Fitness costs of Vip3Aa resistant Helicoverpa zea strains on non-Bt meridic diet

The corn earworm, Helicoverpa zea (Boddie), is a major pest in transgenic crops in the United States. The heavy usage and reliance on Bacillus thuringiensis (Bt) proteins to manage H. zea populations has inadvertently resulted in insects evolving resistance to Bt toxins. Fitness costs occur in the absence of Bt proteins, and the fitness of Bt resistant insect species plays an important role in determining the speed of resistance evolution. The objective of this research is to determine the fitness costs of two Vip3Aa resistant H. zea strains. Three major insect genotypes were used: AC4 Vip3Aa resistant (RR), R15 Vip3Aa resistant (RR), and susceptible (SS). In addition, four F1 heterozygous strains were produced from reciprocal crosses between the Vip3Aa resistant strains and the susceptible. Fitness costs were evaluated on non-Bt meridic diet based on pupal weight, developmental time, survivability, and fecundity. Depending on the strain, we detected a dominant fitness cost for developmental time and fecundity, and a recessive fitness cost for survival. The presence of fitness costs associated with Vip3Aa resistant alleles should help slow the evolution of resistance and development of practical field resistance.