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Biodiversity

Pesticides could be the culprit in bee drop-off

Pesticides kill bumblebees and make colonies vital for pollination likely to fail, a study has found. Scientists have been baffled by the plummeting numbers of bees, mainly in North America and Europe, in recent years.

Over a period of four weeks, scientists led by Richard Gill exposed colonies of 40 bumblebees to neonicotinoid and pyrethroid, nicotinelike chemicals used to protect various crops from locusts, aphids and other pests. The United Nations estimates that one-third of plant-based foods depend on pollination.

"Chronic exposure ... impairs natural foraging behavior and increases worker mortality, leading to significant reductions in brood development and colony success," the scientists wrote in the report, for the journal Nature.

Exposure to the pesticides "increases the propensity of colonies to fail," the researchers found. A 2011 UN report estimated that the efforts of bees and other pollinators such as butterflies, beetles and birds are worth 153 billion euros ($200 billion) a year to the human economy, but are in decline in many nations.

Competing research

The findings show the importance of testing to ensure that pesticides do not target bees. Citing the threat to bees, France banned a pesticide made by the Swiss agrochemicals group Syngenta in June.

Another report, however, found flaws in the research. Juliet Osborne, of England's University of Exeter, wrote in Nature that the study shows the need to understand all factors that may harm bees.

"For example, we have as yet no convincing demonstration of the relative effects of pesticides on bee colonies compared to the effects of parasites, pathogens and foraging resources," Osborne wrote.

Still, Gill endorses the European Food Safety Authority recommendations for longer testing on adult bees and larvae, new ways of assessing cumulative exposure to toxins and separate assessments for different species. He said previous studies had mostly examined pesticides' impact on individual bees, rather than colonies.

The average number of bees lost in the experiment - dead in the nesting box or failing to return - was about two-thirds of the total exposed to a combination of the two pesticides compared to a control group exposed to neither.

mkg/pfd (Reuters, AFP)