Yeast volatiles promote larceny in bumble bee behavior

Authors: SOUTO-VILAROS, DANIEL - Utah State University; MARTIN, VALERIE - Utah State University; DABAGIA, NICHOLAS - University Of Michigan; FRESHOUR, DREW - Utah State University; RODRIGUEZ, NATALIE - Rocky Mountain Biological Laboratory (RMBL); STRYKER, JADE - Rocky Mountain Biological Laboratory (RMBL); GUTIERREZ, ORIANNA - Rocky Mountain Biological Laboratory (RMBL); Rering, Caitlin; IRWIN, REBECCA - North Carolina State University; SCHAEFFER, ROBERT - Utah State University

Submitted to: iScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/4/2026
Publication Date: 2/7/2026
Citation: Souto-Vilaros, D., Martin, V.N., Dabagia, N., Freshour, D.M., Rodriguez, N., Stryker, J., Gutierrez, O., Rering, C.C., Irwin, R.E., Schaeffer, R.N. 2026. Yeast volatiles promote larceny in bumble bee behavior. iScience. 114946. https://doi.org/10.1016/j.isci.2026.114946.
DOI: https://doi.org/10.1016/j.isci.2026.114946

Interpretive Summary: Many crops require pollination to produce food. Bees and other pollinators move pollen between and within flowers, fertilizing them and ensuring crops develop. However, bees can display a variety of different behaviors when visiting flowers and not all interactions achieve pollination. An example of a non-pollinating bee behavior is “nectar robbing”, where a bee chews a hole in the side of a flower to easily access nectar without encountering any of the flower’s reproductive organs. Once a robbing hole is chewed into a flower, later visitors are more likely to also use this hole to access nectar, a behavior known as secondary nectar robbing. Little is known about what factors govern nectar robbing behavior. Additionally, pollinators also respond to microbes that live in floral nectar. These microbes sometimes make flowers more attractive to pollinators but can also deter bee foraging, depending on the circumstances. In this study, a team of researchers from Utah State University, the Rocky Mountain Biological Laboratory, North Carolina University, and an ARS Scientist at the Center for Medical, Agricultural, and Veterinary Entomology, in Gainesville, FL tested how bumble bee nectar robbing behavior was modified when flowers contained nectar yeast. When flowers contained yeast, bumble bees were able to engage in secondary nectar robbing more efficiently; they more rapidly located the robbing holes than when flowers did not contain microbes. Chemical and behavioral tests support the hypothesis that this boost in efficiency is caused by the odors that nectar yeast produce. These results help us understand bee foraging behavior, which is important to crop production.

Technical Abstract: Plant–pollinator mutualisms are widespread in ecological communities; however, their stability is frequently threatened by acts of cheating committed by individual actors. The proximate mechanisms that encourage individual flower visitors to choose to seek benefits without conferring a service in return, such as robbing flowers of their nectar without providing any pollination, remain largely unknown. In this study we combined field and laboratory behavioral assays with gas chromatography mass spectrometry (GC-MS) to test the hypothesis that a nectar-inhabiting yeast can mediate exploitative behaviors displayed by bumble bees with flexible foraging tactics across different floral hosts. In field behavioral assays, Bombus bifarius and B. flavifrons secondary nectar robbers (individuals that take advantage of holes made in flower corollas by primary nectar robbers) discovered robbing holes 2.2 s faster on average and foraged 64% more on Metschnikowia reukaufii-inoculated flowers of both Cordyalis caseana and Mertensia ciliata than controls. Olfactometer assays confirmed a yeast volatile-mediated response, as workers spent significantly more time in the Y-tube arm assigned to the yeast-treated bouquet for Corydalis. Nectar scent was enhanced with fifteen volatile compounds when fermented with yeast for two days relative to unfermented nectar. Collectively, our results suggest an important role for yeast odors in mediating exploitative behaviors displayed by mutualist species, acting as a potential honest signal for resource presence and improving bee foraging efficiency.