Defense of locust eggs against Metarhizium anisopliae invasion

BACKGROUND Insect egg stages represent an underexploited developmental phase in pest management. Locusta migratoria , a globally significant agricultural pest, lacks comprehensive defense studies during this vulnerable period, as existing strategies predominantly target later life stages. This study focused on locust eggs to assess the resistance of different protective structures to Metarhizium anisopliae infection. RESULTS The results show that M. anisopliae infection significantly reduced immune gene expression in eggs while the fungus proliferated with egg development and ultimately caused egg death. The chorion showed no resistance to fungal invasion at the median lethal concentration (LC 50 ) and weak resistance when the fungal concentration was reduced to 0.91 × 10 7 conidia/mL. Inoculating different parts of locust eggs with M. anisopliae can all lead to the death of locust eggs. Subsequent infection with M. anisopliae after knockdown of LmCHS1 , which inhibited serosal cuticle formation, resulted in a significant reduction in egg survival rate. CONCLUSION This study indicates that M. anisopliae can invade various parts of locust eggs. While the chorion improves protection against low dose fungal infections, the serosal cuticle has a critical role in resisting the invasion of foreign substances. In addition, our results reveal the immunosuppressive effect of M. anisopliae on locust eggs. These results elucidate previously unrecognized egg defense mechanisms in locusts and reveal potential targets for novel management approaches during early development. Such findings stand to advance sustainable pest management by shifting intervention focus to the egg stage, boosting control efficacy and reducing reliance on chemical pesticides.