Taipei, April 14 (CNA) A group of Taiwanese scholars has confirmed long-held suspicions that a compound used in imidacloprid, one of the most widely used pesticides, is the culprit behind the worldwide demise of honeybees.

The results of their research show that the insects' ability to find their way home and learn how to feed are severely impaired when they are exposed in the larval stage to trace amounts of chemicals in the neonicotinoid class of insecticides, which includes imidacloprid.

Yang En-cheng, a professor of entomology at National Taiwan University, unveiled the team's findings Monday showing larvae that receive doses of imidacloprid -- presumably contained in the nectar brought back to the hive by adult bees -- of as low as 10 parts per billion (ppb), will grow into adults but will be unable to learn how to gather nectar or to navigate back to their hives.

Ten ppb of neonicotinoid, a product that is suspected to be the cause behind sharp worldwide declines in honeybee colonies since 2006, is not a lethal dose for the insects but can severely damage their central nervous systems, leading to the collapse of bee colonies, Yang said.

Yang observed how adult bees have to "learn" how to gather nectar by sticking out their proboscises when exposed to a scent. He found that larvae treated with low concentrations of the insecticide have this learning ability severely impaired after they emerge from their cocoons.

Moreover, Yang also found that adult bees treated with 50 ppb of the pesticide appear to show signs of discomfort and cannot find their way back to their hives.

Yang is among a team of researchers from the university in various fields, including engineering, that has been tracking bees by engraving codes onto them with lasers and monitoring their movements using infrared devices.

France first reported large numbers of bee deaths from unknown causes in 1994, and inexplicable "disappearances" of bees were reported across the United States in 2006, Yang said.

The number of honeybees, which pollinate 30 percent of the world's crops, is declining at a rate of between 10-30 percent worldwide each year, he added.

The European Commission, which has long suspected neonicotinoids of being behind the problem, decided last year to restrict the use of the class of pesticide for a period of two years.

The decision was made following a report by the European Food Safety Authority -- the EU's risk assessment body for food and feed safety -- that there is "high acute risk" for bees exposed to residue of the pesticide in pollen and nectar in crops.

(By Tseng Ya-chi, Liu Te-tsang and Scully Hsiao)
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