Abstract
Azadirachtin, a natural sesquiterpenoid compound, exhibits broad-spectrum insecticidal activity, yet its mechanism of action remains incompletely understood. This study aimed to elucidate its toxicological mechanisms by developing an azadirachtin-resistant Drosophila strain through continuous laboratory selection. After five years of directional screening, we successfully established the Aza-Sel strain with a resistance ratio of 86.7-fold. Genetic analysis revealed that the resistance trait is incompletely recessive and polygenic in nature. Detoxification enzyme and synergism assays demonstrated that elevated activities of glutathione-S-transferases and esterases play crucial roles in the metabolic resistance of this strain. Cross-resistance spectrum analysis showed that the Aza-Sel strain exhibited 12.4-fold and 6.7-fold cross-resistance to emamectin benzoate and dinotefuran, respectively, while displaying negative cross-resistance to chlorpyrifos and indoxacarb, with no significant cross-resistance to other tested insecticides. Notably, the resistant strain exhibited substantial fitness costs: significant developmental delays across all stages (egg, larva, pupa), prolonged developmental duration, markedly reduced fecundity and egg hatch rate, and significantly shortened male longevity. These findings indicate that the azadirachtin-resistant strain bears severe fitness costs, which may account for the slow development of resistance under laboratory selection conditions. The results confirm the significant advantages of azadirachtin in integrated pest management, particularly its negative cross-resistance characteristics with emamectin benzoate and indoxacarb, making it an ideal option for managing resistant pests.
