Local habitat type influences bumble bee pathogen loads and bee species distribution

Bumble bees (Bombus spp.) perform important ecological services in both
managed and natural ecosystems. Anthropogenically-induced change, however,
has altered the availability of floral resources, climatic suitability,
and exposure to insecticides, factors that impact overall health and
disease levels in these bees. Habitat management presents a solution for
improving bee health and biodiversity, but this requires better
understanding of how different pathogens and bee species respond to
habitat conditions. Herein, we take advantage of the washboard of repeated
ridges (forested) and valleys (mostly unforested and developed) in central
Pennsylvania to examine whether local variation in habitat type and other
landscape factors influence bumble bee community composition and the
levels of four leading pathogens in the common eastern bumble bee, Bombus
impatiens. Loads of viral pathogens (deformed wing virus and black queen
cell virus) were found to be lowest in forest habitats, whereas loads of a
gut parasite, Crithidia bombi, were highest in forests. Ridgetop forests
hosted the most diverse bumble bee communities, including several habitat
specialists. B. impatiens was most abundant in valleys, and showed higher
incidence in areas of greater disturbance, including more developed,
unforested, and lower floral resource sites, a pattern that mirrors its
success in the face of anthropogenic change. Additionally, DNA barcoding
revealed that B. sandersoni is much more common than is apparent from
databases, likely due to misidentification as mimics B. perplexus and B.
vagans. Our results provide evidence that habitat type can play a large
role in pathogen load dynamics, but in ways that differ by pathogen type,
and point to a need for consideration of habitat at both macro-ecological
and local spatial scale