A new study has revealed that a little amount of crop pesticides is enough to harm bumblebees and honeybees, and interfere with their homing abilities.
British and French researchers conducted two studies to find the reasons for the rapid dropping of bee populations in recent years.
Scientists believe the reason was partly related to a phenomenon known as Colony Collapse Disorder. They also suggest that pesticides are destroying bee populations.
"In North America, several bumblebee species which used to be common have more or less disappeared from the entire continent, while in Britain, three species have become extinct,” said Dave Goulson of Stirling University in Scotland, who led the British study.
The team exposed developing colonies of bumblebees to low levels of a neonicotinoid pesticide called imidacloprid, and then placed the colonies in an enclosed field site where the bees could fly around collecting pollen under natural conditions for six weeks.
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 see how much the colony had grown.
Compared to control colonies not exposed to imidacloprid, researchers found the treated colonies to have gained less weight, suggesting less food was coming in. They also produced about 85 percent fewer queens which produce the next generation of bees.
In a separate study, researchers at the French National Institute for Agricultural Research (INRA) in Avignon gave some bees a low dose of the neonicotinoid pesticide thiamethoxam which they knew would not kill them.
Led by Mickael Henry, the team then compared them to a control group of bees that was not exposed to the pesticide.
Results revealed that the treated bees were about two to three times more likely to die while away from their nests. Researchers said this was probably due to the pesticide’s interference with the bees' homing systems making them lose their way.
Bees are important pollinators of flowering plants, including many fruit and vegetable crops.