Fitness costs associated with Vip3A resistance in Helicoverpa zea

The utilization of Bacillus thurginesis (Bt) proteins play an important role of pest control in major Lepidopteran species, such as Helicoverpa zea. However, there has been evolution to resistance to these Bt proteins which poses a risk to the usage of Bt crops. Vip3A is the most recent Bt protein implemented in Bt corn and cotton products. Understanding the risks associated with Vip3A resistance of H. zea is vital for future insect pest management strategies. The fitness cost of resistance is an important factor in determining the speed of resistance development when using the refuge strategy. Fitness costs of Bt resistance occur when in the absence of the Bt toxins, the fitness is lower for resistant insects than for the susceptible insects. Fitness costs associated with Vip3A resistance were evaluated on non-Bt meridic diet and will also be assessed on non-Bt cotton tissues and non-Bt corn ears. Four insect genotypes were used: a Vip3A resistant (RR), a susceptible (SS), and two F1 heterozygous Vip3A-resistant strains that were produced from reciprocal crosses between the RR and SS, which are R♂S♀ and R♀S♂. Survivorship, development, and reproduction rate were used to estimate life time parameters and to assess fitness costs.