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Common pesticides disrupt brain functioning in bees

Honey bee (Apis mellifera) collecting pollen. Photo by: Jon Sullivan.
Honey bee (Apis mellifera) collecting pollen. Photo by: Jon Sullivan.

Exposure to commonly used pesticides directly disrupts brain functioning in bees, according to new research in Nature. While the study is the first to record that popular pesticides directly injure bee brain physiology, it adds to a slew of recent studies showing that pesticides, especially neonicotinoids, are capable of devastating bee hives and may be, at least, partly responsible for on-going Colony Collapse Disorder (CCD).

Christopher Connolly with the University of Dundee in Scotland and his team exposed honeybees to two pesticides at levels encountered in the wild: neonicotinoids and miticidal pesticides. By recording brain activity after exposure, the researchers found that both pesticides directly hampered bee brain functioning, including blocking neurons from firing. The findings are especially notable for studying bees after exposure to the miticidal pesticide, which is used directly on bee hives to safeguard them from a common parasite, the Varroa destructor mite. In this case, however, the cure may be worse than the disease.

“Much discussion of the risks posed by the neonicotinoid insecticides has raised important questions of their suitability for use in our environment,” Connolly explains. “However, little consideration has been given to the miticidal pesticides introduced directly into honeybee hives to protect the bees from the Varroa mite. We find that both have negative impact on honeybee brain function.”

Furthermore the researchers found that when bees were exposed to both chemicals—the neonicotinoids and miticidal pesticides—their brain functioning and learning abilities were hurt even more.

The study is the first to show the direct brain impacts that may explain why bees exposed to these pesticides slow aberrant behavior, including losing their way easily and slow reactions. Scientists both in the U.S. and Europe have recorded the complete collapse of hives following exposure. However, pesticide companies have continually argued that their products cause no harm to bees even as high-profile independent research from multiple sources appears to be telling a very different story.

The research has spurred some policy movement. France has banned the use of neonicotinoids on certain crops. The EU proposed a ban on neonicotinoids for two years after a committee looked at the research for six months. However, the ban was scuttled by opposition from Germany and the UK, though it could still come up in appeal. Most recently, nine beekeeping and environmental groups sued the U.S. Environment Protection Agency (EPA) for failing to take action to protect bees.

Bees are key plant pollinators, and their decline has worried scientists, farmers, and policymakers worldwide. In the U.S. alone, bee pollination is estimated to be worth $8-12 billion. While bee declines have occurred in the past, researchers believe this one is much more severe.

CITATION: Mary J. Palmer,Christopher Moffat, Nastja Saranzewa, Jenni Harvey, Geraldine A. Wright, Christopher N. Connolly. Cholinergic pesticides cause mushroom body neuronal inactivation in honeybees. Nature Communications. 4, Article number: 1634. doi:10.1038/ncomms2648.

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