She may lay more than one egg per seedhead. 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. The overwintering generation emerges as adults from galls in the mature seedheads in the spring as the new flower buds are beginning to form. quadrifasciata produce two generations per year. The larvae of this fly attack the seedhead causing the plant to form a non-lignified gall around each larvae. No oviposition or larval development was found on these three plant species.
The fly was tested against safflower ( Carthamus tinctorius L.), an economically important relative of knapweed, and two US native knapweeds. quadrifasciata attacks plants in the genus Centaurea. quadrifasciata is part of a program to introduce a complex of spotted and diffuse knapweed enemies to help control these weeds. Both weeds will invade well established grassland communities and out-compete the native vegetation. These highly competitive weed species favor and establish quickly on disturbed sites and overgrazed rangeland. 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. The larva is white with a dark brown anal plate. The gall in the seedhead is paper-thin with pappus on top. The female has a long retractable ovipositor. quadrifasciata is a small (2-3 mm) dark bodied fly with a distinctive VU mark on its wings. Establishment has been confirmed in Indiana, Maryland, New York, Pennsylvania, Vermont, New Hampshire, Massachusetts, Rhode Island, Connecticut, and New Jersey.
quadrifasciata has been released and established in Arizona, California, Colorado, Idaho, Michigan, Minnesota, Montana, Nebraska, North Dakota, South Dakota, Utah, Washington, Wisconsin, and Wyoming. Urophora quadrifasciata, a seedhead fly which is a native fly of Europe, was approved for release in 1988. Lang, USDA-APHIS-PPQ, Bozeman Biocontrol Facility, Forestry Sciences Laboratory, Montana State University, Bozeman, MT 59717- 0278.
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