Microbial metabolites mediate bumble bee attraction and feeding

Animals such as bumble bees use chemosensory cues to localize and evaluate essential resources. Increasingly, it is recognized that microbes can alter the quality of foraged resources and produce metabolites that act as foraging cues. The distinct nature of these sensory cues however and their use in animal foraging remain poorly understood. Here, we test the hypothesis that species of nectar-inhabiting microbes differentially influence pollinator attraction and feeding via microbial metabolites in nectar. We examined electrophysiological potential of bumble bee antennae to respond to volatile microbial metabolites, followed by behavioral responses using choice assays. We assessed gustatory responses through both no-choice and choice feeding assays. Antennae responded to some microbial volatiles, and bees chose Asaia bacterial solutions compared to Metschnikowia yeast based on volatiles alone. However, B. impatiens consumed significantly more Metschnikowia-inoculated nectar, suggesting distinct roles for volatile and non-volatile microbial metabolites in mediating feeding decisions, with potential to affect associative learning and future foraging. Our results suggest that microbial metabolites may represent non-reinforcing cues with potential consequences for forager learning, economics and floral host reproduction.