Harvard Study: Insecticides Strongly Linked to Bee Deaths

Certain insecticides seem to cause neurological damage in bees' brains.

May 12, 2014

Since the emergence of honeybee colony collapse disorder (CCD) in 2006, researchers have been trying to figure out exactly what's causing hives across the world to mysteriously empty, leaving only a few dead bees in their wake. New research published in the Bulletin of Insectology is strengthening the argument that neonicotinoid insecticides are to blame.

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In the new study, researchers compared hives treated with a non-lethal amount of clothianidin and imidacloprid (two types of neonicotinoids) to untreated hives. During the summer and early fall, the hives behaved similarly. It wasn't until late October that the numbers began to drop. Interestingly, by January, the untreated hives were back to normal buzzing, but the numbers dwindled away in the hives treated with chemical insecticides. Of the twelve hives treated with neonicotinoids, half had collapsed by the end of the winter.

Chensheng Lu, PhD, associate professor of environmental exposure biology at the Harvard School of Public Health, suspects that CCD may be caused by the chemicals' ability to cause neurological damage in the bees. "For adult bees to leave the colony during the winter is against their nature. Why would they go out when it's so cold?" says Lu. "But the fact is that the CCD hive was empty, so there may be some neurological impairment to the adult bees."

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That makes sense because neonicotinoid bug-killers work by scrambling insects' brain signals.

The insecticide-CCD theory is in stark contrasts to earlier theories suggesting that immune deficiency in bees triggered CCD. The researchers also looked at the effect of Nosema ceranae, a pathogenic mite that commonly infects hives. "During the course of the study, we measured the pathogen and we didn't see any differences," says Lu. "If a hive died from a mite infestation, you'd see thousands of dead bees, but we call it colony collapse disorder because the hive is essentially empty, so we ruled out pathogen issues."

Interestingly, you're helping bees when you eat organic. Many nonorganic, genetically engineered, or GMO, seeds grown in America are coated in neonicotinoid chemicals that wind up in pollen.

Here's how to keep potentially toxic insecticides out of your garden:

Know that prevention is better than a cure. Which would you rather: Spend weeks washing lice out of your hair or not sharing your neighbor's baseball cap in the first place? Think about your plants in the same way. "The best defenses against insect attack are preventive measures," says Deborah Martin, author of Rodale's Basic Organic Gardening. "Pests target weak or unhealthy plants, so choose plants that are suited to the conditions you are putting them in and they'll be less stressed." Besides that, simple water, sun, and low-nitrogen compost should do the trick to happy plants.

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Make diversity a priority. If your plants make meals for mites, think of a row of all one plant as an all you can eat buffet, and mites love to bring all of their friends when they go out to eat. "Mixing different vegetables, herbs, and flowers together in your beds keeps pests from zeroing in on a whole crop of their target plant," says Martin. "The more diverse and abundant the habitat, the more beneficial insects—and the fewer pest insects." This holistic approach is different than attacking one bug at a time with pests, but may be just as (or more!) effective.

Don't do all the work yourself. You don't have to be the only one killing bugs in your garden: Let other bugs do the dirty work. "The most effective and natural way to control pests is to rely on the food chain," says Martin. She recommends planting herbs and flowers to lure predatory insects that will consume pests. "Or put out a birdbath to enlist the appetites of songbirds to your cause," suggests Martin.

For more ways to help protect bees and other beneficial insects that are vitally important to our ecosystem, check out these ways to make your yard honey bee-friendly.