Honey bee hygienic selection impacts virus dynamics of both bees and Varroa mites

The Varroa mite (Varroa destructor) has reshaped the viral landscape of honey bee colonies, significantly contributing to colony mortality. In response, Varroa-resistant honey bee breeding programs have developed as a promising and sustainable long-term strategy to control Varroa mite infestations in managed colonies. These breeding programs drive the coevolution of hygienic bees and Varroa mites, however the impact of such coevolution on bee and mite viral dynamics remains poorly understood. To address this gap, we investigated how Varroa-resistant traits influence the tripartite interaction among honey bees, Varroa mites, and viruses. Two apiaries were established: one in Greensboro, North Carolina, consisting of high and low UBeeO colonies, and another in Stoneville, Mississippi, consisting of Pol-line and Commercial colonies. Worker bees and Varroa mites were collected from each colony throughout the beekeeping season and screened for 7 viruses. Hygienic selection significantly reduced the Varroa mite infestation level and influenced the dynamics of viruses in worker bees and Varroa mites. Specifically, titers of Varroa-associated viruses were significantly reduced in worker bees and in mites collected from hygienic colonies. Additionally, hygienic selection altered the co-occurrence patterns and correlations among multiple critically important viruses in mites and worker bees. These findings highlight the value of selective breeding as an effective strategy for improving honey bee health and colony survival and shed light on the complex tripartite relationships between honey bees, Varroa mites, and viruses.