Imidacloprid exposure is confirmed deadly to bees.

Exposure even to low levels of imidacloprid, a widely used pesticide, can harm the central nervous system of bees and may be a reason behind the global bee colony collapse, a National Taiwan University research team said yesterday in Taipei.

Reports from around the world in recent years have shown that the population of wild bees has rapidly declined in many parts of the world. As bees contribute to the pollination of many crop species, ensuring production of seeds in many flowering plants and playing an important role in the ecosystem, many scientists are concerned about the rapid decline in bee colonies.

The university formed an interdisciplinary research team in 2008 to study whether the collapse was caused by the prevalent use of pesticides. A special method that the team developed — putting a tattoo on experimental bees — was applied to track the bees and observe the effects of insecticides on them.

National Taiwan University entomology professor Yang En-cheng (楊恩誠) said researchers discovered that imidacloprid — an insecticide belonging to a class of chemicals called the neonicotinoids — can cause worker bees to lose their way back to their hives.

“Normally, worker bees fly back to their hives when they have suck enough nectar, but when they consume up to about 50ppb [parts per billion] of imidacloprid, they stay on the flower, rubbing their eyes. We can see that they are uncomfortable, and they don’t fly back immediately,” Yang said.

Moreover, the team observed that even exposure to low levels — or just 10ppb — of imidacloprid can cause harm to bee larvae, depriving them of their ability to form and retain memories as they grow, thus contributing to the decline of the bee population.

The use of imidacloprid on certain crops was banned by the EU last year, but it is still widely used in Taiwan, Yang said.

While Taiwan earns about NT$2.3 billion (US$76 million) from honey each year, the government should evaluate whether it should limit the use of imidacloprid and other neonicotinoids, he said.