LAUSR

BACKGROUND The common cutworm, Spodoptera litura (Fabricius), is one of the most widespread and destructive polyphagous pests in tropical and subtropical Asia. S. litura has evolved resistance to different insecticides, including diamide insecticides. Here, we identified a ryanodine receptor (RyR) mutation (I4728M) associated with target site resistance to diamides in a field-collected population of S. litura. The contribution of this mutation to diamide resistance was investigated through establishing a near-isogenic resistant strain of S. litura. RESULTS The ND21 population of S. litura, collected from Ningde, Fujian province of China in 2021, exhibited 130.6-fold resistance to chlorantraniliprole compared to the susceptible NJ-S strain. S. litura RyR mutation I4728M, corresponding to Plutella xylostella RyR I4790M, was identified in ND21 population. SlRyR I4728M mutation of ND21 was introgressed into a susceptible background strain (NJ-S) with marker-assisted backcrossing. The introgressed strain named ND21-R, which was homozygous for the mutant 4728M allele, shared about 94% of the genetic background with the NJ-S strain. ND21-R strain showed moderate levels of resistance to two anthranilic diamides (19.1-fold to chlorantraniliprole, 19.7-fold to cyantraniliprole) and the phthalic diamide flubendiamide (23.4-fold). Genetic analysis showed that chlorantraniliprole resistance was autosomal, incompletely recessive and tightly linked with SlRyR I4728M mutation in the introgressed ND21-R strain of S. litura. CONCLUSION Identification of the I4728M mutation and its contribution to diamide resistance in S. litura will help develop allelic discrimination assays for resistance monitoring and guide resistance management practices for diamides in S. litura. This article is protected by copyright. All rights reserved.