Neonicotinoids are used for seed dressing of rapeseed, to protect the young plants against flea beetles. Since 2013, use of this type of pesticide has been restricted by the EU for crops that are attractive to bees. The research findings have now been published in the scientific journal Nature, and they show that the insecticide has a negative impact on wild bees. This is a serious matter, because wild bees play an important role in pollination of crops. Wild bees include both bumblebees and solitary bees.

"We saw a clear negative impact on growth and ability to reproduce in bumblebee colonies near treated rapeseed fields," said Maj Rundlöf from Lund University, the coordinator and principal investigator for the field study.

As well as problems with growth and reproduction, there were also fewer wild bees on the treated rapeseed fields. However, the researchers found no negative effect on colony growth of honeybees.

The study demonstrates the need for new ways to evaluate risks in conjunction with the approval of pesticides.

"If we only investigate how a new pesticide affects honeybees, that is not sufficient to predict the consequences for wild bees in a real landscape," said Maj Rundlöf.

"The results show that it is inappropriate to use clothianidin on rapeseed," said Thorsten Rahbek Pedersen, project manager at the Swedish Board of Agriculture. "We need alternative preparations and new cultivation methods if we are to continue growing spring rapeseed in Sweden."

"We are testing new methods of dealing with flea beetles," said Riccardo Bommarco from the Swedish University of Agricultural Sciences.