D3143: Analysis of genomic and transcriptomic factors that lead to the development of emamectin benzoate resistance in Spodoptera exigua

The beet armyworm, Spodoptera exigua, is a polyphagous pest that causes significant economic losses by damaging various vegetables. The extensive use of insecticides, such as pyrethroids, carbamates, diamides, and avermectins to control S. exigua has led to the development of high-level resistance against multiple insecticides, including emamectin benzoate (EB). EB, commonly used to control lepidopteran larvae, targets the glutamate-gated chloride channel (GluCl) in nerves and muscle cells. In this study, a field strain of S. exigua selected for resistance to emamectin benzoate (EB-R) was collected, and the presence of a previously reported resistance mutation in the cyp9a186 gene was confirmed. Additionally, the full sequences of GluCl in both the EB-R and susceptible strains were compared to find the resistance-related mutation. To elucidate the contact toxicity of EB, transcriptome analysis was conducted using samples treated with LD₅ concentrations (1.5 ppm for susceptible strain and 200 ppm for EB-R strain) topically. Analysis of the differentially expressed genes revealed 423 upregulated and 567 down regulated genes in the control groups, while the LD₅-treated group exhibited 397 upregulated and 544 downregulated genes (|log2FoldChange| ≥1 and p_adj< 0.05). KEGG enrichment analysis indicated higher expression levels in the EB-R strain for pathways related to "metabolism of xenobiotics by CYP450," "protein processing in the endoplasmic reticulum," and "longevity regulating pathway."