Are there fewer bees where you live? Is it disease, insecticides, pollution, or that cell phone theory?

My father has been a bee keeper for over 20 years. We have been discussing reasons why bees are dieing. Has anyone else noticed that there aren't ANY honey bees on clover or flowers in general. Bumble bees seem to be doing fine but the honey bee is in serious trouble! For the past 3 summers, my father's hives have barely produced enough honey for the hive to survive the winter. He has treated his hives for infestations, mites and things that plague hives but the population of the hives is in jeopardy. Bees fly out but arent flying back to the hives. No dead bees are being carried out...they are dieing outside away from the hives! Anyone with a great scientific explaination? Is it pesticides,pollution, or the increased use of cell phones which are causing bees to fly from the hives and never return? In NH--I haven't seen one bee all summer! Only bumble bees. I haven't even seen one yellow jacket in the two years that I have lived in the northeast! Start looking around!!!