Urophora affinis (Diptera: Tephritidae) and U. quadrifasciata (Diptera: Tephritidae) are two seedhead flies approved for release in the United States in 1971 and 1988, respectively for biological control of spotted and diffuse knapweed. United States Department of Agriculture, Animal Plant Health Inspection Service, Plant Protection Quarantine (APHIS) released a mixture of 4,000 adult U. affinis and U. quadrifasciata in Isabella County, Michigan, in 1994. No Urophora species were found in pre-release samples in seven counties in 1993. Samples collected in three counties in 1994, prior to the APHIS release, detected U. quadrifasciata in Menominee County. Surveys from 1998 to 2000 found U. affinis in 23 counties around and including Isabella County. Urophora affinis was also found in Schoolcraft County in northern Michigan. Urophora quadrifasciata was found in 86 samples in 83 counties and U. affinis in 42 samples in 24 counties from surveys taken in 1998 to 2000. Centaurea maculosa (Compositae) (spotted knapweed) was found to be present in all 83 counties and C. diffusa (Compositae) (diffuse knapweed) in two Michigan counties.
Lang, R. F.; Richard, R. D.; Winkler, J.; and Wheeler, G.
"Distribution of Urophora Affinis and U. Quadrifasciata (Diptera: Tephritidae) for Biological Control of Spotted Knapweed (Centaurea Maculosa) and Diffuse Knapweed (Centaurea Diffusa) in Michigan,"
The Great Lakes Entomologist, vol 34
Available at: https://scholar.valpo.edu/tgle/vol34/iss1/6