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Hyles euphorbiae
(Lepidoptera: Sphingidae)

by Rich Hansen, USDA-APHIS-PPQ, Forestry Sciences Lab, Montana State University, Bozeman, MT 59717-0278.

Leafy spurge is an Eurasian perennial that was introduced into North America in the 19th century.
It infests several million hectares of rangelands and riparian areas in the United States and is a serious pest across the northern Great Plains where it displaces desirable grasses and forbs normally consumed by foraging cattle. Cattle and horses usually avoid leafy spurge, but should they eat it, its milky latex may cause sickness and even death. Annual direct and indirect economic losses due to leafy spurge infestation in Montana, South Dakota, North Dakota, and Wyoming are estimated to exceed $120 million. In addition, leafy spurge forms monocultures that often displace native plants and degrade wildlife habitats.

Leafy spurge has a number of biological characteristics that have caused it to be difficult to control with herbicides, and infestations generally occur in remote areas consisting of comparatively low-value land. Thus, classical biological control is envisioned as a potentially valuable spurge management tool in North America. To date, ten Eurasian insect species have been released as biocontrol agents of leafy spurge.

The leafy spurge hawk moth was the first classical biological agent released against leafy spurge in the United States, with approval for introduction granted in 1965. Populations of this insect are present in several western states, including Montana, Idaho, and Oregon.

Appearance

Adult moths are large (length: 2-3 cm, wingspan: 5-7 cm) day- flying moths that often exhibit a hummingbird-like flight while visiting flowers. The body is light brown with various white and dark brown markings, while the wings have a conspicuous tan, brown, and pink or red color pattern.

H. euphorbiae larvae are found feeding on leafy spurge leaves. The caterpillars are also conspicuously colored, with a pronounced tail or "horn" near the rear end. Young larvae are variously patterned with green, yellow, and black; older larvae have a distinctive red, black, yellow, and white color pattern. Mature larvae may approach 10 cm in length; when disturbed, they regurgitate a slimy green liquid. Pupae are 3.5-5 cm long and dark brown, and are found in the soil.

Habitat

Leafy spurge-infested grasslands.

Pests attacked

The host range of H. euphorbiae appears restricted to plants in the subgenus Esula of the genus Euphorbia. In Europe, this caterpillar feeds on leafy spurge and several other closely-related spurge species. There are a few native Euphorbia spp. in the U.S. that could potentially be hosts for H. euphorbiae, though no feeding has yet been documented under field conditions. H. euphorbiae will not feed on poinsettia (Euphorbia pulcherrima), and crop species and native plants outside the genus Euphorbia will not be attacked.

Life cycle

Adult moths are present beginning in early to mid-summer. After mating, females lay small clusters of eggs on leafy spurge foliage. After hatching, larvae consume leafy spurge leaves and flowers. Mature larvae enter the soil to pupate. There are one or two generations per year, with soil-inhabiting pupae as the overwintering stage.

Relative effectiveness

H. euphorbiae larvae defoliate leafy spurge plants, but this damage seems to have little or no impact on spurge populations. In addition, hawk moth populations generally remain low in an area, due to predation and disease. Thus, H. euphorbiae plays only a very minor role in leafy spurge biological control.

Pesticide susceptibility

The herbicide 2,4-D appears to have no direct impact on H. euphorbiae populations.

Conservation

For general information about conservation of natural enemies, see Conservation in the Tutorial section on this site, or the Feature Article on conservation in the Midwest Biological Control News.

Commercial availability

Not known.

References

Batra, S. W. T. (1983) Establishment of Hyles euphorbiae (L.) (Lepidoptera: Sphingidae) in the United States for control of two weedy spurges, Euphorbia esula L. and E. cyparissias L. J. NY Entomol. Soc. 91: 304-311.

Rees, N. E. and Fay, P.K. (1989) Survival of leafy spurge hawk moths (Hyles euphorbiae) when exposed to 2,4-D or picloram. Weed Technol. 3: 429-431.

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