Susceptibility of European corn borer, Ostrinia nubilalis (Hubner) (Lepidoptera : Pyralidae) neonate larvae to fipronil

Susceptibility to technical grade fipronil was determined for 10 population s of the European corn borer, Ostrinia nubilalis (Hubner). Field collection s were made from 8 locations across the United States. Two laboratory colon ies were also tested. Most collections were from sites where the biovoltine Z strain of O. nubilalis predominates, but samples of other strains were a lso obtained. Field-collected larvae or egg masses were reared for one gene ration in the laboratory, and susceptibility of neonates was determined wit h feeding bioassays where increasing concentrations of the toxin were appli ed to the surface of artificial diet. Small differences in LC50 and LC90 va lues were observed, but the magnitude of the differences was small (<3-fold ). These results indicate that the observed susceptibility differences were the result of natural variation among populations and unrelated to previou s selection. In addition, these data provide a baseline for future comparis ons to determine if susceptibility has changed as the insecticide becomes w idely used for corn borer management.