Endophytic Beauveria bassiana Blastospores Enhance Susceptibility of Ostrinia furnacalis to Chlorantraniliprole via Modulating Immune-Related Pathways

Endophytic colonization by entomopathogenic fungi represents a promising sustainable pest management strategy. This study investigated the physiological and molecular effects of maize endophytically colonized by <i>Beauveria bassiana</i> (strain BbOFDH1-5) conidia and blastospores on the Asian corn borer, <i>Ostrinia furnacalis</i>. We evaluated larval development, protective enzyme activities, and subsequent susceptibility to the insecticide chlorantraniliprole, utilizing gut transcriptomic analysis to elucidate the underlying mechanism. Results demonstrated that larvae fed on maize colonized by either spore type, particularly blastospores, exhibited significantly reduced food consumption, body weight, and survival rates. Additionally, the activities of protective enzymes (SOD, POD, CAT) were markedly suppressed. Feeding on blastospore-colonized maize significantly increased larval susceptibility to chlorantraniliprole. Transcriptomic analysis revealed that this enhanced sensitivity is linked to the downregulation of detoxification-related genes, <i>ABCC4</i>, and the upregulation of stress-response genes such as <i>HSP70</i>. These findings confirm that <i>B. bassiana</i> blastospores can synergistically enhance the efficacy of chemical insecticides by impairing larval physiology and suppressing gut-associated resistance mechanisms, providing a novel basis for integrated pest management.