Magnitude and Extent of Helicoverpa zea Resistance Levels to Cry1Ac and Cry2Ab2 across the Southeastern USA

Dominic Reisig; G David Buntin; Jeremy K Greene; Silvana V Paula-Moraes; Francis Reay-Jones; Phillip Roberts; Ron Smith; Sally V Taylor

doi:10.3390/insects14030262

Magnitude and Extent of Helicoverpa zea Resistance Levels to Cry1Ac and Cry2Ab2 across the Southeastern USA

Insects. 2023 Mar 7;14(3):262. doi: 10.3390/insects14030262.

Authors

Dominic Reisig¹, G David Buntin², Jeremy K Greene³, Silvana V Paula-Moraes⁴, Francis Reay-Jones³, Phillip Roberts², Ron Smith⁵, Sally V Taylor⁶

Affiliations

¹ Department of Entomology, The Vernon James Center, North Carolina State University, Plymouth, NC 27962, USA.
² Department of Entomology, University of Georgia, Tifton, GA 31793, USA.
³ Department of Plant and Environmental Sciences, Clemson University, Blackville, SC 29817, USA.
⁴ Entomology and Nematology Department, University of Florida, Jay, FL 32565, USA.
⁵ Department of Entomology and Plant Pathology, Auburn University, Auburn, AL 36849, USA.
⁶ Department of Entomology, Virginia Polytechnic Institute and State University, Suffolk, VA 23437, USA.

Abstract

After resistance is first detected, continued resistance monitoring can inform decisions on how to effectively manage resistant populations. We monitored for resistance to Cry1Ac (2018 and 2019) and Cry2Ab2 (2019) from southeastern USA populations of Helicoverpa zea. We collected larvae from various plant hosts, sib-mated the adults, and tested neonates using diet-overlay bioassays and compared them to susceptible populations for resistance estimates. We also compared LC₅₀ values with larval survival, weight and larval inhibition at the highest dose tested using regression, and found that LC₅₀ values were negatively correlated with survival for both proteins. Finally, we compared resistance rations between Cry1Ac and Cry2Ab2 during 2019. Some populations were resistant to Cry1Ac, and most were resistant to CryAb2; Cry1Ac resistance ratios were lower than Cry2Ab2 during 2019. Survival was positively correlated with larval weight inhibition for Cry2Ab. This contrasts with other studies in both the mid-southern and southeastern USA, where resistance to Cry1Ac, Cry1A.105, and Cry2Ab2 increased over time and was found in a majority of populations. This indicates that cotton expressing Cry proteins in the southeastern USA was at variable risk for damage in this region.

Keywords: Bt cotton; bioassays; diet overlay; resistance.

Grants and funding

This work was supported by the USDA National Institute of Food and Agriculture: Biotechnology Risk Assessment Research Grants Program 2017-33522-27090/project accession no. 1013740.