Honey bees might be drawn to the very chemicals that are endangering them, based on experiments in which they preferred drinking sugar water that had been mixed with the poisons rather than sugar water alone.

Evolution may explain why the bees are attracted to the chemicals that are potentially dangerous to their health. But the findings, published in the journal Scientific Reports, suggest herbicides and fungicides pose a greater risk to honey bee populations than previously believed.

The nectar that forager bees bring back to the hive, where it is produced into honey, can have an effect on the health of the entire colony. A type of insecticide called neonicotinoids has been shown, for example, to shorten the lifespans of exposed bees and wreak havoc on the organization of the hive.

Even with chemicals that are known to have negative effects on bees, there is often still the question of how much exposure the insects are really getting, both in terms of how much the chemicals pervade the surrounding environment and how much bees come in contact with them. For the current study, the scientists found that forager bees were drawn to the fungicide chlorothalonil and the herbicide ingredient glyphosate, found in Monsanto’s Roundup, at certain concentrations.

Previous research has shown that chlorothalonil is linked to a fungal parasite called Nosema bombi that affects bumblebees. Glyphosate, meanwhile, could affect bees’ abilities to learn and navigate.

honey-bee-hive Honey bees may be attracted to the very chemicals in fungicides and herbicides that hurt them. Photo: L. Brian Stauffer

“The bees are not only not avoiding this fungicide [chlorothalonil], they’re consuming more of it at certain concentrations,” researcher May Berenbaum said in a statement from the University of Illinois. “People assume that fungicides affect only fungi … 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.”

The bees had been offered plain sugar syrup as well as the sweet mixture blended with several fungicides and herbicides at different concentrations. There were also feeders that had sugar water mixed with naturally occurring chemicals.

In addition to the chlorothalonil, the bees were attracted to a natural chemical called quercetin that is found in a lot of their food sources and has health benefits.

“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,” Berenbaum said.

Although foragers can sniff out potentially hazardous chemicals — “bees have the ability to evaluate food quality and use phytochemicals as cues to make foraging decisions,” according to the study — they also sometimes positively categorize chemicals in agricultural chemicals and are attracted to them.

This could be a function of evolution; the foragers might see the chemicals of a new type of food they can collect during times of scarcity.

“They’re active from early spring until late fall, and no single floral source exists for them for that whole season,” Berenbaum said. “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.”