Mutations in the <i>GSTe2</i> Promoter in the Emamectin Benzoate-Resistant Strain of <i>Spodoptera frugiperda</i> Contribute to Elevated Expression Levels and Enhanced Metabolic Detoxification Capacity against Emamectin Benzoate

While emamectin benzoate (EB) remains a key insecticide against <i>Spodoptera frugiperda</i>, significant resistance has developed, compromising its effectiveness. Identifying response genes and mutations is critical for resistance management. Here, genome resequencing and transcriptome analysis of EB-resistant (EB-R) and EB-susceptible (EB-Sus) strains of <i>S. frugiperda</i> identified 177 candidate genes. Subsequently, four glutathione S-transferase (GST) genes, one Cytochrome P450 gene, and one ABC gene linked to insecticide resistance were selected for functional validation. Among these, <i>GSTe2</i> was highlighted for its most upregulated and high EB affinity. Injection with ds<i>GSTe2</i> increased the larval mortality by 28.3% under EB stress. UPLC-MS/MS confirmed that GSTe2 metabolizes EB in vitro. Crucially, three single-nucleotide polymorphisms in the <i>GSTe2</i> promoter (EB-R) enhanced its transcriptional activity. Collectively, we propose a resistance mechanism: promoter mutations elevate GSTe2 transcription and metabolic capacity for EB. This research provides a foundation for targeted insecticidal strategies using key resistance genes, thereby enhancing the efficacy of pest control measures.