First host record for Pteromalus cardui (Hymenoptera: Pteromalidae) on Urophora quadrifasciata (Diptera: Tephritidae) in spotted knapweed (Centaurea biebersteinii, Asteraceae) in Michigan, U.S.A.

摘要

An association between the biological control agent Urophora quadrifasciata and a parasitoid, Pteromalus cardui, was found within seed heads of spotted knapweed (Centaurea biebersteinii [C. stoebe]) in Michigan, USA. There was a significant correlation between the percentage of seed heads with U. quadrifasciata emerging and those with P. cardui emerging. This parasitoid might reduce the already limited effectiveness of U. quadrifasciata in controlling spotted knapweed.