Bangasternus fausti
Coleoptera: Curculionidae

B. fausti adult weevil. R.Richard

by R.F. Lang, USDA-APHIS-PPQ, Bozeman Biocontrol Facility, Forestry Sciences Laboratory, Montana State University, Bozeman, MT 59717- 0278.

Bangasternus fausti (Reitter), a seedhead weevil, is a native weevil of Europe and was released in the United States in 1991. The weevil has been released in California, Colorado, Idaho, Minnesota, Montana (established), Nebraska (established), Oregon (established), South Dakota, Washington, and Wyoming as part of a program to control spotted and diffuse knapweed (Centaurea maculosa Lam. and C. diffusa). The states listed without confirmed establishment reflect 1994 and 1995 B. fausti releases.

Appearance

B. fausti is a small grey brown weevil (4 mm in length) with a blunt snout that appears to have been cut off. B. fausti may be found feeding on spotted or diffuse knapweed foliage in the spring and in the summer on the flowers.

Habitat

Spotted and diffuse knapweed are weed species that can be found throughout the northern tier of states and as far south as Nebraska and Virginia. These highly competitive weed species favor and establish quickly on disturbed sites and overgrazed rangeland. Both weeds will invade well established grassland communities and out compete the native vegetation. The release of B. fausti is part of a program to introduce a complex of spotted and diffuse knapweed enemies to help control these weeds.

Pests Attacked

B. fausti is considered host specific and limited to a few species in the genus Centaurea, specifically C. diffusa (diffuse knapweed), C. maculosa (spotted knapweed), C. calcitrapa (purple star-thistle), C. squarrosa (squarrose knapweed), and will rarely attack C. solstitialis (yellow star- thistle), all of which are introduced weeds. Extensive host specificity tests were conducted in the field and laboratory in Europe before B. fausti was cleared and released in the United States.

Life Cycle

Adult weevils emerge from the seedheads and ground litter in May and early June. Egg laying begins within one to two weeks after emergence and continues through mid-August. The eggs hatch in eight to twelve days and the larvae then mine into the knapweed seedhead and begin feeding. It takes approximately thirty-two days for the weevil to develop from egg to the adult stage.

Pesticide Susceptibility

Not yet known.

Commercial Availability

B. fausti is not yet available from public or commercial sources.

Effectiveness

B. fausti larvae destroy up to one hundred percent of the seeds in a knapweed seedhead and any seeds that develop do not germinate. This weevil is part of a complex of insect biocontrol agents that contribute to the seed reduction in spotted and diffuse knapweed.

Considerations for Release

Sites that are chosen for B. fausti release should be considered for long term availability of up to ten years that potentially will not be disturbed with development or pesticide use. The weevil should be released in areas with dry summers for the best results.

References

Campobasso, G., P. H. Dunn, L. Knutson, and S. S. Rosenthal. 1988. Petition for release of Bangasternus fausti (Reitter) (Coleoptera: Curculionidae) for the control of diffuse knapweed, Centaurea diffusa Lam. (Compositae). USDA-ARS Biological Control of Weeds European Laboratory Report.

Dunn, P. H. and G. Campobasso. 1987. A petition for the introduction into quarantine for testing Bangasternus fausti (Reitter) (Coleoptera: Curculionidae); a potential biocontrol agent of diffuse knapweed (Centaurea diffusa Lam.). USDA-ARS Biological Control of Weeds European Laboratory Report.

Maddox, D. M. and R. Sobhian. 1987. Field experiment to determine host specificity and oviposition behavior of Bangasternus orientalis and Bangasternus fausti (Coleoptera: Curculionidae), biological control candidates for yellow starthistle and diffuse knapweed. Environ. Entomol. 16: 645-648.

Sobhian, R., G. Campobasso, and P.H. Dunn. 1992. A contribution to the biology of Bangasternus fausti (Col., Curculionidae), a potential biological control agent of diffuse knapweed, Centaurea diffusa, and its effect on the host plant. Entomophaga 37: 171- 179.

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