Field Release of the Gall 

Wasp, Aulacidea 

subterminalis

(Hymenoptera: 

Cynipidae), for Biological 

Control of Invasive 

Hawkweeds (Hieracium

spp.) in the Continental 

United States

Environmental Assessment,

January 2011

United States 

Department of 

Agriculture

Marketing and 

Regulatory 

Programs

Animal and 

Plant Health 

Inspection 

Service
Field Release of the Gall Wasp, 

Aulacidea subterminalis

(Hymenoptera: Cynipidae), for 

Biological Control of Invasive 

Hawkweeds (Hieracium spp.) in the 

Continental United States

Environmental Assessment, 

January 2011

Agency Contact:

Shirley Wager-Page, Branch Chief

Pest Permitting

Plant Protection and Quarantine

Animal and Plant Health Inspection Service

U.S. Department of Agriculture

4700 River Road, Unit 133

Riverdale, MD 20737–1236

 

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Use all pesticides selectively and carefully. Follow recommended practices for

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Table of Contents

I. Purpose and Need for the Proposed Action...........................1

II. Alternatives .............................................. .............................2

III. Affected Environment .............................. .............................5

IV. Environmental Consequences ................. ...........................12

V. Other Issues............................................. ...........................20

VI. Agencies, Organizations, and Individuals Consulted ...........22

VII. References............................................... ...........................23

 Appendix 1 ............................................... ...........................29

 Appendix 2 ............................................... ...........................38

 Appendix 3 ............................................... ...........................46

 Appendix 4 ............................................... ...........................48

 Appendix 5................................................ ...........................52
1

I. Purpose and Need for the Proposed 

Action

The U.S. Department of Agriculture (USDA), Animal and Plant Health 

Inspection Service (APHIS), Plant Protection and Quarantine (PPQ), Pest 

Permitting Branch (PPB) is proposing to issue permits for release of the 

hawkweed gall wasp, Aulacidea subterminalis (Hymenoptera: Cynpidae). 

The agent would be used by the applicant for the biological control of the 

hawkweeds Hieracium pilosella, H. aurantiacum, H. floribundum, and H. 

flagellare in the continental United States. Before permits are issued for 

release of A. subterminalis, the APHIS–PPQ, PPB must analyze the 

potential impacts of the release of this agent into the continental United 

States.

This environmental assessment1(EA) has been prepared, consistent with 

USDA, APHIS' National Environmental Policy Act of 1969 (NEPA) 

implementing procedures (Title 7 of the Code of Federal Regulations 

(CFR), part 372). It examines the potential effects on the quality of the 

human environment that may be associated with the release of A. 

subterminalis to control infestations of hawkweeds within the continental 

United States. This EA considers the potential effects of the proposed 

action and its alternatives, including no action.

The applicant’s purpose for releasing A. subterminalis is to reduce the 

severity of infestations of invasive hawkweeds in the United States. There 

are many species of non-native, invasive hawkweeds in North America. 

These species originated in Europe, which is the native range to a massive 

complex of species, subspecies, and varieties of Hieracium. Invasive 

hawkweeds were probably introduced into the eastern United States and 

Canada during the 1800s. Several hawkweed species are considered 

noxious in many western States. Introduced hawkweeds are highly 

competitive and relatively free of insects and pathogens in North America. 

These species outcompete native and desirable vegetation, forming near 

monocultures and limiting economic use of infested land. 

Existing management options for management of invasive hawkweeds are 

expensive, temporary, and have nontarget impacts. For these reasons, the 

applicant has a need to release A. subterminalis, a host- specific, biological 

control organism for the control of invasive hawkweeds, into the 

environment.

 

1

Regulations implementing the National Environmental Policy Act of 1969 (42 

United States Code 4321 et seq.) provide that an environmental assessment “shall include brief 

discussions of the need for the proposal, of alternatives as required by section 102(2)(E), of the 

environmental impacts of the proposed action and alternatives, and a listing of agencies and persons 

consulted.” 40 CFR § 1508.9. 
2

II. Alternatives

This section will explain the two alternatives available to the PPB—no 

action and issuance of permits for environmental release of A. 

subterminalis. Although the PPB’s alternatives are limited to a decision 

on whether to issue permits for release of A. subterminalis, other methods 

available for control of hawkweeds are also described. These control

methods are not decisions to be made by the PPB, and their use is likely to 

continue whether or not permits are issued for environmental release of A. 

subterminalis, depending on the efficacy of A. subterminalis to control 

hawkweeds. These are methods presently being used to control 

hawkweeds by public and private concerns.

A third alternative was considered, but will not be analyzed further. Under 

this third alternative, the PPB would have issued permits for the field 

release of A. subterminalis; however, the permits would contain special 

provisions or requirements concerning release procedures or mitigating 

measures. No issues have been raised that would indicate special 

provisions or requirements are necessary.

A. No Action 

Under the no action alternative, the PPB would not issue permits for the 

field release of A. subterminalis for the control of invasive hawkweeds. 

The release of this biological control agent would not take place. The 

following methods are presently being used to control hawkweeds; these 

methods will continue under the ―No Action‖ alternative and will likely

continue even if permits are issued for release of A. subterminalis, 

depending on the efficacy of the organism to control invasive hawkweeds.

Hawkweeds may be controlled by using herbicides. Herbicides, such as 

2,4-D, clopyralid, aminopyralid, and picloram have resulted in the greatest 

degree of control when applied at the normally recommended rate for 

perennial pasture weeds (Noel et al., 1979; 1992a; Wilson et al., 1997;

2005; 2006). Studies conducted at the University of Idaho showed that 

over 50 percent control was achieved for 6 years following treatment with 

a 1 pint per acre rate of clopyralid (Lass and Callihan, 1992). Similar 

results were achieved using picloram at the rate of 0.25 to 0.5 pounds of 

active ingredient per acre. Other herbicides either failed to control 

meadow hawkweed or suppression was for less than 3 years (Lass and 

Callihan, 1992; Miller et al., 1998). More recently, aminopyralid 

(MilestoneTM) has been recommended as an effective herbicide 

(http://www.msuextension.org/ruralliving/Dream/PDF/hawk.pdf last 

accessed March 23, 2010).

Mechanical control of invasive hawkweeds has had limited success. 

1. Chemical 

Control

2. Mechanical 

Control
3

Digging the plants or otherwise disturbing the stolons, rhizomes, or roots

only serves to spread the weed because plants can grow from buds on 

small root, stolon, and rhizome fragments. A stolon is a shoot that bends 

to the ground or that grows horizontally above the ground and produces 

roots and shoots at the nodes. A rhizome is similar to a stolon and is a 

horizontal, usually underground, stem that often sends out roots and shoots 

from its nodes. Disturbance by machinery spreads the weeds across the 

field. Local disturbances caused by grazing livestock, ungulates, and 

rodents also enhance the rate of spread of hawkweed. In lawns, mowing 

does not kill invasive hawkweeds because the low-lying stolons and 

rhizomes are missed by the mower blades. Although mowing prevents 

seed production by removing flowering stems, repeated mowing 

encourages faster vegetative spread (Callihan et al., 1997). 

When perennial grasses, legumes, and other beneficial forbs are present in 

the plant community, fertilizers can help control hawkweed by increasing 

the competitive ability of the more desirable species. This may be 

particularly important on rangelands and pastures because these lands are 

generally not priority areas for supplemental fertilization, and soil nitrogen 

levels may be inadequate for optimal grass health. Marked reductions of 

hawkweed density and vigor have been obtained by fertilizer treatments in 

the United States (Reader and Watt, 1981), Canada (Hay and Ouellette,

1959), and New Zealand (Scott et al., 1990) when competing vegetation is 

present. However, Reader and Watt (1981) found that repeated fertilizer 

treatments had no effect on dense patches of hawkweed that contained few 

grasses or other forbs. Depending on soil productivity and grass condition, 

a single nitrogen application may be sufficient for grasses to competitively 

suppress hawkweed growth for 3 to 5 years (Reader, 1990).

Five species of Hieracium-specific insects have been tested and released 

for the biological control of hawkweeds in New Zealand. They are:

(1.) Aulacidea subterminalis (Insecta: Hymenoptera: Cynipidae)—

hawkweed gall wasp;

(2.) Cheilosia psilophthalma (Insecta: Diptera: Syrphidae)—hawkweed 

crown-feeding hover fly;

(3.) Cheilosia urbana (Insecta: Diptera: Syrphidae)—hawkweed rootfeeding hover fly;

(4.) Macrolabis pilosellae (Insecta: Diptera: Cecidomyiidae)—hawkweed 

stem gall midge; and 

(5.) Oxyptilus pilosellae (Insecta: Lepidoptera: Pterophoridae)—

hawkweed plume moth.

None of these insects have been released in North America. An additional 

Aulacidea wasp, besides A. subterminalis, is being considered as a 

biological control candidate for release in North America. Aulacidea 

3. Cultural 

Control

4. Biological 

Control
4

pilosellae, a wasp that forms galls on stems, leaves, and stolons of 

hawkweeds, is currently undergoing testing and appears to be host-specific

(Littlefield et al. 2008).

B. Issue Permits for Environmental Release of 

A. subterminalis

Under this alternative, the PPB would issue permits for the field release of 

the gall wasp, A. subterminalis, for the control of invasive hawkweeds. 

These permits would contain no special provisions or requirements 

concerning release procedures or mitigating measures.

Biological Control Agent Information

Phylum: Arthropoda

Class: Insecta

Order: Hymenoptera

Superfamily: Cynipoidea 

Family: Cynipidae

Subfamily: Cynipinae 

Tribe: Aylacini

Genus: Aulacidea

Species: A. subterminalis Niblett

a. Native Range

Aulacidea subterminalis is fairly common and widespread on H. pilosella

in Northern Europe (Syrett et al., 1998). Fauna Europaea (2007) records 

A. subterminalis as present in Britain, France, and Germany. In its native 

habitat, A. subterminalis occurs on H. pilosella inhabiting arid, nutrient 

poor grasslands, poorly fertilized upland pastures, inland dunes, and manmade heaths (Ellenberg, 1988).

b. Other Areas of Introduction 

A. subterminalis is one of five insect biological control agents introduced 

to New Zealand for suppression of H. pilosella (Syrett et al., 2001). In 

New Zealand, A. subterminalis was approved for import and release in 

1998, and was first released in 1999. It has since been released at 99 sites 

throughout the North and South Island, with establishment confirmed at 

approximately 37 percent of these sites (Aspinall, 2006; Smith et al.,

2007). The failure of many releases was due to drought conditions 

following the release or site disturbance due to cropping or herbicide 

treatment (Smith et al., 2007).

c. Expected Attainable Range of A. subterminalis in North 

1. Taxonomy 

2. Geographical 

Range of A. 

subterminalis
5

America

A. subterminalis is fairly common and widespread on H. pilosella in 

Northern Europe and it is also establishing well in more moist areas of 

New Zealand, but is not well adapted to survive in dry or droughty 

environments where plants may senesce early (Littlefield et al., 2008). 

Climate matching using CLIMEX Version 1.1 (CSIRO Australia) suggests 

that the wasp’s potential range in North America should match much of 

the distributions of the targeted Hieracium species (Littlefield et al., 2008).

A. subterminalis is parthenogenetic (a form of asexual reproduction in 

which females produce eggs that develop without fertilization by males). 

Eggs are laid into the stolen tips. Eggs are milky-white in color, 0.24

millimeters (mm) long and 0.09 mm wide and have a stalk approximately 

1.18 mm long. Larvae develop inside the developing stolon-tip gall. Galls

are abnormal outgrowths of plant tissues and can be caused by various 

parasites, including insects. Galls are about 4.5 mm in diameter (Klöppel 

et al., 2003), but gall size is dependent upon the number of larval chambers 

present. Galls become evident approximately five weeks after the plant is 

exposed to the female wasp. Galls continue to enlarge for an additional 

5 weeks (Littlefield et al., 2008). Mature larvae are somewhat fusiform

(tapered at each end, spindle-shaped), with a distinctive, unpigmented 

head. The wasp overwinters in the larval stage. Pupation occurs in April, 

and adult wasps emerge from the galls from the beginning of May to the 

end of June in Switzerland. A. subterminalis has one generation per year. 

Adults are generally short lived; up to a week under ambient laboratory 

conditions.

III. Affected Environment

A. Target Weeds

(1.) Scientific name: Hieracium pilosella L.

Family: Asteraceae

Synonyms: none

Common name: Mouse ear hawkweed

(2.) Scientific name: Hieracium aurantiacum L. 

Family: Asteraceae

Synonyms: H. brunneocroceum Pugsley. 

Common name: Orange hawkweed, Grim the Collier

3. Life History of 

A. 

subterminalis
6

(3.) Scientific name: Hieracium floribundum Wimm. & Grab.

Family: Asteraceae

Synonyms: none

Common name: King devil hawkweed

(4.) Scientific name: Hieracium x flagellare Willd. (caespitosum x 

pilosella)

Family: Asteraceae

Synonyms: Hieracium x duplex, H. x macrostoloum

Varieties: cernuiforme, flagellare, glatzense

Common name: Whiplash hawkweed

Introduced hawkweeds are perennial plants that contain a milky sap and 

are generally stoloniferous (plants that bear or form stolons). Hieracium 

piloselloides and H. glomeratum are the only non-stoloniferous introduced 

species. Each young plant consists of a rosette of 5 to 12 hairy leaves 

arising from a short, thick rhizome with a shallow, fibrous root system. 

The flowers are yellow or orange (H. aurantiacum is the only orangeflowered species). New plants begin as seedlings or as leaves sprouting 

from stolons, rhizomes (Thomas and Dale, 1974), and/or roots (Peterson,

1979). Juvenile plants consist of low-lying rosettes that develop into 

flowering plants as erect, slender stems arise from the rosette center. 

All of the invasive hawkweeds reproduce asexually by apomixis (asexual 

seed production) and by vegetative spread by stolons, rhizomes, and root 

buds. Orange hawkweed sends out from three to eight long, slender

stolons along the soil surface. Meadow hawkweed also produces long, 

slender stolons, but some of its vegetative structures grow as shallow, 

underground rhizomes. Stolons and rhizomes, initiated from buds at the 

base of rosette leaves, begin to grow when the plant initiates flowering. 

Once established, vigorous stolon growth quickly expands the colony, 

forming dense patches that can have as many as 3,200 plants per square 

yard. The slender, leafy stolons elongate through the summer and form 

daughter rosettes at their tips (Thomas and Dale, 1974). Hawkweeds 

regrow each year from short, below-ground rhizomes. In H. piloselloides, 

axillary buds develop into secondary flowering shoots rather than stolons. 

Invasive hawkweeds also occasionally produce seeds sexually by periodic 

pollination and outcrossing. At lower elevations, flowering occurs around 

mid-June and seeds ripen by early August. Mature seeds can germinate as 

soon as they are released from the plant (Stergios, 1976). Studies have 

shown that seeds are viable in the soil for up to 7 years (Panebianco and 

Willemsen, 1976). Invasive hawkweeds have relatively short life cycles, 

completing a generation within 4 months.

Although most new hawkweed infestations are probably started by seeds, 

expansion of established populations is mostly vegetative. Thomas and 
7

Dale (1974) found that only 1 percent of new plants in a H. floribundum

population were derived from seedlings. Studies in eastern Canada 

showed that seeds are not carried far by the wind; although minute barbs 

along ribs on the seeds enable them to stick to hair, fur, feathers, clothing, 

and vehicles, and can be carried long distances.

B. Areas Affected by Hawkweeds

In their native ranges, hawkweeds occur in the northern, central, and 

eastern portions of Europe as ruderal species (plants that grows in rubbish, 

poor land, or waste) of pastures, roadside cutbanks, abandoned fields, and 

meadows (Skalinska, 1976). In most cases they are found in small, 

isolated pockets. Their highest densities are found on recently disturbed 

areas and they do not persist as dominant members of the early 

successional community (Skalinska, 1976). From Europe, hawkweeds 

spread to North America, New Zealand, Australia, Chile, and Argentina.

In North America, invasive hawkweeds are primarily weeds of moist 

pastures, forest meadows, and mesic (moderately moist) rangeland. Based 

on current infestations, habitats most susceptible to invasion range from 

the lowlands of the northern Pacific Coast to elevations of 5,000 feet or 

more in the Mountain States (Littlefield et al., 2008). Sites most 

vulnerable to invasion include roadsides, mountain meadows, clearings in 

forest zones, permanent pastures, hayfields, cleared timber units, and 

abandoned farmland where the soil is well drained, coarse textured, and 

moderately low in organic matter. Consequently, elk habitat, recreation 

areas, and pristine mountain meadows in areas that have a climate similar 

to that in their native range are particularly susceptible. Although

introduced hawkweeds can grow in open woodlands, they do not tolerate 

shade very well. Across the United States and Canada, introduced 

hawkweeds are closely associated with habitats that can support oxeye 

daisy (Chrysanthemum leucanthemum), sulfur cinquefoil (Potentilla 

recta), spotted knapweed (Centaurea maculosa), gray goldenrod (Solidago 

nemoralis), wild carrot (Daucus carrota), dandelion (Taraxacum 

officinale), and Kentucky bluegrass (Poa pratensis ) (Thomas and Dale, 

1974; Maycock and Guzikowa, 1984). None of the introduced hawkweed 

species are found in the natural grasslands or shrub-steppe of the northern 

Intermountain West, and are not expected to become problem weeds in 

any dry habitat usually associated with western rangelands. Neither 

meadow nor orange hawkweed appears to survive in annually tilled 

cropland.

There are many species of non-native, invasive hawkweeds in North 

America. These species originated from Europe, which is the native range 

to a massive complex of species, subspecies, and varieties of Hieracium. 

Invasive hawkweeds were probably introduced into the eastern United 

States and Canada during the 19th century. Two important subgenera 

1. Native and 

Introduced 

Range of 

Hawkweeds

2. Known and 

Potential 

Distribution of 

Hawkweeds in 

North America
8

distinguish the group of invasive species, subgenera Pilosella and 

Hieracium. Species in these subgenera vary widely, both morphologically 

and in their invasion history and species distribution. The majority of 

species belong to subgenus Pilosella, including the species considered as 

targets for A. subterminalis. (See figure 1 for a proposed phylogeny 

(taxonomic grouping) of North American Hieracium species.) 

Figure 1. Proposed taxonomic grouping of North American Hieracium species by 

Gaskin and Wilson (2007).
9

The present distributions of these exotic species in the United States and 

Canada are provided in table 1.

Table 1. Invasive, Nonnative Hieracium species, from subgenus Pilosella, 

in the United States and Canada (from Wilson et al., 2006).

Species Distribution

H. arvicola Nageli et Peter CAN: NB

H. aurantiacum L. CAN: AB, BC, NB, NL, NS, ON, PE, QC, 

SK

USA: AK, AR, CA, CO, CT, FL, ID, IN, IA, 

MA, MD, ME, MI, MN, MT, NC, NH, NJ, 

NY, OH, OR, PA, RI, SD, VA, VT, WA, WV, 

WI, WY

H. bauhini Schult CAN: BC

USA: CT, ID, MA, MN, NH, NY, VT, WA

H. brachiatum Bertol. ex DC. CAN: QC

USA: NY

H. caespitosum Dumort CAN: AB, BC, NB, NL, NS, ON, PE, QC

USA: CT, DE, GA, ID, IL, IN, KY, MA, MD, 

ME, MI, MN, MT, NC, NH, NJ, NY, OH, 

OR, PA, RI, SC, TN, VT, VA, WA, WV, WI

H. H. derubellum Gottschl. et Schuhw. 

[H. atramentarium act.]

CAN: QC

USA: MI, NY, WI

H. flagellare Willd. H. flagellare Willd.

 [incl. H. macrostolonum]

CAN: BC, NB, NL, NS, ON, PE, QC

USA: CT, ID, MA, ME, MI, NH, NY, PA, 

VA, VT

H. floribundum Wimm. & Grab. CAN: BC, NB, NL, NS, ON, PE, QC

USA: CT, ID, MA, MD, ME, MN, MT, NH, 

NJ, NY, OH, OR, RI, VA, VT, WA, WV

H. fuscoatrum Nageli & Peter USA: CT, NY, RI

H. glomeratum Froel. CAN: BC, ID, WA

H. lactuella Wallr. CAN: NS

H. pilosella L. CAN: BC, NB, NL, NS, ON, PE, QC, Saint 

Pierre and Miquelon

USA: CT, DE, GA, MA, MD, ME, MI, MN, 

NC, NH, NJ, NY, OH, OR, PA, RI, TN, VA, 

VT, WA, WV

H. piloselliflorum Nageli et Peter

[incl. H. apatelium]

CAN: NB, NL, NS, ON, PE, QC 

H. piloselloides Vill.

[incl. H. preaaltum]

CAN: BC, NB, NL, NS, ON, PE, QC

USA: CT, DE, GA, IL, IN, IA, MA, ME, MI, 

MN, MT, NC, NH, NY, OH, PA, RI, SC, VA, 

VT, WI, WV

H. stoloniflorum Waldst. et Kit. CAN: QC
10

Hieracium aurantiacum (orange hawkweed) was introduced into Vermont 

in 1875 as an ornamental and within 25 years spread throughout much of 

northeastern United States and southeastern Canada (Voss and Böhlke,

1978). Within 25 years it had spread throughout much of New England, 

west to Michigan (Voss and Böhlke, 1978) and into Canada from New 

Brunswick to Ontario (Britton and Brown, 1970). It now occurs 

throughout the eastern seaboard and into the Midwest, extending west to 

Minnesota and Iowa, and south to Virginia and North Carolina (Johnson

and Thomas, 1978). First recorded in Spokane, Washington, in 1945 

(Marion Ownbey Herbarium, Wash. State Univ.), H. aurantiacum has 

been collected from gardens in Nevada County, California (Munz and 

Keck, 1959), on the east slope of the Rocky Mountains in Colorado 

(Weber, 1990), from coastal Oregon and Washington (Rickett, 1973), and 

in southwestern British Columbia (Guppy, 1976). In the western United 

States, populations of orange hawkweed were first reported from coastal 

Washington and Oregon (Peck, 1941; Abrams and Ferris, 1960). It has 

also been reported from the lower mainland of British Columbia (Guppy,

1976) where it infests pastures, old fields, and roadsides. H. aurantiacum

is now also recorded in Idaho, Montana, and Wyoming (USDA–NRCS,

2008). It is more widespread than other hawkweed species primarily 

because it is planted as an ornamental and often escapes cultivation. 

Hieracium pilosella (mouse ear hawkweed) is widespread in the eastern 

United States and Canada. In the west, it occurs in western Washington, 

western Oregon, Alaska, and British Columbia.

Hieracium flagellare (whiplash hawkweed) occurs primarily in the 

northeastern United States and eastern Canada, but also occurs in British 

Columbia and Wyoming. 

Hieracium floribundum (king devil hawkweed) was first reported in 

northern New York in 1879 (Voss and Böhlke, 1978) and 1900 

respectively (Kennedy 1902). Recently, infestations of H. floribundum

have been reported in western Washington (WSNWCB, 1997), Northern 

Idaho (L. Wilson, unpubl. data.), and Montana (USDA–NRCS, 2008), and 

is reportedly expanding in range.

Hieracium piloselloides has been recorded in the western States of 

Montana and Washington (USDA–NRCS, 2008), and is also reportedly 

expanding in range. Suspected hybridization between H. caespitosum, H. 

floribundum, and H. piloselloides, and the potential threat of these species 

in western habitats is the rationale for including these species as target 

weeds in the biological control program.

Hieracium caespitosum (meadow hawkweed) was likely introduced into 

the United States in 1828 (Britton and Brown, 1970), and is now 

commonly found from Québec and Ontario (Frankton and Mulligan, 1970) 
11

southward to Georgia and Tennessee (Rickett, 1973). The first record of 

H. caespitosum in the western United States was in Pend Oreille County, 

Washington, in 1969 (Marion Ownbey Herbarium, Wash. State Univ.). H.

caespitosum is now recorded in the western States of Idaho, Montana, 

Oregon, Washington, and Wyoming, and is widespread throughout most of 

southern British Columbia and Alberta.

C. Plants Related to Invasive Hawkweeds and Their

Distribution

Plants related taxonomically to invasive hawkweeds would be the most 

likely to be attacked by the proposed biological control organism A. 

subterminalis. Plants related to the target hawkweeds are discussed below. 

There are many species of Hieracium native to North America (Wilson 

et al., 1997). Distribution of native Hieracium species ranges from the 

east coast to west coast, from sea level to over 9,000 ft. in elevation, and 

from northern to southern latitudes. As with the European hawkweeds, the 

number of native species has long been disputed. In order to understand 

species relationships in Hieracium, a brief outline of the generic divisions 

is provided. 

There are generally considered to be about 36 species of Hieracium

belonging to the three subgenera in America north of Mexico (Strother,

2006). A review of the regional flora revealed that about 25 species are 

native to the United States and Canada and fall into two subgenera: 

Hieracium (3 species) and Chionoracium (22 species). Subgenus 

Hieracium occurs chiefly throughout the boreal regions of North America 

and Eurasia, and is represented in North America by H. umbellatum L., H. 

robinsonii Zahn, and H. canadense Michx. (considered part of 

Chionoracium by Gaskin and Wilson, 2007). 

Subgenus Chionoracium is restricted to the New World and contains most 

of our native taxa. Conflicting characters used to distinguish species have 

generated considerable debate regarding classification. For example, 

Guppy (1978) suggested that H. scouleri Hook., H. albertinum Farr., and 

H. cynoglossoides L. are too closely correlated in characters to be 

distinguished into separate species and, instead, form a complex of 

species. Guppy (1978) also suggested that H. umbellatum L. and its close 

relative, H. canadense Michx., may be two forms of the same species. 

Deardorff (1977) added H. longiberbe Howell and H. nudicale Heller to 

the H. scouleri complex. Kartesz and Meacham (1999) provided a 

comprehensive synthesis of Hieracium spp. in America north of Mexico in 

which they list 108 species, subspecies, and hybrids, clearly giving 

evidence of the myriad of described taxa in the genus.
12

Ten additional hawkweed species found in the United States and Canada 

are introduced from Europe and belong to two subgenera. Four species 

belong to the subgenus Hieracium: H. argillaceum Jordan group, H. 

groenlandicum Arv.-Touv., H. lachenalii K.C. Gmel., H. murorum L., and 

H. sabaudum L. Plants in this subgenus, except for H. lachenalii, have not 

become weedy in North America. The remaining six species belong to the 

subgenus Pilosella and include the species targeted for biological control 

by A. subterminalis.

Species that were used in testing the specificity of A. subterminalis to 

hawkweeds are listed in appendix 1.

IV. Environmental Consequences

A. No Action

Most invasive hawkweeds are perennial, creeping stoloniferous plants that 

can crowd out competing vegetation. They are not drought tolerant and 

cannot withstand prolonged periods of drying. However, they are very 

cold tolerant and easily persist at higher elevation, making the upland 

habitats through the Rocky Mountains and other western mountain ranges 

susceptible to invasion. In northern Idaho and British Columbia, habitats 

are open ponderosa pine and interior cedar-hemlock. There are no known 

medicinal or herbal uses for the invasive hawkweeds, nor do they have any 

known social or recreational uses. 

Invasive hawkweeds do affect threatened, endangered, and sensitive 

species because of their ability to form dense monocultures. One such 

example is encroachment by mouse-ear hawkweed of habitat occupied by 

the threatened golden paintbrush, Castilleja levisecta, in Thurston County, 

Washington (USFWS, 1997). These monocultures compete for soil 

moisture and nutrients, thereby posing risks to indigenous species. As 

hawkweed monocultures invade species-rich range and mountain habitats, 

ecosystem functions and ecological relationships are affected. No known

studies specifically address the effects of hawkweed on nutrient cycling 

and disturbance regimes; however, hawkweed’s ability to dominate a 

community suggests that these species do affect habitat function. 

Hawkweeds generally negatively impact plant and animal diversity, and 

there is serious concern about the loss of native plant biodiversity in 

infested areas. Ecological losses in plant and animal diversity can be 

enormous but cannot be economically calculated. Additional expenditures 

result from control costs. Hawkweeds are tenacious invaders and, once 

established, quickly develop into a patch that continues to expand until it 

covers the site with a solid mat of rosettes. Forage species in pastures and 

abandoned farmland are choked out by the advancing front of hawkweed. 

Hawkweeds also threaten lawns and gardens. Hawkweeds have been 

1. Impact of 

Spread of 

Invasive 

Hawkweeds
13

reported to have allelopathic effects (inhibition of growth in one species of 

plants by chemicals produced by another species) on neighboring 

vegetation (Dawes and Maravolo, 1973; Makepeace, 1976).

Meadow hawkweed causes severe allergenic reactions. Reactions in 

people closely working with meadow hawkweed include minor skin 

rashes, sneezing, congestion, and difficulty in breathing. Similar effects 

have not been reported in animals. It is not known what portion of the 

plant causes this allergenic reaction, although latex and other chemicals of 

closely related Asteraceae plants can cause dermatitis (Dawes et al., 1996). 

Invasive hawkweeds have not been placed on the Federal Noxious Weed 

List but have been listed as noxious in Idaho, Montana, Washington, and 

British Columbia. Regulations vary by State/Province but generally 

involve actions such as restricted importation and/or quarantine and 

prevention, containment, eradication, or other control measures.

The continued use of chemical herbicides, and mechanical and biological

controls at current levels would be a result if the ―no action‖ alternative is 

chosen. These environmental consequences may occur even with the 

implementation of the biological control alternative, depending on the 

efficacy of A. subterminalis to reduce invasive hawkweed populations in 

the Continental United States. 

a. Chemical Control

The use of herbicides, while effective, is limited to relatively accessible 

sites and control is only temporary. Broadcast applications of herbicides 

could have adverse impacts on nontarget vegetation if not carefully 

applied. 

b. Mechanical Control

Disturbance of hawkweeds by machinery spreads the weeds across the 

field. Local disturbances caused by grazing livestock, ungulates, and 

rodents also enhance the rate of spread of hawkweed. In lawns, mowing 

does not kill invasive hawkweeds because the low lying stolons and 

rhizomes are missed by the mower blades. Although mowing prevents 

seed production by removing flowering stems, repeated mowing 

encourages faster vegetative spread. 

c. Biological Control

No organisms for the biological control of hawkweeds have been released 

in North America. Gall formation by A. subterminalis diverts plant 

nutrients from the normal growth of other plant tissues. Under certain 

2. Impact from 

Use of Other 

Control 

Methods
14

conditions, galls may stress the plant, reducing competitive ability, seed 

production, and long distance spread of the weed.

B. Issue Permits for Environmental Release of A. 

subterminalis

Host specificity of A. subterminalis to the invasive hawkweeds Hieracium 

pilosella, H. aurantiacum, H. floribundum, and H. flagellare has been 

demonstrated through scientific literature, field observations, and host 

specificity testing. If an insect species only attacks one or a few closely 

related plant species, the insect is considered to be very host-specific. 

Host specificity is an essential trait for a biological control organism 

proposed for environmental release.

a. Scientific Literature

In previous literature, A. subterminalis has only been reported to induce 

galls on H. pilosella and has not been recorded from any other species 

(Syrett et al., 1998).

b. Field Observations 

In the field, A. subterminalis has not been observed or reported on any 

species other than H. pilosella (Syrett et al., 1998). 

c. Host Specificity Testing

Host specificity tests are tests to determine how many plant species A. 

subterminalis attacks/eats, and whether nontarget species may be at risk. 

In host specificity testing (Syrett et al., 1998; 2001; Grosskopf et al., 2001, 

Littlefield et al., 2008), gall formation by A. subterminals only occurred on 

invasive hawkweed species targeted for biological control. No native 

hawkweeds or plant species of closely related genera were attacked. 

(1) Site of Quarantine and Field Studies

Laboratory tests were conducted at the CABI-Europe Station in Delémont, 

Switzerland, at the insect containment facility located at the Canterbury 

Agriculture and Science Centre, Lincoln, New Zealand, and in quarantine 

facilities at Montana State University (MSU), Bozeman, Montana. Openfield releases began in 1999 in New Zealand.

(2) Test Plant List

The list of plant species used for host specificity testing of A. 

subterminalis is shown in appendix 1. The strategy used for selecting 

1. Impact of A. 

subterminalis

on Nontarget 

Plants
15

plants for testing is based on the phylogenetic approach, where closely 

related species are theorized to be at greater risk of attack than are 

distantly related species (Wapshere, 1974). 

The initial host specificity testing of A. subterminalis was conducted for 

the field release of the wasp in New Zealand. Plants utilized for testing 

were selected from the following categories (Syrett et al., 1998): 

• representatives of the plant family Asteraceae (the family to which 

hawkweeds belong);

• plant species on which the gall wasp has been recorded in the field;

• cultivated plant species and representatives of New Zealand native plant 

species (various non-Asteraceae families) that have not previously been 

exposed to the wasp; and 

• plant species that are hosts of close relatives of A. subterminalis, that is,

hosts of other species of Aulacidea.

Host specificity testing at the CABI-Europe Station, Delémont, and at the 

Canterbury Agriculture and Science Centre, Lincoln, New Zealand,

consisted of eight species within the genus Hieracium, including five from 

the subgenus Pilosella and three from the subgenus Hieracium. Thirteen 

additional species from the tribe Lactuceae were tested, including native 

New Zealand plant species that would not previously have been 

encountered by the wasp (Knightia excelsa, Raoulia hookeri, Kirkianella 

novae-zelandiae, Celmisia lyalli, Helichrysum bellidioides, Gaultheria 

depressa, and Discaria toumatou). A further 11 species within the family 

Asteraceae were tested, including economically significant cultivated plant 

species. Species from 21 other families containing important cultivated 

and native plants were also included, making a total test plant list of 

48 species.

Plants for testing the host range of A. subterminalis were selected from 

seven possible categories. Test categories consisted of the following:

CATEGORY 1: Genetic types of Hieracium (varieties, races, forms, 

genotypes, apomicts, etc.).

CATEGORY 2: North American species in the same genus as Hieracium, 

divided by subgenera, including economically and 

environmentally important plants.

CATEGORY 3: North American species in other genera in the Asteraceae 

family, divided by subtribe, tribe, and subfamily, 

including economically and environmentally important 

plants.
16

CATEGORY 4: Threatened and endangered species in the Asteraceae 

family, divided by subgenus, genus, subfamily, and tribe.

CATEGORY 5: North American species in other families in the Asterales 

order that have some phylogenetic, morphological, or 

biochemical relationship to the target weed, including 

economically and environmentally important plants.

CATEGORY 6: North American species in other orders that have some 

morphological or biochemical relationship to the target 

weed, including economically and environmentally 

important plants.

CATEGORY 7: Any plant on which the biological control agent or its 

close relatives (within the same genus) have been 

previously recorded to feed and/or reproduce.

(See appendix 2 for a more detailed description of plants selected in each 

category.)

Host specificity testing of A. subterminalis at MSU and CABI-Europe 

included as many native North American representatives of the various 

taxa as possible. Aulacidea subterminalis was tested on 65 plant species 

of which 35 are species native to North America (appendix 1). 

(3) Discussion of Host Specificity Testing

New Zealand Tests—In overseas testing, Syrett et al. (1998 and 2001) 

and Grosskopf et al. (2001) reported gall formation on H. pilosella and H. 

aurantiacum but not on other tested plant species, while Grosskopf and 

Senhadji Navarro (2004) reported gall formation on H. pilosella but not on 

H. aurantiacum or other tested plant species.

North American Tests—During the North American host specificity 

test, galls were only induced on four exotic species: H. pilosella (its native 

host), H. aurantiacum, H. flagellare, and H. floribundum (appendix 4). No 

native or other test plants were infested. 

(See appendices 3 and 4 for host specificity study results.)

To assess the impact of A. subterminalis on H. pilosella in New Zealand, 

an experiment was set up to examine the effect of the gall wasp on plant 

growth under stress-free conditions in a shade house trial with potted 

plants (Klöppel et al., 2003). Plants with galls showed a reduction in 

stolon length of 75 percent. They had slightly lower total dry matter and 

reduced root weight. In a glasshouse experiment, the impact of water 

stress, nutrient stress, and plant competition on growth of H. pilosella and 

2. Impact of A. 

subterminalis

on 

Hawkweeds
17

performance of the gall wasp were measured. The number and mean 

diameter of gall clusters were not significantly different between treatment 

and control plants. However, galled plants produced more, but shorter, 

stolons in all stress treatments and stolons that were more branched in 

nutrient- and water-stressed plants, than ungalled plants. Galling by A. 

subterminalis is likely to reduce vegetative reproduction of H. pilosella

whether or not plants are stressed, indicating that the wasp may be a 

successful biocontrol agent (Klöppel et al., 2003).

Researchers expect that A. subterminalis will be able to build up 

substantial populations in North America and, thereby, reduce aboveground biomass and seed output of established invasive hawkweed patches

(Littlefield et al., 2008). It is difficult to predict the long-term impact on 

invasive hawkweed infestations; however, reductions in the above-ground 

growth rate and seed output may lead to reduced competitive ability of the 

weed and reduced patch expansion and long-distance dispersal of invasive 

hawkweed seeds and establishment of new infestations (Littlefield et al.,

2008).

Once a biological control agent such as A. subterminalis is released into 

the environment and becomes established, there is a slight possibility that 

it could move from the target plants (invasive hawkweeds) to attack 

nontarget plants. Host shifts by introduced weed biological control agents 

to unrelated plants are rare (Pemberton, 2000). Native species that are 

closely related to the target species are the most likely to be attacked 

(Louda et al., 2003). If other plant species were to be attacked by A. 

subterminalis, the resulting effects could be environmental impacts that 

may not be easily reversed. Biological control agents such as A. 

subterminalis generally spread without intervention by man. In principle, 

therefore, release of this biological control agent at even one site must be 

considered equivalent to release over the entire area in which potential 

hosts occur, and in which the climate is suitable for reproduction and 

survival.

In addition, this agent may not be successful in reducing hawkweed 

populations in the continental United States. Worldwide, biological weed 

control programs have had an overall success rate of 33 percent; success 

rates have been considerably higher for programs in individual countries 

(Culliney, 2005). Actual impacts on hawkweeds by A. subterminalis will 

not be known until after release occurs and post-release monitoring has 

been conducted. It is expected that A. subterminalis will reduce invasive 

hawkweed populations by reducing above-ground biomass and seed output 

of established invasive hawkweed patches.

A. subterminalis is a wasp but it does not sting or produce venom. It is a 

plant-feeding wasp which poses no risk to humans or other animals. 

3. Uncertainties 

Regarding the 

Environmental 

Release of A. 

subterminalis

4. Human Health
18

―Cumulative impacts are defined as the impact on the environment which 

results from the incremental impact of the action when added to other past, 

present and reasonably foreseeable future actions regardless of what 

agencies or person undertakes such other actions‖ (40 CFR 1508.7).

Many Federal and State agencies, as well as private entities, conduct 

programs to manage hawkweeds, as well as other invasive weeds. 

Chemical and mechanical methods, as described previously in this 

document, are used in a wide range of habitats. Some of these control 

programs in Idaho, Washington, Montana, Oregon, and Alaska are listed 

below. 

Idaho—

Idaho Department of Lands 

Kootenai County Weed Board 

Palouse Clearwater Cooperative Weed Management Area 

Panhandle Lakes Cooperative Weed Management Area

Potlach Corporation 

U.S. Department of Interior (USDI), Bureau of Land Management 

Rimrock Hawkweed Cooperative 

Selkirk Cooperative Weed Management Area 

Benewah County Weed Board 

Pend Oreille County Weed Board 

Washington—

Washington State Weed Board 

Stevens County Weed Board 

King County Weed Board

Montana—

Gallatin National Forest

Lolo National Forest

Bitterroot National Forest

Flathead National Forest

Kootenai National Forest

Glacier National Park 

U.S. Fish and Wildlife Service–Lost Trail Refuge

USDI, Bureau of Land Management 

Lincoln County Weed Department

Flathead County Weed Department

Flathead County Extension

Ravalli County Weed Department

Sanders County Extension

Missoula County Weed Department

Mineral County Weed Department

Lake County Weed Department

Glacier County Weed Department

5. Cumulative 

Impacts
19

Montana cont’d. —

Granite County Weed Department

Powell County Weed Department

Gallatin County Weed District

Judith Basin Weed District

Big Sky Weed Management Area

Montana Department of Agriculture

Montana Noxious Weed Trust Fund 

Montana Department of Natural Resources and Conservation

Confederated Salish Kootenai Tribe

Plum Creek Timber Company

Oregon—

Oregon Department of Agriculture

Union County Weed Control

Deschute County Weed Control

Wallowa County Weed Control 

Asotin County Weed Control

East Multnomah Soil and Water Conservation District

Wallowa Whitman National Forest

Alaska—

Kodiak National Wildlife Refuge

Homer Soil and Water Conservation District

Kodiak Garden Club

Koniag Native Corporation

University of Alaska Fairbanks Cooperative Extension Service

Upper Susitna Soil and Water Conservation District

Juneau Invasive Plants Action

Release of A. subterminalis is not expected to have any negative 

cumulative impacts in the continental United States because of its host 

specificity to invasive hawkweeds. Effective biological control of invasive 

hawkweeds will have beneficial effects for weed management programs, 

and may result in a long-term, non-damaging method to assist in the 

control of hawkweeds.

Section 7 of the Endangered Species Act (ESA) and ESA’s implementing 

regulations require Federal agencies to ensure that their actions are not 

likely to jeopardize the continued existence of federally listed threatened 

and endangered species or result in the destruction or adverse modification 

of critical habitat. 

The adverse effects of hawkweed invasion on threatened and endangered 

species is not fully known; however, it can be assumed that invasive 

hawkweeds do affect threatened, endangered, and sensitive species 

because of their ability to form dense monocultures. One such example is 

6. Endangered 

Species Act
20

encroachment by mouse-ear hawkweed into habitat occupied by the 

threatened golden paintbrush, Castilleja levisecta, in Thurston County, 

Washington (USFWS, 1997). These hawkweed monocultures compete for 

soil moisture and nutrients, thereby posing risks to native plant species. 

As hawkweed monocultures invade species-rich range and mountain 

habitats, it is thought that ecosystem functions and ecological relationships 

are affected (Littlefield et al., 2008). 

Host specificity has been demonstrated by A. subterminalis. From the 

literature, field observations, and host specificity testing, it has been 

determined that A. subterminalis is specific to species in the genus 

Hieracium, subgenus Pilosella (Littlefield et al., 2008). There are no 

Hieracium species federally listed as threatened or endangered. No 

federally listed animal species are known to use invasive hawkweeds. 

For these reasons, APHIS has determined that environmental release of A. 

subterminalis will have no effect, or a potentially beneficial effect, 

depending on the efficacy of the organism, on threatened and endangered 

species.

V. Other Issues

Consistent with Executive Order (EO) 12898, ―Federal Actions to Address 

Environmental Justice in Minority Populations and Low-income 

Populations,‖ APHIS considered the potential for disproportionately high 

and adverse human health or environmental effects on any minority 

populations and low-income populations. There are no adverse 

environmental or human health effects from the field release of A. 

subterminalis and will not have disproportionate adverse effects to any 

minority or low-income populations. 

Consistent with EO 13045, ―Protection of Children From Environmental 

Health Risks and Safety Risks,‖ APHIS considered the potential for 

disproportionately high and adverse environmental health and safety risks 

to children. No circumstances that would trigger the need for special 

environmental reviews are involved in implementing the preferred 

alternative. Therefore, it is expected that no disproportionate effects on 

children are anticipated as a consequence of the field release of A. 

subterminalis.

EO 13175, ―Consultation and Coordination with Indian Tribal 

Governments,‖ was issued to ensure that there would be ―meaningful 

consultation and collaboration with tribal officials in the development of 

Federal policies that have tribal implications....‖
21

APHIS is consulting and collaborating with Indian tribal officials to ensure 

that they are well-informed and represented in policy and program 

decisions that may impact their agricultural interests in accordance with 

EO 13175.
22

VI. Agencies, Organizations, and 

Individuals Consulted

The Technical Advisory Group for the Biological Control Agents of 

Weeds (TAG) recommended the release of A. subterminalis on August 10, 

2009. TAG members that reviewed the release petition (Littlefield et al., 

2008) included representatives from APHIS, Cooperative State Research, 

Education, and Extension Service, Forest Service, Environmental 

Protection Agency, U.S. Army Corps of Engineers, the National Plant 

Board, and representatives from Canada. 

This EA was prepared and reviewed by APHIS. The addresses of 

participating APHIS units, cooperators, and consultants (as applicable) 

follow.

U.S. Department of Agriculture

Animal and Plant Health Inspection Service

Policy and Program Development 

Environmental Services

4700 River Road, Unit 149

Riverdale, MD 20737

U.S. Department of Agriculture

Animal and Plant Health Inspection Service

Plant Protection and Quarantine 

Pest Permitting

4700 River Road, Unit 133

Riverdale, MD 20737

Montana State University

Department of Land resources and Environmental Sciences

P.O. Box 173120

Bozeman, MT 59717–3020
23

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29

Appendix 1. Plant species tested during A. subterminalis host specificity trials (excluding NZ tests). Asteraceae species are listed 

by family, subfamily, tribe, and subtribe with species listed alphabetically within tribes. Common names, State distributions, growth 

habits, durations, and U.S. nativities are from the USDA–NRCS Plants Database (2008) and Canadian from Flora of North America 

North of Mexico (1993) (from Littlefield et al., 2008).

Family

Subfamily

Tribe

Subtribe

Scientific Name Common Name U.S. - State Distribution

Canada - Province Distribution

Growth 

Habit

Duration U.S.

Nativity

Test 

Category1

Asteraceae

Cichorioideae

Lactuceae

Microseridinae

Agoseris glauca pale agoseris AK, AZ, CA, CO, IA, ID, MI, MN, MT, ND, NE, 

NM, NV, OR, SD, UT, WA, WY

AB, BC, MB, NT, ON, SK, YT

Forb/herb

Shrub

Subshrub

Perennial Native 3b

Asteraceae

Cichorioideae

Lactuceae

Microseridinae

Agoseris grandiflora bigflower 

agoseris

CA, ID, MT, NV, OR, UT, WA

BC

Forb/herb Perennial Native 3b

Asteraceae

Cichorioideae

Lactuceae

Catananchinae

Catananche caerulea Cupid’s Dart Cultivated Forb/herb Perennial Cultivated 3b

Ornamental

Asteraceae

Cichorioideae

Lactuceae

unassigned

Cichorium intybus chicory AL, AR, AZ, CA, CO, CT, DC, DE, FL, GA, IA, 

ID, IL, IN, KS, KY, LA, MA, MD, ME, MI, MN, 

MO, MS, MT, NC, ND, NE, NH, NJ, NM, NV, 

NY, OH, OK, OR, PA, RI, SC, SD, TN, TX, UT, 

VA, VT, WA, WI, WV, WY

AB, BC, MB, NB, NF, NS, ON, PE, PQ, SK

Forb/herb Biennial

Perennial

Introduced 3b

Economic

Asteraceae

Cichorioideae

Lactuceae

Crepidinae

Crepis atribarba slender 

hawksbeard

CO, ID, MT, NE, NV, OR, UT, WA, WY

AB, BC, SK

Forb/herb Perennial Native 3b

Asteraceae

Cichorioideae

Lactuceae

Crepidinae

Crepis biennis hawksbeard MI, NY, OH, PA, VA, VT

NF

Forb/herb Biennial

Perennial

Introduced 3b

Asteraceae

Cichorioideae

Lactuceae

Hieraciinae

Hieracium albiflorum white hawkweed AK, CA, CO, ID, MT, NV, OR, SD, UT, WA, WI, 

WY 

AB, BC, NT, PQ, SK

Forb/herb Perennial Native 2

Asteraceae Hieracium argutum southern CA Forb/herb Perennial Native 2
30

Family

Subfamily

Tribe

Subtribe

Scientific Name Common Name U.S. - State Distribution

Canada - Province Distribution

Growth 

Habit

Duration U.S.

Nativity

Test 

Category1

Cichorioideae

Lactuceae

Hieraciinae

hawkweed

Asteraceae

Cichorioideae

Lactuceae

Hieraciinae

Hieracium aurantiacum orange 

hawkweed

AK, AR, CA, CO, CT, FL, GA, IA, ID, IL, IN, 

MA, MD, ME, MI, MN, MT, NC, NH, NJ, NY, 

OH, OR, PA, RI, SD, TN, VA, VA, VT, WA, WI, 

WV, WY

AB, BC, LB, MB, NB, NF, NS, ON, PE, PQ, SK

Forb/herb Perennial Introduced 1

Asteraceae

Cichorioideae

Lactuceae

Hieraciinae

Hieracium bolanderi Bolander’s 

hawkweed

CA, OR Forb/herb Perennial Native 2

Asteraceae

Cichorioideae

Lactuceae

Hieraciinae

Hieracium caespitosum meadow 

hawkweed

CT, DC, GA, ID, IL, IN, KY, MA, MD, ME, MI,

MN, MT, NC, NH, NJ, NY, OH, OR, PA, RI, 

SC, TN, VA, VT, WA, WI, WV, WY

BC, MB, NB, NF, NS, ON, PE, PQ

Forb/herb Perennial Introduced 1

Asteraceae

Cichorioideae

Lactuceae

Hieraciinae

Hieracium canadense Canadian 

hawkweed

MI, ME

AB, BC, LB, MB, NB, NF, NS, NT, ON, PE, PQ, 

SK, YT

Forb/herb Perennial Native 2

Asteraceae

Cichorioideae

Lactuceae

Hieraciinae

Hieracium carneum Huachuca 

hawkweed

AZ, NM, TX Forb/herb Perennial Native 2

Asteraceae

Cichorioideae

Lactuceae

Hieraciinae

Hieracium fendleri yellow hawkweed AZ, CO, NM, TX, VT, WY Forb/herb Perennial Native 2

Asteraceae

Cichorioideae

Lactuceae

Hieraciinae

Hieracium flagellare large 

mouseeared 

CT, DE, IN, MA, ME, MI, NJ, NH, NY, OH, PA, 

VA, VT, WY 

BC, NB, NS, PE, PQ

Forb/herb Perennial Introduced 2

Asteraceae

Cichorioideae

Lactuceae

Hieraciinae

Hieracium floribundum king devil CT, ID, MA, MD, ME, MI, MN, MT, NH, NJ, NY, 

OH, RI, VA, VT, WA, WV, WY

BC

Forb/herb Perennial Introduced 1
31

Family

Subfamily

Tribe

Subtribe

Scientific Name Common Name U.S. - State Distribution

Canada - Province Distribution

Growth 

Habit

Duration U.S.

Nativity

Test 

Category1

Asteraceae

Cichorioideae

Lactuceae

Hieraciinae

Hieracium glomeratum queen-devil WA, ID

BC

Forb/herb Perennial Introduced 2

Asteraceae

Cichorioideae

Lactuceae

Hieraciinae

Hieracium gracile slender 

hawkweed

AK, CA, CO, ID, MT, NM, OR, UT, WA, WY

AB, BC, NT, YT

Forb/herb Perennial Native 2

Asteraceae

Cichorioideae

Lactuceae

Hieracium greenei Greene’s 

hawkweed

CA, OR Forb/herb Perennial Native 2

Asteraceae

Cichorioideae

Lactuceae

Hieraciinae

Hieracium gronovii queen devil AL, AR, CT, DC, DE, FL, GA, IL, IN, KS, KY, 

LA, MA, MD, ME, MI, MO, MS, NC, NJ, NY, 

OH, OK, PA, RI, SC, TN, TX, VA, WY

ON

Forb/herb Perennial Native 2

Asteraceae

Cichorioideae

Lactuceae

Hieraciinae

Hieracium horridum prickly hawkweed CA, NV, OR Forb/herb Perennial Native 2

Asteraceae

Cichorioideae

Lactuceae

Hieraciinae

Hieracium longiberbe longbeard 

hawkweed

OR, WA Forb/herb Perennial Native 2

Asteraceae

Cichorioideae

Lactuceae

Hieraciinae

Hieracium longipilum hairy hawkweed AR, IA, IL, IN, KS, KY, LA, MI, MN, MO, NE, 

OH, OK, TN, TX, WI

ON

Forb/herb Perennial Native 2

Asteraceae

Cichorioideae

Lactuceae

Hieraciinae

Hieracium parryi Scouler’s 

woollyweed

CA, ID, MT, NV, OR, WA, WY Forb/herb Perennial Native 2

Asteraceae

Cichorioideae

Lactuceae

Hieraciinae

Hieracium pilosella mouseear 

hawkweed

CT, GA, MA, ME, MI, MN, NC, NH, NJ, NY, 

OH, OR, PA, RI, TN, VA, VT, WA

BC, NB, NF, NS, ON, PQ

Forb/herb Perennial Introduced 1
32

Family

Subfamily

Tribe

Subtribe

Scientific Name Common Name U.S. - State Distribution

Canada - Province Distribution

Growth 

Habit

Duration U.S.

Nativity

Test 

Category1

Asteraceae

Cichorioideae

Lactuceae

Hieraciinae

Hieracium piloselloides yellow devil 

hawkweed

CT, DE, GA, IA, IL, IN, MA, ME, MI, MN, MT, 

NC, NH, NJ, NY, OH, PA, RI, VA, VT, WA

BC, NB, NF, NS, ON, PE, PQ

Forb/herb Perennial Introduced 1

Asteraceae

Cichorioideae

Lactuceae

Hieraciinae

Hieracium scabrum rough hawkweed AR, CT, DC, DE, GA, IA, IL, IN, KY, MA, MD, 

ME, MI, MN, MO, NC, NH, NJ, NY, OH, OK, 

PA, RI, SC, TN, VA, VT, WI

NB, NS, ON, PE, PQ

Forb/herb Perennial Native 2

Asteraceae

Cichorioideae

Lactuceae

Hieraciinae

Hieracium scouleri var. 

albertinum

western 

hawkweed

ID, MT, OR, WA, WY

BC

Forb/herb Perennial Native 2

Asteraceae

Cichorioideae

Lactuceae

Hieraciinae

Hieracium scouleri var. 

cynoglossoides

houndstongue 

hawkweed

CA, ID, OR, WA

BC

Forb/herb Perennial Native 2

Asteraceae

Cichorioideae

Lactuceae

Hieraciinae

Hieracium scouleri var. 

scouleri

Scouler’s 

woollyweed

CA, ID, MT, NV, OR, WA, WY Forb/herb Perennial Native 2

Asteraceae

Cichorioideae

Lactuceae

Hieraciinae

Hieracium stoloniflorum Not Present in United States or Canada 2

Asteraceae

Cichorioideae

Lactuceae

Hieraciinae 

Hieracium umbellatum narrowleaf 

hawkweed

AK, CO, IA, ID, IL, IN, MI, MN, MO, MT, ND, 

NE, NH, OR, SD, WA, WI, WV, WY

AB, BC, LB, MB, NB, NF, NS, NT, ON, PE, PQ, 

SK, YT

Forb/herb Perennial Native 2

Asteraceae

Cichorioideae

Lactuceae

Hieraciinae

Hieracium venosum rattlesnakeweed AL, CT, DC, DE, FL, GA, IN, KY, MA, MD, ME, 

MI, MO, MS, NC, NH, NJ, NY, OH, PA, RI, SC, 

TN, VA, VT, WY

ON

Forb/herb Perennial Native 2

Asteraceae

Cichorioideae

Lactuceae

Hypochaeris radicata hairy catsear AK, AL, AR, CA, CO, CT, DC, DE, FL, GA, HI, 

ID, IL, IN, KY, LA, MA, MD, ME, MI, MO, MS, 

MT, NC, NH, NM, NJ, NV, NY, OH, OR, PA, 

Forb/herb Perennial Introduced 3b
33

Family

Subfamily

Tribe

Subtribe

Scientific Name Common Name U.S. - State Distribution

Canada - Province Distribution

Growth 

Habit

Duration U.S.

Nativity

Test 

Category1

Hypochaeridinae RI, SC, TN, TX, UT, VA, VT, WA, WI, WV

BC, LB, NF

Asteraceae

Cichorioideae

Lactuceae

Microseridinae

Krigia biflora twoflower 

dwarfdandelion

AL, AR, AZ, CO, CT, DE, GA, IA, IL, IN, KS, 

KY, MA, MD, MI, MN, MO, MS, NC, NJ, NM, 

NY, OH, OK, PA, TN, VA, WI, WV

ON

Forb/herb Perennial Native 3b

Asteraceae

Cichorioideae

Lactuceae

Lactucinae

Lactuca sativa garden lettuce AL, CA, DC, DE, ID, IL, IN, MA, ME, MI, MO, 

ND, NM, NY, OH, OK, OR, PA, WA, WV, 

Puerto Rico, Virgin Islands 

Forb/herb Annual

Biennial

Perennial

Introduced 3b

Economic

Asteraceae

Cichorioideae

Lactuceae

Lactucinae

Lactuca serriola prickly lettuce AL, AR, AZ, CA, CO, CT, DC, DE, FL, GA, HI, 

IA, ID, IL, IN, KS, KY, LA, MA, MD, ME, MI, 

MN, MO, MS, MT, NC, ND, NE, NH, NJ, NM, 

NV, NY, OH, OK, OR, PA, RI, SC, SD, TN, TX, 

UT, VA, VT, WA, WI, WV, WY

 AB, BC, MB, NB, NS, ON, PE, PQ, SK

Forb/herb Annual

Biennial

Introduced 3b

Asteraceae

Cichorioideae

Lactuceae

Lactucinae

Lactuca virosa bitter lettuce AL, CA, DC Forb/herb Annual

Biennial

Introduced 3b

Asteraceae

Cichorioideae

Lactuceae

Stephanomeriinae

Lygodesmia juncea rush 

skeletonplant

AR, AZ, CO, IA, ID, IN, KS, MN, MO, MT, ND, 

NE, NM, NV, OK, OR, SD, TX, UT, WA

AB, BC, MB, SK

Forb/herb Perennial Native 3b

Asteraceae

Cichorioideae

Lactuceae

Microseridinae

Microseris nutans nodding 

microseris

CA, CO, ID, MT, NV, OR, SD, UT, WA, WY

AB, BC

Forb/herb Perennial Native 3b

Asteraceae

Cichorioideae

Lactuceae

Lactucinae

Prenanthes racemosa purple 

rattlesnakeroot

CO, IA, IL, IN, KY, ME, MI, MN, MO, MT, ND, 

NE, NJ, NY, OH, PA, SD, WI, WY

AB, BC, MB, NB, NF, NS, ON, PE, PQ, SK

Forb/herb Perennial Native 3b

Asteraceae

Cichorioideae

Lactuceae

Sonchus asper spiny sowthistle AK, AL, AR, AZ, CA, CO, CT, DC, DE, FL, GA, 

HI, IA, ID, IL, IN, KS, KY, LA, MA, MD, ME, MI, 

MN, MO, MS, MT, NC, ND, NE, NH, NJ, NM, 

Forb/herb Annual Introduced 3b
34

Family

Subfamily

Tribe

Subtribe

Scientific Name Common Name U.S. - State Distribution

Canada - Province Distribution

Growth 

Habit

Duration U.S.

Nativity

Test 

Category1

Sonchinae NV, NY, OH, OK, OR, PA, RI, SC, SD, TN, TX, 

UT, VA, VT, WA, WI, WV, WY, Puerto Rico

AB, BC, LB, MB, NB, NF, NS, ON, PE, PQ, SK, 

YT

Asteraceae

Cichorioideae

Lactuceae

Sonchinae

Sonchus arvensis field sowthistle AK, CA, CO, CT, DC, DE, IA, ID, IL, IN, KS, 

KY, LA, MA, MD, ME, MI, MN, MO, MS, MT, 

NC, ND, NE, NH, NJ, NM, NV, NY, OH, OR, 

PA, RI, SD, TN, TX, UT, VA, VT, WA, WI, WV, 

WY

AB, BC, MB, NB, NF, NS, NT, ON, PE, PQ, 

SK, YT

Forb/herb Perennial Introduced 3b

Asteraceae

Cichorioideae

Lactuceae

Sonchinae

Sonchus oleraceus common 

sowthistle

AK, AL, AR, AZ, CA, CO, CT, DC, DE, FL, GA, 

HI, IA, ID, IL, IN, KS, KY, LA, MA, MD, ME, MI, 

MN, MO, MS, MT, NC, ND, NE, NH, NJ, NM, 

NV, NY, OH, OK, OR, PA, RI, SC, SD, TN, TX, 

UT, VA, VT, WA, WI, WV, WY, Puerto Rico, 

Virgin Islands

AB, BC, MB, NB, NF, NS, ON, PE, PQ, SK, 

YT

Forb/herb Annual Introduced 3b

Asteraceae

Cichorioideae

Lactuceae

Stephanomeriinae

Stephanomeria 

cichoriacea

chicoryleaf 

wirelettuce

CA Forb/herb

Subshrub

Perennial Native 3b

Asteraceae

Cichorioideae

Lactuceae

Stephanomeriinae

Stephanomeria minor lesser wirelettuce AZ, CA, CO, ID, MT, ND, NM, NV, OR, TX, UT, 

WA, WY

BC, SK

Forb/herb

Subshrub

Perennial Native 3b

Asteraceae

Cichorioideae

Lactuceae

Crepidinae

Taraxacum officinale common 

dandelion

AK, AL, AR, AZ, CA, CO, CT, DC, DE, FL, 

GA,HI, IA, ID, IL, IN, KS, KY, LA, MA, MD, 

ME, MI, MN, MO, MS, MT, NC, ND, NE, NH, 

NJ, NM, NV, NY, OH, OK, OR, PA, RI, SC, SD, 

TN, TX, UT, VA, VT, WA, WI, WV, WY, Puerto 

Rico

AB, BC, LB, MB, NB, NF, NS, NT, NU, ON, PE, 

Forb/herb Perennial Native

Introduced

3b
35

Family

Subfamily

Tribe

Subtribe

Scientific Name Common Name U.S. - State Distribution

Canada - Province Distribution

Growth 

Habit

Duration U.S.

Nativity

Test 

Category1

PQ, SK, YT

Asteraceae

Cichorioideae

Cardueae

Centaureinae

Acroptilon repens hardheads AR, AZ, CA, CO, IA, ID, IL, IN, KS, KY, MI, 

MN, MO, MT, ND, NE, NM, NV, OH, OK, OR, 

SD, TX, UT, WA, WI, WY

AB, BC, MB, ON, SK

Forb/herb Perennial Introduced 3c

Asteraceae

Cichorioideae

Cardueae

Carduinae

Cirsium arvense Canada thistle AK, AL, AR, AZ, CA, CO, CT, DC, DE, IA, ID, 

IL, IN, KS, KY, MA, MD, ME, MI, MN, MO, MT, 

NC, ND, NE, NH, NJ, NM, NV, NY, OH, OR, 

PA, RI, SD, TN, UT, VA, VT, WA, WI, WV, WY

AB, BC, MB, NB, NF, NS, NT, ON, PE, PQ, 

SK, YT

Forb/herb Perennial Introduced 3c

Asteraceae

Cichorioideae

Cardueae

Carduinae

Cynara scolymus globe artichoke AZ, CA Forb/herb Perennial Introduced 3c

Asteraceae

Asteroideae

Anthemideae

Artemisiinae

Artemisia dracunculus tarragon AK, AZ, CA, CO, IA, ID, IL, KS, MA, MN, MO, 

MT, ND, NE, NM, NV, NY, OK, OR, SD, TX, 

UT, WA, WI, WY

AB, BC, MB, SK, YT

Forb/herb Perennial Native 3d

Economic

Asteraceae

Asteroideae

Anthemideae

Chrysantheminae

Chrysanthemum 

cinerariifolium

pyrethrum Cultivated Forb/herb Perennial Cultivated 3d

Asteraceae

Asteroideae

Eupatorieae

Eupatoriinae

Eupatoriadelphus 

(Eupatorium) 

maculatum

spotted 

trumpetweed

CT,GA, IA, IL, IN, KY, MA, MD, ME, MI, MN, 

NC, NH, NJ, NY, OH, PA, RI, TN, VA, VT, WI, 

WY

MB, NB, NS, ON, PE, PQ

Forb/herb Perennial Native 3d

Asteraceae

Asteroideae

Helenieae

Pectidinae

Tagetes erecta Aztec marigold AR, CA, CT, FL, KY, LA, MA, MD, MO, NC, 

NY, OH, OK, PA, SC, UT, VA, Puerto Rico, 

Virgin Islands

Forb/herb Annual Introduced 3d

Ornamental

Asteraceae

Asteroideae

Heliantheae

Dahlia sp. dahlia Cultivated Forb/herb

Subshrub

Perennial Cultivated 3d

Ornamental
36

Family

Subfamily

Tribe

Subtribe

Scientific Name Common Name U.S. - State Distribution

Canada - Province Distribution

Growth 

Habit

Duration U.S.

Nativity

Test 

Category1

Coreopsidinae

Asteraceae

Asteroideae

Heliantheae

Helianthinae

Helianthus annuus common 

sunflower

AK, AL, AR, AZ, CA, CO, CT, DC, DE, FL, GA, 

HI, IA, ID, IL, IN, KS, KY, LA, MA, MD, ME, MI, 

MN, MO, MS, MT, NC, ND, NE, NH, NJ, NM, 

NV, NY, OH, OK, OR, PA, RI, SC, SD, TN, TX, 

UT, VA, VT, WA, WI, WV, WY, Puerto Rico

AB, BC, MB, NB, NF, NS, NT, ON, PE, PQ, SK

Forb/herb Annual Native 3d

Ornamental

Economic

Asteraceae

Asteroideae

Vernonieae

Vernoniinae

Stokesia laevis Stokes’ Aster AL, FL, GA, LA, MS, NC, SC Forb/herb Perennial Native 3d

Ornamental

Asteraceae

Gnaphalioideae

Gnaphalieae

Cassiniinae

Antennaria dioica stoloniferous 

pussytoes

AK Forb/herb Perennial Native 3d

Asteraceae

Gnaphalioideae

Gnaphalieae

Gnaphaliinae

Gnaphalium audax Not Present in United States or Canada

Liliaceae Allium cepa garden onion AR, CA, CT, IL, IN, KS, KY, LA, MA, ME, MI, 

MO, MS, MT, NC, NH, NY, OH, OR, PA, SC, 

TX, VT, WI 

Forb/herb Perennial Introduced 5

Economic

Asclepiadaceae Asclepias syriaca common 

milkweed

AL, AR, CT, DC, DE, GA, IA, IL, IN, KS, KY, 

LA, MA, MD, ME, MI, MN, MO, MS, MT, NC, 

ND, NH, NE, NJ, NY, OH, OK, OR, PA, RI, SC, 

SD, TN, TX, VA, VT, WI, WV

Forb/herb Perennial Native 5

Chenopodiaceae Beta vulgaris common beet AL, CA, CT, MA, ME, MI, MO, MT, NC, NH, 

NY, OR, PA, SC, TX, UT, VA, WV

Forb/herb Annual

Biennial

Introduced 5

Economic

Lamiaceae Monarda fistulosa wild bergamot AL, AR, AZ, CO, CT, DC, DE, GA, IA, ID, IL, 

IN, KS, KY, LA, MA, MD, ME, MI, MN, MO, 

MS, MT, NC, ND, NE, NH, NJ, NM, NV, NY, 

OH, OK, OR, PA, RI, SC, SD, TN, TX, UT, VA, 

VT, WA, WI, WV, WY

Forb/herb

Subshrub

Perennial Native 5

Papaveraceae Papaver nudicale Iceland poppy Cultivated

AK

Forb/herb Biennial

Perennial

Cultivated 5

Ornamental
37

Family

Subfamily

Tribe

Subtribe

Scientific Name Common Name U.S. - State Distribution

Canada - Province Distribution

Growth 

Habit

Duration U.S.

Nativity

Test 

Category1

YT

Apiaceae Petroselinum crispum parsley AR, CA, CT, FL, GA, HI, IA, ID, KS, LA, MA, 

MD, MI, MS, MT, NC, NV, NY, OH, PA, RI, TX, 

SC, UT, WA, Puerto Rico

Forb/herb Annual

Biennial

Introduced 5

Economic

Fabaceae Pisum sativum garden pea CA, CT, FL, IL, KS, KY, LA, MA, ME, MI, MO, 

MS, NC, NH, NY, OK, OR, PA, SC, UT, VA, 

WA 

Forb/herb

Vine

Annual Introduced 5

Economic

Fabaceae Vicia faba horsebean CA, CT, DC, MA, MD, ME, MT, NY, OR, PA, 

VA, VT, WA

Forb/herb

Vine

Annual Introduced 5

Economic

1

Test Categories: 1. Genetic types of target weed; 2. Species of the same (or closely related) genus; 3. Species in the same family as the target weed (3a. Plants in same subtribe; 3b. 

Plants in same tribe; 3c. Plants in same subfamily; and 3d. Plants in same family); 4. Threatened and endangered species in the same family; and 5. Species in other families.
38

Appendix 2. Description of plants chosen for each category for host specificity testing 

(from Littlefield et al., 2008)

CATEGORY 1:

Genetic types of Hieracium (varieties, races, forms, genotypes, apomicts, etc.).

The natural host of A. subterminalis is mouse-ear hawkweed, H. pilosella. Although specific 

genotypes of H. pilosella were not tested, plants from Europe, New Zealand, and the United 

States (Washington) were tested. In general, a high proportion of these plant collections 

supported gall development (54 to 97 percent), although infestation levels probably varied 

due to testing conditions. Since galls were also induced in other species within the subgenus 

Pilosella, it is thought that A. subterminalis is not highly specialized or limited to a particular 

H. pilosella genotype. Host specificity tests conducted for New Zealand indicated that 

orange hawkweed, H. aurantiacum, also supported gall development and the emergence of 

viable adults. Orange hawkweed is more widespread and abundant in the western United 

States and Canada and, therefore, a more important target weed. North American testing also 

indicated that this plant host is suitable, but perhaps less so compared to H. pilosella. 

Infestation levels varied from 13 to 67 percent. Although H. pilosella appears to be 

genetically diverse (Trewick et al., 2004), H. aurantiacum has a very limited genetic 

diversity, especially for North American populations (Loomis, 2007). Therefore, Littlefield 

et al. (2008) speculate that differences observed in infestations levels were due more to 

environmental conditions than genotypic differences in H. aurantiacum.

CATEGORY 2:

North American species in the same genus as Hieracium, divided by 

subgenera, including economically and environmentally important plants.

2.a. Species in the same subgenus (Pilosella):

This subgenus is not represented in the native flora of North America - all members of this 

subgenus (or genus) are European. For North American testing H. caespitosum, H. 

glomeratum, H. piloselloides, H. stoloniflorum, H. flagellare, and H. floribundum were 

included. Hieracium praealtum was also tested in New Zealand but was not attacked. Galls 

were induced only on H. flagellare and H. floribundum. Gaskin and Wilson (2007) indicated 

two distinct species grouping within the Pilosella. Hieracium flagellare is more closely 

related to both H. pilosella and H. aurantiacum. Hieracium floribundum however, is more 

closely related to the group containing H. caespitosum, H. glomeratum, and H. piloselloides. 

Although H. floribundum was attacked in tests conducted at MSU, it was not infested in 

CABI tests. Hieracium floribundum is thought to be a cross between H. caespitosum and H. 

lactucella, although back crosses with other Hieraciums (e.g. H. aurantiacum) sometimes 

occur (Krahulec et al., 2008). Hieracium stoloniflorum is another cross (H. aurantiacum x 

H. pilosella) (Krahulec et al., 2008), although based upon host utilization of H. pilosella and 

H. aurantiacum in the host specificity tests H. stoloniflorum was expected to be a potential 

host, but no gall induction was observed.
39

2.b. Species in the subgenus Hieracium: 

From the subgenus Hieracium, the North American representative to this subgenus was 

tested, H. umbellatum, and no gall development occurred. Although H. canadense has 

previously been placed in this subgenus, recent work by Gaskin and Wilson (2007) placed 

this species in the subgenus Chionoracium. Other representatives (H. lepidulum, H. 

murorum, and H. sabaudum) to this subgenus were tested by CABI and in New Zealand, but 

not attacked by A. subterminalis. 

The subgenus Hieracium is poorly represented in North America. Hieracium umbellatum is 

Holarctic in distribution and is thought to be a native. Other subgenus Hieracium species in 

North America include H. argillaceum, H. murorum, H. groenlandicum, and H. sabaudum; 

all of which are introduced. However, these species are generally not considered noxious 

weeds. 

Based on host specificity testing, it is unlikely that any plant in this subgenus would be 

utilized as a host by A. subterminalis since none are stoloniferous (produce stolons). A. 

subterminalis attacks and causes galls only in stolons and not other plant parts.

2.c. Species in the subgenus Chionoracium: 

Subgenus Chionoracium is represented throughout North America. Sixteen species 

representative of the geographic range of native species were tested. From the Northwest 

and Intermountain region, H. gracile, H. longiberbe, H. parryi, and H. scouleri var.

albertinum and scouleri, and the white flowered H. albiflorum were tested. From southern 

Oregon and northern California, H. bolanderi, H. horridum, and H. greenei were used. From

California, H. argutum was tested. From the Southwest, H. carneum and H. fendleri were 

tested, and from the East and Midwest, H. longipilum, H. gronovii, H scabrum, and H. 

venosum were tested. Hieracium canadense was also tested and its distributions extend over 

much of the northern United States and southern Canada. None of these species were 

infested by A. subterminalis and none of the hawkweed species associated with the subgenus 

Chionoracium produces stolons in which the gall wasp induces galls. It is highly unlikely 

that A. subterminalis would utilize these plants as hosts.

CATEGORY 3:

North American species in other genera in the Asteraceae family, 

divided by subtribe, tribe, and subfamily, including economically and 

environmentally important plants.

The Asteraceae is the largest plant family and is divided into 3 subfamilies, 17 tribes, and 

numerous subtribes. In developing our list of plants to be tested, we followed the 

reclassification of the Asteraceae by Bremer (1994). 
40

3.a. Species in the same subtribe (Hieraciinae) as Hieracium:

Other genera in the Hieraciinae subtribe include Andryala, Arnoseris, Hispidella, Hololeion, 

and Tolpis. No species from these genera were tested since they are not native to North 

America, nor do they contain any economically important plants in North America (Bremer,

1994). Only two species, Arnoseris minima and Tolpis barbata are reported to occur in the 

United States and Canada (Flora of North America North of Mexico, 2008; USDA-NRCS 

Plants Database 2008). 

3.b. Species in different subtribes of the same tribe (Lactuceae) as Hieracium:

The Lactuceae is one of the best known tribes of the Asteraceae and is well supported as a distinct 

monophyletic group. Subtribal and generic classifications are more defined in this tribe than in most 

other tribes (Bremer, 1994). The Lactuceae are set apart from other Asteraceae by a ligulate 

capitula, milky latex, and absence of oil ducts (except in Scolymus), although none of these 

characteristics are restricted to the Lactuceae alone (Mañez et. al., 1994). Besides the Hieraciinae, 

there are five Lactuceae subtribes that contain species native to North America (Crepidinae, 

Lactucinae, Malcothrinae, Microseridinae, and Stephanomeriinae); four subtribes with introduced

species (Catananchinae, Hypochaeridinae = Leontodontinae, Scorzonerinae, and Sonchinae); and 

two introduced genera (Cichorium and Scolymus) that have not been assigned to a subtribe (Bremer,

1994).

Two genera in the Crepidinae subtribe (Crepis and Taraxacum) contain species native to North 

America (Bremer, 1994). Crepis is an important genus to test because of the number of native and a 

few introduced species in the United States (Flora of North America North of Mexico 2008, USDANRCS, 2008). The two Crepis species we tested were Crepis atribarba (native) and Crepis biennis

(introduced). Taraxacum is another important genus to test because of the presence of native species 

in Western North America (USDA-NCRS, 2008), some of which are threatened, endangered, or 

sensitive (see Category 4). The cosmopolitan species Taraxacum officinale was tested, and in New 

Zealand, T. magellanicum was also tested.

Within the Lactucinae, two genera contain species native to North America: Lactuca and Prenanthes 

(Bremer, 1994; USDA-NRCS, 2008). Lactuca sativa (lettuce) was included because of its economic 

importance. In addition, Lactuca serriola and L. virosa were tested since they are widespread 

weeds. Prenanthes sagittata was tested since it is a native.

The Microseridinae contains the following genera native to North America: Agoseris, Krigia, 

Microseris, Nothocalais, Phalacroseris, Pyrrhopappus, Stebbinsoseris, and Uropappus (Bremer, 

1994; USDA-NCRS, 2008). Four native species: Microseris nutans, Agoseris glauca, A. 

grandifolia, and Krigia biflora were included in tests. In New Zealand, Microseris scapigera was 

used.

The Stephanomeriinae contains the following genera native to North America: Chaetadelpha, 

Lygodesmia, Prenanthella, Rafinesquia, Shinnersoseris, and Stephanomeria (Bremer, 1994; USDA-
41

NCRS, 2008). Three native western species were tested: Lygodesmia juncea, Stephanomeria 

cichoriacea, and S. minor (= S. tenuifolia). 

The Malcothrinae contains the following genera native to North America: Anisocoma, Atrichoseris, 

Calycoseris, Glyptopleura, Malacothrix, and Pinaropappus (Bremer, 1994; Flora of North America 

North of Mexico, 2008; USDA-NCRS, 2008). Most are native to the Southwestern United States, 

except Glyptopleura (western annuals) and Malacothrix (western annuals and perennials). No

species from this subtribe were tested because sources for seeds and/or plant material were 

identified.

Of the four subtribes with introduced species but no natives, Catanache caerula, an introduced 

ornamental from the Catananchinae was included. For the subtribe Sonchinae: Sonchus arvensis, S. 

asper, and S. oleraceus were tested; plus S. kirkii, which was also tested in New Zealand. No

species from the Hypochaeridinae, or Scorzonerinae were included, as these subtribes are not native 

to North America and contain no economically important introduced species (Bremer, 1994; USDANCRS, 2008). Among the introduced genera unassigned to a subtribe, Cichorium intybus (chicory) 

was used in both New Zealand and North American tests because of its economic importance. 

In summary, 26 species belonging to other subtribes within Lactuceae were tested during North 

American and New Zealand host specificity tests. None were utilized by A. subterminalis as a host. 

3.c. Species in different tribes in the same subfamily (Cichorioideae):

According to Bremer (1994), the subfamily Cichorioideae contains three tribes with natives 

in North America (Cardueae, Mutisieae, and Vernonieae) plus a tribe with some introduced 

ornamentals (Arctoteae). The Mutisieae and the Vernonieae are believed to be closely 

related to the Lactuceae (Mañez et al., 1994; Tomb, 1977). Like the Lactuceae, several 

species of Mutisieae and Stokesia have ligulate corollas (Tomb, 1977). Stokesia laevis, a 

native ornamental in the Veronieae was used for testing. From the Cardueae, we used two 

weedy species that can reproduce asexually by lateral roots, Acroptilon repens (Russian 

knapweed) and Cirisium arvense (Canada thistle), as well as Cynara scolymus (globe 

artichoke). Both Carthamus tinctorius (safflower) and globe artichoke were tested from this 

subfamily for the New Zealand tests. Galls were not induced by A. subterminalis on any of 

these species.

3.d. Species in different subfamilies in the same family (Asteraceae): 

Besides the Cichorioideae, there are two additional subfamilies (Barnadesioideae and 

Asteroideae) in the Asteraceae family (Bremer, 1994).

The Barnadesioideae comprise nine genera and are exclusively South American. Because 

there are no species native to North America (Bremer, 1994), no Barnadesioideae were 

included in testing. 
42

The Asteroideae include the majority of the Asteraceae and comprise eight tribes with 

species native to the United States (Anthemideae, Astereae, Eupatorieae, Gnaphalieae, 

Helenieae, Heliantheae, Plucheeae, and Senecioneae), two additional tribes with ornamental 

species (Calenduleae and Inuleae), and eight genera unassigned to a tribe (Bremer, 1994). 

Although acetylenes are relatively rare in the Lactuceae, those which are present belong to a 

special group which may link the Lactuceae chemotaxonomically with the Astereae and the 

Anthemideae (Mabry and Bohlmann, 1977). In combined North American and New Zealand 

tests, 12 species were used representing the eight subtribes of the Asteraceae. Galls were not 

induced on any of these species. 

Category 3 Summary: From testing these 42 species in all of Category 3, Littlefield et al.

(2008) obtained sufficient evidence to conclude that the feeding range of this gall wasp is 

restricted to the genus Hieracium, subgenus Pilosella, and that species in other subfamilies of 

the Asteraceae family are not at significant risk.

CATEGORY 4:

Threatened and endangered species in the Asteraceae family, divided 

by subgenus, genus, subfamily, and tribe.

4.a. Species in the same subgenus (Pilosella):

There are no Hieracium species belonging to subgenus Pilosella listed as threatened, 

endangered, or sensitive.

4.b. Species in the same genus as Hieracium:

While there are no threatened or endangered species of Hieracium in the United States (or 

Canada), several states identify one or more Hiearcium species as being restricted in 

distribution. 

The following is a list of States that list one or more Hiearcium species on their Special 

Plants List (or equivalent). 

Pennsylvania http://www.dcnr.state.pa.us/forestry/pndi/fullplants.asp lists H. kalmii and H. 

trailii. 

Ohio http://www.dnr.state.oh.us/odnr/dnap/heritage/plantlst.html lists H. canadense and H. 

longipilum. 

Utah http://www.nr.state.ut.us/dwr/dwr.htm lists H. fendleri.

In Oregon, the Oregon Natural Heritage Program http://www.heritage.tnc.org/nhp/us/or/vdl.htm lists H. bolanderi, H. greenei, and H. horridum. 
43

Tennessee http://www.state.tn.us/environment/nh/tnplants.html lists H. longipilum, and H. 

scabrum.

Michigan http://www.dnr.state.mi.us/wildlife/heritage/ lists H. longipilum.

Native Hieracium species were selected from across the geographic range of the genus 

throughout North America. All of the Hieracium species native to North America belong the 

subgenus Chionoracium, none of which were infested by A. subterminalis.

4.c. Species in the same subtribe (Hieraciinae) as Hieracium:

There are no threatened, endangered, or sensitive species within the same subtribe as 

Hieracium.

4.d. Species in different subtribes of the same tribe (Lactuceae) as Hieracium:

Four of the Lactuceaae subtribes (besides Hieraciinae) have threatened, endangered, or 

sensitive species in the continental United States (USFWS, 1993; USFWS, 1996). Because 

obtaining plant material of threatened, endangered, and sensitive species can be difficult and 

can further decimate populations, listed species were not tested. Instead, a more common 

member from each genus was selected as a surrogate.

Two Crepidinae species, Taraxacum californicum Munz & Johnston, proposed endangered, 

and T. officinale ssp. ceratophorum (Ledeb.) Schinz ex. Thellung (syn. T. carneocoloratum), 

sensitive, are listed in the continental United States 

(http://www.fws.gov/r9endspp/endspp.html). The more common species Taraxacum 

officinale was tested (listed in Category 3.b.). The Lactucinae has two species of Prenanthes

listed as sensitive [P. barbata (Torr. & Gray) Milstead and P. boottii (DC.) Gray]. The more 

common native species, Prenanthes sagittata, was substituted (listed in Category 3.b.). The 

Microseridinae has two species of Microseris listed as sensitive (M. decipens Chambers and 

M. howellii Gray). The more common native species, Microseris nutans, was tested (listed in 

Category 3.b.). The Stephanomeriinae has one federally endangered Stephanomeria (S. 

malheurensis Gottlieb), one sensitive Stephanomeria (S. blairii Munz. & Johnston) and one 

sensitive Lygodesmia species (L. doloresensis S. Tomb). Instead Stephanomeria minor (= S. 

tenuifolia), S. cichoriacea, and Lygodesmia juncea were tested (listed in Category 3.b.) 

4.e. Species in different tribes in the same subfamily (Cichorioideae):

The Cardueae has several Cirsium species listed as threatened, endangered, or sensitive in the 

continental United States (http://www.fws.gov/r9endspp/endspp.html): Cirsium fontinale var.

fontinale (fountain thistle), Cirsium fontinale var. obispoense (Chorro Creek bog thistle), 

Cirsium hydrophilum var.hydrophilum (Suisun thistle), Cirsium loncholepis (La Graciosa 

thistle), and Cirsium pitcheri (Pitcher's thistle). All but the last species is federally 

endangered, while C. pitcheri is threatened. Because obtaining achenes and/or plant material 

of threatened, endangered, and sensitive species can be difficult and can further decimate 
44

populations, these rare species were not tested. Cirsium arvense, a more common member 

from this genus which also reproduces asexually by lateral roots was selected. 

4.f. Species in different subfamilies in the same family (Asteraceae):

At this level, no representatives from genera with threatened, endangered, or sensitive 

individuals were tested. With over 20 genera with federally listed threatened or endangered 

species and over 70 additional genera with sensitive species in the continental United States, 

the number of species we would need to test is prohibitively large. Testing was conducted on 

representatives to the various subtribes of Asteraceae (Category 3.d). It was evident from 

MSU testing and testing conducted for New Zealand that A. subterminalis was restricted in 

its host range and plants outside the genus Hieracium subgenus Pilosella are not at risk of 

attack by this agent. 

CATEGORY 5:

North American species in other families in the Asterales order that 

have some phylogenetic, morphological, or biochemical relationship to the 

target weed, including economically and environmentally important plants.

Neither Cronquist nor Dahlgren list any families other than the Asteraceae in the Asterales 

order; however, Thorne lists the Calyceraceae as belonging in the Asterales. Cronquist 

places the Calyceraceae in the Calycerales while Dahlgren places it in the Dipsacales. Since 

two out of three systems list the Calyceraceae in an order other than Asterales, this family is 

discussed in Category 6.

CATEGORY 6:

North American species in other orders that have some morphological 

or biochemical relationship to the target weed, including economically and 

environmentally important plants.

6.a. Species in other orders that are phylogenetically related to the Asteraceae:

The Asteraceae form such a well-defined group that they are sometimes considered 

systematically isolated. The most closely related families are generally considered to be the 

Calyceraceae, Campanulaceae sensu lato, and Goodeniaceae (Bremer, 1994). The 

Calyceraceae contain six genera with about 60 species in southern South America (Bremer,

1994). One species, Acicarpha tribuloides, is listed as present in North America (Kartesz 

and Kartesz, 1980). The Campanulaceae sensu lato contain about 85 genera and more than 

2,200 species (Bremer, 1994). There are about 23 genera and 290 species in the United 

States and Canada (Zomlefer, 1994). The Campanulaceae have been shown to be 

chemotaxonomically linked to the Asteraceae (Mabry and Bohlmann, 1977). The 

Goodeniaceae contain 12 genera and 400 predominately Australian species (Bremer, 1994). 

One genus, Scaevola, has 2 species listed as present in the central and southern United States

(USDA-NRCS, 2008). Due to the apparent specificity of A. subterminalis, plants within 

these orders were not tested (Littlefield et al., 2008). 
45

6.b. Species in other orders that are biochemically similar to the Asteraceae:

Species in the Lactuceae are characterized, in part, by their milky latex. However, more than 

12,500 species in 900 genera and 20 families have been identified worldwide that produce 

latex (Metcalfe, 1967). Over 300 species in the United States have been shown to contain 

latex (Buchanan, 1978). The following four latex-producing species from different families 

were selected for testing: Allium cepa, Asclepias syriaca, Monarda fistulosa L., and Papavar 

nudicaule L. All are native or introduced to the western United States. None of these latexproducing species were attacked by A. subterminalis (Littlefield et al., 2008).

The Lactuceae also differ phytochemically in that their sesquiterpene lactones are 

predominately guaianolides, whereas the other Asteraceae subfamilies contain plants with 

considerable portions of other sesquiterpene lactones (Wapshere, 1983). Unlike most other 

Asteraceae, the Lactuceae possess either no or a low level of polyacetylene compounds 

(Sorensen, 1977). The Apiaceae (= Umbellifereae) have been shown to be 

chemotaxonomically linked to the Asteraceae (Mabry and Bohlmann, 1977). Petroselinum 

crispum (parsley), which is economically important and chemically similar to the Asteraceae,

was not infested during the New Zealand tests (Littlefield et al., 2008).

6.c. Selected cultivated species in other orders:

No cultivated species in other plant orders were tested, although several species were tested 

for the New Zealand project.

CATEGORY 7:

Any plant on which the biological control agent or its close relatives 

(within the same genus) have been previously recorded to feed and/or 

reproduce.

Cynipid wasps of the genus Aulacidea generally have a narrow host range, confined to the 

family Asteraceae. A number of species utilized by other Aulacidea spp. wasps, including

Acroptilon, Hieracium, Hypochoeris, Lactuca, Prenanthes, Senecio, Solidago, Sonchus, and

Tragopogon, were tested. Galls were only induced on several species belonging to the

Hieracium subgenus Pilosella (Littlefield et al., 2008). 

Conclusions

Based upon test results from Montana State University, as well as testing of A. subterminalis

for importation into New Zealand, host utilization by A. subterminalis is confined to a few 

closely related hawkweed species all of which are Old World species. Native North 

American hawkweeds are precluded from attack in that they do not produce stolons, the 

location where the gall wasp induces galls and completes its development. All native North 

American hawkweeds are phylogentically distant and distinct from the exotic, and often 

weedy, hawkweeds of the Pillosella group (Littlefield et al., 2008). 
46

Appendix 3. Galling observed in multiple-choice and larval development tests with A. 

subterminalis (combined results for New Zealand host specificity tests 1995 to 1997; taken 

from Syrett et al., 1998).

Test Plant Species Total No. of Plants

Offered Attacked

Asteraceae

Lactuceae

Subgenus Pilosella

Hieracium pilosella L. EUR 76 74

H. pilosella L. NZ 14 10

H. aurantiacum L. 4 2

H. caespitosum Dumort EUR 6 0

H. caespitosum Dumort USA 5 0

H. praealtum Gochnat 3 0

H.x stoloniferum Waldst. et Kit 3 0

Subgenus Hieracium 0

H. lepidulum (Stenstroem) Omang 6 0

H. murorum L. 7 0

H. sabaudum L. 8 0

Representatives of other Subtribes of Lactuceae

Cichorium intybus L. 7 0

Embergia grandifolia (Kirk) Boules 4 0

Hypochoeris radicata L 8 0

Lactuca sativa L. 4 0

Microseris scapigera (Solex A.Cunn.) Sch.Bip. 5 0

Picris hieracioides L. 7 0

Sonchus kirkii Hamlin 6 0

Sonchus oleraceus L. 6 0

Taraxacum officinale L. 5 0

Taraxacum magellanicum Schutz-Bip. 2 0

Tragopogon porrifolius L. 6 0

Anthemidae

Artemesia dracunculus L. 1 0

Chrysanthemum cinerariifolium (Treviri) Vis. 7 0

Astereae

Celmisia sp. 3 0

Olearia avicenniifolia (Raul.) Hook f. 4 0

Cardueae

Carthamus tinctorius L. 7 0

Cynara scolymus L. 6 0

Heliantheae

Helianthus annuus L. 6 0
47

Test Plant Species Total No. of Plants

Offered Attacked

Senecioneae

 Brachyglottis monroi Hook. f. 2 0

Other Plant Families

Apiaceae: Patroselinum crispum (Miller) A.W. Hill 8 0

Brassicaceae: Brassica oleracea L. 7 0

Cannaceae: Canna edulis Ker-Gawl. 9 0

Caryophyllaceae: Dianithus barbatus L. 7 0

Cyperaceae: Carex testacea Sol ex Booth Hook. f. 5 0

Fabaceae: Trifolium repens L. 7 0

Iridaceae: Gladiolus communis L. 8 0

Lamiaceae: Mentha sp. 8 0

Liliaeae: Allium cepa L. 8 0

Malvaceae: Althea rosea L. 5 0

Myrtaceae: Leptospermum scoparium J.R. et G. Forst. 3 0

Oleaceae: Olea europaea L. 2 0

Poaceae: Poa colensoi Hook. f. 7 0

Poaceae: Agrostis tenuis Sibth. 5 0

Poaceae: Festuca novae-zelandiae (Hack.), Ckn 7 0

Polyganaceae: Rumex acetosella L. 7 0

Rutaceae: Citrus sp. 8 0

Scrophulariaceae: Antirrhinum majus L. 2 0

Solanaceae: Lycopersicon esculentum Miller 8 0

Theaceae: Camellia japonica L. 8 0

Urticaceae: Urtica dioica L. 7 0
48

Appendix 4. No-choice oviposition and larval development tests with A. 

subterminalis conducted from 2000 to 2006 at CABI-Europe and Montana State 

University (Littlefield et al., 2008).

Test Plant

1 No. Reps

Reps. Infested Mean No. Gall 

Clusters/Rep 

No. % (+ SE)

ASTERACEAE

Tribe: Lactuceae

Subtribe: Hieraciinae 

Subgenus: Pilosella

Hieracium aurantiacum ID 15 2 13.3 0.13 (0.09)

H. aurantiacum MT 1 0 0 0

H. aurantiacum NZ 6 4 66.7 1.33 (0.49)

H. aurantiacum ID, MT 44 17 38.6 0.89 (0.21)

H. caespitosum ID 33 0 0 0

H. caespitosum ID 3 0 0 0

H. flagellare NH 16 8 50.0 1.62 (0.79)

H. floribundum US 9 0 0 0

H. floribundum 17 9 52.9 1.24 (0.48)

H. glomeratum BC 2 0 0 0

H. glomeratum WA 6 0 0 0

H. glomeratum ID 7 0 0 0

H. pilosella EUR 28 23 82.1 2.68 (0.42)

H. pilosella US 13 11 84.6 1.92 (0.62)

H. pilosella WA 46 25 54.3 1.35 (0.29)

H. piloselloides US 6 0 0 0

H. piloselloides 11 0 0 0

H. stoloniflorum Eur 9 0 0 0

Subtribe: Hieraciinae 

Subgenus: Hieracium

H. umbellatum 13 0 0 0

Subtribe: Hieraciinae 

Subgenus: Chionoracium

Hieracium. albiflorum 2 0 0 0

H. albiflorum 18 0 0 0

H. argutum 3 0 0 0

H. argutum 18 0 0 0
49

Test Plant1 No. Reps

Reps. Infested Mean No. Gall 

Clusters/Rep 

No. % (+ SE)

H. bolanderi 15 0 0 0

H. canadense 7 0 0 0

H. canadense 15 0 0 0

H. carneum 1 0 0 0

H. carneum 15 0 0 0

H. fendleri 3 0 0 0

H. fendleri 10 0 0 0

H. gracile 7 0 0 0

H. greenei 14 0 0 0

H. gronovii 3 0 0 0

H. gronovii 17 0 0 0

H. horridum 3 0 0 0

H. longiberbe 8 0 0 0

H. longipilum 15 0 0 0

H. parryi 11 0 0 0

H. scabrum 15 0 0 0

H. scouleri var. albertinum 6 0 0 0

H. scouleri var. albertinum 11 0 0 0

H. scouleri var. cynoglossoides 17 0 0 0

H. venosum 5 0 0 0

Other Subtribes of Lactuceae

Subtribe: Catananchinae

Catananche caerula 6 0 0 0

Subtribe: Crepidinae

Crepis atribarba 10 0 0 0

Crepis biennis 15 0 0 0

Taraxacum officinale 6 0 0 0

Subtribe: Hypochaeridinae

Hypochoeris radicata 6 0 0 0

Subtribe: Lactucinae

Lactuca sativa 9 0 0 0
50

Test Plant1 No. Reps

Reps. Infested Mean No. Gall 

Clusters/Rep 

(+ SE) No. %

Lactuca serriola 3 0 0 0

Lactuca virosa 6 0 0 0

Prenanthes racemosa 4 0 0 0

Subtribe: Microseridinae

Agroseris glauca 16 0 0 0

Agoseris grandiflora 5 0 0 0

Agroseris grandifolia 3 0 0 0

Krigia biflora 3 0 0 0

Krigia biflora 13 0 0 0

Microseris nutans 11 0 0 0

Subtribe: Sonchinae

Sonchus arvensis 6 0 0 0

Sonchus asper 8 0 0 0

Sonchus oleraceus 6 0 0 0

Subtribe: Stephanomeriinae

Lygodesmia juncea 14 0 0 0

Stephanomeria cichoriacea 14 0 0 0

Stephanomeria minor 5 0 0 0

Subtribe: unassigned

Cichorium intybus 10 0 0 0

Other Tribes of Asteraceae

Tribe: Anthemideae

Artemisia dracunculus 6 0 0 0

Chrysanthemum cinerariifolium 9 0 0 0

Tribe: Cardueae

Acroptilon repens 8 0 0 0

Cirsium arvense 10 0 0 0

Cynara scolymus 9 0 0 0

Tribe: Eupatorieae

Eupatorium maculatum 9 0 0 0
51

Test Plant1 No. Reps

Reps. Infested Mean No. Gall 

Clusters/Rep 

No. % (+ SE)

Tribe: Gnaphalieae

Antennaria dioica 9 0 0 0

Gnaphalium audax 9 0 0 0

Tribe: Helenieae

Tagetes erecta 9 0 0 0

Tribe: Heliantheae

Dahlia sp. 3 0 0 0

Helianthus annuus 9 0 0 0

Tribe: Vernonieae

Stokesia laevis 5 0 0 0

OTHER FAMILIES

Apiaceae: Petroselinum crispum

(parsley) 3 0 0 0

Asclepiadacea: Asclepias syriaca

(common milkweed) 7 0 0 0

Chenopodiaceae: Beta vulgaris (beet) 9 0 0 0

Fabaceae: Pisum sativum (garden 

pea) 7 0 0 0

Fabaceae: Vicia faba (broad bean) 5 0 0 0

Lamiaceae: Monarda fistulosa (wild 

bergamot) 6 0 0 0

Liliaceae: Allium cepa (onion) 8 0 0 0

Papavaracea: Papaver nudicaule

(Islandic poppy)

3 0 0 0

1 Plant species highlighted in blue indicate those tested at Montana State University.
52

Appendix 5. Response to comments on draft EA

Four comments were submitted on the draft environmental assessment for release of A. 

subterminals for biological control of hawkweeds. A commenter from the Florida 

Department of Agriculture and Consumer Services supported the release of the gall 

wasps as biological control agents. Specific issues were raised by the other three 

commenters. The issues raised are indicated in bold text and the response follows. 

An anonymous commenter indicated general concern with the release of A. 

subterminalis, as well as other concerns with APHIS that are out of the scope of 

this EA. The commenter indicated that more tests should be done to demonstrate 

the safety of release of A. subterminalis. 

Extensive host specificity testing was conducted over a 6-year period that demonstrated 

the safety of A. subterminalis to native plants. Study results were reviewed by The 

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

release of A. subterminalis was recommended by the TAG. TAG members that 

reviewed the release petition included representatives from APHIS, Cooperative State 

Research, Education, and Extension Service (now National Institute of Food and 

Agriculture), Forest Service, Environmental Protection Agency, U.S. Army Corps of 

Engineers, the National Plant Board, and representatives from Canada. 

A commenter from the Alaska Association of Conservation Districts supported the 

release of Aulacidea subterminalis but raised two issues. The first was regarding 

placing a hold on the potential release of A. subterminalis in Alaska until field tests 

prove that it can survive and impact either orange hawkweed (Pilosella aurantiaca 

(=Hieracium aurantiacum)) or Hieracium umbellatum. 

There are no current plans to release the wasp in Alaska. Any releases made within that 

state will be largely dependent upon Alaskan cooperators at the federal, state, county or 

local level. It will likely be a number of years before this gall wasp will be readily 

available for general release and redistribution. By that time data from the field 

indicating the potential impact of the wasp on orange hawkweed may be available. No 

North American native hawkweeds were infested in laboratory host specificity tests, 

including Hieracium umbellatum. Therefore, it is unlikely that A. subterminalis would 

survive on that species in Alaska.

The second issue was in regards to the possible utilization of the native hawkweed 

Hieracium triste by Aulacidea subterminalis. According to the Plants Database 

(USDA, NRCS, 2010) H. triste (woolly hawkweed) has two varieties: H. triste var.

fulvum and H. triste var. triste. Hieracium triste var. fulvum has been reported only 

from Alaska, whereas H. triste var. triste is more widespread occurring in Alaska and in 

the Canadian provinces of Alberta, British Columbia, Yukon, and Northwest 

Territories. The Plants Database also lists several varieties of Hieracium gracile

(slender hawkweed): H. gracile var. alaskanum found in Alaska; H. gracile var.
53

detonsum located in California, Colorado, Idaho, Oregon, and Washington; H. gracile 

var. gracile found in Alaska and most of the western United States; and H. gracile var.

yukonense also found in Alaska. Based upon analyses of certain sequences of 

chloroplast DNA conducted by Gaskin and Wilson (2007), H. triste and H. gracile are 

very genetically similar. This data appears to lend support to the synonymization of H. 

gracile with H. triste by some authors (Brouillet et al., 2010; eFloras.org ,2010). 

Furthermore, both plants seem to share similar life habits and ecological niches 

(eFloras.org , 2010; Rice and Halpop, 2009). Phylogenetically, this species (or species 

group) is contained in the subgenus Chionoracium, a subgenera of the Hieracium to 

which the majority of native North American hawkweeds belong. Hieracium gracile 

var. gracile was tested in host specificity studies but was not infested by A. 

subterminalis. In addition, no North American native hawkweeds were infested in host 

specificity tests.

Gall induction is a complex biochemical and morphological process; thus, gall-inducing 

insects tend to be very host and tissue specific, making them attractive for use as 

biological control agents of weeds. Aulacidea subterminalis only induces galls at the 

tips of stolons which are only produced by invasive hawkweeds of the Pilosella genus 

(formerly considered a subgenus) and not by any of the native hawkweeds. There is no 

evidence that suggests that A. subterminalis will utilize lateral roots or rhizomes should 

they be produced by native plant species. Because A. subterminalis is a stolon feeder 

and host range is restricted to a small group of related invasive hawkweeds of the genus 

Pilosella; the risk to native hawkweeds, which do not produce stolons, is extremely 

low. 

References -

Brouillet, L., F. Coursol, M. Favreau, and M. Anions (compilers). 2010. VASCAN, the 

Database of Vascular Plants of Canada. http://data.canadensys.net/vascan/ (last 

accessed January 25, 2011).

eFloras.org. 2010. Flora of North America. Vol. 19, 20 and 21 Page 280, 282, 291. 

http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=250066959 last 

accessed January 19, 2011.

Gaskin, J.F. and L.M. Wilson. 2007. Phylogenetic Relationships Among Native and 

Naturalized Hieracium (Asteraceae) in Canada and the United States Based on Plastid 

DNA Sequences. Systematic Botany 32: 478–485.

Rice, P., and J. Halpop. 2009. Hawkweed Identification. Montana State University 

Extension. http:// msuextension.org/publications/ AgandNaturalResources/EB0187.pdf.

USDA, NRCS. 2010. The PLANTS Database. National Plant Data Center, Baton 

Rouge, LA 70874-4490 USA. http://plants.usda.gov (consulted on 03 December 2010).
54

A commenter from Habitat Conservation, and Environmental Contaminants, U.S. 

Fish and Wildlife Service, Region 8 Ecological Services, Sacramento, CA raised to 

issues of concern. The first comment was in regards to the geographic, ecological,

and economic impact of invasive hawkweed species. The commenter believed that 

the purpose and need for the proposed action does not adequately describe the 

impact of non-native hawkweeds in a manner that justifies the risk of introduction 

of a non-native insect. 

The Pacific Northwest (PNW) is in a phase of exponential expansion and colonization

by invasive hawkweed species. The number of counties in the PNW reporting new 

infestations of both orange (P. aurantiaca) and meadow hawkweed (P. caespitosa) has 

significantly increased over the past 10 – 15 years (Rice, 2010). In Montana it is 

estimated that 57,000 acres were infested by invasive hawkweeds in 2000, but as of 

2008 this estimate has been revised to well over 120,000 acres (M. Funk, Montana 

Hawkweed Coordinator, pers. comm.). It has been estimated that the annual increase 

of invasive hawkweeds within Flathead County Montana is over 11% per year while 

Wilson (2002 in Duncan and Clark, 2005) reported a 16% annual increase for the 

northwestern U.S. Risk maps of Montanan weeds indicate that large portions of 

western areas of the state could be subject to invasion 

(www.fs.fed.us/r1/cohesive_strategy/data/weeds/wra.ppt last accessed January 25, 

2011). It was estimated by Wilson (2002 in Duncan and Clark, 2005) that over 1.2 

million acres within the United States are infested with hawkweed. Of that, 650,000 

occurs in the northwestern United States (ID, MT, OR, WA). In British Columbia, both 

orange and meadow hawkweeds are widespread in southern and central portions of the 

province (E-Flora BC Klinkenberg, 2010) and are of serious concern in northeastern 

British Columbia (Giroday and Baker, 2006). Information regarding hawkweed 

infestation within eastern United States is often unavailable, but several invasive 

hawkweed species are widespread (see distribution maps below). 

Although hard data regarding the invasiveness of hawkweed in North America is 

difficult to obtain, existing data suggests a moderate to high invasive potential by these 

exotic hawkweed species. Risk analysis of orange and/or meadow hawkweed has been 

conducted in Alaska and northeastern British Columbia and both indicate a moderate to 

a high degree of invasiveness (e.g. in Alaska both orange and meadow hawkweeds 

were rated 79 out of a possible 100 total points 

http://akweeds.uaa.alaska.edu/akweeds_ranking_page.htm last accessed January 25, 

2011) (Carlson et al., 2008; Giroday and Baker, 2006). A 2005–2006 USDA-APHISPPQ Biocontrol Target Pest Canvassing and Evaluation survey of various Federal, 

tribal and state agencies, universities, and weed management districts ranked both 

orange and meadow hawkweeds as western region priority weeds for biological control, 

ranking seven out of 16 noxious weed species cited by land managers (Hansen and 

Bloem, 2006). Orange and/or meadow hawkweeds have been included on noxious 

weed lists in Alaska, Colorado, Idaho, Montana, Oregon, and Washington, and the 

Canadian provinces of Alberta, British Columbia, and Quebec. Regulations vary by 

state/province but generally involve actions such as restricted importation and/or 
55

quarantine and prevention, containment, eradication, or other control measures. In 

some states such as Oregon and Montana, plants are ranked according to various 

criteria including detrimental effects, mode of spread or reproduction, distribution or 

potential distribution, and difficulty in control (Oregon Department of Agriculture,

2010; T. Moon (Montana Department of Agriculture) pers. comm.). Invasive 

hawkweeds also have an adverse economic impact. Wilson (2002 in Duncan and 

Clark, 2005) estimated a $58.2 million dollar impact for the treatment of hawkweeds in 

western United States. 

Invasive hawkweeds have been proven detrimental in other areas of the world. From 

Europe, hawkweeds have spread to North America, New Zealand (Grundy, 1989), 

Australia (Syrett, pers. comm.), Japan (Suzuki and Narayama, 1977), Chile and 

Argentina (Norambuena, pers. comm.). In New Zealand, 10 species of hawkweeds 

infest over 1.25 million acres in the South Island alone (across 42% of the landmass) 

(McMillan, 1991), while other figures list 15 million acres infested in both islands with 

an economic impact of $42 million (New Zealand Dollars) (Sheean, 2009).

In North America, invasive hawkweeds are primarily weeds of moist pastures and 

forest meadows, and mesic rangeland. The potential for spread in the northern Great 

Plains and the Columbia River region is difficult to predict at this time. However, 

invasive hawkweed occurrences as weeds in the northeastern states during the last 

century, and their original distribution in northern and central Europe, suggest that they 

pose the greatest threat to cooler, sub-humid to humid sites in the northern regions of 

the United States and Canada. Habitats most susceptible to invasion range from the 

lowlands of the northern Pacific Coast to elevations of 5,000 feet or more in the 

Intermountain States. Sites most vulnerable to invasion include roadsides, mountain

meadows and clearings in forest zones, permanent pastures, hayfields, cleared timber 

units, and abandoned farmland where the soil is well drained, coarse textured, and 

moderately low in organic matter. Consequently, elk habitat, recreation areas, and 

pristine mountain meadows in areas that have a climate similar to that of hawkweeds in 

their native range are particularly susceptible. None of the introduced hawkweed 

species are found in the natural grasslands or shrub-steppe of the northern 

Intermountain West, and are not expected to become problem weeds in any dry habitat 

usually associated with western rangelands, except where irrigated. Neither meadow 

nor orange hawkweed appears to survive in annually tilled cropland. 

Most invasive hawkweeds are perennial, creeping stoloniferous plants that can displace 

native vegetation. Forage species in pastures and abandoned farmland are choked out 

by the advancing front of hawkweed. Hawkweeds threaten lawns and gardens, as well. 

Hawkweeds have been reported to have allelopathic effects on neighboring vegetation 

by exuding toxic chemicals into the soil (Dawes and Maravolo, 1973; Makepeace, 

1976). These monocultures compete for soil moisture and nutrients, thereby posing 

risks to native species. As hawkweed monocultures invade species-rich range and 

mountain habitats, ecosystem functions and ecological relationships are affected. 

While no studies specifically address the effects of orange hawkweed on nutrient 

cycling and disturbance regimes, hawkweed’s ability to dominate a community 
56

suggests that these species do affect habitat function. Hawkweeds generally negatively 

impact plant and animal diversity and there is serious concern about the loss of native 

plant biodiversity in infested areas. Ecological losses in plant and animal diversity can 

be enormous but cannot be economically calculated. Additional expenditures result 

from control costs. Hawkweeds are tenacious invaders, and once established, quickly 

develop into a patch that continues to expand until it covers the site with a solid mat of 

rosettes. 

Distribution maps of target Hieracium species in North America (USDA Plants Database, 2010). 

 

Hieracium pilosella Hieracium auranticum

Hieracium flagellare Hieracium floribundum
57

The invasion by hawkweeds may potentially contribute to the further decline of native 

bee populations, which are already being severely affected by habitat loss and pesticide 

use. Nearly 70% of native bees are ground nesting (http://www.xerces.org/wpcontent/uploads/2008/11/nests_for_native_bees_fact_sheet_xerces_society.pdf ). 

These bees often nest in open, well drained soils, of which invasive hawkweeds readily 

invade. Because these invasive species form dense mats of vegetation (over 

3,200/square meter) (Wilson et al., 1997), such infestations could limit the ability of 

these bees to construct or maintain nests. Also a loss of biodiversity may occur with 

the introduction of invasive hawkweeds (Rose et al., 1995; Treskonova, 1991). This 

would result in less pollen and nectar sources for native bees and pollinators during the 

course of the summer. The reliance of herbicidal applications to mitigate hawkweed 

invasions may also have a detrimental impact on native pollinators by the short term 

loss of flora diversity of non-target flowering forbs. Although native forbs (if initially 

present) may return after herbicidal treatment, some current research being conducted 

at the University of Montana suggests that flowering of these native forbs may be 

negatively affected for several seasons until they have a chance to recover (Crone et 

al., 2009). 

Meadow hawkweed causes severe allergenic reactions. Reactions in people closely 

working with meadow hawkweed include minor skin rashes, sneezing, congestion and 

difficulty in breathing (Wilson, pers. comm.). Similar effects have not been reported in 

animals. It is not known what portion of the plant causes this allergenic reaction; 

although latex and other chemicals of closely related Asteraceae plants can cause 

dermatitis (Dawes et al., 1996).

Based upon the rate of spread and potential ecological impacts of invasive hawkweeds, 

the introduction of A. subterminalis, a host specific biological control agent with 

potentially negligible secondary impacts (see below), is warranted to help mitigate the 

impacts of these invasive weeds.

The second issue from the Fish and Wildlife commenterwas in regards to possible 

interactions of Aulacidea subterminalis and native hymenopteran species; in 

particular the potential for the introduction of disease-causing pathogens through 

A. subterminalis. 

Few studies have been conducted on interactions between A. subterminalis and nonplant organisms in its native range so it is difficult to predict how the introduction of 

the gall wasp will impact non-plant species, in this case native hymenopterans in North 

America. However, little impact is expected by the presence of A. subterminalis for the 

following reasons.

First, there will be few opportunities for direct interaction (i.e., displacement) of other 

Aulacidea spp. wasps or other wasps in the insect family Cynipdae once A. 

subterminalis is released in North America. Gall wasps of the genus Aulacidea are 

wide ranging in their distributions, being found in both Holarctic (northern) and 

Nearctic (biogeographic region that includes the arctic and temperate areas of North 
58

America and Greenland) regions. Aulacidea species native to the Nearctic region have 

been collected in the eastern half (Missouri eastward) of the United States and Canada 

and none are associated with Hieracium (Burks, 1979). Only two cynipid wasps have 

been collected from Hieracium in North America; a stem infesting wasp on H. scouleri

from Idaho) (L. Wilson (British Columbia Ministry Agriculture and Lands) and J. 

Littlefield (Montana State University), pers. comm.) that has not been identified, and an 

apparent introduced species, Aulacidea hieracii, that has been recorded in the Province 

of Ontario infesting H. umbellatum (Silva and Shorthouse, 2006). These species do not 

occur on the same host plant as A. subterminalis nor in a niche occupied by A. 

subterminalis. Thus, no interactions between A. subterminalis and native or other 

introduced cynipid wasps are expected. 

It is possible that native parasitoids (i.e., mainly hymenopterans) will colonize A. 

subterminalis and, through the gall wasp, have indirect negative effects on their native, 

gall-forming host(s). Because any introduced A. subterminalis will be cleaned of any 

European parasitoids in quarantine before being released in North America, and that the 

parasitoid guilds of native and European Aulacidea are not similar to North American 

species little parasitism of the gall wasp is expected, and thus, potential indirect effects 

are not expected. In New Zealand, where A. subterminalis has been introduced and 

established for nearly 10 years, no parasitism has been observed (Paynter et al., 2010).

No predators have been observed attacking A. subterminalis in the field in Switzerland, 

and no disease has appeared in the populations being reared in Switzerland, Montana, 

Canada, or New Zealand (G. Grosskopf-Lachat (CABI Europe), Littlefield (Montana 

State University), L. Smith (Landcare, New Zealand), R. De Clerck-Floate (Agriculture 

and Agri-Foods Canada) pers. comm., Syrett et al., 1998). Due to the short life of adult 

A. subterminalis (up to a week under laboratory conditions) and that the larvae feed 

within a gall in isolation from the general environment, horizontal transmission of 

pathogens by the wasp would be limited or relatively non-existent. More cryptic insect 

pathogens such as microsporidians or viruses are more likely to be transmitted 

vertically if present in A. subterminalis, and these pathogens are relatively specific to 

single species or closely related species (Solter and Maddox, 1998; Solter et al., 2000). 

Cynipids are distantly related to families to which native bees belong (Ronquist, 1999; 

Sharkey, 2007; Whitfield, 1998). Therefore, should there be any pathogens cryptically 

infesting A. subterminalis, they would be less likely to infect native bees (Superfamily: 

Apidoidae). There is no evidence to date that suggests any disease transmission from 

hymenopterans used for biological control of weeds or for insect pests to species of 

bees. Reports of disease transmission in native bee populations indicate that closely 

related species were responsible for possible transmission 

(http://www.xerces.org/%20bumblebees/ last accessed January 25, 2011). For 

example Nosema bombi has been reported to have been transmitted to native Bombus

spp. bees by the introduction of Bombus occidentalis and B. impatiens for pollination 

(although there appears to be some debate regarding this evidence 

http://www.scientificbeekeeping.com/index.php?option=com_content&task=view&id=

84 last accessed January 25, 2011). 
59

As part of the quarantine process prior to the release of a biological control agent, 

insects are reared through a generation to eliminate any parasitoids or contaminating 

organisms. Laboratory rearing, along with close inspection of the reared insect colony 

for the incidence of either foreign parasitoids or disease-causing pathogens, is an 

advised and reliable first line of defense for reducing the risk of introducing biotic 

contaminants with classical biocontrol agents (Goettel and Inglis, 2006). Aulacidea 

subterminalis has only been collected in one location for rearing and release purposes 

(i.e. collected from the Black Forest (Germany), and has been reared for several 

generations as a pure colony at CABI-Europe Switzerland Station, Delémont). 

Therefore, this population has a known and reliable history of having little parasitism 

and no disease problems. 

References –

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Grundy, T.P. 1989. An economic evaluation of biological control of Hieracium. 

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