It's the new systemic pesticides that become a part of the plant and get into the pollen. The bee colony will usually start to collapse within a year of being exposed to these types of pesticide infested crops. Systemics are now banned in many European countries. There's also a documentary called "The Vanishing of the Bees" that explains the situation. What's bad for bees is also bad for people which is why it's better to buy organic produce when possible. The EPA won't step in with regulation until all the bees in North America are gone.