Neonicotinoids are common pesticides that target the same mechanisms in insect brains that are affected by nicotine in our brains. And according to a new field experiment, neonicotinoids are harmful to the bees we rely on to pollinate our crops. That’s not too surprising, but get this: The bees actually prefer to eat nectar that’s been laced with neonicotinoids! The pair of studies were published in Nature this week.
To protect young oilseed rape plants against flea beetles, seeds are coated with neonicotinoids. But some studies have suggested that these insecticides may threaten helpful, non-target species, like bees who are already suffering colony collapses. So in 2013, the European Union began restricting the use of neonicotinoids for flowering crops that attract bees, though critics of this two-year moratorium suggest simply planting alternative nectar and pollen sources to lower the exposure. That, however, implies that bees know to choose.
So first, to investigate the effects of exposure, a team led by Lund University’s Maj Rundlöf studied bees in an environment that replicates real-world agricultural landscapes. “The fields were managed by individual farmers, just as they would if the study was not conducted," Rundlöf tells New Scientist. The oilseed rape were sown from seeds coated in a neonicotinoid called clothianidin.
Compared to untreated plants, seeds coated with neonicotinoids had a negative impact on the behavior and success of some species: While the bees were able to cope with the exposure, neonicotinoids reduced wild bee density, bumblebee colony growth and reproduction, and the nesting activities of the solitary bee (Osmia bicornis, pictured right). The females build brood cells in nests filled with tubes. Additionally, they found that neonicotinoid exposure didn’t significantly impact honeybee colonies. “Honeybees are the model organism that is used in toxicity testing for pesticides,” Rundlöf tells Nature. However, “if we only investigate how a new pesticide affects honeybees, that is not sufficient to predict the consequences for wild bees in a real landscape,” she adds in a news release.
And what if bees had a choice? Newcastle University’s Geraldine Wright and colleagues allowed bees to choose between sugar solutions that contained sucrose alone or sucrose laced with a neonicotinoid. Bees, it turns out, can’t control their exposure. Neither honeybees (Apis mellifera) nor buff-tailed bumblebees (Bombus terrestris, pictured top) were repelled by the solutions containing pesticides. Further experiments revealed that the bees can’t taste three of the most commonly used neonicotinoids (including clothianidin)—which means they can’t avoid them.
What’s worse, both species (but especially bumblebees) actually preferred to drink the neonicotinoid solutions! And that’s in spite of the fact that consuming pesticides caused them to eat less food overall. The fact that bees show a preference for neonicotinoid-containing sugar suggests that—like nicotine—neonicotinoids may act like a drug to make foods containing these substances more rewarding, Wright explains in a university statement. “If foraging bees prefer to collect nectar containing neonicotinoids, this could have a knock-on negative impact on whole colonies and on bee populations.”
Images: Dara Stanley (top), Morgan Boch (middle)