UROPHORA AFFINIS AND U-QUADRIFASCIATA (DIPTERA, TEPHRITIDAE) RELEASEDAND MONITORED BY USDA, APHIS, PPQ AS BIOLOGICAL-CONTROL AGENTS OF SPOTTED AND DIFFUSE KNAPWEED

USDA, APHIS, PPQ has distributed the seedhead gall flies Urophora affi nis and U. quadrifasciata (Diptera: Tephritidae) as classical biologic al agents of the introduced weeds spotted and diffuse knapweed (Centau rea maculosa and C. diffusa, respectively) (Asteraceae) in the United States. From 1987 to 1996, Urophora spp. have been released in 97 coun ties in 14 midwestern and western states. Established populations of U . affinis and U. quadrifasciata are confirmed in 85 and 95 counties, r espectively, among all 14 states. These include the first reports of s uccessful establishment of Urophora spp, in Arizona (two counties), Co lorado (eight counties), Michigan (one county), Minnesota (six countie s), Nebraska (four counties), Nevada (two counties), North Dakota (one county), South Dakota (four counties), Utah (three counties), and Wis consin (two counties). The first confirmed establishment of U. quadrif asciata in Indiana and Michigan is also reported.