Journal
TOXINS
Volume 14, Issue 4, Pages -Publisher
MDPI
DOI: 10.3390/toxins14040270
Keywords
Helicoverpa zea; Bt maize; F-2 screen; resistance allele frequencies; Cry1Ab; Vip3A
Categories
Funding
- Syngenta Crop Protection (Research Triangle Park, NC, USA) [AWD-000793]
- Louisiana Soybean and Grain Research and Promotion Board [AWD-003027]
- USDA National Institute of Food and Agriculture
- USDA Multistate Research Project [NC246]
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The study found that the resistance allele frequency (RAF) to Cry1Ab maize was high in H. zea populations, while no functional major resistance allele to Vip3Aa20 maize was detected, although functional minor alleles were not uncommon.
The corn earworm/bollworm, Helicoverpa zea (Boddie), is a pest species that is targeted by both Bacillus thuringiensis (Bt) maize and cotton in the United States. Cry1Ab and Vip3Aa20 are two common Bt toxins that are 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 that were collected during 2018 and 2019 from four southeastern U.S. states: Louisiana, Mississippi, Georgia, and South Carolina. By using a group-mating approach, 104 F-2 iso-lines of H. zea were established from field collections with most iso-lines (85) from Louisiana. These F-2 iso-lines were screened for resistance alleles to Cry1Ab and Vip3Aa20, respectively. There was no correlation in larval survivorship between Cry1Ab and Vip3Aa20 when the iso-lines were exposed to these two toxins. RAF to Cry1Ab maize was high (0.256) and the RAFs were similar between Louisiana and the other three states and between the two sampling years. In contrast, no functional major resistance allele (RA) that allowed resistant insects to survive on Vip3Aa20 maize was detected and the expected RAF of major RAs with 95% probability was estimated to 0 to 0.0073. However, functional minor RAs to Vip3Aa20 maize were not uncommon; the estimated 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. Information that was generated from this study should be useful in resistance monitoring and refinement of resistance management strategies to preserve Vip3A susceptibility in H. zea.
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