Nectar-inhabiting microorganisms influence nectar volatile composition and attractiveness to a generalist pollinator

Authors: Rering, Caitlin; Beck, John; HALL, GRIFFIN - University Of California; MCCARTNEY, MITCHEL - University Of California; VANNETTE, RACHEL - University Of California

Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/21/2017
Publication Date: 10/16/2018
Citation: Rering, C.C., Beck, J.J., Hall, G.W., Mccartney, M.M., Vannette, R.L. 2018. Nectar-inhabiting microorganisms influence nectar volatile composition and attractiveness to a generalist pollinator. New Phytologist. 220(3):750-759. doi:10.1111/nph.14809.
DOI: https://doi.org/10.1111/nph.14809

Interpretive Summary: Microbes are common inhabitants of flowers and their nectar. Recently, studies have shown that these floral microbes, depending on the species present, may be capable of either attracting or deterring honey bee visitation. The cause of this shift in preference is not understood, but the odors produced by floral microbes may play an important role by contributing to overall floral aroma sensed by pollinators. Research performed by Scientists at the Center for Medical, Agricultural and Veterinary Entomology, and in collaboration with a University of California, Davis Department of Entomology and Nematology Scientist, sought to determine if specific microbe-produced odors influence the attractiveness of nectar to honey bees. To test this, we identified the odors produced by four microbes (two bacteria and two fungi) and tested whether honey bees could perceive and respond to specific response tests. The odors emitted by the fungi were different from each other, as well as from the bacteria. Three microbes deterred honey bees, while one species (a fungus) was attractive. The attractant fungus produced five odors detectable by bees. Future work will determine if microbes can be safely and efficiently added to the floral nectar and that the odors produced would attract more honey bees. Ultimately, these results indicate that floral microbes may be an eco-friendly, pollination-promoting tool for increasing crop yields.

Technical Abstract: The microbiome of the phyllosphere and anthosphere plays an important role in many plant-plant, plant-insect, and plant-microbe interactions. A particularly essential interaction is that of the plant pollinator, which is important for ensuring high crop yields, pollinator health and successful plant propagation. Despite this importance, little is known about the role of microbe-produced semiochemicals, which may play a critical role in pollinator communication. To evaluate the role of nectar microbe-produced semiochemicals, we performed headspace analysis of synthetic nectar individually inoculated with two common yeast-like fungi and two bacteria. Honey bees were used to conduct electrophysiological and behavioral bioassays on identified volatiles. Overall, the yeasts readily differentiated by distinct biomarker volatiles, and the bacteria, though low in emission, were similar in volatile profiles. The honey bees detected/responded to a number of compounds produced by the yeasts. The overall volatile profiles were sufficiently different for the honey bees to discriminate among tested strains. These findings support the hypothesis that microbe-produced semiochemicals contribute to floral aroma and influence bee behavior, warranting further investigation into microbe-based techniques for pollination enhancement in crops.