Transcriptomic Responses of Cytochrome P450 Genes in Monolepta signata Populations with Differential Resistance to Neonicotinoids

Monolepta signata (Coleoptera: Chrysomelidae) is a major agricultural pest in East and Southeast Asia. Cytochrome P450 genes are commonly involved in xenobiotic detoxification, but their roles in the response of this pest to neonicotinoid insecticides remain unclear. In this study, we integrated resistance bioassays with transcriptomic analysis to investigate gene expression patterns associated with thiamethoxam and imidacloprid stress. GO and KEGG analyses indicated that metabolic and cellular process-related pathways were affected by insecticide exposure. Seven differentially expressed P450 genes, belonging to the CYP3, CYP4, and CYP12 clades, were identified. Across the six field populations, the basal expression of CYP4C1 and CYP6a23 showed significant positive correlations with thiamethoxam relative resistance ratios, whereas no significant correlation was detected between their expression levels and imidacloprid relative resistance ratios. However, after excluding the BETL population, neither correlation remained significant, indicating that the correlation was largely driven by this single population. Constitutive overexpression of these genes may be associated with the thiamethoxam resistance phenotype. Functional validation is still required to clarify their specific roles. This study provides a valuable transcriptomic resource for resistance monitoring and pest management of this pest.