By Matt McGrath
Science reporter, BBC World Service
Bee hives were left deserted by adult worker bees
Scientists say there is no proof that a mysterious disease blamed for the deaths of billions of bees actually exists.
For five years, increasing numbers of unexplained bee deaths have been reported worldwide, with US commercial beekeepers suffering the most.
The term Colony Collapse Disorder was coined to describe the illness.
But many experts now believe that the term is misleading and there is no single, new ailment killing the bees.
In part of California, the honeybee is of crucial importance to the local economy as 80% of the world's almonds come from there - America's most valuable horticultural export.
But without the bee pollinating the trees, there would be no almonds.
In a few frenzied weeks in February and March, billions of honey bees are transported to the state from as far away as Florida to flit innocently among the snowy almond blossoms, and ensure the success of this lucrative crop.
However, since 2004 their numbers have been mysteriously declining, and it was only at the end of 2006 that the severity of the losses began to be fully realised.
It's probably not a unique event in beekeeping to have large numbers of colonies die
Frank Eischen US Department of Agriculture
Commercial bee keeper Dave Hackenberg, from Pennsylvania, was the first to sound the alarm.
He recalled the moment when he first realised something was wrong:
"I started opening a few hives, and they were completely empty boxes, no bees. I got real frantic and I started looking at lots of beehives. I noticed that there were no dead bees on the ground, there weren't any bodies there."
Even stranger than the absence of the insects was the fact that other bees would not go near these deserted colonies.
Since then around two million colonies of bees have disappeared across the US. And the losses have continued this year, albeit at a lower rate.
The unexplained nature of the affliction, with empty hives and no clearly defined infection, has stumped scientists.
Since the 1980s, a rising tide of ailments has assaulted the honeybee, including the varroa mite and many deadly viruses.
Putting the varroa mite under the microscope
But the dramatic and rapid losses of the last five years had convinced experts that something new was at work within the hives.
Researchers around the world are running round trying to find the cause of the disorder - and there's absolutely no proof that there's a disorder there
Dennis Anderson CSIRO
They developed a concept called Colony Collapse Disorder, or CCD.
Dr Jeff Pettis, a researcher with the US Department of Agriculture Bee Lab, said CCD applied to colonies which died although there were no high levels of parasites: "The colony was once strong, it reared a lot of young developing bees and then the adult bee population simply disappeared or died.
"With those symptoms it certainly is unique and it doesn't really match up with our expectations for parasitic mite loss and the like."
But to date researchers have found few clues as to the exact cause of the disorder.
And some senior scientists now say the "disorder" does not exist as a separate illness.
Dr Dennis Anderson, principal research scientist on entomology with the Australian research organisation CSIRO, said the term could be distracting scientists from other work: "It's misleading in the fact that the general public and beekeepers and now even researchers are under the impression that we've got some mysterious disorder here in our bees.
"And so researchers around the world are running round trying to find the cause of the disorder - and there's absolutely no proof that there's a disorder there."
His view is shared by some experts in the US.
Conducting experiments at an isolated almond orchard in the Central Valley area of California, Frank Eischen, of the US Department of Agriculture, said it was "probably true" that there was no new single disease.
"We've seen these kinds of symptoms before, during the seventies, during the nineties, and now," he added.
"It's probably not a unique event in beekeeping to have large numbers of colonies die."
The varroa mite sucks the bees' blood and weakens the immune system
Many experts speak about a "perfect storm" of impacts that are the real reason for the decline.
Principal among them are infestations of the varroa mite, which suck the bees' blood and weaken their immune systems.
There are also concerns that bees are being deprived of nutrition as urbanisation removes their natural pastures.
One of the biggest worries is the possible impact of agricultural pesticides.
It is believed these chemicals can have a similar effect in bees as alcohol has in humans - they disorientate the bees, causing them to get lost on the way home.
The intensity of agriculture could be the real underlying cause of bee stress, some experts believe.
Commercial beekeeper Dave Hackenberg described the working life of a bee as difficult.
"My bees are in California pollinating almonds," he said. "In the middle of March they are going to be trucked all the way across the United States all the way back to Florida to pollinate oranges then they are trucked another thousand miles north to pollinate apples in Pennsylvania.
"When they go to these places, the only thing that's there is the crop that you pollinate; it's a big monoculture.
"We all like steak and potatoes and we all like corn, but if we eat any of these on their own for a month at a time then your body would not be in the best of shape."
Buzz words: Ten amazing facts about bees
Some critics of the bee industry have called the whole concept of CCD a hoax, a public relations stunt designed to attract public sympathy.
Dr Eischen does not believe it was made up, but says CCD has been helpful to highlight problems in the food supply.
He told the BBC: "We rely on farming, and to have that brought to the fore by the press that there is a problem with something as fundamental as getting fruit to produce, trees to bear, vegetables to yield and it all comes together with the bee coming to a flower and performing a vital service, the imagery is great and it strikes at the heartstrings of a lot of citizens; and from that respect it's been good."
"It highlights the hard work it takes to bring a crop to market."
We'd like to know what you think. Are bees dying where you live? Does it matter to humans if the honey bee dies out? What is so special about the bee? And could we really be heading for a world without bees?
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