Efficient pollinators of wild flowering plants and crops, bumblebees provide important ecosystem services, threatened by range contractions and declining populations. In the US, this has been linked to a variety of factors including urbanization, pesticides and pathogens.
In a study of bumblebees in the US, authors attempt to elucidate the relative importance of different stressors associated with range contractions. At 284 sites, they sampled and identified Bombus species, while screening for pathogens and quantifying landscape and pesticide usage.
Combining the field data with GBIF-mediated occurrences of eight target species, the authors used a machine learning model technique to show that the usage of the fungicide chlorothalonil was the best predictor of prevalence of the bumblebee pathogen Nosema bombi in four declining species. They also found that total fungicide usage was correlated with range contractions in all declining species.
Adding to existing evidence, this study highlights fungicide exposure–linked to pathogen prevalence–as a critical factor affecting threatened and endangered bumblebees in the US.