Pesticide-Dosed Bees Can Lose Royals, Way Home: In Tests, Nonfatal Exposures Lead to Shrinking Colonies

Article excerpt

What does not kill them does not in fact make them stronger when it comes to bees and pesticides. Two unusual studies with free-flying bumblebees and honeybees find that survivable exposure to certain pesticides can lead to delayed downturns in bee royalty and a subtle erosion of workforces.

Pesticides appear as a suspect in widespread declines, some subtle and some striking, of bees and other animals that pollinate crops and wild plants. And in one of the most dramatic still-unsolved mysteries in those declines--why honeybee colonies suddenly collapse- one leading hypothesis combines chronic pesticide exposure with other stressors such as disease.

Both new studies, appearing online March 29 in Science, test the risks of foraging on flowers treated with common insect killers from the nicotine-related class called neonicotinoids. These pesticides course through the whole plant, killing aphids and a range of other nibbling and sipping pests, but also work their way into the nectar and pollen that bees collect.

To simulate pesticide exposures that bumblebees might encounter when a field of canola blooms, entomologist Dave Goulson of the University of Stirling in Scotland and his colleagues fed 50 Bombus terrestris lab colonies nonfatal doses of the pesticide imidacloprid. After two weeks of eating spiked pollen and sugar water, bees were set outside and allowed to forage around the Stirling campus at will. By season's end, the pesticide-dosed colonies were an average of 8 percent to 12 percent smaller than 25 unexposed neighbor colonies.

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More noticeably, the contaminated colonies managed to produce only about two young queens each. The other colonies averaged about 14. Pitiful production of new young queens bodes ill for bumblebees because all other colony members die at the end of the growing season. Young queens represent each group's sole hope for making new colonies the next year.

A drop in pollinator reproduction is the kind of finding that can get the attention of agencies regulating pesticide use, says Jeffery Pettis, a U.S. Department of Agriculture bee researcher in Beltsville, Md. With these and previous studies, concerns are growing that usage rules for neonicotinoids may need to be tightened. …