Fungicides contributing to bee declines

Bumblebee on sunflower / Photo: Matt Kelly
Bumblebee on sunflower / Photo: Matt Kelly


The top story coming out of November is research showing that fungicides previous thought to have little impact on bees may actually be playing a significant (if indirect) role in the decline of populations in the United States.

A team of researchers led by Scott McArt, assistant professor of pollinator health at Cornell University, “found that greater usage of the fungicide chlorothalonil was the best predictor of pathogen (Nosema bombi) prevalence in four declining species of bumblebees.”

Nosema bombi is a parasite that infects the midgut and sometimes other tissues of a bee. It impacts colony health by diminishing the reproductive performance of bees and reducing the survival rate of workers. Research has shown that N. bombi is present at much higher rates in declining species of bumble bees than in stable bumble bee species.

The team’s analysis also found that “Greater usage of total fungicides was the strongest predictor of range contractions in declining species, with bumblebees in the northern USA experiencing greater likelihood of loss from previously occupied areas.”

To conduct their multivariate analysis, the researchers used one of the largest data sets to date of bumble bee declines in North America (a contemporary sampling of 10,745 bumblebees across the U.S. that was compared to a 73,759-specimen natural history collection database) to ask two questions: 1. What factors predict pathogen (N. bombi) prevalence in four focal declining bumblebee species? 2. What factors predict range contractions in declining species?

Landscape predictors of pathogen prevalence and range contractions in US bumblebees (2017). S.H. McArt, C. Urbanowicz, S. McCoshum, R.E. Irwin and L.S. Adler. Proceedings of the Royal Society B.

In bee decline, fungicides emerge as improbable villain (EurekaAlert!)