Discovery of reproductive tissue-associated bacteria and the modes of microbiota acquisition in male honey bees (drones).

Honey bees are the third most economically important agricultural animal in the world due to their role as pollinators. Honey bee pollination services and all hive duties are performed by female workers, while the male drones have one job to mate and share their genetics with a virgin queen from another colony. Thus, drone fitness is directly tied to queen success and colony survival, yet they have been severely understudied compared to their female counterparts. In other insects, microbes discovered in the gut and reproductive organs have been shown to be important for reproductive success and/or overall host health. To our knowledge, the existence of microbes in drone reproductive tissues has never been investigated. Moreover, our understanding of the gut microbiota of drones is severely limited, especially when compared to honey bee workers. Here, we sampled conventional drones from healthy colonies and used 16S amplicon sequencing to identify and characterize bacteria in the reproductive organs of immature and mature drones. After identifying bacteria in drone reproductive tissues, we performed a controlled experiment in which newly emerged drones were exposed to different rearing conditions in order to determine when and how they acquire their reproductive and gut microbiota. Overall, we discovered a set of core bacteria in the reproductive and gut tissues of conventionally reared drones and revealed that social interactions are important for the proper development of the drone microbiota. Determining if these bacteria play a role in drone fecundity and health should be a goal of future research efforts.

Importance: Over the last decade, annual honey bee colony loss has increased, resulting in a critical need to determine what factors contribute to honey bee and colony health. Gut microbes have been shown to play important roles in the health of the nonreproductive female honey bee workers, which make up 90% or more of a honey bee colony. However, we currently know very little about the impact of microbes on the health of male honey bees (drones), who only make up a small portion of the colony population but play a very key role in the success of future colonies by mating with virgin queens. Here, we discovered microbes within the reproductive organs of drones and illustrated that social interactions with worker bees are necessary for the proper development of the gut and reproductive tissue microbial communities in drones. Further studies are needed to determine if microbes play an important role in honey bee reproductive health and fitness.