The synergistic effect of CQMa421 and deltamethrin improved the insecticidal ability against to .

(Diptera: Tephritidae) is a highly invasive and destructive quarantine pests worldwide. To improved biological control efficiency, reduce chemical pesticides use, and optimise the application of (Hypocreales: Clavicipitaceae) against . This study evaluated the combined toxicity of with deltamethrin and chlorpyrifos. The biocompatibility of CQMa421 with these pesticides was assessed based on spore germination, mycelial growth, and sporulation. Additionally, the effects of combined treatments on detoxification enzyme and related gene expression in were investigated. The results indicated that the virulence effect of CQMa421 against adults was time-dependent and dose-dependent. Deltamethrin showed good compatibility with CQMa421, achieving 100% mortality at 1 × 10⁸ CFU/mL by 84 hours. Different concentrations of deltamethrin can promote the mycelial growth and sporulation of CQMa421. The toxicity effect of deltamethrin and chlorpyrifos combined with CQMa421 on adults was better than that of single-agent treatment, and the co-toxicity factor of 5 mg/L deltamethrin and 1 × 10 CFU/mL CQMa421 was 24.81, which synergistically affected on control. Enzyme activity assays and qRT-PCR results revealed that the combination treatment differentially activated and enhanced the activities of AChE, CarE, GST, CAT, and SOD. Meanwhile, was significantly inhibited and upregulating 1, , and genes. In conclusion, the combination of deltamethrin and CQMa421 enhanced the insecticidal efficacy against , significantly affected the activity of related detoxification enzymes. Provided a robust basis for integrating biological and chemical control strategies to manage more effectively.