The corn earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), can cause serious losses in many field and vegetable crops throughout the United States. Since their introduction, pyrethroid insecticides have become the primary insecticide class for managing H. zea. However, resistance has been reported in the southern United States and has recently became a concern in the Midwest after the observation of sporadic control failures and a decreased efficacy of pyrethroids in small-plot field trials. Larvae collected from Lafayette, IN, Vincennes, IN, and Collinsville, IL, were used to establish laboratory colonies in 2006 and 2007. Larvae from these colonies were tested for resistance to the pyrethroid insecticide bifenthrin by using topical assays. Adult males collected from pheromone traps in Lafayette were tested for resistance to Cypermethrin by using the adult vial test (AVT) method. Resistance ratios of ≥8 were observed for the larval bifenthrin assays in 2006 and 2007 in all colonies except for the 2007 Illinois colony. AVT assays conducted with Cypermethrin showed ≈15% survival in both 2006 and 2007 at the 5 µg per vial discriminating dose. These results suggest that low to moderate levels of pyrethroid resistance are present in these populations.
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Vol. 102 • No. 6