Characterizing chlorantraniliprole resistance in Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) in Brazil: Susceptibility monitoring, inheritance, cross-resistance, and fitness costs

Abstract

Diamide insecticides are essential for managing Helicoverpa armigera (Hübner) in Brazil. Field-evolved resistance to the phthalic diamide flubendiamide has been reported in H. armigera in Brazil, with no cross-resistance observed with the anthranilic diamide chlorantraniliprole in that resistant strain. To evaluate resistance risk and management of H. armigera to chlorantraniliprole, this study aimed to (i) monitor susceptibility to chlorantraniliprole in H. armigera field populations across Brazilian cropping regions in 2020/21 and 2021/22, (ii) select and characterize a chlorantraniliprole-resistant strain to elucidate inheritance, (iii) evaluate cross-resistance to other diamides, and (iv) assess fitness costs associated with resistance. Toxicological assays revealed a reduction in susceptibility to chlorantraniliprole in field populations, with survival rates up to 30.8% at the diagnostic dose. Using the F2 screen method, a chlorantraniliprole-resistant strain (R-CHL) was selected from a field-population collected in Itiquira, Mato Grosso State. Resistance ratio of R-CHL was 142-fold after ten generations of laboratory selection. Reciprocal crosses between the susceptible and R-CHL strains and backcrosses of heterozygotes with the susceptible strain revealed that resistance of H. armigera to chlorantraniliprole is autosomal, incompletely dominant, and polygenic. R-CHL strain exhibited cross-resistance to cyclaniliprole (28-fold), cyantraniliprole (422-fold), and flubendiamide (>20,000-fold). Fitness costs of H. armigera to chlorantraniliprole were observed when larvae were fed an artificial diet, based on parameters of the fertility life table. However, no fitness cost occurred when larvae were fed on soybean leaves. These findings highlight the rapid evolution of H. armigera to chlorantraniliprole and other diamides, underscoring needs for resistance management in Brazilian agriculture.