Small but Mite-y: Investigating the role of the Varroa mite in driving patterns of pathogen prevalence and severity in wild pollinator communities

A key driver of pollinator decline is infectious disease, particularly single-stranded RNA viruses. In honey bee colonies, virus prevalence and severity are tightly linked with the level of Varroa mite infestation in colonies, since the mite is an important vector of a suite of bee viruses. These same viruses, particularly Deformed Wing Virus (DWV), are now widespread throughout the wild pollinator community. Therefore, while Varroa mites are only found on honey bees and cannot survive on other pollinator species, there may be detrimental indirect effects of Varroa on wild pollinators, via virus transmission between honey bees and wild bees across shared floral resources. We investigated the relationship between Varroa levels in honey bee colonies, and the prevalence and severity of DWV in bumble bees and other wild pollinators. We selected 27 apiaries along a natural gradient of Varroa mite infestation and sampled honey bees, flowers, and wild bumble bees from the surrounding apiaries. In general, DWV loads were very low across all sites. As predicted, we found a positive association between Varroa mite levels and DWV prevalence in wild bumble bees. We are currently exploring the patterns of DWV prevalence in the honey bees and on flowers to explore the transmission mechanism. We believe these results have important ramifications from both a fundamental and applied epidemiological perspective, since beekeepers have the capacity to control mites in their colonies via a broad range of management practices and therefore protect the health of the entire pollinator community.