More than a quarter of the country’s 2.4 million bee colonies have been lost — tens of billions of bees, according to an estimate from the Apiary Inspectors of America, a national group that tracks beekeeping. So far, no one can say what is causing the bees to become disoriented and fail to return to their hive
http://www.nytimes.com/2007/04/24/science/24bees.html