The gut parasiteNosema ceranaeimpairs olfactory learning in bumblebees

Pollinators are exposed to numerous parasites and pathogens when foraging on flowers. These biological stressors may affect critical cognitive abilities required for foraging. Here, we tested whether exposure to Nosema ceranae , one of the most widespread parasite of honey bees also found in wild pollinators, impacts cognition in bumblebees. We investigated different forms of olfactory learning and memory using conditioning of the proboscis extension reflex. Seven days after feeding parasite spores, bumblebees showed lower performance in absolute and differential learning, and reversal learning than controls. Long-term memory was also slightly reduced. The consistent effect of N. ceranae exposure across different types of olfactory learning indicates that its action was not specific to particular brain areas or neural processes. We discuss the potential mechanisms by which N. ceranae impairs bumblebee cognition and the broader consequences for populations of pollinators.