Insecticide resistance monitoring and identification of ryanodine receptor mutations driving diamide resistance in Cnaphalocrocis medinalis

The study focuses on monitoring insecticide resistance and identifying ryanodine receptor (RyR) mutations in the rice leafroller, Cnaphalocrocis medinalis —a destructive migratory pest threatening Asian rice production. Conducted between 2023 and 2025, it evaluated resistance in 37 field populations (collected from 8 major rice-growing provinces in China) to 10 insecticides via standardized rice seedling dip bioassays, and analyzed RyR target-site mutations (I4712M and Y4621C) linked to diamide resistance. Chlorantraniliprole showed severe resistance (RR = 60.4–253.4-fold; 66.7 % of populations with high-level resistance), while tetrachlorantraniliprole (RR = 22.1–76.3-fold) and tetraniliprole (RR = 23.4–114.8-fold) exhibited moderate resistance. Abamectin (RR = 11.2–60.4-fold) and emamectin benzoate (RR = 4.3–52.5-fold) had moderate resistance; spinetoram ranged from low to moderate resistance (RR = 2.9–16.9-fold), and spinosad remained sensitive to low-resistance (RR = 1.3–6.1-fold). Group 22A insecticides (indoxacarb, metaflumizone) and the organophosphate chlorpyrifos retained high efficacy (RR < 5), with no significant resistance detected. RyR mutations (I4712M, Y4621C) were identified in chlorantraniliprole-resistant populations. The I4712M mutation was fixed at 100 % in highly resistant populations (e.g., YZ24, LZ24) and showed a strong positive correlation with chlorantraniliprole resistance, confirming its role in reducing diamide binding affinity. Synergist assays (using PBO, TPP, DEM) revealed high-level chlorantraniliprole resistance was primarily driven by target-site mutations (not metabolic detoxification) and three synergists have no significant synergistic effect on emamectin benzoate and abamectin. Urgent restrictions on diamide use in high-resistance regions, rotation with alternative mode-of-action insecticides (e.g., indoxacarb, metaflumizone), and implementation of integrated resistance management (IRM) strategies are advised.