Worldwide declines in bee colonies, threatening much of global agriculture, may be caused by a new generation of nerve-agent pesticides, two new scientific studies strongly suggest. The findings place a massive question mark over the increasingly controversial compounds, now the fastest growing family of insecticides in the world.Silent menace graphic: The threat to bees
Bee declines represent a serious threat to agriculture because bees are the pollinators of a large percentage of crops. Both honey bees and wild bumble bees are seriously harmed by exposure to neonicotinoid insecticides, even by tiny doses not sufficient to kill them outright, the studies by British and French scientists report today.
The British study, carried out by scientists from the University of Stirling, concludes that "there is an urgent need to develop alternatives to the widespread use of neonicotinoid pesticides on flowering crops wherever possible".
About 30 per cent of British cropland – 3.14 million acres – was being treated with the chemicals in 2010, while in the US the figures for neonicotinoid use are enormous: in 2010, 88 million acres of maize, 77 million acres of soy and 53 million acres of wheat were treated with them. The compounds, which attack insects' central nervous systems, have been increasingly implicated in the widespread decline of honey bees and wild bees over the past decade, which have culminated in the mysterious colony collapse disorder in the US – a phenomenon in which the whole population of a beehive suddenly vanishes.
The value of bees' pollination services has been estimated at £200m per year just in Britain. The global annual value of pollination has been estimated at £128bn annually.
Many beekeepers have become convinced that the new pesticides are behind the declines, and in France, Italy and other countries they have been banned. But in Britain and the US their use continues.
Last year The Independent revealed that the American government's own chief bee researcher, Dr Jeffrey Pettis of the US Department of Agriculture, had conducted a study showing that bees exposed to microscopic doses of neonicotinoids were much more vulnerable to disease – but his study had not been published nearly two years after it was completed. Dr Pettis's findings were eventually published two months ago and were described by The Economist as "a plausible hypothesis for the cause of colony collapse disorder".
The findings of the two new studies, published simultaneously in the journal Science, are explosive.
The British study, led by Stirling's Professor David Goulson, showed that growth of colonies of the common buff-tailed bumble bee, Bombus terrestris, slowed after the insects were exposed to "field-realistic levels" of imidacloprid, a common neonicotinoid insecticide. The production of queens, essential for colonies to continue, declined by a massive 85 per cent in comparison with unexposed colonies used as controls.
"Given the scale of use of neonicotinoids, we suggest that they may be having a considerable negative impact on wild bumble bee populations across the developed world," the Stirling team says.
The French study, led by Mikaël Henry from France's National Institute for Agronomic Research in Avignon, looked at honey bees exposed to another neonicotinoid product, thiamethoxam.
The study found that even though the dose was sub-lethal, the exposure seriously affected the bees' homing abilities to the extent that they proved to be two to three times more likely to die while away from their nests than untreated bees. "Non-lethal exposure... causes high mortality due to homing failure, at levels that could put a colony at risk of collapse," the researchers say.
"These new studies put beyond all reasonable doubt the capacity for neonicotinoids to cause environmental destruction," said Matt Shardlow, director of Buglife, the invertebrate conservation trust. "Our Government must take the precautionary step of banning their use." The Government has twice been formally asked to suspend neonicotinoids; on both occasions the requests were ignored.
The problem posed by neonicotinoids is that they are "systemic" pesticides, which means that they do not just sit on the surface of the plant, but are taken up into every part of it, including the pollen and the nectar; and so even if bees are not the target species, they ingest the chemicals through the pollen and nectar when they are foraging.
Force of nature: The life of bees
Bumble bees are distinctive for their large, furry appearance. They are hugely important as natural crop pollinators. The queen is the only individual that can survive the winter, hibernating underground and emerging in spring to build a nest.
She lays eggs which hatch as worker bees. The workers fly from flower to flower gathering nectar and spreading pollen as they go. Bumble bees pollinate a great variety of plants – both wild and agricultural.
Honey bees have a different life cycle, with all the bees surviving the winter inside the hive. Honey bees are much better than bumble bees at producing honey, made from the nectar and sweet deposits of trees and plants brought back to the hive. It is these bees that are bred by beekeepers all over the world.
Both honey bee and bumble bee populations have dramatically declined in recent decades. In Britain, bumble bees have been vanishing since the 1950s. A UN report last year said that a phenomenon known as Colony Collapse Disorder that had seen the number of honey bee colonies in Europe and the USA plummet since the 1960s, had become a global problem, with beekeepers in Japan and Egypt all reporting losses of their colonies.