A widely used family of pesticides may cause bees to lose their homing instincts and hinder the survival of their colonies, European researchers reported Thursday, suggesting that governments should re-examine their use.
A French study used tiny radiotransmitters to track honeybees as they left and returned to their hives and found that many of them failed to return after being exposed to non-lethal amounts of one pesticide.
British researchers, meanwhile, found that bumblebee colonies exposed to common levels of another pesticide from the same family grew more slowly and produced nearly 85% fewer queens than non-exposed colonies, "which clearly could have very strong implications for bumblebee populations in the wild," co-author Dave Goulson said Thursday in Paris.
"I would suggest that there is a need to urgently re-evaluate the use of these pesticides on flowering crops," said Goulson, a biology professor at the University of Stirling in Scotland.
The studies released Thursday are the latest to point to neonicotinoid insecticides, which are often used to treat seeds for cereals and some flowering crops like corn, as a factor in plunging bee populations. The chemicals mimic the effect of the tobacco ingredient nicotine, which is used as a natural insecticide, and pose less risk to humans and other mammals.
Both papers are being published in this week's edition of the peer-reviewed journal Science.
The research is an attempt to understand the phenomenon known as colony collapse disorder, in which beehives fail to survive. Bees pollinate about a third of U.S. food crops, so the sharp die-offs that beekeepers began to report in 2006 pose a high risk to farmers, according to the U.S. Department of Agriculture.
Mikael Henry, a researcher at France's National Institute for Agricultural Research, said honeybees exposed to a non-lethal amount of the pesticide thiamethoxam "had a probability to disappear away from their nests in much greater proportions than non-intoxicated honeybees."
"Honeybees intoxicated with small doses will just get lost and are not able to find their way back home," Henry said. When he and his colleagues used a mathematical model to project the loss rates, they found that colonies would undergo "a marked decline within several weeks," he said.
That leaves the hives vulnerable to collapsing "if there are other stresses in the environment, such as parasites or climate changes or a loss of natural food resources," Henry said.
Thursday’s papers mark the third time research has tied bee deaths to neonicotinoids in the past month. An Italian study published in the American Chemical Society’s journal Environmental Science and Technology suggested that particles thrown off by seed drilling machines can expose bees to high levels of neonicotinoids, while a study led by Indiana’s Purdue University found the insecticides in pollen collected by bees from corn and other plants.
Regulators in France, Germany, Italy and Slovenia have imposed tighter rules on the neonicotinoids in recent years. The USDA and the Environmental Protection Agency say chemical pesticides are one of several possible suspects behind colony collapse disorder, but the EPA says it is in the process of re-evaluating all neonicotinoids.
“We believe that developing revised risk assessment methods will improve our understanding and strengthen the scientific and regulatory process to protect honeybees and other pollinators,” the agency said in a statement to CNN. “EPA is also engaged in national and international efforts to address the potential impact of pesticides on pollinators.”
Thursday’s studies will be part of that review, the EPA said.
Attempts to contact the manufacturers of the two pesticides used in Thursday’s studies - Bayer’s imidacloprid in the British research and Syngenta’s thiamethoxam in the French paper - were unsuccessful Thursday.