By my opinion, the bees colony collapse disorder (CCD) is the consequence of gradual sensitization of bees by pollens of transgenic plants (GMO), the "roundup ready" soybeans, rape and maize pollen in particular. The reason is similar structure of toxins, which are produced by GMO organism and Bacillus Thuringiensis (bacterial allergen) and the fact, the pollens are food supply for bees. The allergenicity follows from immune response of bees to the unusual proteins in food, which results in gradual sensitization. The same origin is the "white nose" syndrome of bats, which is basically a sort of vasomotor rhinitis. Some modern pesticides, like Imidacloprid can be suspected too - but by my opinion, the GMO is the most probable reason, because of short history of both transgenic plant growing, both the CCD.

The sensitization mechanism is the sort of vaccination: the organism of bee is trying to find a proper antidote in contact with foreign protein (allergen). Normally, the fast mutation of imunoglobuline production succeeds in production of the proper antidote, which neutralizes the foreign protein and it prohibits the infection. The concentration of foreign protein in organism decreases, so that the immune system is informed, his response was successful and it stops the mutation and production of another imunoglobulines.

But at the case, the contact with foreign protein is prolonged/repetitive (which is the case of contact of bees with GMO pollens), the immune system of bees is forced to produce new antidotes again and again, because the concentration of foreign protein in organism cannot decrease. Such stock antidotes are capable to induce the immune response even in contact with common proteins, which are harmless under common circumstances - they become allergens, too. This is the way, how the vasomotor rhinitis evolves in prolonged contact with allergens.