Hundreds of millions of honeybees have vanished in 22 US states, leaving keepers financially crippled and jeopardising £8 billion of crops that need the insects for pollination.

Beekeepers report their hives emptying within days because of an unexplained phenomenon known as colony collapse disorder (CCD), which drives swarms spontaneously to abandon their homes and disappear to die.

A task force involving the US Department of Agriculture and some of the country’s top insect specialists has been set up to investigate the causes. But while fungus, mites and pesticides have caused die-offs in the past, scientists admit that this time they are struggling to solve the mystery.

“There’s no simple answer, no smoking gun,” said Jerry Bromenshank, an entomologist at the University of Montana who is involved in the study.

“This thing is very widespread and very severe. Some beekeepers have gone out of business. We have seen almost unimaginable losses.”

The affliction first became apparent in eastern US states, such as Florida and Georgia, during the last three months of 2006, but in recent weeks reports have been pouring in nationwide.

It has sent shudders through the honey industry and triggered alarm among farmers, who rent the insects to pollinate their crops.

Apiarists move their hives around the country according to the crop seasons; California alone requires half a million colonies at this time of year — around 15 billion bees — to pollinate its almond trees. Because of the mass deaths, bee supplies are down and the cost of renting them has quadrupled.

Dave Hackenburg, a Pennsylvania-based beekeeper since 1962, lost 2,000 colonies — around 60 million bees — over a period of three weeks. Currently in Florida with his remaining hives to pollinate citrus trees, he estimates that CCD has cost him up to £350,000 in lost income and the cost of restocking. He said: “It’s the worst thing I’ve seen in 40 years. It worries me a lot, because honeybees are like the canary in the coalmine — if something’s bothering them, it’s a warning to us humans too.”

Listening devices are even being placed in some hives to try to discern whether the bees sound any kind of alarm among themselves when trouble strikes. But a number of factors are baffling those studying the problem.

Professor Bromenshank explained: “The bees just vanish — that’s one of the really strange things. In pesticide kills you normally find them dead, but in this case, one day you’ve got a big strong colony, two days later you’ve got virtually an empty box.”

Weak or ailing bee colonies are usually raided within hours for their honey by moths, beetles and other bees. But with CCD, the hives are left untouched. He added: “We saw one guy in California with hundreds of boxes empty, each with 30 to 40 pounds of honey inside. There are two bee yards within half a mile and they should have been robbing it blind — we should have been fighting them off. But nothing.”

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