Resistance risk assessment in diamondback moth, Plutella xylostella (L.) to fluxametamide

The diamondback moth Plutella xylostella (L.) (Lepidoptera: Plutellidae) is a devastating pest that infests several cruciferous vegetable crops worldwide and has developed insecticide resistance in most chemical classes. Fluxametamide is a novel neuroactive isoxazoline compound that binds to a unique site on the γ-aminobutyric acid (GABA) receptor and has an exceptional insecticidal activity on a range of lepidopteran caterpillars. The present study aimed to assess the risk of resistance in P. xylostella to fluxametamide under laboratory conditions. After the repeated exposure to fluxametamide for successive 18 generations of P. xylostella, there was 3.095-fold increase in the LC₅₀. When the realized heritability (h²) of P. xylostella to fluxametamide in the open field was assumed to be the laboratory-estimated value (h² = 0.180) and the mortality was 70–90%, only 22.9–33.1 generations were expected to be required to obtain a 10-fold increase in fluxametamide resistance. Compared with the laboratory susceptible strain (F₀), the Flux-SEL (F₁₈) strain exhibited a very low level of cross-resistance to emamectin benzoate (5.17-fold) and no significant cross-resistance to fipronil or flubendiamide. With the F₀ and the Flux-SEL test strains (F₁₂, F₁₅ and F₁₈), the specific activities of cytochrome P450 and glutathione S-transferase showed a remarkable increase during selection, while the esterase activity did not differ significantly. The results indicated that a potential risk of resistance development to fluxametamide exists in P. xylostella after continuous exposure. These pieces of information will be crucial in formulating rational fluxametamide application and resistance management guidelines for controlling P. xylostella under field condition.