Resistance risk assessment and associated fitness cost of fluxametamide in the rice stem borer, Chilo suppressalis Walker (Lepidoptera: Pyralidae)

Abstract

The rice stem borer (RSB), Chilo suppressalis Walker, is a major agricultural pest resistant to multiple insecticides, emphasizing the need for novel insecticides. Fluxametamide, a recently developed isoxazoline insecticide, has demonstrated strong efficacy against lepidopteran pests, including RSB. In this study, the resistance risk of RSB to fluxametamide was evaluated, along with the potential fitness costs associated with resistance. After 10 generations of continuous selection, the LC₅₀ values for third-instar larvae of RSB increased from 0.195 mg/kg to 0.392 mg/kg, resulting in a 2.01-fold rise in resistance. The realized heritability (h²) was 0.082, and the predicted rate of resistance development suggested that with a slope of 1.920 and h² of 0.082, a 10-fold increase in LC₅₀ would require 13 to 29 generations using selection intensities of 90 % and 50 %, respectively. The life table analysis showed a significant increase in durations of the egg stage, first- and sixth- instar larvae, for the fluxametamide-selected (Flux-SEL) strain, while the pupal durations, male and female longevity, pupal weights, and fecundity were significantly reduced compared to the laboratory strain (WT). A significant decrease in the intrinsic rate of increase (r), the finite rate of increase (λ), and the net reproduction rate (R₀) was also observed in the Flux-SEL strain. The final relative fitness (R_f) value of 0.52 was obtained after 10 generations of selection. These findings provide an understanding of laboratory-induced insecticide resistance evolution and the related fitness costs in RSB. This information is valuable for developing effective fluxametamide application strategies aimed at managing resistance in RSB.