Protecting oilseed rape crops with a controversial nicotine-like pesticide has led to the loss of honeybee colonies across England and Wales, a government-backed study has found.

The research, based on large-scale data on pesticide use, crop yields, and honeybee losses spanning 11 years, looked at the effects of coating seeds with imidacloprid in nine regions between 2000 and 2010.

Use of the pesticide led to reduced spraying with other insecticide chemicals – but was also significantly associated with the death of honeybee colonies, the results showed.

As imidacloprid usage went up, so did the decline in bee populations, according to the research.

Information from 126,220 bee colonies indicated a 10% difference in death rate when comparing high and low exposure to imidacloprid.

A Department for Environment, Food and Rural Affairs (Defra) spokesman said: “This paper provides evidence that neonicotinoid [chemical pesticide] seed treatments can reduce the need for more pesticide use on crops. Large-scale field studies are needed to fully understand their effects on the environment.

“The government makes decisions on pesticides based on the best available scientific evidence. The [European] commission has now begun a review of the science relating to neonicotinoids and bees, and the UK will contribute fully to this review.”



Campaigners said the study was further proof that neonicotinoid pesticides are bad for bees, despite that claim being disputed by farmers and the UK government.

Paul de Zylva, from the environmental group Friends of the Earth, said: “This blows apart the denials of the pesticides and industrial farming lobby that pesticides are safe for honeybees. The scientific evidence is overwhelming that neonicotinoid pesticides harm honeybees and wild bees alike.”

From December 2013, imidacloprid and other neonicotinoid pesticides were banned from general agricultural use by the European Union because of fears that they were harmful to bees.

The UK government, while enforcing the ban, has never accepted that it is justified. Last month the government approved the use of two neonicotinoids in four English counties this autumn, as permitted under “emergency” rules incorporated into the ban to avoid severe hardship to farmers.

The new research, published in the Nature journal Scientific Reports, was led by scientists at Fera Science, formerly the Food and Environment Research Agency, which is now a joint private-public partnership.

Significantly, the study found that using imidacloprid had no consistent effect on oilseed rape crop yields.

In one year – 2008 – treatment with the pesticide was associated with a fall in yield, possibly due to heavy rain causing the chemical to leach away.

The most positive finding was that imidacloprid seed coatings led to the reduced use of other chemicals to control pests.

Unlike sprayed pesticides, neonicotinoids applied to seeds work by being incorporated into the whole of the plant as it grows.

De Zylva said: “This study suggests that there’s a correlation between the use of imidacloprid and losses of honeybee colonies. That’s pretty significant. The pesticide and industrial farming lobby have always claimed that there’s no evidence of harm to honeybees.”

He pointed out that since the ban was introduced, 10 independent studies and reviews had added to evidence that neonicotinoids harmed wild bees.

The new findings were the first to link use of one of the pesticides with the loss of honeybees reared in hives.

Last year’s harvest of oilseed rape grown since the ban was a bumper crop, and another good crop was forecast for this year, said De Zylva. “The outlandish claims by the National Farmers Union that the ban is having a devastating impact on oilseed rape harvests just don’t stack up,” he added.

Matt Shardlow, from the wildlife charity Buglife, said: “This new study has again shown that neonicotinoids do not provide any consistent benefit to crop yields or the economy. They do however damage bees, pollinators and freshwater life. A complete ban is long overdue.”

Dr Giles Budge, head of crop science at Fera, said: “Our analyses suggest that honeybee colonies are being lost due to a range of pressures including imidacloprid usage, regional factors, adverse weather and ... pests and diseases.

“The drivers behind these losses are complex but it is important that the science community continue to present a balanced argument to help farmers, beekeepers, and the public understand the costs and benefits of agricultural practices.”