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Title: First documentation of major Vip3Aa resistance alleles in field populations of Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) in Texas, USA

item YANG, F. - Texas A&M University
item SANTIAGO GONZALES, J.C. - Texas A&M University
item Little, Nathan
item REISIG, D. - North Carolina State University
item PAYNE, G. - University Of West Georgia
item DOS SANTOS, R.F. - University Of Tennessee
item JURAT-FUENTES, J.L. - University Of Tennessee
item KURTZ, R. - Cotton, Inc
item KERNS, D.L. - Texas A&M University

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2020
Publication Date: N/A
Citation: N/A

Interpretive Summary: Monitoring the susceptibility of field populations of bollworms is an essential component of insect resistance management plans to maintain sustainability of Bt crop technologies. Third generation Bt crops express a new protein, Vip3A, which is produced during the vegetative stage of the plant. Determining the status of bollworm tolerance to Vip3A is vital for resistance management of this pest. Female bollworm moths were collected from light traps in Texas and returned to the laboratory. Progeny from these females were reared to adulthood and sixty of them mated to their siblings. Progeny from the sib-matings were screened using discriminating doses for tolerance to Vip3A. The assays detected two sibling families carrying major resistance alleles to Vip3A. This study is the first to provide documentation of a major resistance allele conferring high levels of Vip3Aa resistance in a field-derived strain of bollworm in the U.S. This study will contribute to development of new resistance management strategies and provide guidance for the sustainable use of the Vip3A toxin to control bollworm in the U.S.

Technical Abstract: BACKGROUND: The corn earworm, Helicoverpa zea, is a major target pest of the insecticidal Vip3Aa protein used in pyramided transgenic Bt corn and cotton with Cry1 and Cry2 proteins in the U.S. The widespread resistance to Cry1 and Cry2 proteins in H. zea will challenge the long-term efficacy of Vip3Aa technology. Determining the frequency of resistant alleles to Vip3Aa in field populations of H. zea is critically important for resistance management. Here, we provided the first F2 screen study to estimate the resistance allele frequency for Vip3Aa in H. zea populations in Texas, U.S. RESULTS: In 2019, 128 H. zea neonates per isofamily for a total of 114 F2 families were screened with a diagnostic concentration of 3.0 µg/cm2 of Vip3Aa39 protein in diet-overlay bioassays. The F2 screen detected two families carrying a major Vip3Aa resistance allele. The estimated frequency of major resistance alleles against Vip3Aa39 in H. zea in Texas from this study was 0.0065 with a 95% CI of 0.0014-0.0157. A Vip3Aa-resistant strain (RR) derived from the F2 screen showed a high level of resistance to Vip3Aa39 protein, with a resistance ratio of >588.0-fold relative to a susceptible population (SS) based on diet-overlay bioassays. CONCLUSION: We provide the first documentation of a major resistance allele conferring high levels of Vip3Aa resistance in a field-derived strain of H. zea in the U.S. Data generated from this study contribute to development of management strategies for the sustainable use of the Vip3Aa technology to control H. zea in the U.S.