Practical resistance to cry toxins and efficacy of Vip3Aa in bt cotton against helicoverpa zea

Authors: YANG, FEI - Texas A&M University; KERNS, DAVID - Texas A&M University; Little, Nathan; BROWN, SEBE - University Of Tennessee; STEWART, SCOTT - University Of Tennessee; CATCHOT, ANGUS - Mississippi State University; COOK, DON - Mississippi State University; GORE, JEFFREY - Mississippi State University; CROW, WHITNEY - Mississippi State University; LORENZ, GUSTAV - University Of Arkansas; TOWLES, TYLER - Louisiana State University; TABASHNIK, BRUCE - University Of Arkansas

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/17/2022
Publication Date: 8/25/2022
Citation: Yang, F., Kerns, D.L., Little, N., Brown, S., Stewart, S., Catchot, A., Cook, D., Gore, J., Crow, W., Lorenz, G., Towles, T., Tabashnik, B.E. 2022. Practical resistance to cry toxins and efficacy of Vip3Aa in bt cotton against helicoverpa zea. Pest Management Science. 1:1-9. https://doi.org/10.1002/ps.7142.
DOI: https://doi.org/10.1002/ps.7142

Interpretive Summary: This study focuses on practical resistance to crystaline insecticidal toxins, which are produced by transgenic crops, in bollworm (also known as corn earworm), one of most economically important pests of cotton and other crops in the United States. Information gained from insect bioassays and field efficacy trials with bollworm were jointly studied to evaluate the association between these two key aspects of practical resistance to crystaline transgenic insecticides. The bioassays and field efficacy trials showed widespread practical resistance to crystaline transgenic insecticides in the mid-southern U.S. and Texas, effectively leaving a single vegetatively-produced toxin that is highly effective for bollworm control in cotton. Higher levels of bollworm survival in laboratory bioassays were generally associated with decreased efficacy of Bt cotton plants in the field. The findings of this study show that the planting of field corn hybrids that produce vegetative insecticidal toxins in cotton-growing regions of the U.S. likely expedite the development of bollworm resistance to this insecticide. Information gained from this study support recommendations from a Scientific Advisory Panel convened by the US EPA that efffectively limit selection for resistance to vegatatively-produced toxins in corn where bollworm is not a major economic pest, and thereby help to preserve its efficacy against bollworm in cotton where it is a major economic pest.

Technical Abstract: Crops genetically engineered to make insect-killing proteins from Bacillus thuringiensis (Bt) have revolutionized management of some pests. However, the benefits of such transgenic crops are reduced when pests evolve resistance to Bt toxins. Here we evaluated resistance to Bt toxins and Bt cotton plants using lab bioassays and complementary field trials focusing on Helicoverpa zea, one of the most economically important pests of cotton and other crops in the United States. The data from 235 lab bioassays demonstrate resistance to Cry1Ac, Cry1Fa, and Cry2Ab occurred in most of the 95 strains of H. zea derived from Arkansas, Louisiana, Mississippi, Tennessee and Texas during 2016 to 2021. Complementary field data show efficacy decreased for Bt cotton producing Cry1Ac + Cry1Fa or Cry1Ac + Cry2Ab, but not Cry1Ac + Cry1Fa + Vip3Aa. Moreover, analysis of data paired by field site and year shows higher survival in bioassays was generally associated with lower efficacy of Bt cotton. The results confirm and extend previous evidence showing widespread practical resistance of H. zea in the United States to the Cry toxins, but not to Vip3Aa, produced by Bt cotton and corn. Despite deployment in combination with Cry toxins in Bt crops, Vip3Aa effectively acts as a single toxin against H. zea larvae that are highly resistant to Cry toxins. Furthermore, Vip3Aa adoption is increasing and previous work provided an early warning of field-evolved resistance. Thus, rigorous resistance management measures are needed to preserve the efficacy of Vip3Aa against this highly adaptable pest.