The combination of two pesticides commonly used on UK fields can have damaging effects on the behaviour of bumblebees and cause their colonies to collapse, new research by British scientists has found.
And long-term exposure to individual pesticides – for up to a month – is also likely to have damaging effects, the scientists say. They argue that safety tests are insufficient, as guidelines demand only that pesticides are tested on bees for four days.
The findings, which come from a Government-funded study, represent the fifth major piece of research to appear this year linking the worldwide decline of bees to pesticides, and in particular to the use of the relatively new nerve-agent pesticides, the neonicotinoids.
This new study is considered particularly important because bees forage widely so are likely to encounter more than one type of pesticide.
The research was carried out at Royal Holloway College, University of London, as part of the Insect Pollinators Initiative, a £10m British programme looking at threats to pollinating insects such as bees, butterflies, moths and hoverflies.
Published last night in Nature online, the study reports that exposure to two pesticides, one a neonicotinoid and the other from a different pesticide family, a pyrethroid, at concentrations approximating what might be found in the field, impaired the natural foraging behaviour of bumblebees. This led to increased numbers of deaths and in some cases the failure of colonies. The compounds involved were made by major agrochemical manufacturers: the most widely used neonicotinoid, imidacloprid, manufactured by Bayer was one, while the pyrethroid was lambda-cyhalothrin, by Syngenta. The researchers found bees exposed over a month to imidacloprid were less able to collect pollen effectively, which meant that their colonies had less food available.
A spokesman for Syngenta said: "There's no evidence that pesticides damage the bees but yet again we see unrealistic research being used to prove the opposite."