Engineered gut symbiont targets mite and microsporidian parasites and improves honey bee survival

Honey bees (Apis mellifera) have been suffering high annual losses worldwide, in part owing to parasitism. Both the ectoparasite Varroa destructor and the intracellular parasite Nosema ceranae can cause failure of honey bee colonies. Colonies rarely survive when heavily infested by the two parasites simultaneously, and both parasites have developed resistance to small-molecule treatments. Thus, an alternative long-term strategy to combat the parasites is urgently needed. We engineered the honey bee gut symbiont Snodgrassella alvi, inducing self-destruction of parasites by activating their own RNA interference systems. First, we identified genes essential for mite survival and verified these by measuring mite mortality following symbiont-mediated dsRNA delivery. We then engineered S. alvi to express dsRNA targeting Varroa and Nosema concurrently. The symbiont targeting both parasites improves the number of honey bees surviving by 45.6% when bees are simultaneously challenged by Varroa and Nosema parasites in lab conditions. Additionally, the engineered symbiont was transferred to 52% of young and 16% of old honey bees through co-housing with inoculated individuals. Thus, the engineered symbiont offers a potential solution against multiple parasites.