Floral nectar is an important reward for animal-pollinated plants to attract pollinators, but the role of floral nectar as a habitat for microorganisms remains largely unexplored. Furthermore, although floral nectar often harbors multiple species of bacteria and yeast, the role this rich and diverse microflora may play in affecting the relationships between the plant and its nectar consumers remains poorly understood. In the gut of the domesticated honey bee, Apis mellifera, we found two species of proteobacteria: Asaia astilbes, an alphaproteobacteria, and Erwinia tasmaniensis, a gammaproteobacteria. Both species were previously found in floral nectar. To gain a better understanding of pollinator preference, we conducted a simple field experiment near a small apiary in northern California. We aimed to investigate if honey bees were partial to nectar inoculated with these Gram-negative bacteria over nectar inoculated with common nectar yeast, Metschnikowia reukaufii, which we also isolated from the Apis gut.
The results showed that synthetic nectar inoculated with the proteobacteria was removed more slowly than synthetic nectar inoculated with the yeast or no microorganisms. This finding indicates that honey bees prefer nectar that does not contain proteobacteria. This study highlights the importance of considering nectar-inhabiting microbes in understanding plant-pollinator interactions.