Taiwan's bee farmers are feeling the sting of lost business and possible crop danger after millions of the honey-making, plant-pollinating insects vanished during volatile weather, media and experts said on Thursday.

Over the past two months, farmers in three parts of Taiwan have reported most of their bees gone, the Chinese-language United Daily News reported. Taiwan's TVBS television station said about 10 million bees had vanished in Taiwan.

A beekeeper on Taiwan's northeastern coast reported 6 million insects missing "for no reason", and one in the south said 80 of his 200 bee boxes had been emptied, the paper said.

Beekeepers usually let their bees out of boxes to pollinate plants and the insects normally make their way back to their owners. However, many of the bees have not returned over the past couple of months.

Possible reasons include disease, pesticide poisoning and unusual weather, varying from less than 20 degrees celsius (68 degrees Fahrenheit) to more than 30 degrees celsius over a few days, experts say.

"You can see climate change really clearly these days in Taiwan," said Yang Ping-shih, entomology professor at the National Taiwan University. He added that two kinds of pesticide can make bees turn "stupid" and lose their sense of direction.

As affected beekeepers lose business, fruit growers may lack a key pollination source and neighbours might get stung, he said.

Billions of bees have fled hives in the United States since late 2006, instead of helping pollinate $15 billion worth of fruits, nuts and other crops annually. Disappearing bees also have been reported in Europe and Brazil.

The mass buzz-offs are isolated cases so far, a Taiwan government Council of Agriculture official said.

But the council may collect data to study the causes of the vanishing bees and gauge possible impacts, said Kao Ching-wen, a pesticides section chief at the council.

"We want to see what the reason is, and we definitely need some evidence," Kao said. "It's hard to say whether there will be an impact."