Engineered symbionts activate honey bee immunity and limit pathogens

Honey bees are essential pollinators threatened by colony losses linked to the spread of parasites and pathogens. Here, we report a new approach for manipulating bee gene expression and protecting bee health. We engineered a symbiotic bee gut bacterium, <i>Snodgrassella alvi</i>, to induce eukaryotic RNA interference (RNAi) immune responses. We show that engineered <i>S. alvi</i> can stably recolonize bees and produce double-stranded RNA to activate RNAi and repress host gene expression, thereby altering bee physiology, behavior, and growth. We used this approach to improve bee survival after a viral challenge, and we show that engineered <i>S. alvi</i> can kill parasitic <i>Varroa</i> mites by triggering the mite RNAi response. This symbiont-mediated RNAi approach is a tool for studying bee functional genomics and potentially for safeguarding bee health.