Most uses of pesticides known as neonicotinoids represent a risk to wild bees and honeybees, European experts have warned.
A new assessment of three neonicotinoid pesticides, whose use is restricted in the European Union on crops such as oil seed rape because of concerns over harm to bees, has confirmed the danger.
The chemicals are commonly used to treat seeds and are taken up by crops as they grow.
The assessment by the European Food Safety Authority looked at their impact on wild solitary bees and bumblebees as well as honeybees.
Jose Tarazona, head of EFSA's pesticides unit, said: "There is variability in the conclusions, due to factors such as the bee species, the intended use of the pesticide and the route of exposure.
"Some low risks have been identified, but overall the risk to the three types of bees we have assessed is confirmed."