Bumble bees in landscapes with abundant floral resources have lower pathogen loads

AbstractThe pollination services provided by bees are essential for
supporting natural and agricultural ecosystems. However, bee population
declines have been documented across the world. Many of the factors known
to undermine bee health (e.g., poor nutrition) can decrease
immunocompetence and, thereby, increase bees’ susceptibility to diseases.
Given the myriad of stressors that can exacerbate disease in wild bee
populations, assessments of the relative impact of landscape habitat
conditions on bee pathogen prevalence are needed to effectively conserve
pollinator populations. Herein, we assess how landscape-level conditions,
including various metrics of floral/nesting resources, insecticides,
weather, and honey bee (Apis mellifera) abundance, drive variation in wild
bumble bee (Bombus impatiens) pathogen loads. Specifically, we screened
890 bumble bee workers from varied habitats in Pennsylvania, USA for three
pathogens (deformed wing virus, black queen cell virus, and Vairimorpha
(= Nosema) bombi), Defensin expression, and body size. Bumble bees
collected within low-quality landscapes exhibited the highest pathogen
loads, with spring floral resources and nesting habitat availability
serving as the main drivers. We also found higher loads of pathogens where
honey bee apiaries are more abundant, a positive relationship between
Vairimorpha loads and rainfall, and differences in pathogens by geographic
region. Collectively, our results highlight the need to support
high-quality landscapes (i.e., those with abundant floral/nesting
resources) to maintain healthy wild bee populations.