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, Mississippi, were estimated by digging a total of 43,542 m-row. Densities of pupae varied greatly among years. The sex ratio of pupae was variable and significantly male-biased in some years. Following the introduction of Bacillus thuringiensis Berliner (Bt)-transgenic cotton in 1996 but before the widespread adoption of herbicide resistant (HR)-transgenic cotton in 2000, local cotton fields accounted for less than 2% of the total overwintered tobacco budworm population. Due to apparent, long-distance immigration, conclusions for the corn earworm are problematic. In the pre-transgenic cotton production era, it is estimated cotton fields typically accounted for less than 10% of overwintered tobacco budworms. 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 crop year 2000--tillage preemptively destroyed most tobacco budworm pupae overwintering in cotton fields. Adoption of HR-transgenic cotton 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 directly suppress subsequent population densities. However, the absence of such tillage might increase the rate of development of counteradaptation by the tobacco budworm to insecticides and to antibiotic host plant resistance traits including the Bt-transgenic trait.
Species 1: Lepidoptera Noctuidae Heliothis virescens (tobacco budworm)
Species 2: Lepidoptera Noctuidae Helicoverpa zea (corn earworm, bollworm)
Species 3: Bacillales Bacillaceae Bacillus thuringiensis (Bt)
Keywords: pheromone, tillage
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