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

Susceptibility to technical grade fipronil was determined for 10 populations of the European corn borer, Ostrinia nubilalis (Hübner). Field collections were made from 8 locations across the United States. Two laboratory colonies were also tested. Most collections were from sites where the biovoltine Z strain of O. nubilalis predominates, but samples of other strains were also obtained. Field-collected larvae or egg masses were reared for one generation in the laboratory, and susceptibility of neonates was determined with feeding bioassays where increasing concentrations of the toxin were applied to the surface of artificial diet. Small differences in LC₅₀ and LC₉₀ values 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 previous selection. In addition, these data provide a baseline for future comparisons to determine if susceptibility has changed as the insecticide becomes widely used for corn borer management.