Possibly GM?
Re Chaosvoyager's query:
GM got implicated in CCD because to the possibility that pollen containing the Bacillus thuringiensis (Bt) toxin that protects the GM crop may be affecting the bees. One possible pathway, for which there is some evidence, is that the small amounts of the toxin lowers the immune system of the bees, making them more susceptible to disease. It has been noted that the few surviving bees in a dying colony are show signs of diminished immune response. They are frequently sick from multiple bacterial and fungal infections.
The Bt pollen can be found a long way downwind of the crop, particularly from wind-pollenated crops like maize.
Hopefully, this is a red herring. We would be in deep doo-doo if GM was the cause of CCD. Monsanto et al would have to pull out all their stops to develop a GM bee that is resistant to Bt.