An international team of biologists has discovered that yeasts living in flowers help nectar-robbing bumblebees find holes for illicit nectar collection more quickly. Guided by the scent of fermentation, these insects locate such openings on average 2.2 seconds faster, allowing them to save significant time and energy—though this comes at a cost to the plants.

How Bumblebees Steal Nectar

The relationship between plants and pollinators isn’t always based on fair exchange. Bumblebees often resort to so-called “nectar robbing”: they bite into the base of a flower or use existing holes to drink nectar without coming into contact with pollen. As a result, the plant loses resources without receiving pollination in return.

The Role of Yeast in Floral Nectar

Floral nectar isn’t sterile—it’s a thriving environment for bacteria and yeast. Researchers, whose work was published in the journal Cell, hypothesized that the metabolic byproducts of these microorganisms serve as signals to insects about the presence of sugar, thereby influencing their behavior.

Experiment in the Colorado Mountains

To test this hypothesis, scientists conducted field experiments with wild Corydalis and Mertensia flowers in the Colorado mountains. In flower buds, they replaced natural nectar with artificial analogs: some were sterile, while others were inoculated with Metschnikowia reukaufii yeast.

The biologists observed “secondary robbers”—bumblebees that don’t make holes themselves but search for ones already present. Using stopwatches, they recorded the time it took each insect to find a puncture and begin feeding.

Laboratory Tests and Chemical Analysis

In parallel, laboratory olfactometric tests (measuring reactions to scent in a Y-shaped tube) and chemical analyses of volatile compounds were conducted using gas chromatography-mass spectrometry.

Yeast Aroma Speeds Up Nectar Search

The scent of yeast turned out to be a catalyst for robbing: in 63% of cases, bumblebees chose flowers where fermentation was occurring. Guided by the smell of yeast metabolites, bumblebees found entry holes on average 2.2 seconds faster than on sterile flowers. This reduced search time by 30–35% and allowed a bumblebee to visit about 13 flowers per minute instead of 10, providing a significant energy advantage.

Chemical Composition of the Aroma

Chemical analysis showed that yeast enriches nectar aroma with 14 new volatile compounds, including various alcohols and esters (such as 3-methyl-1-butanol). Insects associate this specific “bouquet” with the presence of high-calorie food.

Significance of the Study

This research demonstrates that microorganisms can radically influence the interactions between plants and animals, turning mutually beneficial cooperation (mutualism) into parasitism. By signaling the presence of sugar through fermentation aromas, yeast increases the efficiency of bumblebee foraging, but also intensifies the pressure on plants, whose resources are depleted without pollination.