Hum, but this wouldn't explain some other findings from massive bee deaths being that:
1. Bee colonies continue to suffer mass deaths from an unknown cause until the hive is irradiated. This seems to suggest that the cause is a living pathogen.
2. Colonies collapse because bees are dying outside the hive or never returning. The queen bee is normally still found in the hive along with food stores.
3. The digestive system of dead bees have been found to be completely trashed - in some cases, all that's left is mush. The cause also seems to suppress the immune system of the bees affecting memory and communication.
It's a very interesting and mysterious phenomenon, and very important too. Here's a wiki article about it: http://en.wikipedia.org/wiki/Colony_collapse_disorder