That there was a correlation between the use of pesticides and bee die-offs has long been known. But until now it had always been demonstrated in the laboratory or through short-term field studies.

Now, for the first time, a substantial study has been carried out that links the use of neonicotinoids to the decline of many species of bees. "Impacts of neonicotinoid use on long-term population changes in wild bees in England", published in Nature Communications in August of this year, demonstrates how in the United Kingdom, from 1994 to 2011, a marked drop in numbers was recorded, particularly in areas where the cultivation of oilseed rape — a species treated with this type of insecticide — grew the most.

"Our results show that neonicotinoids are harmful to wild bees," declares Nick Isaac, a researcher at the Centre for Ecology and Hydrology (Ceh) in Wallingford, in the United Kingdom.

Bees and pesticides: now there's proof

Isaac and colleagues studied the impacts on the populations of 62 species of wild bees across England over a period of 18 years.

And the results leave no room for doubt: 10 per cent of the loss of individuals is attributable to the use of the insecticide for at least 34 species that feed in oilseed rape fields. Three times more than that recorded among those that feed on other flowers. In practice, half of the loss of wild bees stems from the use of chemical agents in the fields.
"Historically, if you only have oilseed rape, many bees tend to benefit from this type of crop because it is very rich in food throughout the countryside," notes Ben Woodcock, one of the authors of the research. "This study suggests that once more than 85 per cent of the oilseed rape began to be treated, bees were exposed and began to suffer the negative effects."

Now it's Efsa's turn

The new research will be used by Efsa (the European Food Safety Authority) to issue a ruling next January on the class of insecticides in question, after it had already confirmed the hazardousness of substances such as clothianidin, thiamethoxam and imidacloprid. Since 2013, the use and sale of seeds dressed with plant protection products containing these active substances has been banned across Europe.