The "colony collapse disorder" has been known for more than a century, but still no definitive cause has been found.
Bees baffle beekeepers around the world
It is a phenomenon that has baffled beekeepers for years, when entire swarms of worker bees leave the hive or colony, never to seen again.
So-called "colony collapse disorder" (CCD) has been known about for more than a century, but still no definitive cause has been found.
Cases have been reported across the United States and Europe since 1869 and the debate continues as to how to tackle the problem.
It is widely believed that CCD occurs due to a number of factors, ranging from the use of certain types of pesticides to genetic changes.
CCD may be a source of annoyance for amateur beekeepers but it can have serious commercial implications for professionals and farmers, who rely on bees to pollinate vast amounts of crops.