A pair of studies relating to honey and bumble bees found that pesticides which affect the insects' nervous system could be in danger of wiping out entire colonies.
Although strict limits prevent farmers from using insecticides strong enough to kill bees, the research raises fears that the chemicals could be indirectly putting them at risk by modifying their behaviour.
Prof Dave Goulson of Stirling University, co-author of the study on bumble bees, said the continued use of the pesticides on flowering crops "clearly poses a threat to their health and urgently needs to be re-evaluated."
Both research papers, published in the Science journal, focused on a type of insecticide known as neonicotinoids, which were introduced in the 1990s and are one of the most widely used crop pesticides in the world.
The chemicals, which influence the central nervous system of insects, pose a threat to bees because they spread to the nectar and pollen of flowering crops like sunflowers and oilseed rape.
The Stirling study revealed that after exposure to imidacloprid, a type of neonicotinoid, bumble bee colonies – comprising bees, wax, honey, grubs and pollen – grew eight to 12 per cent smaller than control colonies, suggesting they were bringing in less food.
They also produced far fewer queens, which are needed to establish new colonies after the winter, researchers said.
The second study, by experts from the French National Institute for Agricultural Research found that honey bees exposed to a similar pesticide called thiamethoxam were two to three times more likely to die while away from their hives.
Tracking devices planted on the bees suggested the effect was most likely due to the chemicals interfering with their homing instincts.
Computer simulations suggested the effect was strong enough to lower honey bee populations to the point where they would may struggle to recover, the researchers said.
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