The Bugwood Network

Cypress Spurge

H. Faubert - Department of Plant Sciences, University of Rhode Island, Kingston, Rhode Island, USA

acrobat version
R. A. Casagrande - Department of Plant Sciences, University of Rhode Island, Kingston, Rhode Island, USA

In: Van Driesche, R., et al.., 2002, Biological Control of Invasive Plants in the Eastern United States, USDA Forest Service Publication FHTET-2002-04, 413 p.

Pest Status of Weed

Cypress spurge (Euphorbia cyparissias L.) (Fig. 1) is a herbaceous European perennial introduced into North America as an ornamental plant in the 1860s (Croizat, 1945). It was widely planted in graveyards and often is called graveyard weed (Muenscher, 1936). The plant escaped cultivation and became established on open ground, particularly in pastures (Stuckey and Pearson, 1973).

Nature of Damage

Figure 1. Euphorbia cyparissias L. in bloom. (Photograph by R.A. Casagrande.)
Figure 1. Euphorbia cyparissias L. in
bloom. (Photograph by R.A. Casagrande.)

Economic damage. Although cypress spurge is found throughout much of North America, economic losses are primarily restricted to the northeastern United States (USDA, NRCS, 1999; Stahevitch et al., 1988). Cypress spurge is particularly prevalent in Ontario and Quebec (Gassmann, 1985). In the United States, 25 counties have infestations of more than 500 acres and most of these sites are in the northeast (Dunn, 1979). Cypress spurge is listed as a noxious weed in Canada and some New England states (Stahevitch et al., 1988; Torrey, 1999) and it has the potential to become a major weed in other areas. In 1975, it was found in 26 states; 25 years later it was recorded in 42 states (Dunn, 1979; USDA, NRCS, 1999). At one site in Rhode Island, approximately 70 out of 170 acres of hay meadow were dominated by cypress spurge, making most of the land unfit for cattle and growing hay. Farmers who are unaware of cypress spurge in their hay fields spread the weed when transporting hay infested with cypress spurge seeds. Chemical control of cypress spurge is difficult because of its extensive root system. Plants readily regrow from roots following destruction of above-ground parts, so repeated applications of several herbicides usually are required for control (Pemberton, 1985). Cultivating infested fields can spread cypress spurge by moving root pieces caught on machinery to clean locations where roots produce new plants (Moore and Lindsay, 1953).

All parts of cypress spurge contain a toxic latex (Stephens, 1980) that irritates the eyes, mouth, and gastrointestinal tract and causes dermatitis upon contact in some people (Westbrooks and Preacher, 1986). Most grazing animals avoid cypress spurge. Sheep can browse the plant with no ill effects, but cattle that accidentally ingest it become weak, collapse, and may die (Muenscher, 1964).

Ecological damage. Cypress spurge is primarily found on limestone, sandy, or gravelly soils. It tends to form almost pure stands at open sites and is likely to be responsible for displacement of native species (Moore and Lindsay, 1953; Stuckey and Pearson, 1973). Cypress spurge does not generally occur on intensively cultivated soils, nor is it found in heavily forested areas (Stahevitch et al., 1988). This weed is commonly found along roadsides throughout the northeastern United States, but generally is not considered a problem as it forms an attractive ground cover.

Geographical Distribution

Native to Europe, cypress spurge is found throughout the continent between 40 and 60 ºN (Pritchard, 1959). In North America, it is currently found in 42 states and Canada (Dunn, 1979; USDA, NRCS, 1999). It also is an invasive weed in New Zealand (Stahevitch et al., 1988). There are three cytogenetic variants present in Europe – fertile tetraploids (Fig. 2), fertile diploids, and sterile diploids. Fertile tetraploids, the most widely distributed form, are found throughout the range from southern Finland to northern Greece and west from England to as far east as

Figure 2. Close-up of fruiting structure of tetraploid Euphorbia cyparissias L. (Photo by R.A. Casagrande.)
Figure 2. Close-up of fruiting structure
of tetraploid Euphorbia cyparissias L.
(Photo by R.A. Casagrande.)
Lake Baikal in central Siberia (Pritchard, 1959). Fertile diploids have a relatively southern distribution (France, Italy, Switzerland, Austria, and the former Yugoslavia), while sterile diploids are found primarily in England (Pritchard, 1959). Only sterile diploids and fertile tetraploids are found in North America (Stahevitch et al., 1988). The sterile diploid was probably intentionally introduced as an ornamental plant in North America and the fertile tetraploid was apparently accidentally introduced. The tetraploid form is considerably more vigorous and weedy than the diploid form (Dunn, 1979; Gassmann and Schroeder, 1995), and this form has been increasing in abundance in North America. Reports of fruiting cypress spurge (fertile tetraploid) were rare in North America from 1910 to 1931, but became more common by 1953 (Deane, 1910; Deane, 1912; Muenscher, 1931; Moore and Lindsay, 1953). In Rhode Island during the spring of 2000, we conducted a survey in 54 cypress spurge stands. Fifty-three out of the 54 stands were comprised of fruiting plants, indicating a predominance of tetraploid cypress spurge in the state.

Background Information On The Pest Plant

Taxonomy

Cypress spurge is a member of the Euphorbiaceae, or spurge family. Synonyms for E. cyparissias are Galarhoeus cyparissias (L.) Small and Tithymalus cyparissias (L.) Hill. The genus Euphorbia contains about 1,600 species native to Africa, Asia, Europe, and North America (Gassmann et al., 1991). In North America, native or introduced species are found in four subgenera: Agaloma, Chamaesyce, Esula, and Poinsettia (Pemberton, 1984). Cypress spurge and the closely related leafy spurge, Euphorbia esulae L., belong to subgenus Esula (Gleason and Cronquist, 1991). Leafy spurge is another invasive Eurasian species that has caused considerable damage in the north central United States and the Canadian prairies (Gassmann, 1985). Euphorbiaceae typically have a poisonous white sap in all plant parts (Clark and Fletcher, 1909), which appears to be for defensive purposes (Gassmann et al., 1991).

Native Range

According to Stahevitch et al. (1988), cypress spurge is found throughout Europe from 60ºN in southern Finland to 40ºN is northern Greece, and ranges from Britain to central Siberia.

Biology

Cypress spurge is a perennial that overwinters as root and crown tissue. The fertile tetraploid also can overwinter as seed. The root system consists of two root types. Young seedlings send out a taproot that is persistent and indeterminate. The taproot may reach lengths of three or more meters and give rise to lateral roots, which produce adventitious buds. In early spring, shoots develop from the crown and buds. Shoots grow in masses and reach about 40 cm in height before flowering in mid-spring. The sterile diploid cypress spurge flowers but does not set seed. The fruit of the fertile form is an explosive capsule that splits open when mature and throws its seed up to five meters (Stahevitch et al., 1988)

Analysis of Related Native Plants in the Eastern United States

There are 107 Euphorbia species native to North America, 21 of which are in the subgenus Esula (Pemberton, 1985). In the northeastern United States there are 13 native Euphorbia species, of which three are in the subgenus Esula: Euphorbia commutata Engelm., Euphorbia purpurea (Raf.) Fern., and Euphorbia spatulata Lam. (USDA, NRCS, 1999; Magee and Ahles, 1999) (Table 1). Euphorbia purpurea is listed as a species of concern by the U.S. Fish and Wildlife Service and is under review for protective status. This plant is found in swampy woods in the eastern United States (Pemberton, 1985). The other native Euphorbia species are in one of three other subgenera found in North America: Agaloma, Chamaesyce, or Poinsettia (Gleason and Cronquist, 1991). In addition to cypress and leafy spurge, ten other Euphorbia species in the subgenus Esula have been introduced into the Northeast (USDA, NRCS 1999). Subgenera appear to be natural groupings. Many Euphorbia-feeding insects accept as host plants most of the species in one subgenus and reject species in the other subgenera (Pemberton, 1985).

Table 1. Euphorbia Species in the Northeastern United States

Subgenus Species Origina Formb Statesc
Esula E. commutata Engelm. Nat. A                 PA
E. cyparissias L. Intro. P ME NH VT MA CT RI NY NJ PA
E. epithymoides L. Intro. P.             NY    
E. esula L. Intro. P. ME NH VT MA CT   NY NJ PA
E. exigua L. Intro. A                 PA
E. falcata L. Intro. A                 PA
E. helioscopia L. Intro. A ME NH VT MA CT   NY NJ PA
E. lathyris L. Intro. A/P       MA CT   NY NJ PA
E. lucida
Waldst. & Kit.
Intro. P       MA     NY   PA
E. paralias L. Intro. P                 PA
E. peplus L. Intro. A ME NH VT MA   RI NY NJ PA
E. platyphyllos L. Intro. A     VT MA     NY   PA
E. purpurea
(Raf.) Fern.
Nat. P               NJ PA
E. segetalis L. Intro. A               NJ PA
E. spatulata Lam. Nat. A                 PA
E. terracina L. Intro. P                 PA
Poinsettia E. dentata Michx. Intro. A   NH VT MA     NY NJ PA
Agaloma E. corollata L. Nat. P   NH VT MA CT RI NY NJ PA
E. ipecacuanhae L. Nat. P         CT   NY NJ PA
E. marginata Pursh. Nat. A   NH   MA CT RI NY NJ PA
E. pubentissima Michx. Nat. P   NH             PA
Chamaesyce E. glyptosperma Engelm. Nat. A ME NH VT MA     NY    
E. humistrata Engelm. Intro. A   NH VT       NJ    
E. maculata L. Nat. A ME NH VT MA CT RI NY NJ PA
E. nutans Lagasca Nat. A       MA CT RI NY NJ PA
E. ophthalmica (Pers.) Burch Nat. A                 PA
E. polygonifolia L. Nat. A ME NH   MA CT RI NY NJ PA
E. prostrata Aiton Intro. A       MA         PA
E. serpens HBK Intro. A   NH           NJ PA
E. serpyllifolia Pers. Intro. A   NH           NY  
E. strictospora (Engelm.) Small Intro. A             NY    
E. vermiculata Raf. Nat. A ME NH VT MA CT RI NY NJ PA
a Plant either native (Nat.) or introduced (Intro.) to North America.
b Plant form either annual (A), perennial (P), or both (A/P).
c Plant located in Maine (ME), New Hampshire (NH), Vermont (VT), Massachusetts (MA), Connecticut (CT), Rhode Island
  (RI), New York (NY), New Jersey (NJ), or Pennsylvania (PA).

Background Information On The Pest Plant

Area of Origin of the Weed

Cypress spurge is believed to be indigenous to western Europe where the fertile diploid form of the plant is found. Fertile diploids occur throughout France and northcentral Spain and also in a narrow band across central Europe (excluding the Alps). Fertile tetraploids probably arose from fertile diploids, enabling the plant to colonize new habitats. Tetraploids apparently replaced diploids in most locations and extended the range of the species to the north and east. Fertile diploids and tetraploids are sympatric in southeastern France and the western Balkans (Pritchard, 1959). The sterile diploid is generally associated with human habitation, suggesting that this form was propagated as an ornamental. Since it is most common in England, it was probably propagated there. The sterile diploid was introduced from England into North America as an ornamental and the fertile tetraploid was apparently accidentally introduced as an ornamental and then escaped gardens and cemeteries (Stahevitch et al., 1988).

Areas Surveyed for Natural Enemies

Cypress spurge and leafy spurge are not serious weeds in Eurasia where they are attacked by a large complex of specialized insects and pathogens (Spencer, 1994). Leafy Spurge has been the target of a biological control program since 1961. Because cypress spurge is closely related to leafy spurge, agents released against leafy spurge also were released against cypress spurge.

Leafy spurge probably originated in northern Caucasus or northern China (Kuzmanov, 1964). However, because of political and financial limitations, surveys were conducted in the most western part of its distribution in Europe. Surveys originally funded by Canada began in 1961 at the International Institute of Biological Control of the Centre for Agriculture and Biosciences International (CABI-IIBC) in Delemont, Switzerland (Gassmann, 1990). Insects were collected from leafy spurge and cypress spurge plants in Italy, Switzerland, Germany, Austria, Hungary, and the former Yugoslavia. From 1980 to 1990 field surveys were expanded in scope to include other common perennial spurges in the subgenus Esula. This was done to enlarge the range of plant habitats from very dry to moist. In particular, Euphorbia seguieriana Necker and Euphorbia lucida Waldstein and Kitaibel were included in the survey. Field surveys were terminated in 1990 (Gassmann and Schroeder, 1995).

Natural Enemies Found

Thirty-nine insect species and two rust fungi were found and considered for the biological control of leafy spurge and 22 of the insects were screened as potential control agents. Originally, the selection was based mainly on agent availability and the damage a single individual caused to plants. This led to a focus on species with large individuals, like the sphingid moth Hyles euphorbiae (L). After several early introductions failed to reduce spurge populations, the strategy shifted towards using a large number of natural enemy species, which cumulatively might inflict greater stress on plants. Since spurge plants can tolerate repeated defoliation whether caused by mowing or herbicides, preference was given to root-feeding chrysomelid beetles in the genus Aphthona instead of leaf-feeding agents (Gassmann and Schroeder, 1995).

There appears to be an evolutionary relationship between Aphthona species and spurge. There are 66 known European Aphthona species, which have been collected from 33 plant families. Of these 66 species, almost half were found only on Euphorbia species (Sommer and Maw, 1982). Aphthona species are generally adapted to a single subgenus of Euphorbia and the host range often is restricted to a few species within a subgenus (Gassmann, 1990). Aphthona species found feeding only on plants in the subgenus Esula were collected and considered as potential biological control agents.

In addition to Aphthona species, a cecidomyiid gall midge, Spurgia esulae Gagné, was found on E. esulae in Italy (Pecora et al., 1991). Spurgia esulae has been recorded in nature only on E. esulae (Gagné, 1990).

Host Range Tests and Results

Between 1961 and 1994, tests measuring the host specificity of several species of natural enemies were conducted by the CABI-IIBC (Delemont, Switzerland), and the USDA Agricultural Research Service European Biological Control Laboratory (Montpellier, France). These tests estimated the host range of selected natural enemies to the plant genus level. Insects considered for release in the United States were subjected to a second round of tests at the USDA, ARS laboratory in Albany, California, USA.

Eighteen insects were eventually cleared for release in North America for control of leafy spurge, twelve of which were released in the western United States. Seven of the twelve species released in the western United States also were released in the eastern United States against both leafy and cypress spurge (Table 2). Host specificity results for the seven insects released in the eastern United States are reviewed here.

Table 2. Species Released in North America Against Leafy or Cypress Spurge (1965 to 1994)

Species Canada Western USA Eastern USA
Hyles euphorbiae (L.) 1965 1968 1976
Chamaesphecia empiformis Esper 1969 - -
Chamaephecia tenthrediniformis
(Denis & Schiffermuller)
1972 1975 -
Chamaesphecia hungarica (Tomala) 1991 1993 -
Chamaesphecia astatiformis
(Herrich-Schaffer 1846)
1993 - -
Chamaesphecia crassicomis Bartel 1912 1994 1994 -
Oberea erythrocephala (Schrank) 1979 1980 -
Aphthona cyparissiae (Koch) 1982 1986 1995
Aphthona flava Guill. 1982 1985 1995
Aphthona nigriscutis Foudras 1983 1989 1995
Aphthona czwalinae (Weise) 1985 1987 1995
Aphthona lacertosa (Rosh.) 1990 1993 1995
Aphthona abdominalis Duftschmidt - 1993 -
Pegomya euphorbiae (Kieffer) 1988 - -
Lobesia euphorbiana (Freyer) 1983 - -
Minoa murinata (Scopoli) 1988 - -
Spurgia esulae Gagne 1987 1985 1995
Spurgia capitigena (Bremi) 1990 - -
a Species released on cypress spurge.

Aphthona species host specificity. For the first round of host specificity tests, 50 to 56 plant species in 19 to 22 families of plants were selected to test Aphthona species host specificity. Test plants were selected from four categories: 1) plants related to leafy spurge; 2) plants attacked by other species in the genus Aphthona; 3) plants with latex other than Euphorbia; and 4) economically important plants (Sommer and Maw, 1982). Twenty adult Aphthona beetles were placed in cages with five test plant species. Two series of tests were made, one including a control plant (either E. esulae, E. cyparissias, or Euphorbia virgata) Waldstein-Wartemberg and Kitaibel; the second, a no choice test without a control plant. All plants were examined for insect feeding (Gassmann, 1984, 1985, 1990; Sommer and Maw,1982). To test for larval survival, 50 to 100 newly hatched Aphthona sp. larvae were transferred onto stem bases of potted plants. The same plant species used in adult feeding tests were used for larval feeding tests as well as control plants. All plants were later dissected to check host plant acceptance and larval development (Gassmann, 1984, 1985, 1990; Sommer and Maw, 1982).

Testing in the European laboratories showed that the host ranges for the six selected Aphthona species examined were restricted to the genus Euphorbia. Following the European tests, insects were sent to the USDA, ARS laboratory in Albany, California for the second round of testing. This testing was to determine host range within the genus Euphorbia. In Europe, all Euphorbia species are in the subgenus Esula. In North America there are more than 100 native species representing four subgenera (Agaloma, Chamaesyce, Esula, and Poinsettia) (Pemberton, 1985).

Ten native plant species were selected to represent the four different Euphorbia subgenera. For the first four Aphthona species tested, Euphorbia purpurea was selected as a test plant. This plant is native to some mid-Atlantic states and under review for protective status by the U.S. Fish and Wildlife Service. Euphorbia purpurea did not support larval development of any of four Aphthona species tested (Pemberton, 1986, 1987, 1989; Pemberton and Rees, 1990; Spencer and Prevost, 1992). Euphorbia purpurea was not a test plant for the two other Aphthona species because it was decided that E. purpurea did not grow in areas likely to contain leafy or cypress spurge (Gassmann, 1990; Fornasari, et al.., 1994). Testing in Albany indicated that all six Aphthona species appear to be restricted to a few species in the subgenus Esula.

Spurgia esulae host specificity tests. Following protocols similar to those used with Aphthona species, the Cecidomyid was tested against 56 plants in 22 families. Test plants included species closely related to Euphorbia and economically important plants such as snow-on-the-mountain, E. marginata; flowering spurge, E. corollata; and fire plant, E. heterophylla. Tests performed in 1982 by the USDA, ARS laboratories in Rome, Italy, indicated that S. esulae could complete its development only on plants in the genus Euphorbia. In 1984, host specificity tests were conducted in Albany, California on 11 native North American Euphorbia species to examine the potential host range of S. esulae in North America. Host specificity testing indicated that S. esulae is able to oviposit and complete its development on a limited number of species in the subgenus Esula of the genus Euphorbia. Out of 21 North American native Euphorbia species in the subgenus Esula, seven species were tested for host specificity. Of these seven species, five supported S. esulae development (Pecora et al., 1991).

Hyles euphorbiae host specificity tests. The Canadian Department of Agriculture conducted the host specificity tests for the Sphingidae, Hyles euphorbiae (Gassmann and Schroeder, 1995). In no-choice tests, larvae were successfully reared on E. epithymoides, E. lathyris (subgenus Esula), E. marginata (Agaloma), but not on the subgenera Poinsettia and Chamaesyce or other plants except for Lythrum salicaria L. (Lythraceae). In Europe, H. euphorbiae was primarily found feeding on E. cyparissias (cypress spurge), but also was found on E. esulae, Euphorbia gerardiana (Jacq.) Fourr., E. paralias, and other species in the subgenus Esula (Harris, 1999).

Releases Made

Eleven species of European insects were released in North America to control cypress spurge; seven species in the eastern United States and ten in Canada (Gassmann and Schroeder, 1995; Harris, 1999) (Table 2).

The first biological control agent released was Hyles euphorbiae, in Canada in 1965. Insects initially did not survive, but a subsequent release in 1966 and 1967 at Braeside, Ontario, did survive. From 1976 through 1982, third and fourth instar larvae collected from Braeside, Ontario were released on cypress spurge or leafy spurge in Virginia, New York, and Maryland (Batra, 1983).

A root-boring insect, Chamaesphecia empiformis (Esper) (Lepidoptera: Sesiidae), was released on cypress spurge in Ontario in 1969, but did not establish. Repeated releases of C. empiformis in the 1970s as well as another root-boring insect, Chamaesphecia tenthrediniformis (Denis and Schiffermüller), on North American leafy spurge, did not result in establishment. It later was determined that these Chamaesphecia species are host specific to the European plants E. esulae and E. cyparissias (Gassmann and Schroder, 1995; Harris, 1999).

Between 1982 and 1993, six Aphthona species were released on leafy spurge in the Great Plains of the United States. Researchers in Canada released five Aphthona species on leafy spurge and four Aphthona species on cypress spurge in Ontario and Nova Scotia (Aphthona cyparissiae [Koch], Aphthona czwalinae (Weise), Aphthona flava Guill., Aphthona nigriscutis Foudras, and Aphthona lacertosa [Rosenhauer].) (Gassmann and Schroeder, 1995; Harris, 1999). Spurgia esulae was released in the western United States in 1985. Spurgia capitigena (Bremi), another gall midge, was released together with S. esulae on leafy spurge and cypress spurge in Ontario (Gassmann and Schroeder, 1995; Julien, 1992).

Five of the Aphthona species (A. cyparissiae, A. czwalinae, A. flava, A. nigriscutis, and A. lacertosa) and S. esulae, increased in the Great Plains to populations large enough to permit collection for redistribution to other states (Figs. 3, 4, 5). Beginning in June 1995, adults of various Aphthona species and galls containing S. esulae were collected in Montana and

North Dakota, screened, packaged, and sent by overnight mail to cooperators in New Hampshire, New York, and Rhode Island. Aphthona beetles were released in groups of 500 to 2000 next to marking stakes in one to five acres of cypress or leafy spurge stands. Spurgia esulae was released in bundles of 20 galls at several sites. U.S. Department of Agriculture cooperators in New Hampshire released insects at two leafy spurge and two cypress spurge sites; New York cooperators released insects at two leafy spurge sites in the northeast part of the state; and cooperators in Rhode Island released insects at three cypress spurge sites (Hansen et al., 1997) (Table 3).

Figure 3. Aphthona nigriscutis on Euphorbia cyparissias L. (Photograph by R.A. Casagrande.)
Figure 3. Aphthona nigriscutis on
Euphorbia cyparissias L. (Photograph
by R.A. Casagrande.)

Figure 4. Aphthona flava on Euphorbia cyparissias L.(Photograph by R.A. Casagrande.)
Figure 4. Aphthona flava on Euphorbia cyparissias L.(Photograph by R.A. Casagrande.)
 
Figure 5. Aphthona lacertosa on Euphorbia cyparissias L. (Photograph by R.A. Casagrande.)
Figure 5. Aphthona lacertosa on Euphorbia cyparissias L. (Photograph by R.A. Casagrande.)

Table 3. Biological Control Agents Released in 1995-1998 in Northeastern United States

State County Species Year Statusa
NH Carroll A. czwalinae/A. lacertosa 1995 E
Mixed Aphthona spp. 1995 E
S. esulae 1995 E
Rockingham A. czwalinae/A. lacertosa 1995, 96 E
S. esulae 1995, 96 NE
NY Jefferson A. czwalinae/A. lacertosa 1995, 96 E (A. flava)
Mixed Aphthona spp. 1995, 96 E
S. esulae 1995, 96 E
RI Kent A. czwalinae/A. lacertosa 1995 E
A. flava 1996 E
S. esulae 1995 NE
Newport A. cyparissiae 1995 E
A. czwalinae/A. lacertosa 1995, 96, 98 E
A. flava 1996, 98 E
Mixed Aphthona spp. 1995, 98 E
E. esulae 1995, 96 E
Washington A. czwalinae/A. lacertosa 1996 E
A. flava 1998 E
a Status of biological control agent populations in 2000; E, population(s) established; NE, popluation(s) not established.
b Two or more of the following species released together: Aphthona cyparissiae, A. flava, and A. nigriscutis.

During the 1990s two other insects were released on cypress spurge in Ontario, Canada. Oberea erthrocephala (Schrank), a root-boring beetle in the family Cerambycidae, became established, but Lobesia euphorbiana (Freyer), a leaf-tying moth in the family Tortricidae, did not (Harris, 1999).

Biology and Ecology of Key Natural Enemies

Aphthona Species (Coleoptera: Chrysomelidae)

Aphthona species overwinter in the soil as larvae and pupate in spring in pupal cells. Adult beetles emerge in early to mid-summer and feed on spurge. Adult females mate and then lay eggs in small batches in the soil or near the base of spurge shoots. Females oviposit for several months, producing 50 to 300 eggs each. Larvae emerge in about two weeks, burrow into the soil and feed on small roots, moving to larger roots as they mature. Large larvae may burrow in the soil around spurge roots or tunnel inside large roots and root buds. Larval feeding damages spurge plants by disrupting water and nutrient transport and provides entry points for soil inhabiting fungi. Adult feeding may defoliate plants at high beetle densities, but this has little or no impact on plant health (Hansen et al., 1997).

All Aphthona species released in northeastern United States are univoltine (Gassmann and Shroeder, 1995). Another species, Aphthona abdominalis Duftschmidt, has up to four generations per year in Europe. This species was released in Montana and Colorado, but has not established (Hansen et al., 1997).

Aphthona species are highly specialized and each occupies a specific niche in its native range. Aphthona nigriscutis shows a distinct preference for sandy or gravely sites, while A. cyparissiae prefers sandy loam sites (Gassmann, 1985). Aphthona flava prefers mesic-to-dry habitats and is well adapted to live in alluvial soils above flood lines, as well as in soils of relatively dry, sunny sites. Aphthona flava tolerates light shade and is probably less likely to survive low temperatures than the other species (Sommer and Maw, 1982). Aphthona czwalinae is adapted to mesic habitats with cool summers. Aphthona lacertosa prefers loamy soils and can adapt locally to both dry and wet habitats (Gassmann, 1990).

Spurgia Species (Diptera: Cecidomyiidae)

Spurgia esulae is a multivoltine insect, with two or three generations per year in Montana on leafy spurge and up to five generations per year in Europe. It overwinters in soil as mature larvae and first generation adults emerge in mid to late spring. Females deposit groups of eggs on spurge leaves, near the apical buds, producing 20 to 100 eggs over their one to two day lifespan. First instar larvae migrate to spurge buds and begin feeding within the meristematic tissue. Larval feeding induces hypertrophy in bud tissue

Figure 6. Gall caused by Spurgia esulae on Euphorbia cyparissias L. (Photo by H. Faubert.)
Figure 6. Gall caused by Spurgia esulae on Euphorbia cyparissias L. (Photo by H. Faubert.)
and leads to the formation of a gall (Fig. 6). Larvae feed exclusively within gall tissue and complete development in two to four weeks. Mature larvae construct silken cocoons inside galls from which adult flies emerge. Mature larvae of the final generation drop from galls and burrow into the soil to overwinter (Pecora et al., 1991). Spurgia capitigen, released in Canada, has a similar life cycle.

Hyles euphorbiae (Lepidoptera: Sphingidae)

Hyles euphorbiae requires 42 to 72 days to complete development and has one or two generations per year. It overwinters as pupae in the soil, from which the moths emerge in spring. Mated females deposit light green, spherical eggs on leaves and bracts of spurge plants, producing up to 150 eggs in a lifetime. The conspicuously colored larvae feed on leaves for several weeks before entering the soil to pupate (Poritz, 1988).

Evaluation of Project Outcomes

Establishment and Spread of Agents

Between 1976 and 1982, Hyles euphorbiae was released in Virginia, New York, and Maryland on both cypress spurge and leafy spurge. The only successful release of H. euphorbiae in the eastern United States was on cypress spurge in Warren County, New York in 1977. At all other release sites, this insect did not become established (Batra, 1983; Barbosa et al., 1994). The population in Warren Co. increased from 180 to about one million insects within five years and caused defoliation in some areas. Even where insect populations were high, H. euphorbiae did not inflict significant damage since spurge plants easily tolerate yearly defoliation (Spencer, 1994).

Research with H. euphorbiae halted in the early 1980s due to high insect mortality attributed to predation by several insect species, raccoons, and deer mice. A virus also limited the numbers of H. euphorbiae (Batra, 1983).

Insect releases in the 1990s in New York, New Hampshire, and Rhode Island were more successful (Table 3). Where Aphthona species were released, sweep-net samples were performed following protocols set up by USDA, APHIS-PPQ (Attavian, 1994). Sweep sampling began the year following release and continued for several field seasons. On each sampling date, four sweeps were made adjacent to the marked release point and at 2, 4, 6, and 8 m from the release point, along each cardinal direction (20 sampling points, 80 sweeps total). A voucher sample was collected and sent to Bozeman, Montana for species verification (Hansen et al..,1997).

In the 1990s, one or more insects became established at each of the northeastern states’ release sites. In New York, A. czwalinae, A. lacertosa, and A. flava as well as S. esulae became established, while only two individual A. nigriscutis or A. cyparissiae were recovered as of 1999 (P. Wrege and B. Blossey, pers. comm.). In New Hampshire and Rhode Island, all released species have been recovered. In Rhode Island, A. flava, A. nigriscutis and A. cyparissiae can be found easily, but A. czwalinae and A. lacertosa are scarcer. In New York on leafy spurge, A. czwalinae and A. lacertosa have been the species recovered most often, while A. flava has been detected less frequently (P. Wrege, pers. comm.). Releases in New Hampshire have not been followed as closely, but all released species have been recovered (J. Weaver, pers. comm.).

In Rhode Island and New York, some Aphthona species increased sufficiently to allow redistribution to other sites infested with cypress spurge. In New York in June of 2000, researchers collected a mix of 10,000 A. czwalinae, A. lacertosa, and A. flava from the two leafy spurge release sites. These insects were distributed to two new leafy spurge infested sites on two dairy farms in New York (P. Wrege, pers. comm.). At one release site in Rhode Island during the summer of 2000, approximately 50,000 A. flava were collected from a small stand of cypress spurge where 500 A. flava were released in 1996. Cypress spurge was swept during 16 collecting visits from June 23 to July 17, 2000. These insects were then released at eight other pasture or hay fields in Rhode Island infested with cypress spurge.

Within farms, Aphthona species spread readily on their own. Collecting adult Aphthona beetles and redistributing them to areas heavily infested with cypress spurge on the same farm can sped up this natural dispersal of Aphthona species.

The gall midge, S. esulae, can be found sporadically at New York and New Hampshire release sites and in extremely high numbers at one Rhode Island release site.

In Rhode Island, seven release sites on two farms have realized excellent biological control of cypress spurge, with weed suppression noted the year after releasing insects in many sites (Fig. 7). Six of these releases were with 500 to 1500 adult beetle mixes of A. flava and A. nigriscutis or A. nigriscutis and A. cyparissiae. The seventh successful release was a mix of 1,000 A. czwalinae and A. lacertosa. Most of the suppression at this site may be attributed to feeding from A. flava and A. nigriscutis since many of these beetles were found at the site one year after A. lacertosa and A. czwalinae were released. Within three years, A. flava and A. nigriscutis beetles spread 70 m from their release site.

Figure 7. Aphthona flava defoliating Euphorbia cyparissias L. at URI ALton Jones Cmapus, June, 2000. (Photo by H. Faubert.)
Figure 7. Aphthona flava
defoliating Euphorbia cyparissias
L. at URI ALton Jones Campus,
June, 2000. (Photo by H. Faubert.)

Figure 8. 'Windmill' release site at Watson Farm, Jamesown, R.I., in 1997. Yellow flowers are Euphorbia cyparissias L. (Photo by H. Faubert.)
Figure 8. "Windmill" release site at Watson Farm, Jamesown, R.I., in 1997. Yellow flowers are Euphorbia cyparissias L. (Photo by H. Faubert.)
 
'Windmill' release site at Watson Farm, Jamesown, R.I., in 2000.
Figure 9. "Windmill" release site at Watson Farm, Jamesown, R.I., in 2000. Note relative scarcity of yellow flowers of Euphorbia cyparissias L. (Photo by H. Faubert.)

The second year following release resulted in clearly noticeable suppression at all seven sites in Rhode Island (Figs. 8 and 9), with areas nearly free from spurge extending in a diameter of 3 to 10 m around marking stakes where releases were originally made. Aphthona species were numerous on surrounding cypress spurge plants and sweep counts often reached two beetles per sweep, the amount recommended for redistributing the beetles to other locations (Hansen et al., 1997). At all sites where Aphthona species established, populations increased sufficiently to allow collecting and redistribution.

The third year after release, weed suppression around release stakes reached 5 to 30 m diameters. Aphthona beetles had moved onto other cypress spurge plants and were difficult to find within 10 m of release stakes. At one site, four years after releasing 500 A. flava, nearly all the cypress spurge has been suppressed.

Some Rhode Island releases have not been as successful. Releases of mixes of 500 A. czwalinae and A. lacertosa have provided little or no control after four years. At two sites, A. flava and A. nigriscutis migrated into the area and are providing control. At another site, cypress spurge is being displaced by another invasive weed, black swallowort, Vincetoxicum nigrum (L.) Moench.

Spurgia esulae galls are found in New York, New Hampshire, and Rhode Island, though damage to leafy or cypress spurge is not apparent at this time. The galls are considered a nutrient sink and reportedly kill cypress spurge with repeated heavy attacks (Harris, 1999). An additional benefit of S. esulae is reported to be reduced seed production, however, in the northeast United States, the majority of cypress spurge flowering occurs before galls are present each spring. These flowers continue to develop seeds, and galls form on other shoots. No attempt has been made to redistribute S. esulae within the Northeast because it does not appear to contribute to biological control of leafy or cypress spurge.

Recovery of Native Plant Communities

Since cypress spurge has been suppressed in Rhode Island pastures, pasture grasses such as timothy and other cool-season perennials have grown back, but so have some other invasive weeds, specifically black swallow-wort and Canada thistle (Carduus arvensis [L.]) Robson.

Economic Benefits

At one site in Rhode Island, cypress spurge has been controlled. By 2000, Aphthona species were redistributed to eight different farms in Rhode Island. Several of these sites were in hay fields where growers were unaware of cypress spurge problems. These growers had been harvesting cypress spurge infested hay and selling it for animal food or as construction hay, perhaps assisting the spread of cypress spurge to new areas. Introducing Aphthona species into these areas may eliminate the need for herbicides to control cypress spurge, could help protect farm animals, and reduce the spread of cypress spurge.

Recommendations for Future Work

In the western United States, future efforts against leafy spurge will concentrate on continued introductions of insects that have not been released at many locations, specifically A. abdominalis, C. hungarica, and O. erythrocephala (Hansen et al., 1997). Whether or not these species will contribute to biological control of the target weed has yet to be determined.

The Aphthona species presently available in North America provide good control of leafy and cypress spurge in open grassland habitats, but have not been as successful at controlling spurge in high-moisture or shaded habitats. In Rhode Island, the original Aphthona species releases were made on light, sandy soils in full sunlight. In these habitats the insects are succeeding in suppressing cypress spurge. It is unknown how effective these insects will be controlling cypress spurge in other conditions. Perhaps additional biological control agents can be found in Eurasia that are effective against cypress spurge in shaded or wet environments.

In the eastern United States, where future efforts will likely involve redistributing Aphthona species to other infestations of cypress spurge, it is particularly important to locate infestations of the more aggressive form of cypress spurge, the fruiting tetraploid form. This can be accomplished by surveying for cypress spurge in April and May while it is blooming and most easily detected. Once an infestation is located it must be revisited in June to see whether or not cypress spurge seed is present. In a survey conducted in Rhode Island in 2000, 98% of all cypress spurge sampled was the tetraploid form. This is a dramatic change from when Deane (1912) located only three stands of tetraploid cypress spurge in North America. If this switch to tetraploid cypress spurge is occurring throughout the region, there is added impetus to distribute biological control agents of this pest.

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(Tech. Coordinators). 2003. Invasive Plants of the Eastern U.S.:
Identification and Control. USDA Forest Service - Forest Health
Technology Enterprise Team. Morgantown, WV USA. FHTET-2003-08.