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Aphthona czwalinae
(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 czwalinae was originally approved for release in the United States in 1987. Through 1995, it has been widely released in mixed populations with A. lacertosa in leafy spurge infestations across the northern U.S. (19 states). Large populations are present in several states, including Montana, North Dakota, and Wisconsin. Aphthona flea beetles can kill leafy spurge plants as a direct or indirect consequence of larval feeding on spurge roots.

Appearance

Adult flea beetles are small (2-4 mm) and a shiny, metallic black in color; they are virtually indistinguishable from A. lacertosa adults. A. czwalinae 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. czwalinae 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. czwalinae, though no feeding has yet been documented under field conditions. A. czwalinae 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. czwalinae adults feed on leafy spurge foliage and flowers, and high populations may defoliate spurge plants. Females lay 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. czwalinae 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

Mixed A. czwalinae/A. lacertosa populations have apparently "controlled" leafy spurge infestations at a number of sites in the western and midwestern U.S. These species seem best suited to relatively mesic habitats.

Pesticide susceptibility

Not 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, adults from mixed A. czwalinae and A. lacertosa populations may be obtained at no cost from state weed management agencies.

Reference

Gassman, A. (1984) Aphthona czwalinae Weise (Coleoptera: Chrysomelidae): a candidate for the biological control of leafy spurge in North America. Final screening report. International Institute of Biological Control, Del‚mont, Switzerland. 20 pp.

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