pathogen (Gollasch et al., 2003).

30   GROUP #6: Commercially Produced Invertebrates
Variation in U.S. Standards for Introducing New Species

Banner Photos. Two predatory mammals have been introduced to the U.S. to be farmed for fur: the stone marten, Martes foina (Erxleben) (photos 1, 2), 

which has since established in the wild, and the raccoon dog, Nyctereutes procyonoides (Gray) (photos 3, 4), which was listed as “injurious” and its use 

discontinued before it could escape into the wild. The U.S. fur-rearing industry now relies heavily on the American mink, Neovison vison (Schreber) (photos 

5, 6). (Photos: 1. Gg. Any; 2. Bohuš Číčel; 3. Karlakas; 4. Bernd Schwabe; 5. Wojciech Uszak; 6. Jonn Leffmann) (all photos Wikipedia.org)

GROUP #7: Predatory Mammals Farmed for Fur 31

GROUP #7: PREDATORY MAMMALS FARMED FOR FUR 

HISTORY OF U.S. INTRODUCTIONS OF PREDATORY MAMMALS FARMED FOR FUR

The fur-rearing industry in the United States relies heavily on the American mink, Neovison vison (Schreber), 

which likely has reduced interest in the importation of foreign species. At least one truly predatory 

mammalian furbearer has been introduced to the United States for fur farming—the stone marten, Martes 

foina (Erxleben). It subsequently established feral populations in Wisconsin (Frederickson, 2007). The 

omnivorous raccoon dog, Nyctereutes procyonoides (Gray), is another species that was imported into the 

United States to be reared for fur production. However, this species, which is native to Russia, was listed as 

“injurious wildlife” by the U.S. Fish and Wildlife Service before it could escape into the environment. Its use 

in the industry was then discontinued.

In general terms, the injurious wildlife provisions of the Lacey Act prohibit the importation of wild 

mammals that are on a short black list that includes (1) fruit bats in the genus Pteropus; (2) any mongoose 

or meerkat in the genera Atilax, Cynictis, Helogale, Herpestes, Ichneumia, Mungos, or Suricata; (3) any 

Oryctolagus species of European rabbit; (4) any species of Indian wild dog, red dog, or any species of Cuon; 

(5) any species of multimammate rat or mouse of the genus Mastomys; (6) the raccoon dog, N. procyonoides; 

and (7) the brushtail possum, Trichosurus vulpecula (Kerr). These “injurious wildlife” species may, however, 

be imported with a permit for scientific, medical, educational, and zoological purposes. 

Any other live wild mammal may be imported without a permit unless another law applies (USFWS, 

2019a). While releases of “non-injurious” wildlife into the wild require approval of the relevant state’s 

wildlife conservation agency in the intended area of release, such approval is not required for importation 

for use of captive animals for production of fur. While law prohibits the return of any live member of an 

exotic species of wildlife back into the wild in the United States (50 CFR 12.34), importation of such species 

still poses a risk that escape into the wild may occur. This potential is well illustrated by experience in the 

United Kingdom, where the American mink was introduced to be farmed in captivity (Fig. 7). Subsequently, 

animals escaped or were liberated and populations became established, with severe ecological impacts on 

the northern water vole, Arvicola amphibius (L.), which in the United Kingdom has declined by over 90%, 

largely due to mink predation (Rushton et al., 2000; Macdonald and Harrington, 2003). 

In the United States and other countries, most operations rearing predatory furbearers produce fox 

or mink, species that are native to North America. If an exotic predatory furbearer were desired by this 

industry in the future, nothing in the injurious wildlife section of the Lacey Act or other federal laws would 

prohibit its importation into captivity, provided the species was not protected under statutes due to its rare 
Variation in U.S. Standards for Introducing New Species

a b

Figure 7. The predatory American mink, Neovison vison (Schreber) (a), was introduced to Europe where it was farmed for its fur (b). Mink escaped captivity 

in the U.K., where they have had severe ecological impacts. (Photos: a. Jared Gorrell, iNaturalist.org; b. Vadeve, Wikipedia.org) 

32   GROUP #7: Predatory Mammals Farmed for Fur

or endangered status and it was legally collected or obtained. Also, any such predatory mammal could be 

released if one state gave its approval. From one such state, spread to the species’ ecological limits would then 

follow, covering any number of states. 

REGULATION OF RISKS: WHAT WERE THE PERCEIVED PROBLEMS?

No problems have occurred in North America that have forced the development of regulations specific to 

the rearing of predatory furbearers; however, impacts of American mink in the United Kingdom show the 

potential for such problems.

RISK-REGULATION PROFILE FOR PREDATORS FARMED FOR FUR

Risk 1: Direct attack on non-target species

While no impacts on non-target species have occurred in the United States, harm to the northern water vole 

in the United Kingdom from introduced mink shows the potential for such impacts (Rushton et al., 2000; 

Macdonald and Harrington, 2003). 

Risk 2: Potential to vector pest insects, mites, ticks, or nematodes

This risk might occur, but exotic mammals are inspected for health and the presence of ectoparasites such as 

ticks before being allowed into the country. 

Risk 3: Potential to vector pathogens to non-target animals

This risk might occur, but exotic mammals are inspected for health, and sick animals would be excluded. 

Risk 4: Potential to become pests in crops

This risk would depend on the biology of the introduced species, but it seems less likely for predatory 

mammals than herbivorous or omnivorous species. 

Risk 5: Potential to degrade native habitats or ecosystems

Potential exists for impacts on habitats if key herbivore species’ densities were depressed by the predator. 
Variation in U.S. Standards for Introducing New Species

Risk 6: Potential to reduce density of native species by changing food webs

In theory, this risk may occur, but there are no examples in the United States. 

SUMMARY OF RISK REGULATION FOR PREDATORY FURBEARERS 

Direct attack on non-target species (Risk 1) could occur if an exotic predator were imported, escaped, 

established, and preyed heavily on a particular native species. Importation of exotic predators for fur farming 

could also pose risks of introducing new ectoparasites (Risk 2) or pathogens (Risk 3) able to infest or infect 

native species, but both should be controlled by animal inspections at the time of importation. Risk 4 (crop 

damage) is not applicable for predatory furbearers, while Risk 5 (habitat destruction) and Risk 6 (impacts 

through food web changes) exist in principle and are unregulated; however, there are no known examples 

in the United States.

GROUP #7: Predatory Mammals Farmed for Fur 33
Variation in U.S. Standards for Introducing New Species

Banner Photos. Only a few herbivorous mammals have been introduced to the U.S. to be farmed for fur, including nutria, Myocastor coypus (Molina) 

(photos 1,2); long-tailed chinchilla, Chinchilla lanigera Bennett (photo 3); Australian brushtail possum, Trichosurus vulpecula (Kerr) (photo 4); and capybara, 

Hydrochoerus hydrochaeris (L.) (photos 5, 6). (Photos: 1. Timo Sack, Wikipedia.org; 2. Philippe Amelant, Wikipedia.org; 3. Guérin Nicolas, Wikipedia.org; 4. 

Christopher Watson, Wikipedia.org; 5. Paul Donahue, iNaturalist.org; 6. Douglas Trent, iNaturalist.org)

34   GROUP #8: Herbivorous Mammals Farmed for Fur

GROUP #8: HERBIVOROUS MAMMALS FARMED FOR FUR

HISTORY OF U.S. INTRODUCTIONS OF HERBIVOROUS MAMMALS FARMED FOR FUR

Two non-native herbivorous furbearers have been introduced into the United States to be farmed for fur: 

nutria, Myocastor coypus (Molina), and the long-tailed chinchilla, Chinchilla lanigera Bennett. The capybara, 

Hydrochoerus hydrochaeris (L.), is a third species that is sometimes farmed for fur, but it was likely brought 

into the United States as a pet and is potentially established. Of the 92 species of mammals classified 

as injurious wildlife under the Lacey Act, only three listed species are herbivores that could be farmed 

for fur (for remarks on the omnivorous raccoon dog, see the previous section on predatory mammals): 

(1) European rabbit, Oryctolagus cuniculus (L.); (2) European hare, Lepus europaeus Pallus; and (3) the 

Australian brushtail possum, Trichosurus vulpecula (Kerr). Of these, T. vulpecula was introduced into New 

Zealand for fur farming and became a highly damaging forest pest (Atkinson and Cameron, 1993). Based 

on the exploding population of brushtail possums in New Zealand, this species’ importation into the United 

States was prohibited under the injurious wildlife provisions of the Lacey Act as a proactive measure before 

it could become established (USFWS, 2002). 

In general terms, the Lacey Act prohibits the importation of wild mammals that are on a short black 

list described in the previous section on predatory mammals farmed for fur. Any wild mammal not listed 

as “injurious wildlife,” however, may be imported without a permit for scientific, medical, educational, 

exhibition, propagation, or other legitimate purposes. While release into the wild of such “non-injurious” 

wildlife requires approval of the state wildlife conservation agency in the intended area of release, this is not 

required for importation of captive animals for production of fur. Such importations, however, pose a risk 

for subsequent release into the wild due to escape from rearing farms, release by animal rights activists, or 

release following failure of farming operations. 

Of species used for fur farming in other countries that have not yet been introduced and established 

in the United States, the omnivorous Asiatic raccoon dog, Nyctereutes procyonoides (Gray), stands out as a 

high-risk species. While this species’ diet includes animals (insects, rodents, amphibians, birds, fish, reptiles, 

mollusks) and carrion, it also consumes fruits, nuts, and berries, and it can be a crop pest. The risk of this 

species to the environment is obvious from experience in Europe, where its introduction into Latvia by the 

USSR led to its spread over much of Europe, from Finland to France, causing various impacts to wildlife 

(Kauhala and Kowalczyk, 2011; Dahl and Åhlén, 2019; Wikipedia, 2019a). For this reason, the USFWS listed 

the raccoon dog as injurious in 1983 before it could become established in the wild (USFWS, 1982), and it 

has remained absent from the wild in the United States. 
Variation in U.S. Standards for Introducing New Species

a b

Figure 8. Nutria, Myocastor coypus (Molina) (a), were introduced to the United States to be farmed for their fur. Animals escaped captivity and have since 

caused extensive ecological and economical damage, as evidenced here (b) with the girdling of native bald cypress trees, Taxodium distichumvar. imbricarium 

(Nutt.) Croom. (Photos: a. Royal Tyler, Bugwood.org; b. Gerald J. Lenhard, Louisiana State University, Bugwood.org) 

GROUP #8: Herbivorous Mammals Farmed for Fur 35

Nutria

Of the herbivorous furbearers that have invaded the United States, nutria (Fig. 8a) are a major environmental 

pest, subject to control efforts in various habitats, including attempted eradication in California (CDFW, 

2019). Nutria cause both ecological damage to the marshes they invade and economic damage to waterdistribution systems. Ecological damage is caused by consumption and disturbance of marsh vegetation. 

Nutria feeding destroys approximately 10 times more vegetation than is actually eaten (Fig. 8b). Reduction 

of marsh vegetative cover leads to loss of soil and disappearance of marshland (CDFW, 2019). Economic 

damage results from burrowing. Nutria dens and burrows can be several meters deep and up to 50 m long, 

often leading to streambank erosion, increased sedimentation, levee failures, and roadbed collapses (CDFW, 

2019). Nutria have also caused severe damage to the marshes of southern Louisiana (Taylor and Grace, 

1995) and the wetlands of Chesapeake Bay, both areas to which the nutria were introduced for fur farming 

in the 1930s or 1940s (Wikipedia, 2019b).

Chinchilla

The long-tailed chinchilla (C. lanigera) are endangered in their native range in the South American Andes, 

and while the species has been introduced to the United States, it has not become established there. 

Capybara

Capybara (H. hydrochaeris) are farmed for their meat and hides in various countries. Sightings have occurred 

in Florida and one sighting in Mississippi, but these animals may have come from the release of animals held 

as pets (Benson, 2019).

REGULATION OF RISKS: WHAT WERE THE PERCEIVED PROBLEMS?

All animals farmed for fur are mammals, and the perceived risks of herbivorous or omnivorous species 

used in this way are similar to those for mammals introduced for other purposes, with regulatory focus on 

the risk of introducing pathogens able to spread to other species of importance to people. Farming of furbearing herbivores does not use dangerous mammals capable of injuring people (such as bears or big cats) so 

that has not been an area of concern. The potential impact on native species, ecosystems, or the environment 
Variation in U.S. Standards for Introducing New Species

of herbivorous or omnivorous mammals imported for rearing for fur production has been addressed by 

the U.S. Fish and Wildlife Service principally in the two cases of the Australian bush possum and the Asian 

raccoon dog, whose introductions were prohibited to protect the environment.

RISK-REGULATION PROFILE FOR HERBIVOROUS MAMMALS FARMED FOR FUR 

Risk 1: Direct attack on non-target species

Native plants are consumed by nutria, but since this animal is a generalist herbivore, its impacts are not 

usually focused on rare species, although impacts on rare species may occur in some circumstances (in Italy, 

Prigioni et al., 2005).

Risk 2: Potential to vector pest insects, mites, ticks, or nematodes

Exotic mammals are inspected for health and the presence of ectoparasites such as ticks before being allowed 

into the country.

Risk 3: Potential to vector pathogens to non-target animals

This risk is a serious concern that is addressed by requirements for veterinary inspections to determine the 

health of imported animals.

Risk 4: Potential to become pests in crops

Some potential does exist for herbivorous furbearers to damage crops, but no clear examples exist for the 

United States, except indirectly for nutria, which can damage crops by degrading the physical integrity of 

irrigation canals. 

Risk 5: Potential to degrade native habitats or ecosystems

There is a clear risk of habitat degradation, as illustrated by the impact of nutria on freshwater marshes. 

Risk 6: Potential to reduce density of native species by changing food webs

In theory, this risk may occur, but there are no examples in the United States. 

SUMMARY OF RISK REGULATION FOR HERBIVOROUS MAMMALS FARMED FOR FUR

In the United States, nutria is the only example of an herbivorous mammal imported for fur farming 

escaping and causing harm in the wild. However, the brushtail possum in New Zealand is another important 

example. Taken together, these two examples suggest that the risks posed by species in this group include 

direct consumption of native plants (Risk 1), habitat destruction (Risk 5), and potentially crop damage 

(Risk 4) and food web changes (Risk 6). All four of these risks are unregulated. Ectoparasites (Risk 2) and 

pathogens (Risk 3) might be inadvertently introduced along with exotic mammals, but should be controlled 

by animal inspections at the time of importation. 

36   GROUP #8: Herbivorous Mammals Farmed for Fur
Variation in U.S. Standards for Introducing New Species

Banner Photos. Only a few species of birds and mammals have been introduced to the United States for hunting in the wild; however, many more have been 

introduced into containment for hunting purposes. Species introduced include (from left to right) the ring-neck pheasant, Phasianus colchicus L. (Chung-Yen); 

Russian wild boar, Sus scrofa L. (Eric Graham); chukar partridge, Alectoris chukar (Gray) (Yael Orgad); gray partridge, Perdix perdix (L.) (Admss); Sahara oryx, 

Oryx dammah (Cretzschmar) (Sara Hollerich Giles); and Himalayan snowcock, Tetraogallus himalayensis G.R. Gray (Cnarraway) (all photos iNaturalist.org).

GROUP #9: Birds and Mammals for Hunting 37

GROUP #9: BIRDS AND MAMMALS FOR HUNTING 

HISTORY OF U.S. INTRODUCTIONS OF BIRDS AND MAMMALS FOR HUNTING

Birds

Relatively few birds have been introduced into the United States for hunting, with most introductions being for 

use as pets. This outcome may be due to the prohibition, from 1900 to 1948 by an early version of the Lacey Act, 

of wild bird importations, with the exception of caged birds. Since 1948, the injurious wildlife section of the 

Lacey Act has prohibited the importation of certain wild birds, forming a short black list that currently includes 

four species: (1) the “pink starling,” Sturnus roseus (L.); (2) the dioch, Quelea quelea (L.); (3) the Java sparrow, 

Lonchura oryzivora (L.); and (4) the red-whiskered bulbul, Pycnonotus jocosus (L.). Unless prohibited by the 

Convention on International Trade in Endangered Species (CITES) or other foreign laws, any species of wild 

birds not listed as “injurious wildlife” may be imported without a permit for scientific, medical, educational, 

exhibition, or propagation purposes. Release of any such imported birds into the wild may occur with the 

approval of the relevant state wildlife conservation agency having jurisdiction over the area of release.

Before 1900, some game bird introductions were made by private individuals. The ring-neck 

pheasant, Phasianus colchicus L., was first introduced privately into Oregon from China in 1881 (Oldham, 

2008). It was subsequently spread by state fish and game agencies to nearly all other states. It has established 

especially well in northern, grain-producing states and become an abundant species much appreciated by 

hunters, stimulating fish and game agencies to consider other possible introductions. The chukar partridge, 

Alectoris chukar (Gray), was introduced into the United States in 1893 by W. O. Blaisdell of Illinois who 

brought in five pairs of chukars from Karachi, India (Cottam et al., 1940; Christensen, 1970). Following 

this initial introduction, a majority of the U.S. states and Canadian provinces made releases of this bird. It 

established throughout the Great Basin between the Cascade/Sierra Mountains and the Rocky Mountains, 

with a distribution from southern California to Canada. Similarly, the gray partridge, Perdix perdix (L.), 

which was first introduced about 1900, was further spread by state agencies and now has a distribution in 

the northern United States that stretches from Washington to Wisconsin (Carroll, 1993). The Himalayan 

snowcock, Tetraogallus himalayensis G.R. Gray, was first introduced into the United States in 1963 by the 

Nevada state agency responsible for fish and game into the high alpine areas of Nevada’s Ruby Mountains; it 

successfully established, but without further spread (Christensen, 1998). 

These introductions share a common set of beliefs and a common mechanism. The underlying belief 

is that new species for hunting are a pure benefit, with no risks or negative side effects. Early releases were 
Variation in U.S. Standards for Introducing New Species

a b c

Figure 9. Sika deer, Cervus nippon Temminck (a), were intentionally introduced from Asia into the wild in North America and elsewhere for hunting. 

Populations have since increased, causing damage to crops (b) and forests, and reducing forage (c) for domestic livestock and native ungulates (Feldhamer 

and Demarais, 2009). (Photos: a. Yan Vincent; b. Chris Moody; c. Anna; all iNaturalist.org)

38   GROUP #9: Birds and Mammals for Hunting

done privately by individuals with this belief, but later introductions (such as much of the spread of chukar 

and the entire Himalayan snowcock program) were done by state agencies charged with protecting game 

and increasing opportunities for hunting. The introduction of Himalayan snowcock, specifically, was guided 

by the belief that high alpine habitats in Nevada had an “empty niche” in the sense that there was no suitable, 

huntable, native game bird there. 

Mammals

(See previous section on mammals imported as furbearers for general information on the restrictions of the 

“injurious wildlife” section of the Lacey Act on the importation of mammals). Efforts to increase huntable 

exotic animals other than birds occurred in two different ways in the United States: (1) releases of new 

species into the wild to create self-sustaining, spreading populations, as was done for the Russian wild boar 

Sus scrofa L. and other species (Fig. 9); and (2) creating fenced populations of diverse exotic mammals for 

hunting, from which the animals are not expected to escape or establish breeding populations outside of the 

fenced area. 

(1) Release of new species into the wild

In the 1900s (in California in 1925 and again in 1950 [Waithman et al., 1999]), the Eurasian or Russian 

wild boar was introduced to the United States for sport hunting. It has since spread rapidly and caused 

great economic and environmental damage (Snow et al., 2017), leading to a formal U.S. Department 

of Agriculture (USDA) swine suppression program (USDA APHIS, 2019a). See Fig. 4 (Group 4) for 

images and additional information.

(2) Creating fenced populations of exotic mammals subject to hunting

A wide range of exotic ungulates, goats, and other mammals are held in large, outdoor fenced areas. 

Stock is bred on site and sold to other parties. It is estimated that more than 1,000 captive-mammal 

hunting operations are operating in at least two dozen states, with the greatest concentration in Texas. 

No federal law bans the practice, and only about half of the states have policies that ban or restrict this 

type of animal importation. While escape is not intended, there is potential for caged animals to escape 

during extreme weather events or civil disruptions if fences are breached.
Variation in U.S. Standards for Introducing New Species

REGULATION OF RISKS: WHAT WERE THE PERCEIVED PROBLEMS?

Importation of living individuals of wildlife into the United States for any purpose, including use for 

hunting, is subject to restrictions that have as their primary purposes (1) the prevention of the introduction 

of pathogens and (2) the protection of animals that were not legally collected in their country of origin 

or whose commercial exploitation is prohibited under international agreements protecting rare or overexploited species (e.g., CITES) (USDA APHIS, 2019c).

Risk of pathogen introduction

Because of the risk that bird introductions pose for moving pathogens (e.g., the Highly Pathogenic Avian 

Influenza [H5N1 virus]), for all sources except Canada, the USDA quarantines birds for 30 days in special 

USDA animal importation facilities to screen for infected individuals. The Center for Disease Control 

prohibits the importation of African rodents due to their potential to vector the monkeypox virus. This virus 

did occur in a shipment of giant Gambian rats (Cricetomys gambianus Waterhouse) that were imported into 

the United States by the pet trade. 

Species protected under CITES

Species that are protected under CITES require permits to move protected animals from one country to 

another, and importation may be subject to permit requirements or restrictions. Commercial and recreational 

use of such species is prohibited.

RISK-REGULATION PROFILE FOR BIRDS AND MAMMALS FOR HUNTING

Risk 1: Direct attack on non-target species

Exotic birds likely eat native insects, and exotic herbivorous mammals eat native plants. These events are not 

seen as posing risks unless impacts occur on rare or endangered native species. 

Risk 2: Potential to vector pest insects, mites, ticks, or nematodes

Exotic animals are inspected for health and the presence of ectoparasites such as ticks before being allowed 

into the country.

Risk 3: Potential to vector pathogens to non-target animals

This risk is a significant concern, especially for birds, but also for some mammals, and is a key focus of 

regulation of this type of importation. 

Risk 4: Potential to become pests in crops

Some species, such as wild boar, destroy crops through foraging and rooting. 

Risk 5: Potential to degrade native habitats or ecosystems

Extreme risk for some species, as demonstrated by Russian wild boar. 

Risk 6: Potential to reduce density of native species by changing food webs

Theoretically, this is a risk, and potentially one of considerable importance. Some consideration is now given 

to not placing native species in direct competition with a similar exotic species. For example, whitetail deer, 

GROUP #9: Birds and Mammals for Hunting 39
Variation in U.S. Standards for Introducing New Species

Odocoileus virginianus (Zimmermann), are not being considered for introduction to California because 

they would compete with native deer. 

SUMMARY OF RISK REGULATION FOR BIRDS AND MAMMALS FOR HUNTING 

Regulations address the risk that pathogens (Risk 3) or ectoparasites (Risk 2) might be inadvertently 

introduced along with exotic birds or mammals, but no regulations examine the ecological effects of the 

introduced species themselves, either through feeding (Risk 1), changing native habitats (Risk 5) or food 

webs (Risk 6), should they by intent or accident establish wild populations, with the caveat that any species 

can be reviewed for listing as “injurious wildlife” for any or all of these criteria under the relevant sections of 

the Lacey Act. Exotic game held in fenced areas are treated as if fencing prevents escape completely, which 

in the long run is likely not to be the case. The potential for introduced sport species to become agriculture 

pests (Risk 4) is illustrated by Russian wild boar, whose rooting and feeding can destroy fields of some crops.

40   GROUP #10: Exotic Fish for Sport or Commercial Fishing
Variation in U.S. Standards for Introducing New Species

Banner Photos. Many exotic fish species have been introduced or redistributed by federal or state agencies or private individuals for the purposes of sport 

fishing. Several have had severe impacts on native ecosystems. Introduced or redistributed species include (from left to right) northern snakehead, Channa 

argus (Cantor) (Pmk00001); Ohrid trout, Salmo letnica (Karaman) (Albinfo, Wikipedia.org); bigeye lates, Lates mariae Steindachner (Oliver Drescher, 

iNaturalist.org); tench, Tinca tinca (L.) (Matt Gorton, iNaturalist.org); tiger trout, hybrid of Salmo trutta L. x Salvelinus fontinalis (Mitchill) (Wasatch_hunter, 

iNaturalist.org); and silver carp, Hypophthalmichthys molitrix (Valenciennes) (H.T.Cheng, iNaturalist.org).

GROUP #10: Exotic Fish for Sport or Commercial Fishing 41

GROUP #10: EXOTIC FISH FOR SPORT OR COMMERCIAL FISHING 

HISTORY OF U.S. INTRODUCTIONS OF FISH FOR SPORT OR COMMERCIAL FISHING

Fish have been introduced into the United States both privately and by government agencies since the 1840s 

for many reasons, including (1) use for aquaculture to grow fish for consumption (5 spp.); (2) fish for control 

of weeds or mosquitoes (8 spp.); (3) medical uses (1 sp.); (4) ornamental fish reared for the aquarium pet 

trade (134 spp.); (5) private introduction of food or sport fish (9 spp.); (6) food or sport fish released into 

wild waters by government agencies (26 spp.); and (7) introductions whose reasons and circumstances of 

introduction are historical and unknown (12 spp.) (USGS, 2019a). Separate from these are an even larger 

number of translocations of fish native to parts of the United States into areas outside their natural range, 

which biologically is the same as an exotic introduction (e.g., movement of smallmouth bass [Micropterus 

dolomieu Lacépède] from Lake Champlain to California [Moyle, 1976]). However, these movements are not 

federally regulated and not considered here.

Of the 195 species of exotic introduced fish listed above (USGS, 2019a), most were introduced as 

species to be sold as ornamental fish for ponds or aquaria—fish that later either escaped from outdoor 

rearing ponds (often during flooding) or were released by customers when the fish became too large for 

their tanks. That group of fish introductions is discussed in a later section on the pet trade. Here we focus 

on the fish introduced into wild waters for food or sport, which includes five species released historically 

before the era of government involvement (e.g., common carp, Cyprinus carpio L.), nine that were released 

illegally by private persons in more modern times (e.g., species of snakehead fish [Channidae]), and 26 

whose releases were sponsored by government agencies, e.g., the Ohrid trout, Salmo letnica (Karaman). 

These releases were concentrated in two periods, the first being seven introductions by the U.S. Fish 

Commission between 1865 and 1885 (Fig. 10), and the second being 15 species released by state fish and 

game departments or other agencies between 1950 and 1980. After 1980, the practice seems to have died 

out, with only two additional releases of exotic fish sourced directly from outside the United States, Lates 

mariae Steindachner and Sander lucioperca (L.) (USGS, 2019a). However, such releases are still federally 

allowed if states wish to make introductions. Also, exotic species that were previously introduced into 

the United States continued to be released into new states via interstate transfers long after the original 

introduction, including (1) tench, Tinca tinca (L.), from 1884 in Nebraska to 1999 in Vermont; (2) tiger 

trout, hybrid of Salmo trutta L. x Salvelinus fontinalis (Mitchill), from 1950 in Minnesota to 2017 in Idaho; 

(3) blue tilapia, Oreochromis aureus (Steindachner), from 1961 in Florida to 2017 in Ohio; and (4) silver 
Variation in U.S. Standards for Introducing New Species

a b c

Figure 10. Stocking of fish into lakes and rivers (a) has occurred in the U.S. since at least 1865. Introducing exotic species, such as German trout, Salmo 

trutta L. (b), as well as native rainbow trout, Oncorhynchus mykiss (Walbaum), to areas where they previously didn’t occur has had harmful effects on some 

native fish species due to predation, introduction of disease, competition and hybridization with threatened species such as the Gila trout, Oncorhynchus 

gilae (Miller). (Photos: a. Pacific Southwest Region USFWS; b. David_Taylor, iNaturalist.org; c. Melanie Dabovich, USFWS)

42   GROUP #10: Exotic Fish for Sport or Commercial Fishing

carp, Hypophthalmichthys molitrix (Valenciennes), from 1972 in Puerto Rico and Arizona to 2012 in Ohio 

and Oklahoma (USGS, 2019a).

REGULATION OF RISKS: WHAT WERE THE PERCEIVED PROBLEMS?

Early in the history of exotic fish introductions or the mixing of fish faunas regionally within the United 

States, no risks were perceived; the general attitude was one of trial and error to see how local fisheries 

could be “enhanced” by adding fishable, edible species favored in other regions of the United States or other 

countries. The Lacey Act (18 U.S.C. 42) checked such movement to a degree, allowing undesirable species 

to be designated as “injurious wildlife” and therefore making their movement into the United States or 

between named jurisdictions subject to regulations. Such listings occurred because the listed non-native 

species were expected to cause harm to people, agriculture, horticulture, forestry, or wildlife in the United 

States. Listing under this law in some cases targeted an already-introduced species of injurious fish (to limit 

further spread) and their relatives, or additional species believed by the agency to be potentially damaging 

based on experience in other countries. The Lacey Act’s requirements for the importation of fish (USFWS, 

2019b) include (1) the importer must file a written declaration of importation; (2) the release of imported 

live fish into wild waters is prohibited, unless authorized by the State wildlife conservation agency having 

jurisdiction over the area, (3) the importation of fish species found on the agency’s list of “injurious wildlife” 

is prohibited (see below for listed fish); (4) the movement of salmonoids is regulated for the purpose of 

preventing the spread of pathogens, especially the Oncorhynchus masou virus and viruses causing viral 

hemorrhagic septicemia, infectious hematopoietic necrosis, and infectious pancreatic necrosis. Screening 

for these viruses is required. Also, live fish eggs of foreign origin must be disinfected following procedures 

specified in the regulation. 

 There are 408 fish on the list of “injurious wildlife” (USFWS, 2019a), including 6 carp (Cyprinidae, 

of which 3 are already in the U.S.): bighead carp, Hypophthalmichthys nobilis (J. Richardson) (in 26 states); 

black carp, Mylopharyngodon piceus (J. Richardson) (in 9 states); crucian carp, Carassius carassius (L.) (not 

in the U.S.); largescale silver carp, Hypophthalmichthys harmandi Sauvage (not in the U.S.); Prussian carp, 

Carassius gibelio (Bloch) (not in the U.S.); and silver carp, H. molitrix (in 15 states and Puerto Rico); 122 

walking catfish (Clariidae), of which Clarias batrachus (L.) is established in Florida; wels catfish, Silurus glanis

L. (not in the U.S.); Eurasian minnow, Phoxinus phoxinus (L.) (not in the U.S.); stone moroko, Pseudorasbora 

parva Temminck & Schlegel (not in the U.S.); European perch, Perca fluviatilis L. (not in the U.S.); Nile 

perch, Lates niloticus (L.) (formerly in Texas; current status not clear); roach, Rutilus rutilus (L.) (not in the 
Variation in U.S. Standards for Introducing New Species

U.S.); 228 salmonids (Salmonidae) (due to the risk of pathogen introductions); Amur sleeper, Perccottus 

glenii Dybowski (not in the U.S.); 44 snakeheads (Channidae) (4 species in the U.S.); and the zander, S. 

lucioperca (already in the U.S.).

In addition, Ecological Risk Screening Summaries have been created by the U.S. Fish and Wildlife 

Service to quickly identify the level of invasion risk (high, uncertain, low) of species of fish (and other 

vertebrates, invertebrates, and plants) (USFWS, 2020c) as a way to rank species for decision-making, but this 

characterization has no force of regulation.

RISK-REGULATION PROFILE FOR FISH RELEASED FOR SPORT OR COMMERCIAL FISHING

Risk 1: Direct attack on non-target species

This risk is recognized and regulated in some cases (e.g., snakeheads and some others) by placing certain 

species on the list of fish designated under the Lacey Act as “injurious wildlife.” However, most exotic fish 

consume many species of non-target fish, plants, amphibians, or insects, and those risks are generally not of 

concern to regulators. 

Risk 2: Potential to vector pest insects, mites, ticks, or nematodes

Not applicable.

Risk 3: Potential to vector pathogens to non-target fish

A definite and significant risk for fish introductions to spread pathogens is well recognized for salmonids, 

and provisions in the Lacey Act exist to control this risk. However, the requirement is specific for this fish 

group. Control of fish introductions to prevent invasion of pathogens associated with other fish families 

(e.g., cyprinid herpesvirus 3 [CyHV-3] in carp [McColl et al., 2016]) could be addressed under the injurious 

wildlife section of the Lacey Act; however, the U.S. Fish and Wildlife Service does not have the authority to 

directly regulate the pathogens themselves. 

Risk 4: Potential to become pests in crops

Not applicable. 

Risk 5: Potential to degrade native habitats or ecosystems

This is a recognized but unregulated risk. Carp, by virtue of how they feed, are known to reduce water 

clarity, destroy native macrophytes, and promote algal growth (e.g., Tapia and Zambrano, 2003; Badiou and 

Goldsborough, 2015). 

Risk 6: Potential to reduce density of native species by changing food webs

This risk certainly exists potentially, but has not been regulated. Each introduction would have to be studied 

to assess the significance of this risk. 

SUMMARY OF RISK REGULATION FOR FISH RELEASED FOR FISHING 

In summary, the risk of direct attack on non-target species (Risk 1) is regulated for some predatory fish that 

attack valuable existing fish species, but not for fish that only prey on native plants or insects, unless this 

affects at-risk species or ecosystems. Also, fish importations are regulated at the federal level for the purpose 

of limiting the spread of pathogens (Risk 3) that can affect salmonoids by including many salmonoids on a 

black list of species under the Lacey Act; however, other groups of fish pathogens are not addressed. Risks 

GROUP #10: Exotic Fish for Sport or Commercial Fishing 43
Variation in U.S. Standards for Introducing New Species

to habitats (Risk 5) and native food webs (Risk 6) clearly exist but are largely ignored, with the exception 

of placing some species of carp (the group that to date has caused the greatest degradation of habitat) on 

the Lacey Act black list. However, for fish species that are not black listed, no pre-introduction review is 

required, and any state may introduce into wild waters any species it wishes to release. Risk 2 (vectoring 

pests such as insects or nematodes) and Risk 4 (damaging crops) are generally not applicable.

44   GROUP #10: Exotic Fish for Sport or Commercial Fishing
Variation in U.S. Standards for Introducing New Species

Banner Photos. The pet trade is an increasing pathway for exotic species introductions in the United States. Many species introduced in this manner 

have escaped containment or were intentionally released into the wild where they have since established and caused ecological harm, including (from left to 

right) the red lionfish, Pterois volitans (L.) (Sarah-sydneydives); bearded dragon, Pogona vitticeps(Ahl) (John Sullivan); Nile monitor lizard, Varanus niloticus

(L.) (Copper); monk parakeet, Myiopsitta monachus (Boddaert) (Donata Jonuškienė); green iguana, Iguana iguana (L.) (Daniel Onea); and rhesus macaque, 

Macaca mulatta (Zimmermann) (Dr. Vijay Anand Ismavel MS MCh) (all photos iNaturalist.org).

GROUP #11: Animals Sold as Pets 45

GROUP #11: ANIMALS SOLD AS PETS 

HISTORY OF U.S. INTRODUCTIONS OF ANIMALS SOLD AS PETS

For vertebrates, the pet trade is a large and increasing pathway for establishment of exotic species, and it is 

the dominant pathway for reptiles and amphibians (Kraus, 2009; Lockwood et al., 2019). Of the 140 nonnative species in these latter two groups that have been introduced into Florida, 85% came in through the 

pet trade (Krysko et al., 2011). The U.S. market for tank marine fish is the largest in the world, with annual 

imports of over 11 million individual fish, including 2,300 species from 125 families (Rhyne et al., 2012, 

2017). The number of freshwater fish species imported for the aquarium trade (worldwide) is at least ten 

times as large as the number of marine species (Livengood et al., 2014). In North America, of the many 

species of freshwater fish imported by the aquarium trade, at least 100 have been released in wild water 

bodies and 40 are known to be established (Rixon et al., 2005). Increasingly, insects are also being imported 

for sale as pets (Thomas, 1995).

REGULATION OF RISKS: WHAT WERE THE PERCEIVED PROBLEMS?

Under the Lacey Act (18 U.S.C. 42), a small number of pet species that are associated with pathogens, are 

known crop pests, or are known environmental pests have been placed on the list of “injurious wildlife” 

(USFWS, 2019a).

(1) Pathogens

Some pet species are on the Lacey Act list of “injurious wildlife” because they are associated with pathogens 

able to infect wildlife, such as 20 genera of European salamanders, which are listed because they can 

potentially vector the chytrid fungus Batrachochytrium salamandrivorans Martel et al., which would threaten 

U.S. native salamanders.

(2) Crop pests

The four cage birds listed under the Lacey Act are all important crop pests in their native ranges.
Variation in U.S. Standards for Introducing New Species

(3) Environmental pests

Some pet species known to become invasive environmental pests are also black listed, including (a) walking 

catfish, (b) yabby crayfish, (c) Chinese mitten crabs, and (d) certain large constrictor snakes (anacondas and 

pythons) related to snakes that have already established as environmental pests in Florida. 

Insects sold as pets are regulated if “they might be a crop pest, or a biocontrol agent, or affect a 

biocontrol agent” (Robert Pfannenstiel, USDA, APHIS, pers. comm.). Other species of insects imported as 

pets are not regulated.

RISK-REGULATION PROFILE FOR EXOTIC SPECIES SOLD AS PETS

Risk 1: Direct attack on non-target species

Regulations do not require any consistent attempt to discover (before importation) if a risk of attack on nontarget species might be posed by species proposed for importation as pets. In a few cases in which such a risk 

is well recognized (e.g., pythons in Florida), or where the U.S. Fish and Wildlife Service has evaluated the 

risk of harm for species not yet established in the United States, some species have been listed as “injurious 

wildlife.” 

Risk 2: Potential to vector pest insects, mites, ticks, or nematodes

Exotic animals are inspected for health and the presence of ectoparasites such as ticks before being allowed 

into the country.

Risk 3: Potential to vector pathogens to humans or wildlife

Some groups have been identified as potential sources of human or wildlife pathogens and have been put on 

the Lacey Act black list. However, no systematic effort is made before importation to determine the level of 

threat from this risk posed by new species being imported for use as pets. 

Risk 4: Potential to become pests in crops

A few birds that are well known crop pests have been prohibited, but this risk is not consistently evaluated 

before new species are introduced in the United States. Rather, the risk is only controlled if the species 

already has a history of being a crop pest elsewhere, which could cause the USFWS to list it as “injurious 

wildlife.” This process, however, allows unrecognized pests to be introduced without evaluation. 

Risk 5: Potential to degrade native habitats or ecosystems

A few crustaceans have been listed as “injurious wildlife” because they pose risk to native habitats, but this 

risk is not consistently evaluated before new species are introduced in the United States. Rather, the risk is 

only controlled if the species already has a history of degrading native habitats or ecosystems elsewhere, 

which could cause the USFWS to list it as “injurious wildlife.” This process, however, allows unrecognized 

pests to be introduced without evaluation.

Risk 6: Potential to reduce density of native species by changing food webs

This risk is addressed if a species is chosen for review for potential listing as “injurious wildlife.” However, this 

risk is not consistently evaluated before introduction of all new species in the United States. Rather, the risk is 

only addressed if the species already has a history of changing food webs elsewhere. In the absence of such a 

history, species can be introduced without evaluation that turn out to cause such damage in the United States. 

46   GROUP #11: Animals Sold as Pets
Variation in U.S. Standards for Introducing New Species

a b c

Figure 11. The Burmese python, Python bivittatus (Kuhl) (a), was introduced to the U.S. via the pet trade and established populations in the Everglades 

after it escaped or was intentionally released. Pythons are currently destroying populations of native birds and mammals, such as the native Virginia 

opossum, Didelphis virginiana Kerr (b), which is shown partially digested in a dissected python (c). Extensive predation on opossums and other nest-feeding 

mammals has disrupted food webs by increasing the nesting success of turtles (Willson, 2017). (Photos: a. J.D. Willson, iNaturalist.org; b. David Cappaert, 

Bugwood.org; c. Lori Oberhofer, National Park Service, Bugwood.org)

GROUP #11: Animals Sold as Pets 47

SUMMARY OF RISK REGULATION FOR ANIMALS SOLD AS PETS 

In summary, pets are assumed to be risk free unless a particular species or its relatives have previously been 

determined to be harmful and consequently been placed on the “injurious wildlife” list of the Lacey Act. No 

evaluation of the potential risks of individual new species (ones not on the Lacey Act “injurious wildlife” list) 

is required before importation. Risk of direct attack on non-target species (Risk 1) is not regulated, unless the 

species has been listed as “injurious wildlife.” Such listing has occurred for some snakes, such as the Burmese 

python Python bivittatus (Kuhl), which is well documented as causing dramatic damage to native species’ 

populations (Fig. 11; Dorcas et al., 2012; Sovie et al., 2016), as well as seven other pythons and anacondas. 

The risks that some pet species pose as vectors of pathogens of wildlife are well known, and the sale of 

some such species is prohibited (e.g., salamanders able to transmit the salamander chytrid fungus) (Risk 3). 

Ectoparasites (Risk 2) might be inadvertently introduced along with exotic pets, but should be controlled by 

animal inspections at the time of importation. Similarly, four bird species have been prohibited under the 

Lacey Act because they are well known crop pests (Risk 4). Potential to degrade native habitats (Risk 5) is 

known for some crustaceans, and some species are listed under the Lacey Act, but this risk is not evaluated 

for non-listed species before their introduction. Effects of introduced pets on food webs (Risk 6) clearly exist 

but are largely ignored.
Variation in U.S. Standards for Introducing New Species

Banner Photos. Several species used in the medical industry have escaped captivity or potentially can do so and establish wild populations, such as the 

African clawed frog, Xenopus laevis Daudin (left image, Erestor, iNaturalist.org). Other species frequently used in the medical industry include (from left 

to right) mice, Mastomys coucha (Smith) (_3foxes iNaturalist.org); rats, Rattus norvegicus domestica (Berkenhout) (Janet Stephens); guinea pigs, Cavia 

porcellus (L.) (Sandos, Wikipedia.org); rabbits, Oryctolagus cuniculus domesticus (L.) (Jameson Nagle); and chimpanzees, Pan troglodytes (Blumenbach) 

(Scott Bowers, iNaturalist.org).

48   GROUP #12: Animals Introduced for Medical Uses

GROUP #12: ANIMALS INTRODUCED FOR MEDICAL USES

HISTORY OF U.S. INTRODUCTIONS OF ANIMALS FOR MEDICAL USES

Live animals have been used in medicine for various reasons, including testing and as models of human 

diseases. No particular protocols govern importation for this use, and the implicit assumption is that such 

animals live and die in captivity. However, this pathway provides opportunities for unauthorized releases 

similar to those from the pet trade. Such medical-use animals may, under some circumstances, be released 

by people involved in the animals’ care or final disposal. Such releases may result in the animals becoming 

established as invasive species. Also, some medical-use species have the potential to move their pathogens 

to new geographical locations. Under modern standards, laboratory animals are bred in controlled colonies 

and disposed of after use, limiting both of these concerns. So, for example, even though multimammate 

rodents such as Mastomys spp. are hosts for viruses that can infect people (e.g. the Lassa virus [Lecompte 

et al., 2006]), the rodent Mastomys coucha (Smith), which is used as a model species (Vinzón et al., 2014), 

is derived from laboratory colonies. However, in the past, wild collected animals were used in some cases. 

For example, in the 1930s, Shapiro and Zwarenstein (1935) developed a test for human pregnancy based on 

injecting a woman’s urine into a female of the African clawed frog, Xenopus laevis Daudin. If the frog laid 

eggs, the woman was pregnant. This simple test was widely used for about 30 years, and, during this period, 

wild-collected African clawed frogs were distributed around the world. Although X. laevis is no longer used 

for pregnancy tests, the species’ eggs and embryos are still a popular model system in medical research 

(Wallingford et al., 2010; Harland and Grainger, 2011). Releases of X. laevis have resulted in established wild 

populations in at least four continents (Measey et al. 2012; Fig. 12), partly due to medical use and partly 

through sale as pets. 

REGULATION OF RISKS: WHAT WERE THE PERCEIVED PROBLEMS?

Few risks have been formally associated with the use of live animals in medical research or practice, apart 

from the use of rare species in Chinese and other medicines, for which the Convention on International 

Trade in Endangered Species (CITES) is the intended control mechanism. Here we focus on species that 

are not rare, endangered, or illegally obtained. One risk is that such species may pose risks of introduction 

of pathogens, and indeed some species are precisely imported because they host pathogens that make them 
Variation in U.S. Standards for Introducing New Species

a b

Figure 12. The African clawed frog, Xenopus laevis Daudin (a), has been widely used in the medical industry. It has established wild populations in at least four 

continents, partly due to medical use and partly through sale as pets. Introduced populations prey upon and compete with native species, make water bodies 

turbid, provide a novel food source to both native (b) and non-native predators, and can potentially vector the chytrid fungus Batrachochytrium dendrobatidis 

Longcore, Pessier & D.K. Nichols (Somma, 2019; Global Invasive Species Database, 2020a). (Photos: a. Alex Rebelo; b. Mickey Long; both iNaturalist.org)

GROUP #12: Animals Introduced for Medical Uses 49

useful model systems for studying related pathogens affecting people (e.g., the rodent M. coucha, which is 

used as a model species [Vinzón et al., 2014]). Presumably, modern rules for housing animal colonies, the 

need for control of the animals’ environment to make them useful in research, and rules for disposal of 

medical waste should prevent this being an accidental pathway for pathogen introduction. However, the 

pathway may remain open if non-hazardous animals (such as X. laevis frogs) that are surplus to needs and 

are directed to be euthanized are instead released into the wild by employees who do not wish to kill animals. 

RISK-REGULATION PROFILE FOR ANIMALS INTRODUCED FOR MEDICAL USES

Risk 1: Direct attack on non-target species

In California, Xenopus laevis—released either from medical colonies or by owners of individuals held as pets—

consumes native invertebrates; native frogs (all life stages); western toads, Anaxyrus boreas (Baird and Girard); 

arroyo chubs, Gila orcuttii C.H. Eigenmann & R.S. Eigenmann; the endangered tidewater goby, Eucyclogobius 

newberryi (Girard); and locally endangered three-spined sticklebacks (Gasterosteus aculeatus L.) (McCoid and 

Fritts, 1980; Lafferty and Page, 1997; Stebbins, 2003; Stebbins and McGinnis, 2012; Dodd, 2013). 

Risk 2: Potential to vector pest insects, mites, ticks, or nematodes

Not applicable.

Risk 3: Potential to vector pathogens to non-target species

This risk is possible, but is presumably controlled by “good practices” in research laboratories.

Risk 4: Potential to become pests in crops

Not applicable.

Risk 5: Potential to degrade native habitats or ecosystems

In theory, this risk may occur, but there are no examples in the United States.
Variation in U.S. Standards for Introducing New Species

Risk 6: Potential to reduce density of native species by changing food webs

In theory, this risk may occur, but there are no examples in the United States.

SUMMARY OF RISK REGULATION FOR ANIMALS INTRODUCED FOR MEDICAL USES

This pathway needs to be studied to understand the scope of exposure it poses by determining the range 

of species held in research colonies or imported live for immediate use, noting in particular if specimens 

come from the wild or from rearing facilities. Training on risks to the environment of unauthorized releases 

for employees of facilities holding such species should be required and disposal records maintained. 

The greatest risk may be the spread of pathogens (Risk 3), which may be self-regulated by the medical 

establishment, provided animals are in fact not released into the wild after being used. Risk of harm to nontarget species (Risk 1) has been demonstrated in California by the introduction of the African clawed frog, 

but is not regulated. Risk of harm to native habitats (Risk 5) or food webs (Risk 6) exist in principle and are 

unregulated; however, there are no known examples in the United States. Risks of vectoring insects (Risk 2) 

or being crop pests (Risk 4) do not seem to apply.

50   GROUP #12: Animals Introduced for Medical Uses
Variation in U.S. Standards for Introducing New Species

Banner Photos. Though no longer practiced in the U.S., the introduction of vertebrates for pest control often had severe ecological impacts from nontarget predation, competition, altering food webs, disease introduction, and more. Predaceous vertebrates introduced for pest control include (from left to 

right) the western mosquito fish, Gambusia affinis (Baird & Girard) (Corey Lange); cane toad, Rhinella marina (L.) (Antonio Rodríguez Arduengo); barn owl, 

Tyto alba (Scopoli) (Mikael Bauer); cattle egret, Bubulcus ibis (L.) (Jhon Velasquez); the poison dart frog Dendrobates auratus (Girard) (Noah Morales); and 

grass carp, Ctenopharyngodon idella (Valenciennes) (Vsvogelaar) (all photos iNaturalist.org).

GROUP #13: Vertebrates for Pest Control 51

GROUP #13: VERTEBRATES FOR PEST CONTROL 

HISTORY OF U.S. INTRODUCTIONS OF VERTEBRATES FOR PEST CONTROL

The kinds of species that people have tried to use to reduce pests have evolved over the centuries. The 

earliest and most familiar predators used in this way were mammals, the group with which people are 

most familiar. Since remote historical times, cats have been used to lower rodent numbers around houses 

and barns. In the 18th and 19th centuries (pre-1900), familiarity with predatory vertebrates led European 

plantation owners and farmers in certain areas (e.g., New Zealand, Caribbean islands, Hawaii) to try to 

use predatory vertebrates to reduce populations of rodents and other pests. Introductions of vertebrates 

in this period of history were made by private individuals and were neither sanctioned nor prohibited by 

governments, although governments began to play a role by the end of the 19th century. During the period 

that preceded governmental oversight, some generalist vertebrate predators, such as species of mongoose, 

stoats, and insectivorous birds, were released in Hawaii and other locations. These introductions were 

generally ineffective against their targets and often caused important ecological damage (Davis et al., 1976). 

Because pre-1900 private introductions of species for control of rodents or other pests—e.g., the 

mongoose Herpestes javanicus (É. Geoffroy Saint-Hilairein) released in Hawaii in 1883—caused significant 

damage to native vertebrate wildlife (Fig. 13), the territory of Hawaii enacted legal controls in 1903 intended 

to prevent the unplanned introduction of new potentially damaging species and ensure the proper use of 

biological control agents (Funasaki et al., 1988). A few terrestrial vertebrates were introduced after 1900, 

including the cane toad—Rhinella marina (L.)—and the poison dart frog Dendrobates auratus (Girard) in 

1932, the barn owl, Tyto alba (Scopoli), in 1958, and the cattle egret, Bubulcus ibis (L.), in 1959 (Funasaki et 

al., 1988). In general, however, the introduction of terrestrial vertebrates (mammals, birds, amphibians) for 

biological control ended in the United States (including Hawaii) by about 1960. 

In contrast, the use of exotic fish for biological control continued longer—for example, guppies, 

Poecilia reticulata Peters; and western mosquito fish, Gambusia affinis (Baird & Girard), for mosquito 

control and grass carp, Ctenopharyngodon idella (Valenciennes), for aquatic weed control (USGS, 2019a). 

To some extent, this occurred because introduced fish were more effective against their target pests than 

were terrestrial predaceous vertebrates, and their risks were harder to detect or more acceptable to the 

public. Indeed, exotic fish that consumed mosquito larvae were encouraged as a safer replacement for 

pesticides. The harm these introduced fish caused to native top-feeding minnows through competition or 

hybridization became clear, at least to fish biologists, by the 1980s (e.g., Courtenay and Meffe, 1989). The use 
Variation in U.S. Standards for Introducing New Species

a b

Figure 13. The Javan mongoose, Herpestes javanicus (a), has been introduced to many islands worldwide for control of rats and snakes. Native oceanic island 

fauna, which typically evolved in the absence of predatory mammals, proved particularly susceptible to mongoose predation (b). Several native mammals, birds, 

reptiles, and amphibians around the world have declined or gone extinct following Javan mongoose introductions (Global Invasive Species Database, 2020b). 

(Photos: a. J.M.Garg, Wikipedia.org; b. Вых Пыхманн, Wikipedia.org)

52   GROUP #13: Vertebrates for Pest Control

of grass carp for weed suppression in ponds continued at least as late as 1992 (first release in Pennsylvania) 

(USGS, 2019a). In addition, the black carp—Mylopharyngodon piceus (J. Richardson)—was used not only 

as a food fish, but also for control of the yellow flatworm, Clinostomum margaritum (Rudolphi), which is a 

pest in aquaculture fish ponds (Nico and Neilson, 2019). Black carp is now established in many states (Nico 

and Neilson, 2019).

REGULATION OF RISKS: WHAT WERE THE PERCEIVED PROBLEMS?

The principal risk associated with introduced terrestrial vertebrates for animal control was indiscriminate 

predation on native birds and mammals. An associated economic risk was that most introduced terrestrial 

vertebrates also failed to control their target pests. For introduced mosquito-feeding fish, impacts on native 

fish—through competition or hybridization—were not fully appreciated until the 1980s. For introduced 

plant-feeding fish, destruction of native macrophytes, greater water turbidity, and low aquatic insect 

biodiversity in ponds or canals were outcomes that took even longer to be recognized as problems. 

RISK-REGULATION PROFILE FOR VERTEBRATES USED FOR BIOCONTROL

Risk 1: Direct attack on non-target species

Damage to populations of native vertebrates (birds, mammals, amphibians) is the main harm associated 

with terrestrial predaceous vertebrates introduced on islands for pest control. The earliest, clearest example 

was the impact of the Javan mongoose in the Caribbean islands (e.g., Pimentel, 1955 [Puerto Rico]; Seaman 

and Randall, 1962 [Virgin Islands]).

Risk 2: Potential to vector pest insects, mites, ticks, or nematodes

Exotic animals are inspected for health and the presence of ectoparasites such as ticks before being allowed 

into the country. 
Variation in U.S. Standards for Introducing New Species

Risk 3: Potential to vector pathogens to non-target animals

This risk likely exists for vertebrates used for pest control, as it does with vertebrates introduced for any 

reason, including for use as pets or for hunting or fishing. 

Risk 4: Potential to become pests in crops

Not applicable.

Risk 5: Potential to degrade native habitats or ecosystems

This risk can occur. For example, see the previously mentioned impact of feeding of carp species on pond 

habitats through destruction of macrophytes. However, this risk would now be considered before any new 

vertebrate introduction, and the potential agents would be rejected.

Risk 6: Potential to reduce density of native species by changing food webs

This risk can occur. In Australia, the harm to native marsupial predators that consume introduced cane 

toads is well documented (Jolly et al., 2015). However, this risk would now be considered before any new 

vertebrate introduction, and the potential agents would be rejected.

SUMMARY OF RISK REGULATION FOR VERTEBRATES USED FOR PEST CONTROL

In summary, risk of direct attack on non-target species by vertebrates used for pest control (Risk 1) is a 

serious problem (e.g., Pimentel, 1955; Seaman and Randall, 1962). Damaging effects on habitats (Risk 5) 

are known for herbivorous fish used for aquatic plant suppression. Effects on food webs (Risk 6) occurred 

in Australia when native marsupials were poisoned by toxins after eating cane toads (Jolly et al., 2015). 

Because of issues with all three risks, releases of vertebrates for pest control (apart from the use of fish) 

was ended in the United States nearly 60 years ago. Ectoparasites (Risk 2) and pathogens (Risk 3) might be 

inadvertently introduced along with exotic mammals, but should be controlled by animal inspections at the 

time of importation. Risk 4 (damaging crops) is not applicable. 

GROUP #13: Vertebrates for Pest Control 53
Variation in U.S. Standards for Introducing New Species

Banner Photos. Many parasitoids with narrow host ranges have been introduced as biocontrol agents in North America for control of key pests of 

vineyards, forage crops, vegetables, ornamentals, and fruit and forest trees, including (from left to right) Cosmocomoidea ashmeadi (Girault) (Hymenoptera: 

Mymaridae) (Ron Matsumoto, iNaturalist.org); Peristenus digoneutis Loan (Hymenoptera: Braconidae) (Scott Bauer, USDA Agricultural Research Service, 

Bugwood.org); Cotesia rubecula (Marshall) (Hymenoptera: Braconidae) (David Cappaert, Bugwood.org); Anagyrus kamali Moursi (Hymenoptera: Encyrtidae) 

(Jeffrey W. Lotz, Florida Department of Agriculture and Consumer Services, Bugwood.org); Spathius galinae Belokobylskij & Strazanac (Hymenoptera: 

Braconidae) (USDA ARS); and Lathrolestes thomsoni Reshchikov (Hymenoptera: Ichneumonidae) (Anna Soper, Bugwood.org).

54   GROUP #14: Parasitoids for Insect Biological Control

GROUP #14: PARASITOIDS FOR INSECT BIOLOGICAL CONTROL

HISTORY OF U.S. INTRODUCTIONS OF PARASITOIDS FOR INSECT BIOLOGICAL CONTROL

Parasitoids are insects that develop at the expense of other insects and are key components of all terrestrial 

ecosystems, being largely responsible for restraining herbivorous insects from devastating plants. 

Consequently, they are key tools useful in correcting some pest invasions damaging to either crop plants or 

plants in native ecosystems. Insect biocontrol began in the United States in the 1880s with the introduction 

of agents, including one parasitoid, a tachinid fly, to control a new invasive scale that was devastating the 

young California citrus industry (Caltagirone and Doutt, 1989). In contrast, plant biological control (see 

Group 16) using herbivorous insects or plant pathogens to control invasive plants began later in the 1920s 

in the continental United States. While plant biocontrol agents in the U.S. were regulated under the Plant 

Quarantine Act (1912) as being potentially a risk to plants, this law did not apply to insect biocontrol agents, 

which did not have any potential to be direct plant pests. Rather, the introduction of agents for classical 

biological control of insects and mites in the United States is guided by several laws or executive orders: 

the Plant Quarantine Act (1912), the Federal Plant Pest Act (1957), the Plant Protection Act (PPA, 2000), 

and Executive Order 13112 (1999) for invasive species. 

The Plant Protection Act (2000) provided the first legal definition in the United States of a biological 

control agent. Authority over the introduction of new species of biological control agents is vested in the Plant 

Protection & Quarantine section of the USDA Agricultural Plant Health Inspection Service (APHIS), and this 

agency is responsible for issuing permits for the importation and release of natural enemies used as biological 

control agents, following a review of each proposed agent’s risk. Initial permits allow researchers to import 

live natural enemies into approved U.S. quarantine facilities, where their host ranges are further investigated. 

Subsequently, following review of a proposed agent’s potential risks, a second permit is required from APHIS 

for the release of the species from quarantine and its interstate movement. Before 1993, the permitting of 

parasitoids and predators was automatic because they did not pose any risk to plants, which was the risk 

regulated by the Plant Quarantine Act (1912). Later, the Plant Protection Act (2000) provided APHIS with 

explicit authority to regulate parasitoids and predatory insects when used as biological control agents, and 

that Act also charged APHIS with facilitating the use of biological control agents in solving invasive species 

problems. In summary, the approach used by APHIS is neither a black list (as done under the 18 U.S.C. 42 

section of the Lacey Act for vertebrate introductions or by USDA under NAPPRA) nor a white list of pre-
Variation in U.S. Standards for Introducing New Species

approved species, but rather an individual review of risk for each new species proposed for its first introduction 

to the United States. This is the highest level of regulatory review for any group of new species’ introductions.

Host range estimates are the heart of parasitoid risk assessments done by APHIS as they address the 

major presumed potential risk—direct attack on non-target species (see Box 1 for example). Host range 

estimates entail both compilation of known host records from published literature and new data from 

quarantine laboratory testing against species that are taxonomically or ecologically close to the target pest 

and are found in the United States. Such work is done in quarantine laboratories, working with colonies of the 

parasitoid or predator, exposing selected test species to the agents for oviposition (or predation in the case of 

predatory insects) and then measuring agent development in any non-target species accepted for oviposition. 

Quarantine studies do not address the filter of host finding, which in nature acts strongly to shape realized 

host ranges, but which is logistically difficult to measure in a laboratory setting. However, surveys in the 

native range provide information on the realized field host range where all filters on host range operate.

In North America since 1985, 208 releases (geographic area x species of agent) of parasitoids (170 

distinct species of parasitoids) have been made, where a “release” is the first release of a new parasitoid 

species in a particular geographic area within “North America” (defined as Canada, Mexico, the continental 

United States, Hawaii, Guam, Puerto Rico, the Northern Mariana Islands, and the U.S. Virgin Islands) (Van 

Driesche et al., 2018). Of these, 112 (54%) “species x geographic area combinations” have led to parasitoids 

establishing in the wild as intended. Of those, 57 (51% of those establishing) have contributed to reduction 

of densities of the pest they were released against. 

GROUP #14: Parasitoids for Insect Biological Control 55

Box 1. Risk assessments for three parasitoids imported to suppress emerald ash borer 

(Agrilus planipennis Fairmaire, Coleoptera: Buprestidae) (Van Driesche and Reardon, 2015). 

Oobius agrili Zhang & Huang (Hymenoptera: Encyrtidae). In laboratory no-choice tests with O. agrili, there were 

no attacks on moth eggs or eggs of long-horned borers (Coleoptera: Cerambycidae). Attacks did occur on eggs of other 

similar-sized Agrilus species, including the bronze birch borer, Agrilus anxius Gory; the two-lined chestnut borer, Agrilus 

bilineatus (Weber); and red-necked cane borer, Agrilus ruficollis (Fabricius). There were no attacks on Agrilus species with 

dissimilar-sized eggs, including A. cyanescens (Ratzeburg), A. egenus Gory, and A. subcinctus Gory. In choice tests, O. 

agrili showed a preference for emerald ash borer eggs. These data (Bauer and Liu, 2007; Federal Register, 2007; Gould et 

al., 2015) show that the laboratory host range is limited to Agrilus species with similar-sized eggs as A. planapennis. As 

none of these occur in ash trees, the field host range is predicted to be narrower than these laboratory findings.

Tetrastichus planipennisi Yang (Hymenoptera: Eulophidae). In laboratory no-choice tests with T. planipennisi,

there were no attacks on three species in two other orders (two moths and one hymenopteran sawfly), five species of longhorned borers, or eight species of other buprestids (five in Agrilus and three in Chrysobothris). These data (Liu and Bauer, 

2007; Federal Register, 2007; Gould et al., 2015) suggest that the laboratory host range of T. planipennisi is limited to 

the target species.

Spathius galinae Belokobylskij & Strazanac (Hymenoptera: Braconidae). In laboratory no-choice tests with 

S. galinae, there were no attacks on two borers in two other orders (one moth, one sawfly) and no attacks on eight borers in 

other (non-buprestid) beetle families. There were no attacks on four species of Agrilus or one of Chrysobothris. Attack did 

occur on one Agrilus species (Agrilus auroguttatus Schaeffer), an invasive pest of oaks in California. These data (Federal 

Register, 2015; Gould et al., 2015; Duan et al., 2015) suggest that the laboratory host range of S. galinae includes the 

target pest and the invasive pest species A. auroguttatus. However, the latter is not a suitable field host because the 

species of oaks it infests have bark too thick for S. galinae to penetrate.
Variation in U.S. Standards for Introducing New Species

REGULATION OF RISKS: WHAT WERE THE PERCEIVED PROBLEMS?

The initial risk that led to governmental regulation of biological control agent introductions was the same as 

the Plant Quarantine Act of 1912, namely that introduced insects might feed on crops or other economically 

important crops. Logically, this risk had no application to introductions of parasitoids, which do not attack 

plants. Later, the concern developed in certain circles (Howarth, 1991) that introduced parasitoids might 

damage populations of native insects, and this potential risk is the principal focus of current regulation of 

new species of introduced parasitoids. 

The belief that some biocontrol agents could become invasive pests damaging native species or 

ecosystems was first effectively raised by Howarth (1991), who outlined evidence for significant nontarget impacts from some species historically used as biological control agents. This assessment, however, 

included vertebrate introductions, some made as far back as the 1700s by private individuals rather than 

by government scientists after biological control developed as a science (post 1920s). A popular narrative 

has been promoted that biological control agents are particularly dangerous (Simberloff and Stilling, 1996; 

Simberloff, 2012). This stems in part from how biocontrol agents are described, being intended to attack 

and kill their target pest species. This labeling has shaped the public’s sense that the group poses high risks. 

However, this perception is different from the public’s view of similar events in other groups of introduced 

species with different labeling. For example, while an introduced fish and an introduced parasitoid may 

both feed on and thus kill native insects, only for the introduced parasitoid is this considered a problem. 

The fact that introduced fish will eat native insects is considered normal and simply accepted. A key failing 

in public understanding of the issue is that it does not separate impacts at the level of effects on individuals 

(feeding or parasitism on some individuals of a prey or host species) from population-level impacts that lead 

to population declines. Finally, because insects in general are less familiar to people than vertebrates, much 

public thinking about the risks to non-target species from biocontrol introductions was driven by a few 

examples that became highly popularized. Four cases have shaped public perception of risk to native insects 

from introduced biocontrol agents targeting pest insects: (1) two predaceous coccinellid beetles, Harmonia 

axyridis (Pallas) and Coccinella septempunctata L. (Harmon et al., 2007; Losey et al., 2007) (discussed in the 

following section) and (2) two parasitoids, the tachinid flies Compsilura concinnata (Meigen) (Boettner et 

al., 2000) and Bessa remota (Aldrich) (Kuris, 2003; Hoddle, 2006; Fig. 14). 

a b c

Figure 14. Compsilura concinnata (Meigen) (Diptera: Tachinidae) (a) was introduced to North America in 1906 for control of the invasive gypsy moth, Lymantria 

dispar (L.), and browntail moth, Euproctis chrysorrhoea(L.). While C. concinnata had significant impacts on browntail moth, its impact on gypsy moth was smaller. 

Importantly, its naturally wide host range led to frequent attacks on native non-target species, including Hyalophora cecropia L. (Lepidoptera: Saturniidae) and 

other giant silk moths (b) (Elkinton and Boettner, 2012). Though this introduction occurred over 100 years ago, decades before biological control developed as 

a science, the negative attention this introduction garnered demonstrated the importance of introducing only agents with narrow host ranges. Today, rigorous 

field and laboratory host range testing (c) is required before a new parasitoid can be introduced to North America. (Photos: a. Joyce Gross, Bugwood.org; b. 

Hayleyreynolds, iNaturalist.org; c. Sharlene E. Sing, USDA FS RMRS)

56   GROUP #14: Parasitoids for Insect Biological Control
Variation in U.S. Standards for Introducing New Species

Because the above four cases are highly publicized and discussed, they are believed by most of the 

general public to be “typical.” This poster-child generalization has led to gross overestimation of risk. Reviews 

of non-target impacts of releases of parasitoids or predatory insects and mites (van Lenteren et al., 2006; Van 

Driesche and Hoddle, 2017) suggest that, to the contrary, the risk from parasitoids is very small. From 1880 

to 2000, approximately 5,000 species x country releases of parasitoids were made worldwide, as reported in 

the database BIOCAT (van Lenteren et al., 2006). Of these releases, only 17 of the 5,000 records (0.34%) have 

been reported to have harmed non-target native insect populations. 

RISK-REGULATION PROFILE FOR PARASITOIDS USED FOR INSECT BIOLOGICAL CONTROL

Risk 1: Direct attack on non-target species

This risk is the focal concern for evaluation of parasitoid introductions. A highly developed evaluation 

system has been created (Van Driesche and Hoddle, 1997; Van Driesche and Reardon, 2004) and is routinely 

applied to each species of parasitoid proposed for introduction before it is approved for release. 

Risk 2: Potential to vector pest insects, mites, ticks, or nematodes

The only such risk would be from hyperparasitoids that attack the beneficial parasitoids being introduced. 

These unwanted species are routinely and efficiently eliminated in quarantine (e.g., Hoddle et al., 2013). 

Risk 3: Potential to vector pathogens to non-target plants

This risk has not been demonstrated for parasitoids. However, theoretically, it might occur if a parasitoid’s 

host vectored a plant pathogen that itself was able to be spread mechanically as a surface contaminate. In 

such cases, a parasitoid might pick up the pathogen on its ovipositor and move it to a second host during a 

subsequent oviposition. Greening disease of citrus was a high-risk pathogen in Florida before the pathogen’s 

eventual introduction there on live plants. Before the pathogen’s invasion, there was concern that parasitoids 

of the citrus psyllid (Diaphorina citri Kuwayama—the vector of the pathogen), which were being imported 

for suppression of the vector, might inadvertently introduce the pathogen. To prevent such an eventuality, 

parasitoids in quarantine were screened for DNA of the pathogen (Liberobacter asiaticum Jagoueix et al.) 

before parasitoids were released. No pathogen DNA was found, and releases were able to be made safely (Hoy 

et al., 2001). Other than this, there are no known examples of this risk being associated with parasitoids. 

Risk 4: Potential to become pests in crops

Not applicable.

Risk 5: Potential to degrade native habitats or ecosystems

This risk is regulated if it can be foreseen. In some cases, parasitoids improve habitats if they control invasive 

pests that damage the habitat (e.g., wax scales in Queensland rain forest [Waterhouse and Sands, 2001; Van 

Driesche et al., 2010]). Conversely, if parasitoids are used to suppress an insect attacking an invasive plant 

that damages the habitat, then successful biocontrol of the pest insect could be construed as damaging to 

habitat (e.g., biocontrol of exotic scales [Pulvinaria spp.] attacking exotic ice plants [Carpobrotus spp.] in 

California dunes [Tassan et al., 1982; Magnoli et al., 2013]). Good vs. bad impact may depend on social 

values placed on introduced plants.

Risk 6: Potential to reduce density of native species by changing food webs

Harmful effects on native food webs are possible from introductions of parasitoids, and one mechanism 

GROUP #14: Parasitoids for Insect Biological Control 57
Variation in U.S. Standards for Introducing New Species

for food web effects is termed “apparent competition” in which the introduced parasitoid, in addition to 

attacking the target pest, attacks related native species. For example, the parasitoid Cotesia glomerata (L.)

(Hymenoptera: Braconidae), introduced to North America in the 1880s to control the imported cabbage 

worm, Pieris rapae (L.) (Lepidoptera: Pieridae), caused the decline of the native butterfly Pieris oleracea

(Harris) in Massachusetts (Benson et al., 2003). Interestingly, this effect was later reversed by P. oleracea’s 

use of a non-native host plant (Herlihy et al., 2014) and the displacement of C. glomerata as the dominant 

parasitoid of P. rapae in crops by Cotesia rubecula (Marshall), another introduced biocontrol agent that was 

more specialized, attacking only P. rapae (Herlihy et al., 2012). 

However, it is also possible to obtain large beneficial impacts on native food webs from parasitoid 

introductions if the pest for which the parasitoid is being introduced is distorting native food webs to 

the detriment of native species. In Queensland, Australia, for example, biological control of two invasive 

wax scales attacking crops (Ceroplastes destructor Newstead and Ceroplastes rubens Maskell; Hemiptera: 

Coccidae) also reduced the densities of invasive ants foraging on the scales’ honeydew on native plants. 

Invasive ants and the scales together reduced health and quality of forest plants for larvae of native lycaenid 

butterflies, such as Hypochrysops miskini (Waterhouse) and Pseudodipsas cephenes Hewitson. Reduction of 

the scales’ density by the introduced parasitoids led to fewer invasive ants, improved host plant quality for 

the butterfly larvae, and allowed native ants needed as symbiotic partners for the butterflies’ larvae to return 

(Waterhouse and Sands, 2001; Van Driesche et al., 2010). 

Similarly, on Christmas Island (property of Australia) in the Indian Ocean, the parasitoid 

Tachardiaephagus somervilli (Howard) (Hymenoptera: Encyrtidae) is being introduced to suppress the 

invasive scale Tachardina aurantiaca (Cockerell) (Hemiptera: Kerriidae) (Ong et al., 2017). The larger 

purpose is to reduce the supply of honeydew this abundant scale provides to the invasive yellow crazy ant, 

Anoplolepis gracilipes (F. Smith) (Hymenoptera: Formicidae), which is decimating populations of the local 

red land crab, Gecarcoidea natalis (Pocock), through direct attack and poisoning (O’Dowd et al., 2003). The 

crab itself is both a world-renowned biodiversity phenomenon and the island’s principal tourist attraction, 

as well as an engineering species controlling forest structure on the island (Green et al. 1997). 

SUMMARY OF RISK REGULATION FOR PARASITOIDS FOR INSECT BIOLOGICAL CONTROL

In summary, direct attack on non-target species by parasitoids (Risk 1) is a possible risk, but it is highly 

regulated by studying the host ranges of new parasitoids in quarantine laboratories before permission is 

given for their release. Risk 2 (vectoring pests such as insects or nematodes) is only applicable in the case 

of hyperparasitoids that attack the parasitoid itself. These are excluded during quarantine evaluation. Risk 

3 (spreading plant pathogens) has not been observed, and Risk 4 (damaging crops) is not applicable due to 

basic biology of the species. Damage to habitats (Risk 5) may occur indirectly if the introduced parasitoids 

control an invasive species that affects the health of habitat-shaping plants. If the plants are native, then such 

insect control would be ecologically positive, but if the plants themselves are invasive, then control of their 

pests would be ecologically negative. Effects on food webs (Risk 6) may be either negative, as when native 

herbivores are affected through apparent competition, or positive, as when biological control of an invasive 

insect leads to improvement in the health of important native plants or animals. 

58   GROUP #14: Parasitoids for Insect Biological Control
Variation in U.S. Standards for Introducing New Species

Banner Photos. Though not as frequently used as parasitoids, several species of predatory insects have been introduced to the U.S. for control of pest 

insects and mites attacking citrus and ornamental plants, to protect native hemlocks in forests, and to control aphids and whiteflies in crops, including 

(from left to right) Novius (formerly Rodolia) cardinalis (Mulsant) (Coleoptera: Coccinellidae) (Division of Plant Industry, Florida Department of Agriculture 

and Consumer Services, Bugwood.org); Laricobius nigrinus Fender (Coleoptera: Derodontidae; native to the Pacific Northwest) (Ashley Lamb, Virginia 

Polytechnic Institute and State University, Bugwood.org); Coccinella septempunctata L. (Coleoptera: Coccinellidae) (Russ Ottens, University of Georgia, 

Bugwood.org); Chilocorus kuwanae Silvestri (Coleoptera: Coccinellidae) (Tom Murray, Bugwood.org); Cryptolaemus montrouzieri Mulsant (Coleoptera: 

Coccinellidae) (Budak, iNaturalist.org); and Curinus coeruleus (Mulsant) (Coleoptera: Coccinellidae) (Ísis Meri Medri, iNaturalist.org).

GROUP #15: Predatory Arthropods for Biological Control 59

GROUP #15: PREDATORY INSECTS AND MITES FOR BIOLOGICAL CONTROL 

HISTORY OF U.S. INTRODUCTIONS OF PREDATORY INSECTS AND MITES FOR BIOLOGICAL 

CONTROL

In the United States, the first dramatically successful use of biological control, which saved the young 

California citrus industry from collapse in 1888, was based on the use of the ladybird beetle Novius (formerly 

Rodolia) cardinalis (Mulsant) (Coleoptera: Coccinellidae) (Caltagirone and Doutt, 1989). As a consequence, 

many other ladybirds were introduced against various other pests in the ensuing decades, with the hope that 

they too would control various pests. Most of these other coccinellids failed to establish, and few had any 

useful impact on their target pests (Caltagirone and Doutt, 1989). Unknown at the time was the fact that N. 

cardinalis is a highly specialized predator of scales in the genus Icerya, while most of the other introduced 

ladybirds have wide diets. Over time, the advantages of the greater dietary specialization found in parasitoids 

caused biocontrol introductions to shift away from predators. Practitioners only occasionally imported 

some of the more specialized predators, such as Laricobius nigrinus Fender (Coleoptera: Derodontidae) 

released against the hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae) (Mausel et al., 

2010), especially if the target pest had no parasitoids. In the past 35 years in North America, only 27 species 

of predatory insects have been introduced (Van Driesche et al., 2018). Apart from this difference in diet 

breadth, regulation of predatory arthropod introductions for biocontrol has been identical to that applied in 

the case of parasitoids, as described in the previous section, Group #14. 

REGULATION OF RISKS: WHAT WERE THE PERCEIVED PROBLEMS?

Early regulation of predaceous insects used as biological control agents had the same legal basis as parasitoids 

(Plant Quarantine Act, 1912). Because most predatory insects do not feed on plants (apart from some mirid 

bugs, which have not been imported), this law was only loosely applicable. Later, the concern that introduced 

predators might damage populations of native insects became the main focus of regulation. While no cases 

are known of introduced predatory insects directly harming populations of native, non-target, non-pest 

insects through their feeding behaviors, two introduced (or perhaps, as has been suggested, just naturally 
Variation in U.S. Standards for Introducing New Species

a b c

Figure 15. The Asian ladybird beetle Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) (a) was introduced to the United States for biological control 

of aphid pests on pecans (b). Though highly effective in managing some pest aphids, this species often receives negative public attention because of its 

tendency to overwinter in large masses in and around structures and dwellings (c). Though competition, it has also contributed to population reductions of 

native ladybird beetles that also feed on invasive crop aphids. (Photos: a. Ryzhkov Oleg; b. Keene Haywood; c. Curtis Eckerman) (all photos iNaturalist.org)

60   GROUP #15: Predatory Arthropods for Biological Control

invasive) coccinellid beetles—Harmonia axyridis (Pallas) (Fig. 15) and Coccinella septempunctata L.—

reduced populations of some native coccinellids by reducing the abundance of various invasive aphids used 

by native ladybirds as prey in crop fields (Harmon et al., 2007; Losey et al., 2007). Other than these two 

species, no other introductions of predatory insects in the United States have created any problems for the 

public that have led to regulation. 

RISK-REGULATION PROFILE FOR PREDATORY INSECTS AND MITES USED FOR BIOLOGICAL 

CONTROL

Risk 1: Direct attack on non-target species

While all predatory insects must on occasion include non-target insects in their diet, ladybird beetles 

introduced as biocontrol agents have not been reported to cause population-level effects on non-target 

aphids through prey consumption. Some introduced ladybird species have been observed feeding on some 

aphid species of interest, e.g., the woolly alder aphid Prociphilus (formerly Paraprociphilus) tesselatus (Fitch) 

(Hemiptera: Aphididae). This aphid is a required prey for one butterfly and some lacewings. Two introduced 

ladybird beetles, H. axyridis (Butin et al., 2004) and Propylea quatuordecimpunctata (L.) (Wheeler, 1990), 

have been noted feeding on this aphid, in laboratory studies and field observations, respectively. However, 

no effect on field densities of this aphid have been reported. 

This lack of concern is similar to how the public views the consumption of native insects by 

introduced fish, namely “yes it exists, but is not a problem.” Nevertheless, consumption of non-target insects 

in quarantine screening tests is now sufficient for the Animal and Plant Health Inspection Service to deny 

permission for a predator’s introduction. For example, the Thailand-native Phaenochilus kashaya Giorgi 

& Vandenberg (Coleoptera: Coccinellidae) is a predator of the cycad scale, Aulacaspis yasumatsui Takagi 

(Hemiptera: Diaspididae), an invasive scale that kills and threatens populations of native cycads in Guam. 

Phaenochilus kashaya was denied any possibility of introduction into the United States because it was not 

sufficiently limited in its diet range (Ron Cave, University of Florida, pers. comm.). 

Risk 2: Potential to vector pest insects, mites, ticks, or nematodes

Any hyperparasitoids of the beneficial predaceous insects would be eliminated when the colony was held in 

quarantine for testing.
Variation in U.S. Standards for Introducing New Species

Risk 3: Potential to vector pathogens to non-target plants

Populations for introductions are screened for fungal or microsporidian pathogens, and laboratory colonies 

are cleared of pathogens before introduction.

Risk 4: Potential to become pests in crops

Some predatory insects have potential to be minor crop pests. The ladybeetle H. axyridis has become a minor 

pest of wine vineyards because even relatively low numbers of beetles mixed with grapes can impart an off 

taste to the wine (Linder et al., 2009). Also, plant feeding/predaceous mirids are used in greenhouses for 

pest control in Europe. Should they be proposed for introduction for use in the United States in the future, 

their possible effects on crops would have to be assessed. Risks of this type are recognized and regulated in 

the United States.

Risk 5: Potential to degrade native habitats or ecosystems

This risk is regulated, but no clear examples of such effects are known from introduced predatory insects.

Risk 6: Potential to reduce density of native species by changing food webs

Two important, well documented examples of effects on native insects (native ladybirds) exist in the United 

States, namely H. axyridis and C. septempunctata, whose reduction of populations of various aphids (mostly 

invasive species in crops) have also reduced the density of some native ladybirds in crops, especially Adalia 

bipunctata (L.) and Coccinella novemnotata Herbst (Wheeler and Hoebeke, 1995; Elliott et al., 1996; Turnock 

et al., 2003; Harmon et al., 2007; Fothergill and Tindall, 2010). 

SUMMARY OF RISK REGULATION FOR PREDATORY INSECTS AND MITES FOR BIOLOGICAL 

CONTROL

In summary, direct attack on nontarget species by predaceous insects used as biocontrol agents (Risk 1) 

is possible, although no clear examples exist of such predation causing population changes in prey. This 

risk is, however, highly regulated by study of the prey ranges of new predators in quarantine laboratories 

before permission is given for their release. Risk 2 (vectoring pests such as insects or nematodes) and Risk 

3 (spreading pathogens to native species) are generally not applicable to predatory insect introductions 

but are within the scope of regulated risks. Risk 4 (becoming crop pests) is regulated and some examples 

of real risk of this type exist, including the effect mentioned above of H. axyridis on the taste of wine. Also, 

some predaceous mirids used in greenhouse biocontrol in Europe also feed on crop plants. Should this 

type of predator be proposed for introduction in the future, possible effects on crops would have to be 

evaluated. Effects of predatory insects on habitats (Risk 5) are unknown but regulated. Effects on food webs 

of predatory insects used for biocontrol (Risk 6) have occurred in the case of two coccinellids that greatly 

reduced pest aphids that were also used as prey by native coccinellids, which then became rare.

GROUP #15: Predatory Arthropods for Biological Control 61
Variation in U.S. Standards for Introducing New Species

Banner Photos. As of 2020, approximately 190 species of insects and mites have been introduced to the United States (including Hawaii) as biological control 

agents of weeds. Many have led to spectacular success against their target weeds, without causing population-level impacts to any non-target species, including 

(from left to right) Chrysolina quadrigemina (Suffrian) (Coleoptera: Chrysomelidae) (Cheryl Moorehead, Bugwood.org); Mecinus janthiniformis Toševski & Caldara 

(Coleoptera: Curculionidae) (Gary Chang, iNaturalist.org); Galerucella calmariensis (L.) (Coleoptera: Chrysomelidae) (Mark Schwarzländer, University of Idaho, 

Bugwood.org); Longitarsus jacobaeae (Waterhouse) (Coleoptera: Chrysomelidae) (USDA ARS European Biological Control Laboratory, Bugwood.org); Lilioceris 

cheni Gressitt & Kimoto (Coleoptera: Chrysomelidae) (Leslie J. Mehrhoff, University of Connecticut, Bugwood.org); and Oxyops vitiosa Pascoe (Coleoptera: 

Curculionidae) (Gary Buckingham, USDA ARS, Bugwood.org). The agents listed and pictured have wholly or partially suppressed invasive populations of the 

target weeds (from left to right) common St. Johnswort, Hypericum perforatum L.; Dalmatian toadflax, Linaria dalmatica (L.) Mill.; purple loosestrife, Lythrum 

salicaria L.; tansy ragwort, Jacobaea vulgaris Gaertn.; air potato, Dioscorea bulbifera L.; and melaleuca, Melaleuca quinquenervia (Cav.) S.T. Blake.

62   GROUP #16: Arthropods for Weed Biological Control

GROUP #16: INSECTS AND MITES FOR WEED BIOLOGICAL CONTROL 

HISTORY OF U.S. INTRODUCTIONS OF INSECTS AND MITES FOR WEED BIOLOGICAL CONTROL

Historically, plant-feeding insects introduced for control of unwanted plants seemed rather too close to 

pest insects attacking crops in the popular and governmental minds. As a consequence, host-range testing 

was required from the beginning of such importations (in the 1940s in the continental United States), and 

introductions were regulated under the Plant Quarantine Act (1912) to protect crops or horticultural plants, 

largely by screening lists of locally important crops. By the mid-1980s, the proposed idea of introducing 

weed biocontrol agents against pestiferous native plants had become controversial in the United States 

(DeLoach, 1985; Pemberton, 1985), and the idea of targeting native plants was abandoned before any 

significant application (apart from one project in Hawaii in the 1960s against false puncture vine, Tribulus 

cistoides L.). In the 1970s, the first Endangered Species Act (1973) was passed in the United States, with 

the goal of protecting rare or threatened native species, including plants. In this same time period, the goal 

of ensuring that introduced plant biocontrol agents would not damage economic plants was expanded 

to protect native plants. While rare plants received special attention in testing, the goal was to protect all 

native plants from any significant population-level damage. This caused the testing protocol applied to 

candidate agents to shift from being just an exclusionary exercise (providing evidence of lack of attack on 

a small list of particular crops) to estimating the boundaries of the agent’s host range so as to be predictive 

of risk for untested species. This was achieved by testing plants at various taxonomic distances from the 

target weed, using the centrifugal method of Wapshere (1974). Improvements in the science of host range 

estimation continued to be made, with increased focus on the role of preference among accepted plants 

and the role of attractants causing foraging adults to seek out specific plant species for oviposition (Briese, 

2005). 

Administratively, petitions for the release of weed biocontrol agents in the United States are reviewed 

by an inter-agency committee known as the Technical Advisory Group (TAG), which after its review makes 

a recommendation to the Animal and Plant Health Inspection Service (APHIS) concerning the advisability 

of releasing a proposed agent (Cofrancesco and Shearer, 2004). The TAG committee has representatives 
Variation in U.S. Standards for Introducing New Species

from the following federal agencies, countries, and organizations: (1) Canada, Agriculture and Agri-Food 

Canada, (2) Mexico, SAGARPA-SENASIA-DGSV, (3) National Plant Board, (4) Army Corps of Engineers 

in the U.S. Department of Defense, (5) U.S. Environmental Protection Agency, (6) U.S. Department of 

Agriculture (USDA) Agricultural Research Service, (7) APHIS, (8) USDA Forest Service, (9) USDA 

National Institute of Food and Agriculture, (10) USDA Natural Resources Conservation Service, (11) U.S. 

Department of Interior (USDI), Bureau of Indian Affairs, (12) USDI Bureau of Land Management, (13) 

USDI Bureau of Reclamation, (14) USDI Fish and Wildlife Service, (15) USDI National Park Service, (16) 

USDI, U.S. Geological Survey, and (17) the Weed Science Society of North America. 

Through consultation, the TAG committee makes recommendations on target suitability and nontarget species for use in quarantine testing, and comments on the advisability of issuance of a release permit. 

A reviewer’s manual defines the requirements for petitions, petitioners, and reviewers (Cofrancesco and 

Shearer, 2004; USDA APHIS, 2019d). 

Presence on the TAG committee of representatives from Canada and Mexico provide opportunities 

for concerns of those countries related to new weed biocontrol agents to be raised. Following positive 

recommendations from the TAG, APHIS then prepares a “Biological Assessment (BA)” that is shared 

with the Fish and Wildlife Service for the Section 7 Endangered Species Act consultation. If USFWS find 

sufficient data to show safety of the agent in regards to Threatened and Endangered Species and they concur 

with the proposed release, USFWS provides a “Letter of Concurrence” to that effect. APHIS then prepares 

an Environmental Assessment document and shares that with Native American tribes in areas within the 

range of the target plant as a “Tribal Consultation.” APHIS then submits the release petition for publication 

in the Federal Register for public comments. The agency then responds to public comments and reaches its 

decision, which, if positive, is called a FONSI (Finding of No Significant Impact). This procedure is the most 

rigorous review process for any group of new species being imported into the United States.

REGULATION OF RISKS: WHAT WERE THE PERCEIVED PROBLEMS?

The principal risk for which new weed biocontrol agents are assessed is the possibility of direct attack on 

non-target species, including crops, horticultural plants, or native plants. Exotic plants used as ornamentals 

are not considered protected if they are of limited economic importance. No other risks have been identified 

for weed biocontrol agents, but some potential exists for effects on habitat structure or food webs are 

theoretically possible. 

RISK-REGULATION PROFILE FOR INSECTS AND MITES FOR WEED BIOLOGICAL CONTROL 

Risk 1: Direct attack on non-target species

The review process for weed biocontrol agents (Wapshere, 1974) is primarily focused on evaluating risk 

to non-target plants. Of the approximately 465 arthropod species that have been introduced as biocontrol 

agents at the world level (Winston et al., 2020), only two species seem to have the potential to cause 

population-level impacts on native non-target species: the cactus-feeding moth Cactoblastis cactorum Berg 

(Lepidoptera: Pyralidae) (Fig. 16; Stiling et al., 2004; Pemberton and Liu, 2007) and the thistle-feeding 

weevil Rhinocyllus conicus Fröelich (Coleoptera: Curculionidae) (Louda, 1998; Louda et al. 2005). Of these, 

only R. conicus was introduced intentionally to the United States.

Risk 2: Potential to vector pest insects, mites, ticks, or nematodes

Parasitic insects, mites, or nematodes attacking candidate weed biocontrol agents are eliminated during 

quarantine.

GROUP #16: Arthropods for Weed Biological Control 63
Variation in U.S. Standards for Introducing New Species

a b c

Figure 16. Cactoblastis cactorum Berg (Lepidoptera: Pyralidae) (a) is a biological control agent highly effective at controlling weedy Opuntia cactus species 

in numerous countries worldwide (b). In the 1950s and 60s, it was introduced to several islands in the Caribbean. It subsequently spread naturally and via 

the nursery trade throughout the Caribbean and to the southeastern United States, where it has attacked native Opuntia species and prompted a sterile 

moth breeding and eradication program. Though only two arthropod species used for weed biocontrol worldwide (out of 465) have had population-level 

impacts on non-target species, the concern of weed biocontrol agents damaging crops and native species led to stringent field and laboratory host-testing 

requirements (c). This review process is the most rigorous for any group of new species being imported into the United States. (Photos: a. Jeffrey W. Lotz, 

Florida Department of Agriculture and Consumer Services, Bugwood.org; b. Christine Sydes, iNaturalist.org; c. Fritzi Grevstad, Oregon State University)

64   GROUP #16: Arthropods for Weed Biological Control

Risk 3: Potential to vector pathogens to non-target plants

Plant pathogens of concern can be detected as pathogen DNA inside weed biocontrol agents during 

quarantine and, if present, eliminated from agent colonies by destroying groups of affected individuals.

Risk 4: Potential to become pests in crops

Crop species that are potentially suitable for agent feeding are included in tests for evaluation of host range, 

and agents are rejected if they have potential to feed on crops (e.g., Cristofaro et al., 2013).

Risk 5: Potential to degrade native habitats or ecosystems

Habitats produced by native plants would not be affected because feeding on native plants by biocontrol 

agents is nil to incidental. However, habitats created by invasive plants may be affected if the pest weed is 

suppressed. Speculatively, two scenarios might exist in which this direct, desired effect might indirectly 

damage native species. The first is when a second invader in the habitat expands to fill the space opened up 

by control of the target pest. This outcome would be damaging if the second pest were worse than the first. 

A second scenario that may be of concern in some cases occurs when the habitat created by the 

targeted invasive plant has some valuable features, which might be lost if the invasive plant was suppressed 

by biological control agents. To some extent this is the case for invasive saltcedars (Tamarix spp.) in 

the southwestern United States, which provide poor but accepted nesting habitat for the endangered 

southwestern willow flycatcher, Empidonax traillii ssp. extimus Phillips. The risk expected by some was that 

saltcedar reduction would occur rapidly enough to lower the rate of nesting success for this bird. However, 

restoration of native willow and cottonwood, if properly executed and well timed, provides higher quality 

habitat that can more than offset loss of saltcedar as nesting sites (Dudley and Bean, 2012).

Risk 6: Potential to reduce density of native species by changing food webs

No real example is known, but a theoretical one is provided. The native butterfly Pieris oleracea (Harris) 

(Lepidoptera: Pieridae) was reduced to low levels in Massachusetts by parasitism of the braconid parasitoid 
Variation in U.S. Standards for Introducing New Species

Cotesia glomerata (L.) (Hymenoptera: Braconidae), which was introduced into North America in the 1880s 

to control the imported cabbage worm, Pieris rapae (L.) (Lepidoptera: Pieridae) (Benson et al., 2003). 

Currently the native butterfly’s population is recovering in the western part of Massachusetts due to two 

factors. First, the impact of C. glomerata on P. oleracea has been greatly reduced by the introduction of 

Cotesia rubecula (Marshall) (Hymenoptera: Braconidae), a second, more specialized parasitoid of P. rapae 

made in 1988. This more specialized parasitoid has drastically reduced the number of P. rapae that are 

available for C. glomerata to use as hosts, reducing that parasitoid’s spillover onto P. oleracea (Herlihy et 

al., 2012, 2014). However, another critical factor driving this recovery has also been the invasion of cuckoo 

flower, Cardamine pratensis L., which provides a high quality, full-season host plant for P. oleracea in open 

wet meadows, supporting up to four generations of the butterfly per year (Herlihy et al., 2014). Theoretically, 

if the importance of cuckoo flower to P. oleracea were unknown and if a successful weed biocontrol program 

were mounted against the invasive plant, the introduction of the weed biocontrol agents would slow or 

prevent the recovery of the native butterfly. 

SUMMARY OF RISK REGULATION FOR INSECTS AND MITES FOR WEED BIOLOGICAL CONTROL 

Of the six possible risks associated with novel species introductions for plant biocontrol, Risk 2 (vectoring 

unwanted insects or nematodes) and Risk 3 (vectoring pathogens) could occur, but in practice can be 

eliminated effectively by screening of weed biocontrol agents for parasitoids, pathogens, or misidentified 

similar herbivorous species in quarantine. Risk 1 (attack on native species) and Risk 4 (attack on crops) 

overlap and both are tightly regulated. These risks are effectively prevented by host range testing in quarantine 

before agents are introduced. This approach has been highly successful since it was adopted in the United 

States in the 1940s. Risk 5 (unwanted effects on habitats) might occur if the targeted invasive plant species 

itself created habitats with some desired attributes. In such a context, the benefits the invasive target weed 

might would have to be determined and weighed against the weed’s harm before proceeding. Finally, the 

risk of effects mediated through food webs (Risk 6) would, in a similar way, have to be recognized by field 

studies of the invasive plant’s biology and ecology to determine if any species strongly benefited from it as 

a host plant.

GROUP #16: Arthropods for Weed Biological Control 65
Variation in U.S. Standards for Introducing New Species

Banner Photos. Several pathogens have been released against weeds and insects in the United States. None of these introduced species have caused 

population-level impacts to non-target species (Hajek et al., 2007; Winston et al., 2020). Weed biocontrol pathogens include (from left to right) Puccinia 

carduorum Jacky (Pucciniales) (Loke T. Kok, Virginia Polytechnic Institute and State University, Bugwood.org); Puccinia chondrillina Bubák & Syd. 

(Pucciniales) (Gary L. Piper, Washington State University, Bugwood.org); and Puccinia jaceae var. solstitialis (Pucciniales) Savile (Eric Coombs, Oregon 

Department of Agriculture, Bugwood.org) released, respectively, against musk thistle (Carduus nutans L.), rush skeletonweed (Chondrilla juncea L.), and 

yellow starthistle (Centaurea solstitialis L.). Insect biocontrol pathogens include Metarhizium anisopliae (Metschn.) Sorokīn (Hypocreales) (Sunnetchan, 

iNaturalist.org); Beauveria bassiana (Bals.-Criv.) Vuill. (Hypocreales) (David Whyte, iNaturalist.org); and Entomophaga maimaiga Humber, Shimazu, & R.S. 

Soper (Entomophthorales) (Steven Katovich, Bugwood.org). The first two are species with worldwide distributions used as biorational pesticides, and the 

final species is an introduced agent against gypsy moth, Lymantria dispar (L.).

66   GROUP #17: Pathogens for Weed or Insect Biological Control

GROUP #17: PATHOGENS FOR WEED OR INSECT BIOLOGICAL CONTROL

HISTORY OF U.S. INTRODUCTIONS OF PATHOGENS FOR WEED OR INSECT BIOLOGICAL CONTROL 

In the United States, pathogens have been introduced against both insect pests and weeds. Insect and plant 

pathogens have different regulatory histories in the United States, and insect pathogens have been regulated 

under a number of laws. 

Against weeds

Plant pathogens have been regulated in a consistent manner, with all groups of plant pathogens being 

evaluated in the same general way over the whole period of use historically. Twelve species of plant 

pathogens have been released in the United States, including Hawaii, as classical biocontrol agents 

(two nematodes and 10 fungi) (Winston et al., 2020). No plant viruses, bacteria, or microsporidia (now 

considered fungi) have been intentionally introduced. The regulatory process applied to plant pathogens 

has been the same as that applied for insects used for weed biocontrol, as described in Group 16, with 

early introductions being regulated under the Plant Quarantine Act (1912) and, more recently, under the 

Plant Protection Act (2000). 

Against insects

Pathogens introduced as classical biocontrol agents of insects and mites include species of nematodes, viruses, 

microsporidia (now considered fungi), bacteria, and fungi (Hajek et al., 2016). The regulation of these agents 

was different from that used for plant pathogens, inasmuch as the U.S. Environmental Protection Agency 

(EPA) treated most insect microbial agents as pesticides subject to the Federal Insecticide, Fungicide, and 

Rodenticide Act (FIFRA) and later laws regulating pesticides, even when used as classical biocontrol agents 

rather than as formulated products (Fig. 17). Insect pathogenic nematodes, however, were not regulated in 

this manner by EPA, but rather treated as augmentative biocontrol insects and mites under the oversight of 

the U.S. Animal and Plant Health Inspection Service (APHIS). In contrast to nematodes, microbial agents and 

fungi directed against insects were reviewed under rules designed for the regulation of chemical pesticides 
Variation in U.S. Standards for Introducing New Species

a b c

Figure 17. Potential weed and insect biocontrol pathogens are subject to stringent field and laboratory host-testing requirements (a) before approval for 

their use in the United States. The fungus Beauveria bassiana (Bals.-Criv.) Vuill. (Hypocreales), a cosmopolitan species affecting many pest insects (b), is 

commercially available in many formulations that can be applied in a similar fashion as pesticides (c). (Photos: a. Tim Vickers, Wikipedia.org; b. USDA ARS, 

Wikipedia.org; c. Howard F. Schwartz, Colorado State University, Bugwood.org)

GROUP #17: Pathogens for Weed or Insect Biological Control 67

until 2000, when the North American Plant Protection Organization (NAPPO) endorsed a standard similar 

to that of its European counterpart (European and Mediterranean Plant Protection Organization [EPPO, 

2000]), based on the FAO Code of Conduct (FAO/IPPC, 1996). APHIS then provided instructions on how 

to petition for the release of non-native entomopathogens and insect parasitic nematodes for biological 

control (as discussed in Hajek et al., 2007).

Hajek et al. (2007) notes that 37 species of viruses, bacteria, fungi, microsporidia, or oomycetes and 

eight species of nematodes had been introduced to one or more countries for insect biocontrol, with fungi 

being the most frequently released group, followed by viruses and nematodes. Other groups have rarely been 

used. The species most frequently employed (at the world level) have been the Oryctes rhinoceros nudivirus, 

the fungi Metarhizium anisopliae (Metschn.) Sorokīn (Hypocreales) and Entomophaga maimaiga Humber, 

Shimazu, & R.S. Soper (Entomophthorales), and the nematodes Romanomermis culicivorax Ross & Smith 

(Mermithida) and Deladenus siricidicola Bedding (Tylenchida).

REGULATION OF RISKS: WHAT WERE THE PERCEIVED PROBLEMS?

Plant pathogens

The risk that is the focus of regulation for pathogens used for weed biocontrol is potential for infection of 

plants other than the target weed. None of the other risks are applicable to weed biocontrol pathogens. 

Insect pathogens

Entomopathogens may pose direct risks to native non-target insects related to the target pest (e.g., Lockwood, 

1993). Hajek et al. (2007), however, found no documented cases in the literature of substantial mortality to a 

non-target species caused by an introduced insect pathogen. None of the other risks are applicable to insect 

biocontrol pathogens. 

RISK-REGULATION PROFILE FOR PATHOGENS USED FOR WEED OR INSECT BIOCONTROL

Risk 1: Direct attack on non-target species

This is the principal risk of concern for pathogens used for weed biocontrol, and new agents must have 
Variation in U.S. Standards for Introducing New Species

narrow host ranges that do not threaten populations of native plants. This risk is also the principal regulatory 

focus for pathogens used for insect biocontrol; their host ranges, however, are broader, however, and many 

species used as biorational pesticides are native or cosmopolitan species.

Risk 2: Potential to vector pest insects, mites, ticks, or nematodes

Not applicable.

Risk 3: Potential to vector pathogens to non-target plants

Not applicable.

Risk 4: Potential to become pests in crops

Weed biocontrol pathogens might, potentially, be able to infest crop plants and so this is a regulated risk. For 

insect pathogens, however, there is no biological possibility for attack on plants (also some species can act as 

beneficial endosymbionts in plants) and so this risk is not applicable.

Risk 5: Potential to degrade native habitats or ecosystems

There are no known examples of this risk for this group.

Risk 6: Potential to reduce density of native species by changing food webs

There are no known examples of this risk for this group.

SUMMARY OF RISK REGULATION FOR PATHOGENS USED FOR WEED OR INSECT BIOCONTROL

Plant pathogens

The concern that introduced plant pathogens might harm populations of native plants (Risk 1) or crops 

(Risk 4) through direct attack has been the primary focus of regulatory review. Risk 2 (vectoring insects) and 

Risk 3 (vectoring plant pathogens) are not applicable. Risk 5 (effects on habitats) and Risk 6 (effects on food 

webs) are regulated, but there are no known examples.

Insect pathogens 

Before 2000, newly introduced pathogens were regulated in the United States using the same criteria as 

chemical pesticides (except for nematodes, which were exempt). After 2000, the concern that introduced 

insect pathogens might harm populations of native insects through direct attack (Risk 1) has been the 

primary focus of regulatory review. Risk 2 (vectoring insects), Risk 3 (vectoring plant pathogens), and Risk 

4 (becoming crop pests) are not applicable. Risk 5 (effects on habitats) and Risk 6 (effects on food webs) are 

regulated, but there are no known examples.

68   GROUP #17: Pathogens for Weed or Insect Biological Control
Variation in U.S. Standards for Introducing New Species

CREATING A UNIFORM, RISK-BASED SYSTEM FOR ALL GROUPS OF 

ORGANISMS

THE PAST: AN AD HOC COLLECTION OF NARROWLY FOCUSED REGULATIONS

The current rules used to evaluate requests to introduce new species into the United States have no crossgroup, unifying standards, but are rather an ad hoc collection of narrow rules designed for particular 

problems at various points of U.S. history. This ad hoc nature of current regulations creates a highly variable 

level of regulation (Fig. 18), with some groups such as biological control agents being more stringently 

regulated than other groups such as horticultural plant introductions or species used in the pet trade (Fig. 

19). The current situation arose because no attempt was ever made to react to the larger problem of how to 

reduce risks across the board for new species introductions. Rather, each sector was seen in isolation, and its 

most obvious problems were the drivers shaping the legislative response, often to the neglect of other, less 

obvious risks. Also, for many groups, the organisms that were being introduced were historically accepted 

as “good” without review. In such cases, the risks being regulated were not the species themselves, but rather 

the chance that these “good” organisms would act as vectors for hitchhiking pests. This is most clear in 

the 1912 Plant Quarantine Act, which was not intended to regulate threats posed by new plants becoming 

pests (since the free introduction of new plants was seen as completely good), but rather to prevent those 

plant introductions from transporting pest insects or plant pathogens. Much the same sort of thinking 

has gone into control of other sectors. In aquaculture, for example, the exotic oyster was not seen as the 

problem; rather, the possibility of it bringing in another oyster pathogen was the risk to control. In many 

sectors, therefore, little thought was given to the possibility of the introduced species themselves becoming 

damaging pests. A noticeable exception to the above scenario was the ban on the importation of any new 

species of birds or mammals (under a previous version of the Lacey Act) from 1900 until 1948, when the ban 

was lifted and applied only to species classified by the government as “injurious.”

For some sectors, the Lacey Act (18 U.S.C. 42) provides some measure of regulation. However, the 

Lacey Act’s regulator power, based on designation of species as “injurious wildlife,” has several important 

limitations, including (1) no authority over plants or any invertebrates except for mollusks and crustaceans; 

(2) the use of black lists (= species listed as “injurious wildlife”) as the main regulatory tool; and (3) no 

authority to require prior review of proposed introductions of species not already on the black list. This 

approach is similar to the status of chemicals used as pesticides before the 1947 Act regulating pesticides (the 

Federal Insecticide, Fungicide, and Rodenticide Act [FIFRA]). Before the 1947 Act, the federal government 

bore the burden of proving that a chemical proposed for use as a pesticide was dangerous. After FIFRA, the 

burden of proof shifted from the government (black list approach) to the company proposing the use of a 

new compound as a pesticide (a prior-review, data-based system). With respect to the introduction of new 

plant and animal species, the United States’ current regulatory position is similar to that used to control 

pesticides before 1947, where the burden of proof to identify harmful species is on the federal government, 

with the single exception of species whose reason for introduction is biological control of invasive pests—all 

CONCLUSION: Creating a Level Regulatory Across Groups 69
Variation in U.S. Standards for Introducing New Species

GROUP RISK 1

non-target

attacks

RISK 2

vector insects, 

mites, ticks

RISK 3

vector

pathogens

RISK 4

damage

crops

RISK 5

degrade

habitats

RISK 6

change food

webs

#1 FORESTRY, FORAGE, OR 

FODDER PLANTS Not Applicable Regulated Partially 

Regulated

Partially 

Regulated 

Partially 

Regulated Not Regulated

#2 ORNAMENTAL PLANTS Not Applicable Regulated Partially 

Regulated

Partially 

Regulated 

Partially 

Regulated Not Regulated 

#3 CROP PLANTS Not Applicable Regulated Partially 

Regulated

Partially 

Regulated 

Partially 

Regulated Not Regulated 

#4 TERRESTRIAL MAMMALS 

FOR RANCHING OR VIEWING Not Regulated Regulated Regulated Not Regulated Not Regulated Not Regulated

#5 FISH USED FOR 

AQUACULTURE 

Partially 

Regulated Not Applicable Regulated Not Applicable Not Regulated Not Regulated

#6 COMMERCIALLY 

PRODUCED INVERTEBRATES Not Applicable Not Applicable Partially 

Regulated

Partially 

Regulated

Partially 

Regulated Not Regulated

#7 PREDATORY MAMMALS 

FARMED FOR FUR Not Regulated Regulated Regulated Not Applicable Not Regulated Not Regulated

#8 HERBIVOROUS 

MAMMALS FARMED FOR FUR Not Regulated Regulated Regulated Not Regulated Not Regulated Not Regulated

#9 BIRDS AND MAMMALS 

FOR HUNTING Not Regulated Regulated Regulated Not Regulated Not Regulated Not Regulated

#10 FISH FOR SPORT OR 

COMMERCIAL FISHING

Partially 

Regulated Not Applicable Partially 

Regulated Not Applicable Not Regulated Not Regulated

#11 ANIMALS SOLD AS PETS Not Regulated Regulated Partially 

Regulated

Partially 

Regulated

Partially 

Regulated Not Regulated

#12 ANIMALS INTRODUCED 

FOR MEDICAL USES Not Regulated Not Applicable Not Regulated Not Applicable Not Regulated Not Regulated

#13 VERTEBRATES USED 

FOR PEST CONTROL Regulated Regulated Regulated Not Applicable Regulated Regulated

#14 PARASITOIDS FOR 

INSECT BIOCONTROL Regulated Regulated Regulated Not Applicable Regulated Regulated

#15 PREDATORY 

INSECTS AND MITES FOR 

BIOCONTROL

Regulated Regulated Regulated Regulated Regulated Regulated

#16 INSECTS OR MITES FOR 

WEED BIOCONTROL Regulated Regulated Regulated Regulated Regulated Regulated

#17 PATHOGENS FOR WEED 

OR INSECT BIOCONTROL Regulated Not Applicable Not Applicable Regulated Regulated Regulated

70   CONCLUSION: Creating a Level Regulatory Across Groups

Figure 18. Summary of degree of regulation for 17 groups (purpose of introduction) versus six risks. Biological control agents, groups 13 to 17, in boxed 

portion of figure.
Variation in U.S. Standards for Introducing New Species

Figure 19. Number of risks that are regulated (green striped), partially regulated (yellow dotted), or not regulated (red) for each of the 17 categories of 

novel species, under U.S. law (risks judged “not applicable” make up the remainder in each group).

CONCLUSION: Creating a Level Regulatory Across Groups 71

of which require pre-release review. For those organisms, a prior-review, data-based system has been in 

place since the 1940s for weed biological control agents, since 1993 for parasitoids and predatory insects, 

and since 2000 for insect pathogens, with regulation of each sector of biocontrol addressing over time a 

progressively more comprehensive suite of risks.

In this section, we consider the need for a harmonized system in which all new species introductions 

would follow a pre-introduction, data-driven review process. It also seems reasonable that species being 

considered for introduction would be judged based on their attributes, not on the reason for which they 

are being introduced. This influence of the reason for a species introduction on its regulation is similar to 

differences in U.S. law between regulation of chemicals used as pesticides (“to kill pests”) versus chemicals 

used for industrial applications (“to do many things”), with the latter group often being equally as toxic, but 

nevertheless held to lower standards under a different law (Toxic Substances Control Act, 1976). Currently, 

biological control agents are equated with pesticides and are held to higher standards than other species, 

which can be as or more damaging. In addition, for all species, it would seem valuable to consider the 

benefits of the introduction. Currently, benefits are the principal item considered for non-biological control 

agents (“it is good to eat”; “it will boost aquaculture”; “it will provide excellent sport fishing or hunting”; “it 

will be highly profitable to sell”). The benefits of a biocontrol agent potentially controlling a pest are taken 

into account during the agent’s review; however, far more emphasis is placed on the potential for the agent 

to have negative impacts on people, plants, animals, soil, water, and other elements of the environment.

Furthermore, adoption of a uniform, defined risk-review process would force some assumptions to 

be considered—assumptions that we consider faulty but which have been allowed to go unchallenged. For 

example, new species of fish are imported virtually daily for the aquarium trade, and potential risks of these 

species escaping and becoming damaging are not reviewed because the fish are not initially being released 
Variation in U.S. Standards for Introducing New Species

into the environment. However, the assumption of non-release is amply refuted by the documentation of 

end-users routinely releasing unwanted, oversized fish too big for home aquaria rather than killing them 

(Simberloff et al., 1997; USGS, 2019a).

ARGUMENTS FOR RETAINING THE PRESENT U.S. SYSTEM (SPECIAL RULES FOR SPECIAL GROUPS)

Argument #1. Some groups do not cause invasions and hence can be lightly regulated. 

One might argue that a universal set of standards for new species introductions is not needed because only 

some types of introductions are the source of new, damaging invaders. If so, then the implied expectation 

would be that the groups serving as the strongest sources of new invaders would be the most strongly 

regulated. Examination of one such list (“100 of the World’s Worst Invasive Alien Species” [Global Invasive 

Species Database, 2014]) found that 63 of the 100 were deliberately introduced. The rank order of importance 

as sources for deliberately introduced species on this list (Fig. 20) was (1) ornamental plants (38%), (2) 

forestry/forage/fodder plants (14.3%), (3) the pet trade (14.3%), (4) predaceous vertebrates historically used 

for biocontrol (7.9%), (5) animals and birds for hunting (6.3%), (6) fish for fisheries or sport fishing (6.3%), 

(7) fish for aquaculture (3.2%), (8) crops (3.2%), and (9) herbivores for fur production (3.2%). These sources 

accounted for 61 of the 63 deliberately introduced pests on this list (two species not fitting any category). The 

types of agents used in the last 50 years for biocontrol (i.e., parasitoids for biocontrol of insects or insects and 

pathogens as agents for weed biocontrol) each had zero species listed (Fig. 20). While one might argue that 

any list’s choices would be subjective, this distribution shows that deliberate introductions that create new 

important pests come from a wide range of groups, topped by ornamental plants, pet species, and vertebrate 

Figure 20. Percentage of deliberately introduced species (n = 63) from list “100 of the World’s Worst Invasive Alien Species” (Global Invasive Species 

Database, 2014) divided by intended use.

72   CONCLUSION: Creating a Level Regulatory Across Groups
Variation in U.S. Standards for Introducing New Species

animals. This distribution provides no support, rather the contrary, for under-regulating new introductions 

in these groups. 

Argument #2. Some groups are too economically important to restrict their importation. 

This argument is an economic argument, not an ecological one. Nevertheless, it also is not supported by facts. 

Fish importations, for example, have caused damage far in excess of the benefits from the pet and aquaculture 

industries, and so allowing species in these groups to be introduced freely is not justified economically. 

This argument might hold in some sectors and some regions, such as the introduction of softwood lumber 

species to the Southern Hemisphere, where economic and social benefits were enormous and the damage 

to date has been moderate. If this is the justification for the regulator posture of a country, then it should be 

explicitly stated as such and supported by financial assessments. Because many species have some economic 

benefits, the analyses must quantify how great the benefits are and who receives them, versus the damage 

done by a sector’s introductions. For example, it may be easier to justify fish introductions for aquaculture 

(with significant social benefits) than introductions by the pet industry (with the only economic benefits 

being to private industry and minor aesthetic benefits to consumers). 

Argument #3. Public support does not exist for a new system. 

It is likely not an accident that New Zealand and Hawaii, regions that have suffered the most from previous 

ill-considered species introductions, have the most rigorous policies for new species introductions. For the 

continental United States, this level of recognition and aversion of invasions is not present; most concern is 

focused retrospectively on remediation of the effects of bad introductions that have already occurred, rather 

than on policies that might reduce the chances of new, high-impact introductions. However, opportunities 

exist to increase public understanding of this problem. One important obstacle is that among the many 

sectors making species introductions, different groups are perceived independently. Public views are often 

based on impressions about benefits, limited information about harm (often less easy to see), and images 

produced by mass media about particular cases, which then become the face of introductions for particular 

sectors (e.g., Strong, 1997).

ARGUMENTS FOR CREATING A NEW, RISK-BASED SYSTEM, APPLIED EVENLY TO ALL SPECIES 

GROUPS

The basic argument for a new, risk-based system with parity among all the sectors introducing new species 

is that this is the only rational way to adjust the intensity of restrictions and the volume of regulatory effort 

in accordance with the real need. If each sector is regulated based on how much the public (or other smaller 

groups of people such as commercial interests, biological scientists, or ecologists who dislike biocontrol, 

etc.) like or dislike an activity, then regulatory rigor will depend on politics, not risk. In the United States, 

the current regulatory system is highly political. The risks that are perceived and accepted or, conversely, 

required to be regulated, are the product of politics, not science. However, getting to a better system from 

the current one would be a formidable task. The authors of this publication are under no illusions about the 

feasibility of such a change in the near or even medium term. However, by re-framing the conversation as an 

examination of risks that exist versus risks that the U.S. has chosen to regulate, we hope to increase public 

understanding of a new potential regulatory framework for evaluating risks of new species introductions, 

based on their traits, not their purpose. 

CONCLUSION: Creating a Level Regulatory Across Groups 73
Variation in U.S. Standards for Introducing New Species

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