Pesticides not yet proven guilty in bee die-offs: study

Posted by Bridget in Biology, Life

Courtesy of the University of Exeter and World Science staff

Contrary to some previous studies, crop pesticides are unlikely to cause devastating declines in honeybee populations, the authors of new research say.

Writing in the 20 September issue of the journal Science, UK scientists from the University of Exeter and Food and Environment Agency said more work is needed to predict the impact of widely used agricultural insecticides, called neonicotinoids, on honeybees. The UK researchers in particular took issue with one previous study that they said failed to reflect correctly  the rate at which honeybee colonies recover from losing members.

Sudden losses of honeybee colonies in the United States and Europe, estimated at between 30% and 90% of colonies since 2006 in the US alone, have alarmed scientists, policymakers, farmers, and beekeepers. Beyond producing honey, the insects are prime crop pollinators.

Neonicotinoids are among the most widely used agricultural insecticides. Honeybees ingest residues of the chemicals as they gather nectar and pollen from treated plants.

Previous research has been cited by scientists, environmentalists and policy-makers as evidence of the future impact of these pesticides on honeybees, the authors of the Science study said.

Colony collapse disorder

Past research led by French scientist Mikaël Henry showed that the death rate of bees increased when they drank nectar laced with a neonicotinoid pesticide, thiamethoxam. It calculated that this would cause their colony population to collapse. The UK group said this research was probably instrumental in the French government’s recent decision to ban the use of thiamethoxam, a neonicotinoid used in Cruiser OSR, a pesticide produced by the Swiss company Syngenta.

The new work explains how the calculation may have used an inappropriately low birth rate, said study author James Cresswell of the University of Exeter. ‘We know that neonicotinoids affect honeybees, but there is no evidence that they could cause colony collapse,’ he added. The drastic honeybee population declines have been dubbed colony collapse disorder.

‘When we repeated the previous calculation with a realistic birth rate, the risk of colony collapse under pesticide exposure disappeared,’ he added. ‘I am definitely not saying that pesticides are harmless to honeybees, but… our research shows that the effects of thiamethoxam are not as severe as first thought.’

Source: World Science, http://www.world-science.net