Resistance allele frequency to Cry1Ab and Vip3Aa20 in Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) in Louisiana and three other southeastern U.S. states

Authors: LIN, SHUCONG - Louisiana State University; OYEDIRAN, ISAAC - Syngenta Crop Protection; NIU, YING - Louisiana State University; BROWN, SEBE - Louisiana State University; COOK, DON - Louisiana State University; Ni, Xinzhi; ZHANG, YAN - Clemson University; REAY-JONES, FRANCIS - Clemson University; CHEN, JENG SHONG - Syngenta Crop Protection; WEN, ZHIMOU - Syngenta Crop Protection; DIMASE, MARCELO - Louisiana State University; HUANG, FANGNENG - Louisiana State University

Submitted to: Toxins
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/2/2022
Publication Date: 4/11/2022
Citation: Lin, S., Oyediran, I., Niu, Y., Brown, S., Cook, D., Ni, X., Zhang, Y., Reay-Jones, F.P., Chen, J., Wen, Z., Dimase, M., Huang, F. 2022. Resistance allele frequency to Cry1Ab and Vip3Aa20 in Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) in Louisiana and three other southeastern U.S. states. Toxins. 14(4):270. https://doi.org/10.3390/toxins14040270.
DOI: https://doi.org/10.3390/toxins14040270

Interpretive Summary: A total of 104 second-generation sister lines of the corn earworm collected from the four southeastern U.S. states, that is, Georgia, Florida, Louisiana, and Mississippi) were screened for resistance to the two bacterial toxins Cry1Ab and Vip3Aa20, which are commonly used in transgenic maize and cotton cultivars. Results show that resistance alleles to maize cultivars with the Cry1Ab toxin are abundant in natural corn earworm populations, while functionally major resistant alleles to maize cultivars with the Vip3Aa20 toxin are uncommon in the region. The group-mating approach used in the study provides an alternative to the commonly used single-pairing method for the second-generation sister line establishment.

Technical Abstract: The corn earworm/bollworm, Helicoverpa zea, is a pest species targeted by both Bacillus thuringiensis (Bt) maize and cotton in the U.S. Cry1Ab and Vip3Aa20 are two common Bt proteins expressed in transgenic maize. The objective of this study was to determine the resistance allele frequency (RAF) to Cry1Ab and Vip3Aa20 in H. zea populations collected during 2018 and 2019 from four southeastern U.S. states: Louisiana, Mississippi, Georgia, and South Carolina. By using a group-mating approach, 104 F2 female isolines of H. zea were established from the field collections with most lines (85) from Louisiana, and these F2 female isolines were screened for resistance alleles to Cry1Ab and Vip3Aa20, respectively. The F2 screenings showed no correlations in the larval survivorships of the iso-lines between the screenings against Cry1Ab and Vip3Aa20. RAF to Cry1Ab maize was high (0.254) and the RAFs were similar between Louisiana and the other three states and between the two sampling years. In contrast, no functionally major resistance allele (RA) to Vip3Aa20 maize were detected in the 101 iso-lines screened, thus the expected RAF of major RAs to Vip3Aa20 maize with 95% probability was 0 to 0.0073. However, functionally minor RAs to Vip3Aa20 maize were not uncommon; the estimated Vip3Aa20 RAF for minor alleles was 0.028. The results provide further evidence that field resistance to Cry1Ab maize in H. zea has widely occurred, while major RAs to Vip3Aa20 maize are uncommon in the southeastern U.S. region. The group-mating approach used in this study provides an alternative to the commonly used single-pairing method for F2 isoline establishment. Information generated from this study should be useful in resistance monitoring and refinement of resistance management strategies to preserve Vip3A susceptibility in H. zea.