Testing the invasive pathogen hypothesis of rapidly declining bumble bee populations in North America

Bumble bees are one of our most important wild pollinators, and populations are declining globally. Causes of decline appear to vary geographically. In Europe, for example, the proposed drivers are climate change, loss of floral resources and pesticides. In North America, however, a widely accepted hypothesis suggested that contact with an exotic European strain of fungal pathogen, Nosema bombi, was the sole cause of a precipitous decline. We have tested this exotic pathogen hypothesis using multiple genetic and genomic tools.