Microbial metabolites elicit distinct olfactory and gustatory preferences in bumblebees

Authors: SCHAEFFER, ROBERT - Washington State University; Rering, Caitlin; MAALOUF, ISABELLE - University Of California, Davis; Beck, John; VANNETTE, RACHEL - University Of California, Davis

Submitted to: Biology Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/21/2019
Publication Date: 7/17/2019
Citation: Schaeffer, R.N., Rering, C.C., Maalouf, I., Beck, J.J., Vannette, R.L. 2019. Microbial metabolites elicit distinct olfactory and gustatory preferences in bumblebees. Biology Letters. 15(7):20190132. https://doi.org/10.1098/rsbl.2019.0132.
DOI: https://doi.org/10.1098/rsbl.2019.0132

Interpretive Summary: Plants that require pollination advertise the presence of floral rewards via traits such as scent. Microbes are frequent residents of nectar and can influence the chemistry of the nectar, including odors and the aqueous chemical composition. Here, we test the hypothesis that nectar-inhabiting microbes can influence both pollinator attraction and feeding. University scientists in collaboration with scientists at the Center of Medical, Agricultural, and Veterinary Entomology in Gainesville, FL examined certain physical and behavioral characteristics of bumble bees. Tested bumble bees displayed a clear preference for a floral bacterium compared to a floral yeast, based on emitted odors alone. However, the tested bumble bees consumed significantly more yeast-inoculated nectar, suggesting distinct roles for both non-odors and odors produced by the microbes and their ability to influence feeding decisions. These results suggest bumble bees may use multiple microbial cues to assess floral attractiveness and reward quality, with potential consequences for forager economics and floral host reproduction. Results from this research will help direct future studies on increasing pollinator and plant health for agriculture commodities.

Technical Abstract: Animals such as bumble bees use chemosensory cues to both localize and evaluate essential resources. Increasingly, it is recognized that microbes can alter the quality of foraged resources and produce metabolites that may act as foraging cues. The distinct nature of these chemosensory 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 produced in nectar. We first examined the electrophysiological potential for bumble bee (Bombus impatiens) antennal olfactory sensilla to respond to microbial volatile organic compounds (mVOCs), followed by an olfactory preference test. We also assessed gustatory preferences for microbial altered nectar through both no-choice and choice feeding assays. Antennal olfactory sensilla responded to some mVOCs, and bees preferred nectar solutions inoculated with the bacterium Asaia astibles over the yeast Metschnikowia reukaufii based on volatiles alone. However, B. impatiens foragers consumed significantly more Metschnikowia-inoculated nectar, suggesting distinct roles for mVOCs and non-volatile metabolites in mediating both attraction and feeding decisions. Collectively, our results suggest that microbial metabolites have significant potential to shape interspecific, plant-pollinator signaling, with consequences for forager learning, economics and floral host reproduction.