Biogeography, climate, and land use isolate host populations and create a mosaic landscape of parasite risk in bumble bees

Bee population dynamics are responsive to the conditions of the local landscape, while long term population connectivity and stability are influenced by processes at larger spatial scales. As central place foragers they are tied to the local environment near their nests, and the stress from living in sub-optimal conditions is likely to compound over their lifetime. Furthermore, landscape composition decidedly influences dispersal, and stressful land use patterns are known to isolate populations and reduce genetic diversity, potentially with detrimental consequences for population stability. In this study, we conduct a landscape epidemiological assessment of the drivers of pathogen prevalence across broad geographic scales by screening for detrimental gut pathogens from an existing dataset of B. vosnesenskii landscape genetics. We found high rates of infection from Crithidia bombi, and Crithidia expoekii, which show strong spatial autocorrelation and are more prevalent in northern latitudes. We show that geographic and land use resistance distance help to explain differences in parasite prevalence and community composition, while local habitat factors including precipitation, elevation, and B. vosnesenskii nesting density are also crucial for understanding the disease ecology of this complex system. These results indicate that continued land use change will negatively impact bumble bee populations through changes in connectivity and habitat suitability for both hosts and parasites. Region specific conservation measures for bumble bees should take into account the independent and interacting influences of climate, biogeography, land use, and population dynamics on the stability of host populations.