Hints of self-medication? Pathogen exposure-dependent foraging decisions of bumblebees

Abstract Self-medication is the selective consumption of compounds that reduce infection and is a widespread form of adaptive plasticity across animals. However, relevant medicinal floral compounds remain poorly tested in bees. Here, we used robotic flowers to test the hypothesis that bumblebees (Bombus terrestris) modify nectar choice after pathogen exposure, focusing on quercetin, a common nectar secondary compound with antimicrobial activity. Colonies were maintained as healthy controls or exposed to the fungus Ascosphaera apis or the bacterium Serratia marcescens. Colonies exposed to A. apis showed higher visitation rates and longer probing times on quercetin-supplemented flowers, whereas healthy colonies and those exposed to S. marcescens showed no significant preference. Healthy colonies also showed no significant avoidance of quercetin, despite altered solution colour and palatability, and potential detoxification costs. These contrasting responses probably reflect pathogen life history: although A. apis primarily affects brood, increased quercetin foraging may indicate social medication, whereas for S. marcescens, an opportunistic gut pathogen of adults, any colony-level benefit is likely to be more indirect. Overall, these results indicate that pathogen identity shapes behavioural plasticity in nectar foraging and demonstrate the value of robotic flowers for studying adaptive foraging responses to pathogens.