Nearly 30 percent of all honeybees literally disappeared last winter, fleeing their hives never to return.

Researchers have studied colony collapse disorder since it was identified in 2006. They are now uncovering answers to this problem.

A combination of factors contribute to colony collapse disorder, or CCD, including pesticide exposure, environmental and nutritional stresses, new or re-emerging pathogens and a virus that targets the bees' immune systems, said Keith Delaplane, an entomologist with the University of Georgia College of Agricultural and Environmental Sciences.

Delaplane is the national director of the $4.1 million Managed Pollinator Coordinated Agriculture Project. Funded by the U.S. Department of Agriculture, the consortium of U.S. honeybee scientists and educators is working to reverse honeybee decline.

And the varroa mite, an old bee enemy, is emerging as a key to the problem, Delaplane said.

Honeybees get the parasitic, blood-feeding varroa mite when they co-mingle with other colonies. Once the colony is sick, the brood gets sick. Adults don’t live as long, and the population doesn’t replace itself. The mites spread viruses and activate those already in the bees.

“There seems to be a trigger that when they stress the bees, the viruses the bee has been carrying are suddenly awakened,” Delaplane said. “The mites are both a vector and an activator.”

Pesticides are available to treat bee colonies for the parasites, but recent research has shown these pesticides in conjunction with other chemicals are harmful.