A new study from Harvard [PDF] points to a class of agricultural pesticides called neonics as a primary cause of honeybee colony collapse disorder, or CCD.
Tom Philpott at Mother Jones:
Working with nearby beekeepers, Harvard researcher Chensheng Lu and his team treated 12 colonies with tiny levels of neonics and kept six control hives free of the popular chemicals. All 18 hives made it through summer without any apparent trouble. Come winter, though, the bees in six of the treated hives vanished, leaving behind empty colonies—the classic behavior of colony collapse disorder.None of the six control hives experienced a colony collapse disorder "disappearing act." More at Mother Jones.