Overwintering of Heliothis virescens (F.) and Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) in cotton fields of northeast Mississippi

Following the 1995-2001 crop seasons, population densities of pupae of tobacco budworm, Heliothis virescens (F.), and corn earworm, Helicoverpa zea (Boddie), overwintering in cotton fields, Gossypium hirsutum L., in Monroe County, MS, were estimated by digging a total of 43,542 m-row. Densities of pupae varied greatly among years with the highest densities occurring in years with low rainfall in the late summer and early fall. The sex ratio of pupae was variable and significantly male-biased in some years. The total area-wide, tobacco budworm population emerging from all overwintering sites was estimated from catches in pheromone traps whose absolute efficiency is known. After the introduction of Bacillus thuringiensis Berliner (Bt)-transgenic cotton in 1996 but before a several-fold increase in use of herbicide resistant (HR)-transgenic cotton cultivars in 2001, local cotton fields accounted for <2% of the total overwintered tobacco budworm population. In the pretransgenic cotton production era, it is estimated cotton fields typically accounted for <10% of the overwintered tobacco budworm population. Driving surveys of the tillage status of cotton fields and pheromone trapping to determine the timing of adult emergence in the spring indicate that--until the 2000 crop season--postseason tillage destroyed most tobacco budworm and corn earworm pupae overwintering in cotton fields. Adoption of HR-transgenic cultivars has quintupled cotton field area planted no-till, but the contribution of cotton fields to overwintered tobacco budworm populations has remained low. Preemptive tillage of cotton fields to kill overwintering tobacco budworm pupae would not appreciably suppress in-season population densities of this pest. However, the absence of such tillage might increase the rate at which the tobacco budworm develops resistance to insecticides and counteradaptation to antibiotic host plant resistance traits including the Bt-transgenic trait.