The preliminary assessment will help form the scientific basis for US government policy as it considers whether to control the use of the pesticides

The US government has acknowledged for the first time that one of the world’s most widely used pesticides can be harmful to honeybees.

The results of field trials, released Wednesday by the US Environmental Protection Agency (EPA), show imidacloprid, a common neonicotinoid, can cause hive populations to fall among the world’s most important pollinators.

“This is a pretty big step forward in increasing our understanding of the potential for imidacloprids to impact colony health,” said Jim Jones, the EPA’s assistant administrator for chemical safety and pollution prevention.

Declines in the number of bees and the honey they produced were seen when imidacloprid was at the “low level” of 25 parts per billion (ppbn) in the nectar and pollen of the plants, which worker bees carry back to their hive, Jones said.

The preliminary assessment, which has not yet been peer reviewed, is the first of four assessments of different classes of neonicotinoid to be released by the EPA this year.

These will form the scientific basis for US government policy as it considers whether to control the use of the pesticides. Three neonicotinoids, including imidacloprid, are currently banned in the EU. Imidacloprid was the first of the neonicotinoid chemicals to come on the market in the US and has been in wide use since 1994 on crops from corn to vegetables. The global production of the substance in 2010 was 20,000 tonnes, making it one of the world’s most-used pesticides.

Wednesday’s finding fuelled long-standing demands from campaign groups and beekeeper organisations to restrictthe use of neonicotinoids.

“We have been saying for several years now that the EPA has enough information and data available to them to take strong action and to severely reduce the amount we are using these chemicals,” said Larissa Walker, who heads the pollinator programme at the Centre for Food Safety. “The new report supports the need for the EPA to really reduce and restrict the use of these chemicals.”



A ban on the use of such chemicals would not be enough on its own to revive the honeybee population, which Walker said have also been affected by habitat loss, disease and parasites. “But this is one factor we can control immediately,” she said.



Neonicotinoids are popular with farmers because they are “systemic” pesticides, which mean they are absorbed and spread throughout a plant, therefore killing a variety of pests.

But the toxins also infiltrate the plant nectar and pollen, which has led to the long-held suspicion among environmentalists and many scientists that neonicotinoids are at the root of the great bee decline. The number of managed honeybee colonies in the US has fallen from 6 million in 1947 to just 2.5 million today.

Wednesday’s report was faulted for its relatively narrow focus on large honeybee colonies – instead of the native bee species and smaller colonies that may also be at risk.



Jones said it was the EPA’s assessment that honeybees would make a good surrogate for other species. But Walker and Chris Connolly, who studies the effects of neonicotinoids on bees at Dundee University in Scotland, disagree, arguing that the level at which the EPA had found honeybees were harmed was much higher than the threshold for other bee species.

“They only mention honeybees, but I’m sure that Obama also cares about the ecosystem and its role in our food security, not just honeybees,” he said. Honeybees are crucial to the production of at least 90 crops in North America and are worth $15bn to the US economy. But native bees, such as bumble bees, are worth an additional $9bn.

“If they were to suggest that so long as the levels stayed below 25ppbn everything’s fine, then that’s a completely outrageous thing to say,” Connolly told the Guardian. Effects can be seen in other bee species at much lower levels, Conolly added. “For a bumble bee, we’d be worried about 2.5ppbn of imidacloprid.”

The EPA findings, formally presented to the annual meeting of the American Beekeeping Federation on Wednesday morning, were greeted with some bitterness by farmers who have watched their colonies collapse.

Dave Hackenberg, one of the first beekeepers to raise the alarm about the collapse of the honeybees 10 years ago, saw the findings as a vindication. But he said the EPA had moved far too slowly and remained too closely connected with the chemical industry.

“The problem is we should have all been looking at this stuff a long time ago,” he said. “The same people who produced the chemicals are the ones that did the testing in the first place, and now all the EPA has gone and done is asked those companies to retest those chemicals.”

“It’s like letting the fox guard the henhouse,” Hackenberg said.

Bayer, a German agrochemical company which manufactures the pesticide, had mentioned the risks in its applications for approval by the EPA, he said. “In this whole compilation Bayer gave them they could have read Bayer’s own admission that in heavy clay this could last 7,000 days. That is 19 years.”

Jones said Bayer had again tested its own product during this latest trial. Bayer did not respond to a request to comment.

Hackenberg said he had lost more hives in the last decade than in the previous 40 years keeping bee hives.

The findings also came too late for Jim Doan, a beekeeper in New York who was forced to sell what was left of his business on Tuesday, after losing 1,400 hives over the summer.

He was sceptical of EPA’s conclusions. “It’s probably watered down to the point where it says you can drink imidacloprid day and night and not be harmed by it,” he said.

Doan said he first noticed the effects on his bees in 1995, when the pesticide was first sold for use in apple orchards. By 2005, when the pesticide began to be used more widely on corn and vegetables such as pumpkin, squash and cabbage, the effects were devastating, Doan said.



In 2005, he had 5,300 hives. By the time he sold his business, there were only a few hundred hives left. “It was just impossible to keep the bees alive,” he said.

Quantifying the impact of neonicotinoids on hives outside the laboratory has proven to be difficult due to the prevalence of the pesticides in the environment and creating a “control group” in which they are not present has proven difficult.

The pesticide industry has consistently lobbied against controls on neonicotinoids. Bayer’s “Bee Care” website maintains that “no adverse effects to bee colonies were ever observed in field studies at field-realistic exposure conditions”.

A major field study reported in the journal Nature last April found neonicotinoids have a “dramatic” impact on populations of bumble bees and other wild bees, including when they are applied through seed coating. A study in the UK in August provided the first large-scale field evidence that honeybees could also be affected by poisoned nectar carried to the hive from oilseed rape fields.