LAUSR

BACKGROUND The striped rice stem borer, Chilo suppressalis (Lepidoptera: Pyraidae), is one of the most serious rice pests in China. Chlorantraniliprole was extensively used for C. suppressalis control in the past ten years, and some field populations have developed high resistance. In this study, we report chlorantraniliprole resistance status of C. suppressalis in China and the resistance mechanism. RESULTS Significant geographical variations of chlorantraniliprole susceptibility were observed among 28 C. suppressalis field populations in 2019-2020. The LC50 values varied from 2907.874 mg/L (XS19) to 1.524 mg/L (QW19). Most tested field populations collected from Zhejiang, Jiangxi, Hunan and Anhui provinces in 2020 showed high level of resistance to chlorantraniliprole (RR = 311.9-2060.1), while Jiangsu and Sichuan provinces' populations remained susceptible. Analysis of RyR mutations showed that mutations of I4758M, Y4667D, Y4667C and Y4891F were present in resistant populations of C. suppressalis with different levels of chlorantraniliprole resistance. The frequency of Y4667C mutation is correlated to chlorantraniliprole resistance in YY19 (RR = 702.6) and YY20 (RR = 1426.8) populations, with the homozygous mutation frequency of 15.6% and 29.4%, respectively. High contribution of I4758M and Y4667C double mutation to diamide resistance was demonstrated with CRISPR/Cas9 modified D. melanogaster. Flies bearing Y4667C mutation (I4758M and Y4667C double mutation in C. suppressalis) exhibited high resistance to chlorantraniliprole (RR = 172.1), and moderate resistance to cyantraniliprole (RR = 79.2) and tetra chlorantraniliprole (RR = 43.6), which were higher than that of single mutations. CONCLUSIONS Chlorantraniliprole resistance in C. suppressalis is intensifying in China. RyR double mutations (i.e., I4758M and Y4667C) confer higher diamide resistance than single mutations. This article is protected by copyright. All rights reserved.