Interfering with Bumble and Honeybees’ Extraordinary Feats of Navigation

by Kathy Wren and Natasha D. Pinol

A honeybee is tagged with an RFID microchip to track the effects of pesticide exposure on bee homing systems.

[Image © Science/AAAS]

A widely used insecticide can threaten the health of bumblebee colonies and interfere with the homing abilities of honeybees, according to a pair of new studies. The reports, one by a UK team and one by a French team, were published at the Express Web site of the journal Science.

Bumblebees and honeybees are important pollinators of flowering plants, including many major fruit and vegetable crops. Each year, for example, honeybee hives are driven from field to field to help pollinate almond, apple, and blueberry crops, among others.

In recent years, honeybee populations have rapidly declined, in part due to a phenomenon known as Colony Collapse Disorder. Bumblebee populations have been suffering as well, according to Dave Goulson of the University of Stirling in Stirling, UK, who is a co-author of one of the studies.

“Some bumblebee species have declined hugely. For example in North America, several bumblebee species which used to be common have more or less disappeared from the entire continent,” he said. “In the UK, three species have gone extinct.”

Researchers have proposed multiple causes for these declines, including pesticides, but it’s been unclear exactly how pesticides are inflicting their damage.

“It’s been difficult to make direct connections between pesticides as they would be encountered in natural conditions, and the negative impacts we’ve seen in laboratory studies,” said Associate Editor Sasha Vignieri.

Both of the Science studies looked at the effects of neonicotinoid insecticides, which were introduced in the early 1990s and have now become one of the most widely used crop pesticides in the world. These compounds act on the insect’s central nervous system, and they spread to the nectar and pollen of flowering crops.

In one study, Penelope Whitehorn of the University of Stirling and colleagues exposed developing colonies of bumblebees, Bombus terrestris, to low levels of a neonicotinoid called imidacloprid, found in brand names pesticides such as Gaucho, Prestige, Admire, and Marathon. The doses were comparable to what the bees are often exposed to in the wild.

The researchers then placed the colonies in an enclosed field site where the bees could forage under natural conditions for six weeks. “These bees perform extraordinary feats of navigation in the real world” to find and bring food back to their colonies, Goulson said . “Anything that reduced its ability to learn or to navigate could have a very big effect in the wild which would not be detected or detected very weakly in a lab situation.”

At the beginning and end of the experiment, the researchers weighed each of the bumblebee nests — which included the bees, wax, honey, bee grubs, and pollen — to determine how much the colony had grown.

The researchers then placed the colonies in an enclosed field site where the bees could forage under natural conditions for six weeks. “These bees perform extraordinary feats of navigation in the real world” to find and bring food back to their colonies, Goulson said at the press conference. “Anything that reduced its ability to learn or to navigate could have a very big effect in the wild which would not be detected or detected very weakly in a lab situation.”

At the beginning and end of the experiment, the researchers weighed each of the bumblebee nests — which included the bees, wax, honey, bee grubs, and pollen — to determine how much the colony had grown.