Identification of the ryanodine receptor mutation I4743M and its contribution to diamide insecticide resistance in Spodoptera exigua (Lepidoptera: Noctuidae)

Abstract

Insect ryanodine receptors (RyRs) are the targets of diamide insecticides. Two point mutations G4946E and I4790M (numbering according to Plutella xylostella, PxRyR) in the transmembrane domain of the insect RyRs associated with diamide resistance have so far been identified in three lepidopteran pests, P. xylostella, Tuta absoluta and Chilo suppressalis. In this study, we identified one of the known RyR target site resistance mutations (I4790M) in a field-collected population of Spodoptera exigua. The field-collected WF population of S. exigua exhibited 154 fold resistance to chlorantraniliprole when compared with the susceptible WH-S strain. Sequencing the transmembrane domains of S. exigua RyR (SeRyR) revealed that the resistant WF strain was homozygous for the I4743M mutation (corresponding to I4790M in PxRyR), whereas the G4900E allele (corresponding to G4946E of PxRyR) was not detected. The 4743M allele was introgressed into the susceptible WH-S strain by crossing WF with WH-S, followed by three rounds of backcrossing with WH-S. The introgressed strain 4743M was homozygous for the mutant 4743M allele and shared about 94% of its genetic background with that of the recipient WH-S strain. Compared with WH-S, the near-isogenic 4743M strain showed moderate levels of resistance to chlorantraniliprole (21 fold), cyantraniliprole (25 fold) and flubendiamide (22 fold), suggesting that the I4743M mutation confers medium levels of resistance to all three diamides. Genetic analysis showed diamide resistance in the 4743M strain was inherited as an autosomal and recessive trait. Results from this study have direct implications for the design of appropriate resistance monitoring and management practices to sustainably control S. exigua.

Diamide resistance: 10 years of lessons from lepidopteran pests

“…It took just a few years for borderline control failures involving diamide insecticides to emerge in East Asia, with farmers in Jiangsu, China reporting a 44-fold resistance in 2010 (Lai et al 2011; Biondi et al (2018); data from references in text and CABI invasive pest monitoring et al 2013). By 2018, resistance had increased to 150-fold and spread to Shandong (Zuo et al 2019). Now, S. frugiperda is predicted to be heading towards the same area.…”

“…That being said, almost all investigations of TSR-mediated field resistance have found that metabolic pathways also participate. When TSR is isolated against a non-resistant background, resistance levels fall by a factor of ten or more (Douris et al 2017;Zuo et al 2019), suggesting that metabolic effects, although small in isolation, play an important combinatorial role with the more dramatic TSR component.…”

“…In Diptera, anthranilic acid diamides such as CLR are thought to bind at a separate, albeit overlapping, location from the phthalic acid diamide FLB, potentially explaining this discrepancy in susceptibility in the engineered Drosophila strain (Qi and Casida 2013;Isaacs et al 2012). A recent backcrossing experiment in S. exigua found that introgression of the I4790M mutation caused approximately 20-fold resistance to both diamides (Zuo et al 2019).…”

“…Interestingly, laboratory selection of the Brazilian population with CLR led to a slight increase in CLR resistance (237-fold), but dramatic increases in FLB resistance (> 42,000-fold) (Bolzan et al 2019). Another noctuid pest, S. exigua, also carries the equivalent of I4790M, which is present in almost all surveyed Chinese populations and is associated with 150-fold CLR resistance (Zuo et al 2019). The mutation is also fixed in certain Chinese populations of C. suppressalis, associated with 250-fold CLR resistance .…”

“…A major missing piece of the resistance puzzle is how TSR and metabolic resistance combine to generate a potent resistance ratio, and so far, only one half of this picture has been resolved. In the context of TSR, isolation of G4946E in a wildtype lepidopteran background produces just 223-fold CLR resistance (Zuo et al 2019); a tenfold reduction on the > 3000-fold CLR field resistance in some Lepidoptera , implying that other components are critical. On the other hand, studies that combine TSR observations with synergism experiments have shown some reduction in CLR resistance when P450s are blocked (Boaventura et al 2020).…”