There are many thoughts around this. Personally I think that all things are accumulating to cause the hive collapse. Whether that be GMO, Neonicticides, pesticides and insecticides.
To Matt's list I'd add loss of habitat diversity, too many bee colonies per square mile, excessive artificial feeding, trucking thousands of miles, the Varroa mite which our bee is not fully adapted to yet, etc.
You get good luck from rubbing the belly of a tiny ad:
montana community seeking 20 people who are gardeners or want to be gardeners