Researchers in the lab are interested in how microbial communities influence multispecies interactions, often between plants and insects. Below are some of our current directions. For specific research interests of graduate students and postdocs, see Lab Members page.

Our work is and has been funded by:

National Science Foundation

United States Department of Agriculture (Hatch and Multistate funds)

The Almond Board of California

The California Tomato Research Institute

California Pear Board

University of California Davis internal grant support

Davis Botanical Society


Ecology of plant-microbe-floral visitors interactions

Overview: Yeasts and bacteria are common inhabitants of flowers, and can attain high densities in floral nectar. I am interested how (and when) these microbes influence plants and pollinators, the mechanisms involved, and evolutionary ecology of these interactions. In the plant species Mimulus aurantiacus, we have found that bacteria and yeasts can influence pollinator visitation, via changes in nectar chemistry, including secondary metabolites in nectar.

In the Vannette Lab, we use chemical ecology and community ecology to studying interactions between floral visitors, nectar microbial communities, and nectar characteristics by surveying flowering plant species at various natural and managed sites in northern California. We use intensive surveys at Stebbins Cold Canyon Reserve and plots maintained by N. Williams at Laidlaw Bee Biology Research Facility to investigate plant-microbe-floral visitor interactions and how nectar mediates such interactions. Data on microbial presence among species and microbial VOCs have been published in Rering et al 2018 (New Phytologist). Collaboration with instructors of the freshman seminar Nectar CURE is facilitating the identification and phenotypic profiling of strains isolated from these field sites. Collaboration with Caitlin Rering and John Beck is further investigating the role of microbial metabolites within floral systems.


Stebbins Cold Canyon Reserve


Extracted flowers

We are also examining microbial dispersal and effects on plant-pollinator interactions in the plant species Epilobium canum.  This hummingbird-pollinated plant species is also robbed by carpenter bees and visited by other insects including honey bees. Students in the Animal Biology ABI 50A class survey plants in the Arboretum as part of this course, and also develop independent research projects to investigate links between floral traits and visitation by pollinators and other species. (More information here)

Epilobium canum flower

This work is supported by funding from the National Science Foundation.








Bee-microbe interactions

Microbial communities are common in the gut and in food resources for many bee species. Most bee species are solitary (not social) and provision their offspring with enough nectar and pollen for larval development. Recent work has shown that these provisions contain bacterial and yeast communities that seem to be obtained from flowers, and may be important for pollen preservation or bee nutrition.  However, these bee species and their microbiomes are poorly understood and have received only little study. In collaboration with Bryan Danforth, Quinn McFrederick, and Shawn Steffan among other collaborators, and support from the National Science Foundation, we are aiming to investigate the microbial communities associated with many solitary bee species and probe the functions and effects on bees. We have worked on multiple bee genera including Osmia, Megachile, Anthophora and Diadasia.

Want to learn more about Mason bees and other native bees and their use in agriculture? Check out the SARE (Sustainable Agriculture Research and Education) guide to alternative pollinator management to learn more.

O. ribifloris brood cells
O. ribifloris brood cells

We are also interested in bee-microbe interactions more broadly, including in Bombus vosnesenskii, in a project led by Danielle Rutkowski; in Xylocopa sonorina, in a project led by Madeline Handy. We also collaborate with Neal Williams to investigate microbiomes of Osmia lignaria and O. ribifloris in California.

Ecology of nectar-inhabiting microbes

One particularly abundant group of microorganisms found in nectar are bacteria in the genus Acinetobacter. A clade within the genus Acinetobacter contains taxa that are only found in floral nectar and we are investigating the genomic signatures of a floral-dwelling lifestyle and functional adaptations to this environment. This project is led in our lab by Meg Christensen in collaboration with Tory Hendry and lab, with contributions by our other nectar-studying collaborators including Tadashi Fukami, Sergio Alvarez-Perez, Bart Lievens, and others.


Effects of belowground microorganisms on plant defense and aboveground interactions

All plants associate with fungi and bacteria belowground, and agricultural practices influence belowground microbial communities. I am interested in how fungal and bacterial communities change in response to different management practices, and how these changes influence plant-microbe interactions, plant phenotype, and plant-insect interactions.

In tomato, we are examining the influence of agricultural management strategies on rhizosphere microbial community structure and plant defense, with Amelie Gaudin and Clare Casteel. This work is supported by the California Tomato Research Institute.


Applications of microbial community ecology in agricultural systems

Microbial pathogens can be devastating to crops. We are investigating if floral nectar microbes may be employed as biocontrol to help prevent infection by floral pathogens. One focal system is  Erwinia amylovora, the cause of fire blight. Our current work on Erwinia in pear is led by Robert Schaeffer in collaboration with Steven Lindow and John Beck, and is supported by the Pear Pest Management Research Fund.

Amber Crowley-Gall, a current postdoc, is leading a project in collaboration with Elina Niño and Florent Trouillas examining microbial antagonists of Monilinia laxa, the causal agent of brown rot blossom blight in almond, and their effects on honey bee behavior and health. This project is funded by the Almond Board of California.

Robert marking almond flowers for microbial application