Chaetorellia acrolophi
Diptera: Tephritidae

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

Chaetorellia acrolophi, a seedhead fly, is a native of Europe and was cleared for release in the United States in 1992. The fly has been released in Montana, Oregon, Washington and Wyoming. Recovery has been confirmed in Oregon. Releases are limited by the availability of this biocontrol agent in Europe. This fly is being released to enhance the complex of biocontrol insects for spotted knapweed control.

Appearance

C. acrolophi is a small (3 mm) yellow-brown fly with bright green eyes and light brown wing bars. This fly is found resting or displaying on the buds of spotted knapweed in the early summer.

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 plants 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 C. acrolophi is part of a program to introduce a complex of spotted and diffuse knapweed enemies to help control these weeds.

Pests Attacked

C. acrolophi has a limited host range with a preference for species in the Centaurea subgenus Acrolophus. C. acrolophi was tested against fifty-eight plant species in the family Asteraceae including United States endangered and economically important species.

Life Cycle

Adults begin to emerge from the spotted knapweed seedheads in the spring from mid May into early June. Mating begins as soon as the females emerge and eggs are laid within a few days of mating. The eggs hatch in four to five days, then the larvae burrow into the knapweed flower bud and start feeding. The overwintering generation larvae pupate in the spring. In her lifetime, the female fly will lay an average of sixty-nine eggs. She may lay as many as twelve eggs each day. The adults can live up to four weeks.

Pesticide Susceptibility

Not yet known.

Commercial Availability

C. acrolophi is not yet available from public or commercial sources.

Relative Effectiveness

C. acrolophi larvae considerably reduce the seed production of spotted knapweed, typically destroying the entire contents of an infested seedhead. The effect on diffuse knapweed is not clear at this time. The larvae can develop on diffuse knapweed but in field tests C. acrolophi did not lay eggs on this plant.

Conservation

C. acrolophi release sites should be selected considering long term availability. Ten years without the threat of being disturbed by development or pesticide use is required.

References

Groppe, K. and K. Marquardt. 1989. Chaetorellia acrolophi White & Marquardt (Diptera: Tephritidae), a suitable candidate for the biological control of diffuse and spotted knapweed in North America. Intl. Inst. of Biol. Control, DelÇmont, Switzerland Final Report. 30 p.

White, I. M. and K. Marquardt. 1989. A revision of the genus Chaetorellia Hendel (Diptera: Tephritidae) including a new species associated with spotted knapweed, Centaurea maculosa Lam. (Asteraceae). Bull. Entomol. Res. 79: 453-487.

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