A central challenge to understanding patterns of pathogen prevalence is that pathogens move within complex communities composed of multiple hosts and multiple pathogen strains. Until recently, most infectious disease research has focused on single host-pathogen interactions. Here, we investigate whether honey bee (Apis mellifera) pathogen prevalence is diluted or amplified by the number of species interacting in the surrounding pollinator community. Three RNA viruses, Deformed Wing Virus (DWV), Sacbrood Virus (SBV), and Black Queen Cell Virus (BQCV), are rapidly spreading among honey bees and native pollinator species through shared floral resources within these different communities. However, the relationship between pollinator community richness and increased virus prevalence has not been analyzed. The dilution effect predicts that increased pollinator species richness will reduce virus prevalence, while the amplification effect predicts pollinator species richness will increase virus prevalence in the focal host. I sampled pollinator communities from 14 agricultural sites in southeastern Michigan in 2015 and 2016, with varying pollinator community compositions. RT-PCR was used to test 1,000 Apis mellifera, Bombus impatiens, Peponapis pruinosa, and Lasioglossum spp., the most common species across all sites, for the presence of replicating DWV, BQCV, and SBV.
My data shows that native pollinators and honey bees interact in the community and several non-Apis species share viruses with honey bees. The 14 pollinator communities varied from 7 to 50 species, and 53 to 760 individual pollinators collected at a site. My results show that many native species are interacting with honey bees and there is substantial variation in the number and type of native species that honeybees interact with across communities.
Testing for the presence of replicating DWV, BQCV, and SBV among honey bees and native bees collected in 2016 is currently underway. Virus prevalence results from 2015 show substantial variation in virus prevalence across co-occurring pollinator species and across communities. Virus prevalence in Apis mellifera ranged from 18-100% DWV, 67-91% BQCV, and 27-50% SBV. On average, Apis mellifera had higher virus prevalence (DWV: 63%, BQCV: 82%, and SBV: 37%) than the other native bee species tested (DWV: 32%, BQCV: 23%, and SBV: 15%), which may suggest differences in susceptibility or exposure to viruses among different pollinator species. We will analyze how differences in species richness across native bee communities are linked with honey bee virus prevalence to test whether pollinator communities dilute or amplify viruses.