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

Darin J Mcneil,Heather M Hines,Christina M Grozinger,Margaret R Douglas,Elyse Mccormick,Ashley C Heimann,Sarah C Goslee,Melanie Kammerer

doi:10.1038/s41598-020-78119-2

Abstract

The 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.

Highlights

The pollination services provided by bees are essential for supporting natural and agricultural ecosystems
We collected 890 workers from sites spanning a diversity of habitats across Pennsylvania, USA (Fig. 1A), for 2–3 weeks during the peak of bumble bee abundance, and across 2 years, including 21 sites in 2018 (n = 310 bees) and 41 sites in 2019 (n = 580 bees)
Screens of loads of pathogens among pooled bees (n = 5 bees/pool) from each site, performed via quantitative PCR, revealed that most bumble bee samples (97%) contained BQCV and that BQCV exhibited a broad range of pathogen load values

Summary

Introduction

The pollination services provided by bees are essential for supporting natural and agricultural ecosystems. 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. Our results highlight the need to support high-quality landscapes (i.e., those with abundant floral/nesting resources) to maintain healthy wild bee populations. Extensive habitat loss and degradation results in a dearth of floral resources and nest sites which has contributed to loss of wild bee abundance and d iversity[5,6] Bee losses, especially those of honey bees (Apis mellifera) and bumble bees (Bombus spp.), have more recently been ascribed to rising levels of novel bee pathogens[3,7]. A study in bumble bees using data compiled from across the United States found that Vairimorpha prevalence in declining bumble bee species is best predicted by usage of the insecticide c lothianidin[31]

Methods

Results

Conclusion