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Aphthona nigriscutis
(Coleoptera: Chrysomelidae)

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.

Aphthona nigriscutis was originally approved for release in the United States in 1989. Through 1995, it has been widely released in leafy spurge infestations across the northern U.S. (19 states) and western Canada. Large populations are present in several western states, including Wyoming, Montana, North Dakota, and Colorado. Aphthona flea beetles can kill leafy spurge plants as a direct or indirect consequence of larval feeding on spurge roots.

Appearance

The adult flea beetle is small (2-4 mm) and yellowish-brown or bronze in color above, and a darker brown below. A black spot is present on the dorsal surface, behind the head. A. nigriscutis adults typically hop rather than fly when disturbed. Larvae are found in the soil, on or near leafy spurge roots. They are 1-5 mm long, with short legs, yellow heads, and creamy-white bodies.

Habitat

Leafy spurge-infested grasslands.

Pests attacked

The host range of A. nigriscutis appears restricted to plants in the subgenus Esula of the genus Euphorbia. In Europe, this beetle 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 A. nigriscutis, though no feeding has yet been documented under field conditions. A. nigriscutis will not feed on poinsettia (Euphorbia pulcherrima), and crop species and native plants outside the genus Euphorbia will not be attacked.

Life cycle

Depending on location, adults emerge from the soil beginning in May to July, and are present for several weeks to several months. A. nigriscutis adults feed on leafy spurge foliage and flowers, and high populations may defoliate spurge plants. Females lay small groups of eggs at, or just below, the soil surface, near the base of a leafy spurge stem. Newly-hatched larvae burrow into the soil and begin feeding on very small leafy spurge roots. Larvae feed on progressively larger roots and root buds as they develop. A. nigriscutis larvae overwinter, resume feeding in the spring, and then pupate in a soil cell in late spring to early summer. There is one generation per year.

Relative effectiveness

A. nigriscutis populations have significantly reduced spurge infestations over large areas in several western states and in Canada. Drier sites appear optimal for this species.

Pesticide susceptibility

Not yet known.

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

In some states, A. nigriscutis adults may be obtained at no cost from state weed management agencies. Several commercial suppliers can also provide A. nigriscutis adults (see the off-site publication, Suppliers of Beneficial Organisms in North America, page of the California Department of Pesticide Regulation website).

Reference:

Gassman, A. (1985) Aphthona nigriscutis Foudras (Coleoptera: Chrysomelidae): a candidate for the biological control of cypress spurge and leafy spurge in North America. Final screening report. International Institute of Biological Control, DelÇmont, Switzerland. 19 pp.

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