Bulk Segregant Mapping and Transcriptome Analyses Reveal the Molecular Mechanisms of Buprofezin Resistance in Laodelphax Striatellus

The small brown planthopper, Laodelphax striatellus, exhibits escalating buprofezin resistance, yet the underlying molecular mechanisms remain unclear. In this study, we established a highly resistant near-isogenic line and utilized bulk segregant mapping to localize a major resistance locus on chromosome 2. This led to the identification of a G932C target site mutation in chitin synthase 1 ( LsCHS1 ), which was found at high frequencies in field populations. Molecular docking indicated that this mutation induces steric hindrance, disrupting buprofezin binding within the transmembrane chitin translocation channel. Additionally, synergism assays, transcriptome analyses, and RNAi confirmed that the overexpressions of cytochrome P450 LsCYP6CW1 and ATP-binding cassette transporter LsABCG11 collectively confer metabolic resistance. Notably, significant cross-resistance between buprofezin and pymetrozine was observed. These findings demonstrate a dual mechanism of target-site and metabolic resistance to buprofezin in L. striatellus, providing crucial molecular markers for resistance monitoring and guidance for sustainable insecticide application strategies.