CRISPR/Cas9-based evidence that overexpression of Gm-mGST1 mediates abamectin resistance in the oriental fruit moth, Grapholita molesta.

Abamectin-based insecticides are widely used in integrated pest management and are particularly effective against fruit borers such as the oriental fruit moth, Grapholita molesta. However, rapid resistance evolution threatens their long-term efficacy. This study elucidates the role of the glutathione S-transferase gene Gm-mGST1 in abamectin resistance in G. molesta. A laboratory-selected resistant strain (AB-R) exhibited an 85.5-fold increase in resistance compared with a susceptible strain (AB-S). Sequencing of glutamate-gated chloride channel (GmGluCl) gene revealed no target-site mutations, implicating a metabolic resistance mechanism. In AB-R, GST enzymatic activity was significantly elevated. GST synergist diethyl maleate (DEM) increased the toxicity of abamectin more strongly in the abamectin-resistant G. molesta strain than in the susceptible strain, indicating that GSTs contribute to abamectin resistance. Gm-mGST1 showed strong and stage-specific overexpression under abamectin exposure. Functional analysis using CRISPR/Cas9 knockout of Gm-mGST1 in the AB-R strain reduced resistance 16.3-fold, providing the definitive evidence that a GST gene directly mediates abamectin resistance in G. molesta. The catalytic activity of recombinant Gm-mGST1 was verified in vitro using CDNB as the substrate. Additionally, abamectin exhibited a certain degree of inhibitory effect on the activity of Gm-mGST1. HPLC analysis further revealed that the peak area of abamectin significantly decreased in the presence of recombinant Gm-mGST1, while ectopic expression in Drosophila melanogaster increased abamectin tolerance by 1.97-fold. There is a significant positive correlation between the abamectin resistance levels and the expression levels of Gm-mGST1 in field populations of G. molesta. These findings identify Gm-mGST1 as a critical gene involved in abamectin resistance and establish it as a potential molecular marker for monitoring resistance in field populations. More broadly, this study sets a precedent for integrating CRISPR/Cas9 gene editing into insecticide resistance research, bridging the gap between correlative evidence and functional validation, and providing a framework for developing GST-targeted resistance management strategies in orchard pests. This study provides evidence using CRISPR/Cas9 to confirm the contribution of GST to abamectin resistance in insects.