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Bee Studies Stir Up Pesticide Debate04-28-15 | News

Bee Studies Stir Up Pesticide Debate

A study in Sweden has monitored how bees respond to neonicotinoids in the wild. Based on that study, the threat that neonicotinoids pose to bees has become clearer.
Picture Courtesy of Home Depot

The case for restricting a controversial family of insecticides is growing. Two studies, published on April 22 in "Nature," address outstanding questions about the threat that the chemicals pose to bees. It comes as regulators around the world gear up for a fresh debate on pesticide restrictions.

Many bee populations are in steep decline, with multiple causes identified, including parasites and the loss of food sources. Also blamed are neonicotinoids, a widely used class of insecticides that are often applied to seeds and find their way into the pollen and nectar of plants.

Currently, the use of three pesticides -- clothianidin, imidacloprid and thiamethoxam -- is temporarily banned in the European Union because of concern that they might harm pollinators; the ban is up for review in December. In the United States, there are no such restrictions, but the US Environmental Protection Agency said on April 2 that it was unlikely to approve new outdoor neonicotinoid-pesticide uses without new bee data.

So far, the data are mixed. Many studies that link poor health of bee colonies to pesticides have been criticized for not using realistic doses. Some defenders of the chemicals have argued that if neonicotinoids are harmful, then bees will learn to avoid treated plants.

Geraldine Wright, an insect neuroethologist at Newcastle University, UK, and her colleagues investigated this aspect. They confined honeybees (Apis mellifera) and bumblebees (Bombus terrestris) to boxes and gave them a choice between plain nectar and nectar laced with imidacloprid, thiamethoxam or clothianidin. The researchers found that the bees showed no preference for the plain nectar. In fact, the insects were more likely to choose the nectar containing imidacloprid or thiamethoxam, although it is not clear whether the preference would occur in the wild.

Wright's team also analyzed the response of the bees' taste neurons to neonicotinoids, and found that they reacted the same regardless of concentration. This indicates that the bees cannot taste the pesticides and that the preference is caused by some other mechanism. Other studies have shown that neonicotinoids activate receptors in bee brains linked to memory and learning.