The tripartite system formed by the early-blooming perennial herb Helleborus foetidus (Ranunculaceae), the yeasts inhabiting its floral nectar, and the bumble bees that pollinate the plant and disseminate the yeasts, was investigated to test whether nectar-dwelling yeasts can influence pollinator behavior and plant reproductive success. Under both laboratory and field conditions, bumble bees (Bombus terrestris) preferred yeast-containing nectar. In addition, experimental yeast inoculation of the nectar of H. foetidus flowers in the field was associated with reductions in number of pollen tubes in the style, fruit set, seed set, and mass of individual seeds. This provides direct evidence that nectar yeasts can modify pollinator foraging patterns, pollination success, and the quantity and quality of seeds produced by insect-pollinated plants.
These photographs illustrate the article “Yeasts in nectar of an early-blooming herb: sought by bumble bees, detrimental to plant fecundity,” by Carlos M. Herrera, María I. Pozo, and Mónica Medrano, published in Ecology 94:273–279, February 2013. doi: http://dx.doi.org/10.1890/12-0595.1