RNAseq-based molecular insights into three insecticide resistances in Laodelphax striatellus: Structural perspective...

The small brown planthopper (Laodelphax striatellus, SBPH) is a major pest of rice across Asia, where rising resistance to multiple insecticide classes poses a serious threat to crop protection. To understand the molecular basis of resistance, field populations from Korea were selected over six years with carbosulfan (1 A), etofenprox (3 A), and imidacloprid (4 A), generating three resistant strains. Bioassays confirmed exceptionally high resistance, with resistance ratios exceeding 350-fold for carbosulfan, >1200-fold for etofenprox, and > 800-fold for imidacloprid. Target-site analyses revealed Ace1 mutations (F331H, F439H) in carbosulfan- and imidacloprid resistant strains, whereas no classical sodium channel substitutions were detected in the etofenprox-resistant strain. RNA-seq profiling uncovered widespread transcriptional reprogramming, most pronounced in the etofenprox-resistant strain, which exhibited large-scale metabolic and signaling adjustments. In contrast, the imidacloprid-resistant strain showed marked overexpression of CYP6ER2, a cytochrome P450 closely related to Nilaparvata lugens CYP6ER1, suggesting a potential role in imidacloprid detoxification. qRT-PCR analysis confirmed significant upregulation of CYP6ER2 across all resistant strains, with the highest expression observed in the imidacloprid-resistant strain (>35-fold), independent of gene amplification. Molecular docking indicated that carbosulfan, etofenprox, and imidacloprid can theoretically fit into the CYP6ER2 active site with favorable binding energies and catalytically relevant orientations, supporting its putative broad-spectrum detoxification function. Together, these findings reveal that resistance in SBPH arises from a combination of target-site mutations and transcriptional activation of metabolic genes, with CYP6ER2 emerging as a candidate mediator of cross-class detoxification. These results emphasize the urgent need for resistance management strategies that limit reliance on shared metabolic pathways rather than relying solely on mode-of-action rotation.