Fungicides are among the top contaminants of honey bee hives and can interfere with the bees’ ability to metabolize other pesticides.
Credit: Photo by L. Brian Stauffer
When given the choice, honey bee foragers prefer to collect sugar syrup laced with the fungicide chlorothalonil over sugar syrup alone, researchers report in the journal Scientific Reports.
The puzzling finding comes on the heels of other studies linking fungicides to declines in honey bee and wild bee populations. One recent study, for example, found parallels between the use of chlorothalonil and the presence of Nosema bombi, a fungal parasite, in bumble bees. Greater chlorothalonil use also was linked to range contractions in four declining bumble bee species.
Other research has shown that European honey bees have a very limited repertoire of detoxifying enzymes and that exposure to one potentially toxic compound — including fungicides — can interfere with their ability to metabolize others.
“People assume that fungicides affect only fungi,” said University of Illinois entomology professor and department head May Berenbaum, who led the new research with postdoctoral researcher Ling-Hsiu Liao. “But fungi are much more closely related to animals than they are to plants. And toxins that disrupt physiological processes in fungi can also potentially affect them in animals, including insects.”
Some scientists have argued that bees may be less susceptible to agricultural chemicals than laboratory studies suggest because the bees might detect potentially toxic chemicals in the environment and avoid them. But a 2015 study found that European honey bees and at least one species of bumble bee actually prefer food laced with neonicotinoid pesticides.
To test whether foraging honey bees showed a preference for other chemicals they are likely to encounter in the wild, Liao set up two feeding stations in a large enclosure. Foraging honey bees could fly freely from one feeder to the other, choosing to collect either sugar syrup laced with a test chemical or sugar syrup mixed with a solvent as the control. Over the course of the study, she tested honey bee responses to nine naturally occurring chemicals, three fungicides and two herbicides at various concentrations.