Danielle Rutkowski: Symbiotic Fungi Associated with Social Bees

If you've been following the outstanding academic accomplishments of UC Davis doctoral candidate Danielle Rutkowski, you know that she researches the symbiotic fungi associated with social bees; is a 4.0 student; engages in public service; and is a major award winner in multiple graduate student competitions hosted by the Entomological Society of America (ESA).

Rukowski, who studies with community ecologists Rachel Vannette, associate professor and vice chair of the UC Davis Department of Entomology and Nematology, and distinguished professor Rick Karban, will present her exit seminar on "Identity and Functions of Symbiotic Fungi Associated with Social Bees" on Monday, May 20.

Her hour-long seminar starts at 4:10 p.m. in Room 122 of Briggs Hall. It also will be on Zoom. The Zoom link:
https://ucdavis.zoom.us/j/9 5882849672.

"Social bees interact with diverse microbial communities that reside in flowers, in their nests, and within their guts," Rutkowski says in her abstract. "Fungi are common inhabitants of these environments, but despite their prevalence, little is known about their interactions with bees and their impacts on bee health. In my thesis, I identified common fungal associates of social bees and investigated their effects on bumble bee health, specifically focusing on their roles in bee response to fungicide, bee nutrition, and protection from pathogens."

"I identified several yeast groups frequently associated with social bees, including the genera Starmerella and Zygosaccharomyces," she relates. "Addition of these yeasts to bee diets improved survival and reproduction, and for one species, helped bees recover from negative effects of fungicide exposure. However, a follow-up study determined that these benefits to bee health are inconsistent and unrelated to bee nutrition. Rather, benefits of these yeasts instead may be mediated through pathogen suppression, as Starmerella yeasts are able to inhibit the growth of multiple fungal pathogens of bees. These results highlight the important impacts of these currently understudied microbes on bumble bee health, with implications for conservation of these pollinators."

Active in ESA, Rutkowski received the President's Prize (first place) in 2017, 2021, and 2022 for her research presentations in her section, Plant-Insect Ecosystems. 

In her 2021 ESA presentation, she drew attention to fungicide applications that are linked to declining bumble bee populations. She wrote in her abstract: "Native bees including bumble bees are important pollinators but face threats from multiple sources, including agrochemical application. Declining bumble bee populations have been linked to fungicide application, which could directly affect the fungi often found in the stored food and GI tract of healthy bumble bees. Here, we test the hypothesis that fungicides impact bee health by disrupting bumble bee -fungi interactions. Using two species, Bombus vosnesenskii and B. impatiens, we test the interactive effect of the fungicide propiconazole and fungal supplementation on the survival, reproduction, and microbiome composition of microcolonies (queenless colonies). We found that both bee species benefitted from fungi, but were differentially affected by fungicides. In B. vosnesenskii, fungicide exposure decreased survival while fungal supplementation mitigated fungicide effects. For B. impatiens, fungicide application had no effect, but fungal supplementation improved survival and offspring production. Fungicides altered fungal microbiome composition in both species, and reduced fungal abundance in B. vosnesenskii microcolonies, but not in B. impatiens, where instead fungal addition actually decreased fungal abundance. Our results highlight species-specific differences in both response to fungicides and the nature of fungal associations with bees, and caution the use of results obtained using one species to predict the responses of other species. These results suggest that fungicides can alter bee- fungi interactions with consequences for bee survival and reproduction, and suggest that exploring the mechanisms of such interactions, including interactions within bee-associated fungal communities, may offer insights into bumble bee biology and bumble bee conservation strategies." 

Her many activities include:

  • A 2023 graduate of The Bee Course, a 10-day workshop on bee collection and identification at the Southwestern Research Station in Portal, AZ.  
  • Co-chair of the department's entomological activities, 2022 UC Davis Picnic Day, with forensic entomologist Robert Kimsey.
  • As a member of the UC Davis graduate student group, Equity in Science, Technology, Engineering, Math, and Entrepreneurship (ESTEME), she helped plan activities and lessons for middle school students in the Davis area. 
  • Former secretary and vice president of the UC Davis Entomology Graduate Student Association.
  • Mentored prospective graduate students from groups underrepresented in STEM through a month-long program, and provided application advice and feedback on application materials. 

Rutkowski holds a bachelor of science degree from Cornell University in entomology and biological sciences, with a concentration in ecology and evolutionary biology. She graduated in May 2018 summa cum laude with distinction in research.

At Cornell, Rutkowski did independent research with Professor Jennifer Thaler, carrying out an independent honor's thesis research project on ecological interactions between insect herbivores, plants, and arbuscular mycorrhizal fungi. Rutkowski also worked with Thaler on numerous other projects, studying interactions between potato plants, Colorado potato beetles, and their predators, as well as projects studying the interactions between arbuscular mycorrhizal fungi, tomato plants, and insect herbivores. She also worked with Professor Richard Lindroth at the University of Wisconsin, Madison, investigating how genotype and environmental conditions interact to affect the growth, defense and insect community of aspen trees.

Rutkowsk is the lead author or co-author in a number of publications:

  • Rutkowski, D., Weston, M., Vannette, R.L. (2023) Bees just wanna have fungi: A review of bee associations with non-pathogenic fungi. FEMS Microbiology Ecology 99(8) https://doi.org/10.1093/femsec/fiad077
  • Karban, R., Rutkowski, D., Murray, N. (2023) Flowers that self?shade reduce heat stress and pollen limitation. American Journal of Botany 110(2) https://doi.org/10.1002/ajb2.16109
  • Pepi, A., Pan, V., Rutkowski, D., Mase, V., Karban, R. (2022) Influence of delayed density and ultraviolet radiation on caterpillar baculovirus infection and mortality. Journal of Animal Ecology 91(11):2192-2202 https://doi.org/10.1111/1365-2656.13803
  • Rutkowski, D., Litsey, E., Maalouf, I, Vannette, R.L. (2022) Bee-associated fungi mediate effects of fungicides on bumble bees. Ecological Entomology 47(3):411-422 https://doi.org/10.1111/een.13126
  • Mola, J.M., Stuligross, C., Page, M.L., Rutkowski, D., Williams, N.M. Impact of “non-lethal” tarsal clipping on bumble bees (Bombus vosnesenskii) may depend on queen stage and worker size. Journal of Insect Conservation 25, 195–201 (2021). https://doi.org/10.1007/s10841-021-00297-9

The UC Davis Department of Entomology and Nematology seminars are coordinated Brian Johnson, associate professor. For any technical issues with Zoom, contact him at brnjohnson@ucdavis.edu. The full list of spring seminars is here.