ABSTRACT

The susceptibility of the tobacco budworm (Heliothis virescens [F.]) and bollworm (Helicoverpa zea [Boddie])populations from 14 cotton-producing states to Cry1Ac protein of Bacillus thuringiensis was monitored for the eighth consecutive year in 2003. The survivorship of first generation larvae obtained from mass mating males captured in pheromone traps near cotton fields (wild population) with laboratory-adapted females (susceptible strain), was determined at 2 diagnostic concentrations for each species plus an untreated control. Survivorship of those larvae was compared to survivorship of the laboratory strain. Survival of the 40 strains of Heliothis virescens and 97 strains of Helicoverpa zea tested between April and October, 2003 was not elevated above that in the susceptible strain using current methodology. However, the current method does have limitations, and additions and modifications to that methodology are discussed.