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Landscape predictors of pathogen prevalence and range contractions in US bumblebees

This landscape-scale correlation study sought to identify the relative importance of stressors associated with range contraction of and pathogen presence in imperiled U.S. bumble bee species. Bumble bees were sampled in 284 locations in 40 states. At each site researchers quantified 24 habitat, land use and pesticide use variables potentially associated with bee health.

Total fungicide use was the strongest predictor of range contraction for four declining bumble bee species. The greater the use of fungicides, the greater the range loss. Latitude was also positively related to range loss. Loss from sites occurred more often towards the species’ northern range boundaries, a finding that differs from a recent worldwide synthesis showing range loss occurring at southern range limits. 

Of the variables evaluated, the best predictor of the prevalence of the common pathogen Nosema bombi in declining bumble bee species was the use of the fungicide chlorothalonil. The greater the use of chlorothalonil, the greater the prevalence of N. bombi. Authors also found two other variables that affected pathogen prevalence. First, as the amount of developed area increased, prevalence of N. bombi decreased, which demonstrates a potential benefit from habitat in populated areas. Second, there was a trend for greater N. bombi prevalence at higher latitudes.

This study’s findings lend support to toxicological studies that found negative effects from fungicide exposure. The authors caution against drawing causal links from this study and noted the need for more research. 

McArt, S.H., C. Urbanowicz, S. McCoshum, R.E. Irwin, and L.S. Adler
Proceedings of the Royal Society B: Biological Sciences
Year published: