Estimation of resistance allele frequencies to Cry1A.105 and Cry2Ab2 in the corn earworm (Lepidoptera: Noctuidae) with F2 isolines generated from a mass-mating method

Authors: YU, WENBO - Louisiana State University Agcenter; HEAD, GRAHAM - Bayer Corporation; PRICE, PAULA - Bayer Corporation; BROWN, SEBE - Louisiana State University Agcenter; COOK, DON - Mississippi State University; Ni, Xinzhi; REAY-JONES, FRANCIS P.F. - Clemson University; DIMASE, MARCELO - Louisiana State University Agcenter; HUANG, FANGNENG - Louisiana State University Agcenter

Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/7/2022
Publication Date: 7/12/2022
Citation: Yu, W., Head, G.P., Price, P., Brown, S., Cook, D., Ni, X., Reay-Jones, F., Dimase, M., Huang, F. 2022. Estimation of resistance allele frequencies to Cry1A.105 and Cry2Ab2 in the corn earworm (Lepidoptera: Noctuidae) with F2 isolines generated from a mass-mating method. Crop Protection. 161:106054. https://doi.org/10.1016/j.cropro.2022.106054.
DOI: https://doi.org/10.1016/j.cropro.2022.106054

Interpretive Summary: The use of the same or similar bacterial toxins in transgenic crops has led to the field populations of the corn earworm developed resistance to the bacterial toxins. The current study used insects collected during 2018 and 2019 from the southeastern states of Louisiana, Mississippi, Georgia, and South Carolina to understand the genetics of natural corn earworm populations. The mass-mating method has allowed us to successfully establish 103 sister populations of the 2nd generation corn earworms. Each of these sister populations was established using the eggs from a single female. The screening of the 2nd generation sister populations is more sensitive than other resistance monitoring methods. The screenings of 24-h old larvae of the 2nd generation sister populations demonstrated high frequency of bacterial toxin resistance alleles in the field collected corn earworms. The detection of high resistance allele frequencies in the corn earworm sister populations validated that bacterial toxin resistance is common in natural corn earworm populations in the four southeastern states.

Technical Abstract: The corn earworm/bollworm, Helicoverpa zea (Boddie), is targeted in the United States by transgenic corn and cotton expressing Bacillus thuringiensis (Bt) proteins, including Cry1A.105 and Cry2Ab2. Previous studies have shown that field resistance to Cry1A/Cry2A corn has occurred in the United States. In this study, we established 103 F2 isolines by mass-mating of H. zea populations collected during 2018 and 2019 in four southeastern U.S. states: Louisiana, Mississippi, Georgia, and South Carolina. The F2 isolines were screened for resistance alleles to Cry1A.105 and Cry2Ab2, the two Bt proteins expressed in MON 89034 corn event. The results showed that resistance allele frequencies in the H. zea populations were high for both Bt proteins, averaged 0.405 for Cry1A.105 and 0.330 for Cry2Ab2. The detected high resistance allele frequencies validate that resistance to Cry1A/Cry2A is common in the southeastern region. In addition, the F2 screening showed that resistance allele frequencies (0.490 for Cry1A.105 and 0.541 for Cry2Ab2) in populations collected in 2019 were significantly greater than the frequencies (0.312 for Cry1A.105 and 0.081 for Cry2Ab2) in populations collected in 2018, suggesting that field selection of the resistance were still ongoing. Information generated from this study is useful to assess resistance risk, refine resistance modeling, and improve IRM programs to mitigate Cry protein resistance in H. zea for sustainable use of Bt crop technology in the United States.