The ongoing decline in wild bumblebee populations has caused worldwide concern, with evidence suggesting that the loss of critical pollination services could lead to a decrease in crop yields and the loss of many wildflower species. A number of reasons for the decline have been suggested and debated, but research from the University of Stirling, published in the journal Science last week, provides new evidence that pesticides used on flowering crops are having a significant effect.

The study, carried out by Dr Penelope Whitehorn and Steph O’Connor and supervised by Professor Dave Goulson at the University of Stirling, investigated the effects of neonicotinoid insecticides used as a seed dressing on flowering crops such as oilseed rape and sunflowers. These insecticides are systemic, travelling through the plant and occurring at low levels in nectar and pollen.

Findings reveal that bumblebee nests exposed to these low levels for just two weeks grew more slowly as a result, and showed an 85% reduction in the number of new queens they produced. Prof Goulson notes “Our work suggests that trace exposures of our wild bees to insecticides is having a major impact on their populations. Only queen bumblebees survive the winter to build new nests in the spring, so reducing the number produced by 85% means far fewer nests the following year. Repeated year on year, the long term cumulative effects are likely to be profound.”

Neonicotinoid insecticides are the best-selling insecticides worldwide and used broadly on a wide range of crops. As bumblebees often forage over a kilometre from their nest to find food, the study suggests that most nests in agricultural landscapes are likely to be exposed to these compounds. With insect pollination worth an estimated €22 billion a year to European agriculture, and many species of wildflower entirely dependent on bumblebees for pollination, Dr Whitehorn states “There is a clear need to re-evaluate the safety of these chemicals”.

This research is published as Whitehorn PR, O’Connor S, Wackers FL & Goulson D. Neonicotinoid pesticide reduces bumblebee colony growth and queen production and appears in the journal Science online and at the Science Express website.