Uninheritable but Widespread Bacterial Symbiont Enterococcus casseliflavus Mediates Detoxification of the Insecticide Chlorantraniliprole in the Agricultural Invasive Pest Spodoptera frugiperda

Host–symbiont interaction plays a crucial role in determining the host’s fitness under toxic stress, as observed in numerous insect species. However, the mechanism of the symbionts involved in the detoxification of insecticides remains poorly known. In this study, through microbiome, proteomic, and genomic analysis, we identified a prevalent symbiont, Enterococcus casseliflavus EMBL-3, in a major invasive insect pest, Spodoptera frugiperda . This symbiont enhances the host’s insecticide resistance to chlorantraniliprole by breaking amide bonds and dehalogenating insecticides. Complying with the increase in exposure risk of chlorantraniliprole, the E. casseliflavus isolates of insects’ symbionts but not those from mammals or environmental strains showed a significant enrichment of potential chlorantraniliprole degradation genes. EMBL-3 is popular in field population insects with efficient horizontal transmission ability through cross-diet and cannibalism. This study provides a new therapeutic target for agricultural pests based on symbiont-targeted insect control for global crop protection.