Differential contributions of the ryanodine receptor I4723M and I4723K mutations to diamide resistance in Spodoptera litura

Abstract

The common cutworm, Spodoptera litura, is a significant pest that damaging various crops. Previous research has shown that the I4723M mutation in the ryanodine receptor of S. litura (SlRyR), which is equivalent to the Plutella xylostella RyR I4790M, confers approximately 20-fold resistance to chlorantraniliprole. Recently, we identified a new I4723K mutation in SlRyR, in addition to I4723M, from the HZ23 population of S. litura collected in 2023 from Huizhou, Guangdong province, China. This study characterized the resistance to diamides conferred by these two point mutations of SlRyR. The HZ23 population demonstrated an 81-fold resistance to chlorantraniliprole, and the frequencies of the wild type allele 4723I and two mutant alleles 4723M and 4723K were 0.055, 0.93 and 0.015, respectively. Through marker-assisted selection, we isolated three strains from the HZ23 population, named HZ-4723I, HZ-4723M, and HZ-4723K, homozygous for each of the three alleles. Compared to the HZ-4723I strain, the HZ-4723M strain displayed medium-level resistance (23- to 43-fold), whereas the HZ-4723K strain exhibited high-level resistance (> 500-fold) to four diamides including chlorantraniliprole, cyantraniliprole, flubendiamide, and tetraniliprole. Genetic analysis revealed that resistance to chlorantraniliprole conferred by either I4723M or I4723K mutations was autosomal, incompletely recessive, and tightly linked with the SlRyR mutations. Given that the I4723K mutation confers much higher levels of diamide resistance than the I4723M mutation, the continued intensive use of diamide insecticides is likely to increase the frequency of the I4723K mutation in S. litura field populations. Our findings provide valuable insights for the monitoring and management of diamide resistance in this pest species.