The cross‐resistance to etofenprox in Nilaparvata lugens with a high adaptability to resistant rice variety IR56

The application of resistant rice varieties and insecticides represents two crucial strategies for managing the brown planthopper (BPH), Nilaparvata lugens (Stål). Insects often employ similar detoxification mechanisms to metabolize plant secondary metabolites and insecticides, which poses a potential risk that BPH population adapted to resistant rice may also obtain resistance to some insecticides. Here in a BPH population (R-IR56) that has adapted to the resistant rice variety IR56 through continuous selection, the moderate resistance to etofenprox was observed. Insect P450s often contribute to insecticide resistance in insects. Through transcriptome sequencing of R-IR56 and control populations, it was found that two P450 genes, CYP439A1 and CYP439A2, were over-expressed in R-IR56. RNA interference confirmed the importance of two P450s in etofenprox resistance in vivo. The metabolite identification and catalytic activity of recombinant P450 proteins revealed the metabolism of etofenprox by both CYP439A1 and CYP439A2 in vitro, which catalyzed an O-de-ethylation on etofenprox. However, the up-regulation of two P450 genes did not contribute to the adaptation of BPH to IR56 variety. The study reveals that BPH adapted to resistant rice variety IR56 exhibits a moderate level of resistance to etofenprox, but the cross-resistance to etofenprox in BPH is unidirectional. The findings here provide theoretical guidance for the integrated pest management strategy, especially focusing on the interplay between applications of resistant variety and insecticides. © 2025 Society of Chemical Industry.