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

Abstract

BackgroundPyramiding 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.ResultsDiet 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.ConclusionOur findings indicate that Vip3Aa‐resistant H. zea does not exhibit positive cross‐resistance to Cry1 or Cry2 proteins. Additionally, 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.This article is protected by copyright. All rights reserved.

Diverse genetic basis of Vip3Aa resistance in five independent field‐derived strains of Helicoverpa zea in the US

“…† Larval mortality at each concentration of Vip3Aa39 was corrected based on the mortality observed on the control diet. 6 Collectively, these findings suggest that both high-dose refuge and gene-pyramiding strategies should be effective in managing Vip3Aa resistance in H. zea, contingent upon meeting additional conditions such as ensuring abundant refuge plants and a rare initial resistance allele frequency. However, it is important to acknowledge that resistance to Cry1 and Cry2 is currently widespread in H. zea across US corn and cotton fields.…”

“…5 Currently in the US, there are three primary families of Bt proteins employed to control H. zea, which include two crystal insecticidal proteins (Cry1 and Cry2) and one vegetative insecticidal protein (Vip3Aa). 6 Field-evolved H. zea resistance to Cry1 and Cry2 proteins in pyramided Bt corn and cotton is widespread in the US, as evidenced by the increasing number of documented fields with greater than expected damage levels in Bt crops producing only Cry1/Cry2 proteins, [7][8][9][10][11][12][13] and the increasing frequency of Cry1 and Cry2 resistance alleles in field populations of H. zea. 14,15 Consequently, Vip3Aa is the only effective Bt protein in pyramided Bt crops for control of H. zea in these regions.…”