SOUTH DEERFIELD, Massachusetts (Reuters) - Birds do it, fleas do it but when bees do it, the value is $212 billion to the world economy.
That's why scientists are seeking a way to stem mass deaths of the world's primary pollinator -- the honeybee -- which affect more than 30 percent of bee colonies in the United States and more than 20 percent in some European countries.
Researchers have identified some probable causes of colony collapse disorder (CCD), including blood-feeding parasites, bee viruses, fungi, pesticide exposure and decreased plant diversity causing poor nutrition for honeybees, experts say.
"It's a complex interaction of several different factors that are causing bees to die, resulting in quick colony decline," said Jeff Pettis, entomologist and chief researcher at the U.S. Department of Agriculture's Bee Research Lab in Beltsville, Maryland.
Losses are alarming not just for honey lovers but for a huge chunk of the global agricultural market as well. Some 52 of the world's 112 leading crops -- from apples and soybeans to cocoa and almonds -- rely on pollination. One 2009 study by economists put the value of insect pollination, mainly by bees, at about $212 billion.
And with human population increasing quickly, observers worry that the bee decline will deepen a global crisis unfolding from limited crops and soaring food prices.
The threat to bees is international. England lost more than half its hives in the last two decades, and baffling bee losses are occurring in Asia, South America and the Middle East.
A single silver bullet to end the problem is still out of reach. But recent discoveries are shedding light on possible answers to the puzzle.
Some scientists blame commercial agricultural pesticides such as clothianidin, which has been linked to millions of bee deaths near farming areas in different countries. Banned in some European countries, clothianidin remains EPA-approved and is commonly used on U.S. crops such as corn, wheat and soy.
Another bee threat is parasites such as the varroa destructor, which clings to a bee as it feeds on hemolymph, or bee's "blood," and spreads dangerous viruses. Major infestations will typically wipe out beehives, said Keith Delaplane, entomology professor at the University of Georgia.
To fight those viral infections, a U.S.-Israeli biotech called Beeologics now makes an antiviral medicine that exploits a native immune mechanism and boosts bees' tolerance for disease, say multiple researchers involved with the studies.
Finally, another possible cause for bee deaths is a combination of a virus and a fungus, which was found in all collapsed colonies in a U.S. study last year. The viral-fungal duo may destroy bees' memory or navigation functions and contribute to colony collapse.
Commercial apiaries are far harder hit than independent honey producers, said small producer Dan Conlon, who owns 700 hives at Warm Colors Apiary in South Deerfield, Massachusetts. His bees tend to be resilient, living in a rural, diverse habitat.
"Most of those reporting heavy losses run large operations and are focused on migratory pollination for their income," Conlon said.
Early bee reports are poor throughout the United States this winter, including Georgia, which appears to be losing about one-third of its colonies, said Delaplane.
Managed U.S. hives numbered 2.68 million last summer, USDA said. That's only about half of the nation's 5 million hives tallied back in the 1940s.
The nation produced 176 million pounds of honey last year, with wholesale prices reaching a record $1.603 per pound, the USDA said.
Editing by Barbara Goldberg and Ellen Wulfhorst