Imbalance of intestinal microbial homeostasis caused by acetamiprid is detrimental to resistance to pathogenic bacteria in Bombyx mori.

The neonicotinoid insecticide acetamiprid is widely applied for pest control in agriculture production, and its exposure often results in adverse effects on a non-target insect, Bombyx mori. However, only few studies have investigated the effects of exposure to sublethal doses of neonicotinoid insecticides on gut microbiota and susceptibility to pathogenic bacteria. In this study, we aimed to explore the possible mechanisms underlying the acetamiprid-induced compositional changes in gut microbiota of silkworm and reduced host resistance against detrimental microbes. This study indicated that sublethal dose of acetamiprid activated the dual oxidase-reactive oxygen species (Duox-ROS) system and induced ROS accumulation, leading to dysregulation of intestinal immune signaling pathways. The evenness and structure of bacterial community were altered. Moreover, after 96 h of exposure to sublethal dose of acetamiprid, several bacteria, such as Pseudomonas sp (Biotype A, DOP-1a, XW34) and Staphylococcus sp (RCB1054, RCB314, X302), invaded the silkworm hemolymph. The survival rate and bodyweight of the acetamiprid treated silkworm larvae inoculated with Enterobacter cloacae (E. cloacae) were significantly lower than the acetamiprid treatment group, suggesting that acetamiprid reduced silkworm resistance against pathogens. These findings indicated that acetamiprid disturbed gut microbial homeostasis of Bombyx mori, resulting in changes in gut microbial community and susceptibility to detrimental microbes.