British scientists have branded a study that prompted a French ban on a valuable oilseed rape pesticide as “flawed”.

France withdrew Syngenta’s marketing licence for Cruiser OSR in June, amid claims in a study that neonicotinoids cause honeybee colony collapse.

But research from the Food and Environment Agency and the University of Exeter, published in the Science journal, has highlighted flaws with the original study.

The previous 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, an active ingredient in Cruiser OSR, a pesticide produced by the Swiss company Syngenta.

It calculated that this would cause their colony to collapse.

However, new research by the British team explained that the calculation might have used an inappropriately low birth rate and underestimated the rate at which colonies could recover from the loss of bees.

Lead author James Cresswell, of Biosciences at the University of Exeter, said: “We know that neonicotinoids affect honeybees, but there is no evidence that they could cause colony collapse.

“When we repeated the previous calculation with a realistic birth rate, the risk of colony collapse under pesticide exposure disappeared.”

Dr Cresswell could not, however, determine that pesticides were harmless to honeybees but he said the research showed that the effects of thiamethoxam were not as severe as first thought.

“We do not yet have definitive evidence of the impact of these insecticides on honeybees and we should not be making any decisions on changes to policy on their use,” he added.

More research was needed to understand the real impact of neonicotinoids on honeybees, Dr Cresswell said.

Meanwhile, the Environmental Audit Committee has launched an inquiry looking at the effects of pesticide use in the UK on biodiversity with a specific focus on bees.

In a letter sent to The Guardian, Joan Walley, chair of the committee, said: “DEFRA ministers may want to start doing their homework on pesticide policy and biodiversity, because we will be calling them before parliament on these issues.

“In particular, we will be scrutinising the evidence behind the government’s decision not to revise pesticide regulations or to follow other European countries in temporarily suspending the use of insecticides linked to bee decline.”

Luke Gibbs, Syngenta UK spokesman, said he welcomed the inquiry and hoped it would focus on science and not the politics.

“It’s an opportunity for the industry and the relevant government advisory agencies to outline the science that underpins neonicotinoid pesticides, to detail how these products protect crop yield and quality, and how in practice this advanced class of pesticide works to reduce adverse impacts on beneficial insects such as bees,” he added.

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

The French ban does not affect British growers and Cruiser seed treatment is still free to use as normal in the current planting season.

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