Abstract: Cryptorhynchus lapathi L., a globally distributed wood-boring pest, significantly threatens poplar (Populus spp.) and willow (Salix spp.) trees. Entomopathogenic fungi (EPFs), particularly Beauveria bassiana (Bals.-Criv.) Vuilla, play a crucial role in integrated pest management because of their broad-spectrum insecticidal properties. This study clarifies the pathogenic mechanisms of B. bassiana CFCC81428 treatment and its oil-based formulation against male and female C. lapathi adults, alongside their impacts on cumulative mortality, enzyme activity and nutrient metabolism. The results indicated that the oil-based formulation significantly enhanced B. bassiana pathogenicity, achieving cumulative mortality rates of 91.7% and 83.8% for male and female adults, respectively, with LT50 values of 7.9 and 8.7 d, markedly outperforming the B. bassiana treatment. Scanning electron microscopy revealed that the oil-based formulation improved spore adhesion to the insects’ cuticle, accelerated spore germination and hyphal growth, and significantly improved cuticular penetration efficiency. Within the host, the activities of detoxification enzymes (GST and CarE) were upregulated, whereas the activities of catalase and peroxidase enzymes were suppressed. Superoxide dismutase activity remained elevated throughout most of the observation time points. Polyphenol oxidase activity significantly increased between 24 and 120 h postinfection, indicating its critical role in preventing B. bassiana invasion. The infection also triggered substantial shifts in the host’s nutrient metabolism, with time-dependent changes observed in carbohydrates, free fatty acids, and soluble proteins. The oil-based formulation exacerbated the depletion of these nutrients, ultimately leading to metabolic collapse. This study indicates that the oil-based formulation optimizes spore germination conditions and accelerates infection, thereby significantly increasing B. bassiana pathogenicity in C. lapathi males, whereas female adults exhibited stronger physiological and metabolic responses, providing new insights for the application of B. bassiana in the biological control of pests.

Key words: Biological control, Beauveria bassiana,  , Oil-based formulation, Cryptorhynchus lapathi , Gender specific responses