National Geographic News
A honeybee pollinates a flower.

Honeybees learn and remember the locations of flowers, but a new study shows they may be losing their way.

Photograph by John Kimbler, My Shot

Christy Ullrich

National Geographic News

Published February 13, 2013

A single honeybee visits hundreds, sometimes thousands, of flowers a day in search of nectar and pollen. Then it must find its way back to the hive, navigating distances up to five miles (eight kilometers), and perform a "waggle dance" to tell the other bees where the flowers are.

A new study shows that long-term exposure to a combination of certain pesticides might impair the bee's ability to carry out its pollen mission.

"Any impairment in their ability to do this could have a strong effect on their survival," said Geraldine Wright, a neuroscientist at Newcastle University in England and co-author of a new study posted online February 7, 2013, in the Journal of Experimental Biology.

Wright's study adds to the growing body of research that shows that the honeybee's ability to thrive is being threatened. Scientists are still researching how pesticides may be contributing to colony collapse disorder (CCD), a rapid die-off seen in millions of honeybees throughout the world since 2006.

"Pesticides are very likely to be involved in CCD and also in the loss of other types of pollinators," Wright said. (See the diversity of pollinating creatures in a photo gallery from National Geographic magazine.)

Bees depend on what's called "scent memory" to find flowers teeming with nectar and pollen. Their ability to rapidly learn, remember, and communicate with each other has made them highly efficient foragers, using the waggle dance to educate others about the site of the food source.

Watch as National Geographic explains the waggle dance.

Their pollination of plants is responsible for the existence of nearly a third of the food we eat and has a similar impact on wildlife food supplies.

Previous studies have shown certain types of pesticides affect a bee's learning and memory. Wright's team wanted to investigate if the combination of different pesticides had an even greater effect on the learning and memory of honeybees.

"Honeybees learn to associate floral colors and scents with the quality of food rewards," Wright explained. "The pesticides affect the neurons involved in these behaviors. These [affected] bees are likely to have difficulty communicating with other members of the colony."

The experiment used a classic procedure with a daunting name: olfactory conditioning of the proboscis extension reflex. In layman's terms, the bee sticks out its tongue in response to odor and food rewards.

For the experiment, bees were collected from the colony entrance, placed in glass vials, and then transferred into plastic sandwich boxes. For three days the bees were fed a sucrose solution laced with sublethal doses of pesticides. The team measured short-term and long-term memory at 10-minute and 24-hour intervals respectively. (Watch of a video of a similar type of bee experiment.)

This study shows that when pesticides are combined, the impact on bees is far worse than exposure to just one pesticide. "This is particularly important because one of the pesticides we used, coumaphos, is a 'medicine' used to treat Varroa mites [pests that have been implicated in CCD] in honeybee colonies throughout the world," Wright said.

The pesticide, in addition to killing the mites, might also be making honeybees more vulnerable to poisoning and effects from other pesticides.

Stephen Buchmann of the Pollinator Partnership, who was not part of Wright's study, underscored how critical pollinators are for the world. "The main threat to pollinators is habitat destruction and alteration. We're rapidly losing pollinator habitats, natural areas, and food-producing agricultural lands that are essential for our survival and well being. Along with habitat destruction, insecticides weaken pollinators and other beneficial insects."

Donald Sutherland
Donald Sutherland

The USDA Agricultural Research Service says pesticides may be having an unexpected impact, “but no common environmental agent or chemicals stand out as a causative”.

And the EPA states, “to date we’re aware of no data demonstrating that an EPA registered pesticide used according to the label instructions has caused CCD.”

But that isn’t true.

In January 2012 Purdue University scientists published results of their two year study showing the insecticides clothianidin and thiamethoxam, commonly used to coat corn and soybeans seeds, were killing pollinating bees.

“We know that these insecticides are highly toxic to bees: we found them in each sample of dead and dying bees,” quoted Christian Krupke, associate professor of entomology and co-author of the findings in the Purdue University News Service.

The Purdue Study sited the neonicotinoids as compounds that can persist for months or years with plants growing in the treated soil taking up the compounds in leaf tissue and or pollen.

In March 2012 in the journal of Science two teams of researchers, one in France and the other in Britain, published studies showing neonicotinoids have significant negative impacts on bee health and colony survival.

And in April 2012 the Harvard School of Public Health released their study to be published in the June issue of the Bulletin of Insectology, citing new research providing evidence linking imidaloprid and bee CCD.

The authors of this study proved bees exposed to imidaloprid in a plant’s pollen or through the high fructose corn syrup beekeepers use to feed their bees, and it resulted in CCD. Over 90 percent of conventionally grown corn in the US has been treated with neonicotinoids and it is in corn syrup.

The governments of France, Germany, and Italy are not waiting for more studies tying bee CCD with neonicotinoids. Since 2008 there have been bans on seed treatment using neonicotinoids in all of these countries.

Bee keepers and their associations recognize the agricultural pesticide threat but say a bigger danger contributing to bee CCD is with lawn and garden products being used by consumers.

“A more immediate threat is the lawn care companies that mix neonicotinoids into sprays and they are more widely distributed then talc on corn seed and other modes of distribution,” says Dan Conlon, President of the Massachusetts Beekeepers’s Association.

In a recent report on bee colony collapse by the environmental organization Xerces, a nonprofit that protects wildlife through the conservation of invertebrates and their habitat, their scientists found products approved for homeowners to use in gardens, lawns, and on ornamental trees have manufacturer-recommended application rates up to 120 times higher than rates approved for agricultural crops.


Popular Stories

The Future of Food

  • Why Food Matters

    Why Food Matters

    How do we feed nine billion people by 2050, and how do we do so sustainably?

  • Download: Free iPad App

    Download: Free iPad App

    We've made our magazine's best stories about the future of food available in a free iPad app.

See more food news, photos, and videos »