Bees don’t have the mouthpart sensitivity to taste — and thus can’t avoid — nectar tainted with neonicotinoid pesticides, new lab tests indicate. And the charm of nicotine may even seduce bees into favoring pesticide-spiked nectar.
Outdoor tests also show that neonicotinoid exposure for some wild bees can be worrisome, a second paper reports. Together, the studies renew questions about the widespread use of these pesticides on crops.
In the mouthpart tests, taste nerves in honeybees and buff-tailed bumblebees failed to show any jolt of reaction to three widely used neonicotinoid pesticides, says Geraldine Wright of Newcastle University in England. “I don’t think they can taste it all,” she says. Bees buzzing among the floral riches outside laboratories would therefore not be able to avoid neonicotinoid-tainted nectar, she and her colleagues argue online April 22 in Nature.
Even though bees don’t taste the pesticides, something about their nicotine-related chemistry may bias bees to keep returning to the location of the spiked nectar, Wright suggests. Offered a choice in the lab, both honeybees and bumblebees sipped more of the sugar water with a touch of a neonicotinoid pesticide in it than the plain sugar water.
Worries about what neonicotinoids do to pollinators reached such a peak in 2013 that the European Union banned use of those pesticides for two years, calling for more research. Studies have reported that exposure can impair bees’ skills at bringing home pollen and nectar, dimming their ability to navigate a landscape, for example. Debate has broken out over how lab studies apply to bees that can pick and choose flowers outdoors and how to interpret the results from field studies in complex landscapes.
In a new outdoor study, also reported April 22 in Nature, researchers paired eight fields in Sweden planted with rape seeds coated by pesticides including the neonicotinoid clothianidin with comparable fields sprouting untreated seeds. Honeybee colonies that foraged over treated fields and those that foraged over untreated ones grew at about the same rate. Yet bumblebee colonies foraging in the treated fields failed to grow, report Maj Rundlöf of Lund University in Sweden and colleagues. And Osmia bicornis bees, a wild species that doesn’t live in colonies, nested at six of the eight untreated sites but at none of the treated ones.
“At this point, it is no longer credible to argue that agricultural use of neonicotinoids does not harm wild bees,” says Dave Goulson of the University of Sussex in England, who has studied bumblebees but was not involved in the new test.
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Honeybees have been the main species tested for harmful effects of pesticides, Rundlöf says. Yet their reactions may not reflect what happens to other pollinators. Also, she points out, her experiment couldn’t detect changes of less than about 20 percent in honeybee colony growth. So she urges caution in assuming that the pesticides had no effect on the honeybees.
Editor’s note: This story was updated April 28, 2015, to note that colonies that foraged on treated and untreated fields grew at the same rate, not increased in weight at the same rate as previously stated.