Urophora quadrifasciata

Left: Urophora quadrifasciata adult female.
Right: U. quadrifasciata larva in gall (left) and spotted knapweed seed (right).
R.Richard (both)

Urophora quadrifasciata
Diptera: Tephritidae

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

Urophora quadrifasciata, a seedhead fly which is a native fly of Europe, was approved for release in 1988. U. quadrifasciata has been released and established in Arizona, California, Colorado, Idaho, Michigan, Minnesota, Montana, Nebraska, North Dakota, South Dakota, Utah, Washington, Wisconsin, and Wyoming. Establishment has been confirmed in Indiana, Maryland, New York, Pennsylvania, Vermont, New Hampshire, Massachusetts, Rhode Island, Connecticut, and New Jersey.

Appearance

U. quadrifasciata is a small (2-3 mm) dark bodied fly with a distinctive VU mark on its wings. The female has a long retractable ovipositor. The gall in the seedhead is paper-thin with pappus on top. The larva is white with a dark brown anal plate.

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 U. quadrifasciata is part of a program to introduce a complex of spotted and diffuse knapweed enemies to help control these weeds.

Pests Attacked

U. quadrifasciata attacks plants in the genus Centaurea. The fly was tested against safflower (Carthamus tinctorius L.), an economically important relative of knapweed, and two US native knapweeds. No oviposition or larval development was found on these three plant species. The larvae of this fly attack the seedhead causing the plant to form a non-lignified gall around each larvae.

Life Cycle

U. quadrifasciata produce two generations per year. The overwintering generation emerges as adults from galls in the mature seedheads in the spring as the new flower buds are beginning to form. The female fly after mating, uses her ovipositor to penetrate flower buds that are over half grown to lay her eggs among the developing stamens. She may lay more than one egg per seedhead. The eggs hatch in three to four days and the larva chews down in a floret into the ovary causing the plant to start forming a gall about eight days after the larva has hatched. The gall will have reached maximum size in fifteen days after hatching. It takes about eight to nine weeks from hatching for the new adult generation to appear. The next generation or late summer generation will overwinter as mature larvae in the seedheads, emerging next spring as adults.

U. quadrifasciata is a strong flier and disperses great distances. This fly is rapidly colonizing the knapweed patches of North America.

Pesticide Susceptibility

Though high rates of 2,4-D may cause increased larval and pupal mortality, spring applications of the herbicides 2,4-D and picloram (applied when knapweeds are primarily in the rosette stage) appear to have no significant negative impacts on U. quadrifasciata populations (McCaffery and Callihan, 1988).

Commercial Availability

In some states, U. quadrifasciata adults may be obtained at no cost from state weed management agencies. Several commercial suppliers can also provide U. quadrifasciata adults.

Effectiveness

The floret that the larva occupies is destroyed and adjacent florets will abort. The gall does not form a nutrient sink and thus has a minimal impact on the total plant. Each gall displaces 1.9 seeds in a diffuse knapweed seedhead. Combined with U. affinis, the two flies have been reported to have destroyed up to 95% of the knapweed seed at two British Columbia sites. U. quadrifasciata in combination with other seedhead agents and root borers will help get diffuse and spotted knapweed under control.

Conservation

Release sites should be chosen that will not be disturbed for at least ten years by development or pesticide use. U. quadrifasciata prefers open sunny sites to closed shady areas.

References

Harris, P. 1986. Biological control of knapweed with Urophora quadrifasciata, Mg. Agriculture Canada, Ottawa Canadex: 641.613. 2 p.

Harris, P. 1980. Establishment of Urophora affinis Frfld. and U. quadrifasciata (Meig.) (Diptera: Tephritidae) in Canada for the biological control of diffuse and spotted knapweed. Z. angew. Entomol. 89: 504-514.

Hoebeke, E. R. 1993. Establishment of Urophora quadrifasciata (Diptera: Tephritidae) and Chrysolina quadrigemina (Coleoptera: Chrysomelidae) in portions of the eastern United States. Entomol. News 104: 143-152.

McCaffrey, J. P. and R.H. Callihan. 1988. Compatibility of picloram and 2,4-D with Urophora affinis and U. quadrifasciata (Diptera: Tephritidae) for spotted knapweed control. Environ. Entomol. 17: 785-788.

Rees, N. E. and J.M. Story. 1991. Host plant testing of Urophora quadrifasciata (Diptera: Tephritidae) against Carthamus tinctorius and two North American species of Centaurea. Entomophaga 36: 115-119.

Roitberg, B. 1988. Comparative flight dynamics of knapweed gall flies Urophora quadrifasciata and U. affinis (Diptera: Tephritidae). J. Entomol. Soc. B.C. 85: 58-64.

Story, J. M. 1985. First report of the dispersal into Montana of Urophora quadrifasciata (Diptera: Tephritidae), a fly released in Canada for biological control of spotted and diffuse knapweed. Can. Entomol. 117: 1061-1062.

Story, J. M., W.R. Good, and N.W. Callan. 1993. Supercooling capacity of Urophora affinis and U. quadrifasciata (Diptera: Tephritidae), two flies released on spotted knapweed in Montana. Environ. Entomol. 22: 831-836 .

Wheeler, A. G. Jr. 1996. Urophora quadrifasciata (Diptera: Tephritidae), an introduced seedhead fly new to midwestern North America. Great Lakes Entomol. 28: 235-236.

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