Do volatiles produced by nectar-dwelling microbes affect honey bee preferences?

Authors: Rering, Caitlin; VANNETTE, RACHEL - University Of California; Beck, John

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 8/24/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary: Plants use floral aroma to attract pollinators. Microbes commonly live in floral nectar and recent research has shown that some microbes may enhance or deter honey bee affinity to flowers. In addition to flower-produced aromas, microbes also produce odors which may contribute to overall floral aroma and influence honey bee attraction. 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. Identified, were odor components released into the air by four microbes (two fungi and two bacteria). These odors were then analyzed to determine if they were recognized by honey bees. Other tests were performed to determine if the honey bees were actually attracted to the specific microbe-produced odors. The aroma profiles produced by the fungi were different from each other and 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 plants mediates many interactions in natural and managed systems. Among these, plant-pollinator interactions are important for ensuring high crop yields, pollinator health and successful plant reproduction. Despite initial work demonstrating effects of floral microbes on pollination, little is known about the role microbe-produced volatiles play in pollinator behavior. Here we test the hypothesis that microbial contribution to nectar volatile composition influences the attractiveness of nectar to honey bees (Apis mellifera). Headspace analysis of four nectar-inhabiting microbes (a yeast, a yeast-like fungus and two bacteria) was performed to identify their volatile profiles. Single strains were grown in synthetic nectar and headspace samples were taken after 0, 2 and 4 days post-inoculation. Electrophysiological and behavioral bioassays were conducted using identified volatiles and inoculated analog nectar, respectively. Honey bees had equal preference for sterile and yeast-inoculated synthetic nectar, while presence of the yeast-like fungus and both bacteria diminished preference. The yeast and yeast-like fungus produced distinct volatile profiles from one another and the bacteria, while bacteria volatile profiles were indistinguishable. The yeast and yeast-like fungus produced a more abundant and diverse volatile profile than the bacteria. Five compounds, all of which elicited electrophysiological responses by bees, were unique to the non-deterrent yeast. 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.