“Colony collapse disorder (CCD) is the phenomenon that occurs when the majority of worker bees in a colony disappear and leave behind a queen, plenty of food and a few nurse bees to care for the remaining immature bees and the queen. While such disappearances have occurred throughout the history of apiculture, and were known by various names (disappearing disease, spring dwindle, May disease, autumn collapse, and fall dwindle disease), the syndrome was renamed colony collapse disorder in late 2006 in conjunction with a drastic rise in the number of disappearances of western honey bee (Apis mellifera) colonies in North America.European beekeepers observed similar phenomena in Belgium, France, the Netherlands, Greece, Italy, Portugal, and Spain,Switzerland and Germany, albeit to a lesser degree, and the Northern Ireland Assembly received reports of a decline greater than 50%”
Source ; Wikipedia
A number of possible causes have been suggested, including
• Pesticides • Pathogens and immunodeficiency problems • Fungicides • Antibiotics and miticides • Climate Change • Bee rentals and migratory beekeeping • Selective commercial breeding and lost genetic diversity in industrial apiculture • Malnutrition • Electromagnetic radiation • Parasitic phorid fly • Genetically modified crops
There is as yet no solid agreement amongst experts as to which (if any) of the theories are applicable.