Cross‐resistance and redundant killing of Vip3Aa resistant populations of Helicoverpa zea on purified Bt proteins and pyramided Bt crops

BACKGROUND Pyramiding Bt proteins is a key strategy to delay insect resistance development. However, the durability of pyramided Bt crops for controlling insect pests is threatened by cross‐resistance among Bt proteins, which can ultimately contribute to resistance development. The corn earworm, Helicoverpa zea, is a major agricultural pest of pyramided Bt crops. Previous studies have examined cross‐resistance and redundant killing of Cry resistance in H. zea, but such information is lacking for Vip3Aa resistance in this pest. Here, we evaluated cross‐resistance and redundant killing of Vip3Aa‐resistant H. zea to purified Bt proteins, as well as Bt corn and Bt cotton. RESULTS Diet bioassays demonstrated high susceptibility of Vip3Aa‐resistant H. zea to Cry1Ac, Cry1A.105, and Cry2Ab2 purified proteins. No Vip3Aa‐susceptible, ‐heterozygous, or ‐resistant H. zea could survive on pyramided Bt corn containing Cry1 and/or Cry2 proteins. Complete redundant killing was observed in pyramided Bt corn containing Cry1 and/or Cry2 proteins against Vip3Aa resistance in H. zea. Vip3Aa‐susceptible, ‐heterozygous, and ‐resistant H. zea exhibited survival rates ranging from 0.0% to 22.5% on pyramided Bt cotton with Cry1 and/or Cry2 proteins. Incomplete to complete redundant killing was observed for Vip3Aa‐resistant H. zea on pyramided Bt cotton containing Cry1 and/or Cry2 proteins. CONCLUSION Our findings indicate that Vip3Aa‐resistant H. zea does not exhibit positive cross‐resistance to Cry1 or Cry2 proteins. In addition, most pyramided Bt crops showed complete or nearly complete redundant killing of Vip3Aa‐resistant H. zea. These results indicate that a pyramiding strategy would often be effective for managing Vip3Aa resistance in regions of the United States where H. zea has not evolved resistance to Cry1 and Cry2 toxins. © 2023 Society of Chemical Industry. The Vip3Aa‐resistant Helicoverpa zea does not exhibit cross‐resistance to Cry1 or Cry2 purified Bt proteins, and pyramided Bt crops containing Cry and Vip3Aa proteins could provide complete redundant killing of Vip3Aa‐resistant H. zea. These findings support the use of pyramiding strategy for managing Vip3Aa resistance in H. zea.