Extended investigation of field-evolved resistance of the corn earworm Helicoverpa zea (Lepidoptera: Noctuidae) to Bacillus thuringiensis Cry1A.105 and Cry2Ab2 proteins in the southeastern United States

Authors: YU, WENBO - Louisiana State University Agcenter; LIN, SHUCONG - Louisiana State University Agcenter; DIMASE, MARCELO - Louisiana State University Agcenter; NIU, YING - Louisiana State University Agcenter; BROWN, SEBE - Louisiana State University Agcenter; HEAD, GRAHAM - Bayer Cropscience; PRICE, PAULA - Bayer Cropscience; REAY-JONES, FRANCIS - Clemson University; COOK, DON - Mississippi State University; REISIG, DOMINIC - North Carolina State University; THRASH, BEN - University Of Arkansas; Ni, Xinzhi; PAULA-MORAES, SILVANA - University Of Florida; HUANG, FANGNENG - Louisana State University

Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/12/2021
Publication Date: 2/22/2021
Citation: Yu, W., Lin, S., Dimase, M., Niu, Y., Brown, S., Head, G.P., Price, P.A., Reay-Jones, F.P., Cook, D., Reisig, D., Thrash, B., Ni, X., Paula-Moraes, S.V., Huang, F. 2021. Extended investigation of field-evolved resistance of the corn earworm Helicoverpa zea (Lepidoptera: Noctuidae) to Bacillus thuringiensis Cry1A.105 and Cry2Ab2 proteins in the southeastern United States. Journal of Invertebrate Pathology. 183:107560. https://doi.org/10.1016/j.jip.2021.107560.
DOI: https://doi.org/10.1016/j.jip.2021.107560

Interpretive Summary: The use of stacked bacterial traits expressing multiple insecticidal proteins can enhance pest control efficacy, broaden target pest spectrum, and delay the development of insect resistance to insecticidal proteins. The corn earworm is an economically important pest in the Western Hemisphere on corn, cotton and other crops. The stacked traits producing multiple insecticidal proteins has been available since 2002 in cotton, and these traits were highly effective initially against the corn earworm. Across the Cotton Belt of the southern United States, maize and cotton are often adjacently cultivated. In a crop growing season, corn earworm larvae usually feed on maize first. When maize plants become unsuitable for oviposition, the moth switches to cotton and other alternative host crops. Larvae feed on these alternative crops and continue their life cycle for multiple generations in a field season. Thus, in the Cotton Belt, the corn earworm is a cross-crop pest targeted by both transgenic cotton and corn varieties. Currently, transgenic maize and cotton plantings in the United States account for >80 and >90% of the total areas of the two crops, respectively. In the current cropping landscape, the similarities in transgene traits in maize and cotton, and the phenology of the corn earworm in the Cotton Belt, create a high risk of natural corn earworm populations to develop resistance to transgenic insecticidal toxins. The present study was an extended investigation, following a series of previous studies to determine the current status and distribution of corn earworm resistance to transgenic insecticidal toxins across the southeastern states. During 2018 and 2019, a total of 31 field populations of the corn earworm were collected from the major maize production areas of seven southeastern states of the United States. These populations were examined against two transgenic insecticidal toxins, that is, the Cry1A.105 and Cry2Ab2 proteins. The results revealed that resistance to these two insecticidal proteins is widely distributed in the region. Moreover, correlations between the resistance to these two insecticidal proteins and the presumable ongoing field selection for resistance are also discussed.

Technical Abstract: Previous studies have reported that the corn earworm/cotton bollworm, Helicoverpa zea (Boddie), has developed field resistance to pyramided Bacillus thuringiensis (Bt) Cry1A/Cry2A maize and cotton in certain areas of the southeastern United States. The objective of the current study was to determine the current status and distribution of the resistance to Cry1A.105 and Cry2Ab2 in H. zea. In the study, 31 H. zea populations were collected from major maize planting areas across seven southeastern states of the United States during 2018 and 2019 and assayed against the two Bt proteins. Diet-overlay bioassays showed that almost all populations collected during the two years were highly resistant to the Cry1A.105 protein. Most populations collected during 2019 were also highly resistant to Cry2Ab2, while significant variances in Cry2Ab2 susceptibility existed among populations collected during 2018. The results showed that Cry1A.105 and Cry2Ab2 resistance in H. zea has become widely distributed in the regions sampled. The resistance to Cry1A.105 appears to have plateaued, while selection for Cry2Ab2 resistance is likely still occurring. Thus, effective measures for managing the Cry1A/Cry2A resistance need to be developed and implemented to ensure the sustainable use of Bt biotechnology.