Bumblebees Shifted Toward Antimicrobial Nectar After Fungal Exposure

Bumblebees exposed to a fungus changed their foraging behavior, showing a growing preference for nectar containing quercetin, according to a study published in Royal Society Open Science. Researchers from KU Leuven in Belgium and the University of Valladolid in Spain studied 18 commercial colonies of buff-tailed bumblebees, Bombus terrestris. The colonies were kept in flight tents equipped with eight robotic flowers. Four flowers were blue and four were yellow, and each dispensed either plain sugar water or sugar water containing a microdose of quercetin. Quercetin is a natural compound found in plant nectar and pollen and is known to have antimicrobial properties. Sensors recorded each visit, while the flowers automatically refilled after the bees fed. Before the five-day foraging period, the colonies were divided into three groups. One group was exposed to Ascosphaera apis, a fungus that mainly infects and kills bee larvae. A second group was exposed to Serratia marcescens, a bacterium that can infect adult bees. The control colonies received pollen with a sterile sugar solution. The colonies exposed to the fungus became increasingly likely to visit the quercetin flowers and spent more time drinking from them as the experiment continued. Bees exposed to the bacterium did not show a significant change in their preference. The control group also showed no significant shift. That difference suggests the bees’ response may depend on the particular pathogen they encounter. In the study, the researchers described the result as evidence that pathogen identity can shape changes in nectar-foraging behavior. The findings do not show that the bees consciously treated themselves, or that quercetin cured the infection. The experiment did not measure whether drinking the compound lowered infection levels or helped more larvae survive. As a result, the researchers said the work was not a definitive demonstration of self-medication or social medication. Instead, the study provides evidence of a disease-specific change in feeding behavior—one that may help explain how bumblebees respond to some infections in their environment.