Effects of resistance to Bt proteins Cry1Ac and Vip3Aa on flight traits of Helicoverpa zea

BACKGROUND: Genetically engineered crops producing insecticidal Bacillus thuringiensis proteins are useful for managing some key insect pests, including Helicoverpa zea (corn earworm or bollworm). In the United States, widespread practical resistance to crystalline (Cry) proteins and early warning of resistance to the vegetative insecticidal protein Vip3Aa have been reported for H. zea. To test the hypothesis that resistance to Cry1Ac or Vip3Aa causes fitness costs affecting flight and related traits in H. zea, we compared lab-selected Cry1Ac-resistant and Vip3Aa-resistant strains with their susceptible parental strains, and with an unrelated standard susceptible strain. We used flight mills to analyze flight (flight propensity, total distance, distance per flight, duration, number of flights, and speed) and related traits (post-flight survival, body mass, forewing area, wing loading, flight muscle mass, and abdominal lipid mass). RESULTS: The results show that H. zea resistance to Cry1Ac or Vip3Aa generally did not cause fitness costs affecting flight and related traits. One notable exception is that male post-flight survival was lower in a Vip3Aa-resistant strain than its Vip3Aa-susceptible parent strain. CONCLUSION: Together with the limited fitness costs previously reported in Cry-resistant H. zea, the lack of fitness costs in Cry1Ac-resistant H. zea affecting flight and related traits reported here aligns with the rapid evolution of practical resistance of H. zea to Cry proteins. If the reduced post-flight survival of Vip3Aa-resistant males in the laboratory also occurs in the field, it could help to delay the evolution of resistance and the geographic spread of alleles conferring resistance to Vip3Aa.