In the fall of 2006, beekeepers began reporting the disappearances of entire colonies of honey bees. Scientists named this phenomenon Colony Collapse Disorder, or CCD.
Colony Collapse Disorder refers to the complete absence of adult honey bees in a colony, with few or no dead adults remaining behind. Though the adult honey bees are gone, the hive will contain capped brood and food stores. Honey bees will not usually abandon their developing young, making their disappearance all the more mysterious. Unguarded food stores will not be robbed by other bees or pests, at least for several days.
Beekeepers should be alert to the signs that a colony may collapse: insufficient numbers of worker bees to care for the brood; young adult workers present, but no older workers in the colony; and unwillingness of the bees to accept food from the beekeeper. The queen will still be present.
Similar disappearance have been documented over the last one hundred years, though not in the numbers beekeepers are reporting now. Past incidents of disappearing bees were given other names, including disappearing disease, spring dwindle, May disease, autumn collapse, and fall dwindle disease.
Scientists aren't yet sure what is causing CCD, though a number of theories are being tested.
Source: Pest Alert, Colony Collapse Disorder (CCD) in Honey Bees, University of Florida, 4/16/07.