Resistance Allele Frequency of Helicoverpa zea to Vip3Aa Bacillus thuringiensis Protein in the Southeastern U.S.

is a major target pest of Bt crops expressing Cry and/or Vip3Aa proteins in the U.S.A. Widespread practical resistance of to the Cry1 and Cry2 proteins makes Vip3Aa the only effective Bt protein against this pest. Understanding the frequency of resistance alleles against Vip3Aa in field populations of is crucial for resistance management and the sustainability of Vip3Aa technology. Using a modified F screen method by crossing susceptible laboratory female moth with feral male moth of , we successfully screened a total of 24,576 neonates from 192 F families of collected from Arkansas, Louisiana, Mississippi, and Tennessee during 2019-2020. We found five F families containing ≥3rd instar survivors on the diagnostic concentration of 3.0 µg/cm Vip3Aa39. Dose-response bioassays confirmed the high levels of Vip3Aa resistance in these F families, with an estimated resistance ratio of >909.1-fold relative to the susceptible strain. The estimated resistance allele frequency against Vip3Aa in for these four southern states is 0.0155 with a 95% CI of 0.0057-0.0297. These data should provide critical information for understanding the risks of Vip3Aa resistance in and help design appropriate resistance management strategies for the sustainability of the Vip3Aa technology.