Baseline susceptibility and frequency of resistance to diamide insecticides in Helicoverpa armigera (Lepidoptera: Noctuidae) populations in Brazil

Abstract

Diamide insecticides have been widely used to manage Helicoverpa armigera (Hübner) since the official detection of this pest in Brazil in 2013. Characterizing the baseline susceptibility of H. armigera populations to insecticides is the first step to implement an effective resistance-management program. In this study, we characterized the susceptibility and estimated the frequency of resistance allele to diamide insecticides in populations of H. armigera collected in different Brazilian agricultural regions. First, the baseline susceptibilities to flubendiamide, chlorantraniliprole and cyantraniliprole were established for seven H. armigera populations collected in 2013 and 2014, and the allele frequency of resistance to chlorantraniliprole was estimated using the F2 screening method. Then, the susceptibility to diamide insecticides was monitored based on diagnostic doses (LD99) in H. armigera populations collected from 2014 to 2018. Low initial variations in susceptibility (<5-fold) to flubendiamide, chlorantraniliprole and cyantraniliprole were found in the populations tested, based on the median lethal dose (LD50). The allele frequencies of H. armigera resistance to chlorantraniliprole were 0.00694 (95% CI, 0.00018–0.02561) in 2014 and 0.04348 (95% CI, 0.01216–0.09347) in 2015. Significant reductions in susceptibility to these insecticides were observed in H. armigera populations throughout the crop seasons, with survival rates increasing from 0% in the 2014 crop season up to 51.99% in the 2018 crop season based on diagnostic dose bioassays. Our results indicate a rapid evolution of resistance to diamide insecticides in H. armigera and an urgent need for implementation of resistance management strategies to extend the usefulness of these insecticides in Brazil.