Researchers prove bees gravitate toward sugar laced with the fungicide chlorothalonil over plain sugar. While the fungicide itself is not deadly to bees, it could have a deadly outcome.
New research indicated that exposure to fungicides interferes with honey bee ability to metabolize the treatments beekeepers use to kill varroa mites—meaning their preference for the chemicals could lead to more complications and even death.
“The dose determines the poison,” says May Berenbaum, Illinois Entomology professor and department head who lead the research project. “If your ability to metabolize poisons is compromised, then a therapeutic dose can become a toxic dose. And that seems to be what happens when honey bees encounter multiple pesticides.”
University experts decided to test the theory that bees prefer fungicide-soaked food and set up two feeding stations. Bees could fly from one to the other and collect syrup with chemicals or without. Postdoctoral researcher Ling-Hsiu Liao tested honey bee responses to nine naturally occurring chemicals, three fungicides and two herbicides.
The test proved that bees prefer the naturally occurring chemical quercetin at any concentration.
“That makes sense, because everything the honey bees eat has quercetin in it,” Berenbaum says. “There’s quercetin in nectar, there’s quercetin in pollen. Quercetin is in honey and beebread, and it’s a reliable cue that bees use to recognize food.”
In addition, bees preferred syrup laced with glyphosate, but only at 10 parts per billion or lower. Bees avoided syrup with prochloraz and showed a small preference for syrup laced with chlorothalonil at .5 and 50 parts per billion, but not at 500 parts per billion.
The study concludes that bees don’t avoid fungicide soaked foods, they’re in fact “consuming more of it at certain concentrations,” Berenbaum says.
While they don’t know why bees gravitate toward these potentially toxic chemicals and bring them back into the colony this behavior is not unexpected.
“Honey bee foragers are gleaners,” Berenbaum says. “They’re active from early spring until late fall, and no single floral source exists for them for that whole season. If they don’t have a drive to search out something new, that’s going to seriously compromise their ability to find the succession of flowers they need. Unnatural chemicals might be a signal for a new food.”