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

Authors: MCNEIL, DARIN - Pennsylvania State University; MCCORMICK, ELYSE - Pennsylvania State University; HEIMANN, ASHLEY - Pennsylvania State University; KAMMERER, MELANIE - Pennsylvania State University; DOUGLAS, MARGARET - Dickinson College; Goslee, Sarah; GROZINGER, CHRISTINA - Pennsylvania State University; HINES, HEATHER - Pennsylvania State University

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2020
Publication Date: 12/18/2020
Citation: McNeil, D., McCormick, E., Heimann, A., Kammerer, M., Douglas, M., Goslee, S.C., Grozinger, C., Hines, H. 2020. Bumble bees in landscapes with abundant floral resources have lower pathogen loads. Scientific Reports. 10:22306. https://doi.org/10.1038/s41598-020-78119-2.
DOI: https://doi.org/10.1038/s41598-020-78119-2

Interpretive Summary: Wild and managed bees provide pollination for both agricultural and natural vegetation. Bees have been declining world-wide due to factors like poor nutrition and pesticide exposure, which can make bees more vulnerable to disease. The surrounding landscape provides flowers for pollen and nectar, and nesting habitat, but also pesticide exposure. We examined 890 bumble bees over two years for diseases. Bees from lower-quality landscapes had higher levels of disease. The availability nesting habitat and of spring flowers were particularly important, suggesting that improving these landscape attributes could help to maintain healthy wild bee populations.

Technical Abstract: The pollination services provided by bees are critical for supporting healthy and diverse natural and agricultural ecosystems. However, declines have been documented in wild and managed bee populations across the world. Many of the factors known to undermine bee health (e.g., poor nutrition, exposure to pesticides) often decrease bee immunocompetence and, thereby, increase susceptibility to diseases. Given the myriad of environmental stressors that can exacerbate disease in wild bee populations, assessments of how components of habitat quality impact bee disease pathogen prevalence are sorely needed to effectively conserve pollinator populations. Herein, we assess the extent to which several potential landscape-level stressors, including floral abundance, nesting habitat quality, pesticide exposure, and interactions with managed honey bees (Apis mellifera), drive variation in pathogen loads in wild bumble bees (Bombus impatiens). From 2018-19, we captured 890 worker bumble bees from varied habitats across the state of Pennsylvania and screened them for three pathogens (deformed wing virus, black queen cell virus, and Nosema spp.), expression of the immune response gene Defensin, and body size. Landscape analyses indicated that bees collected within low-quality landscapes exhibited higher levels of pathogens and parasites, with spring floral resources and nesting habitat availability serving as the main drivers. We also found impacts of honey bee abundance, weather, and geography on pathogen loads, however, patterns varied between years and among pathogens. 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.