Pyrethroid-resistant Helicoverpa zea and transgenic cotton in South Carolina

Abstract Failures to control Helicoverpa zea (Boddie) on cotton in South Carolina were associated with resistance to pyrethroid insecticides. Resistance to cyhalothrin, cypermethrin, and permethrin was observed in a colony collected as larvae from cotton in Estill, SC, in September 1996. Cyhalothrin resistance was expressed as an incompletely dominant trait. In 1997, resistance to cyhalothrin was observed in males captured in pheromone traps in Estill and nearby Ulmer. Resistance was also observed in Cameron and Holly Hill (Santee), SC, 150 km to the north, in adults reared from larvae collected from cotton. In contrast, all moths trapped in the Pee Dee River drainage 300 km to the north were susceptible. Putative mechanisms for resistance as related to improved monitoring of population genetics and implications for control of pests on transgenic insecticidal cotton are discussed.