I'm pleased to say I'm an entomologist by scientific training, and I've worked with my bee people at the University of Guelph for a long time.
The number one reason is actually biological organisms. There's a number of mites, actually tracheal mites, that get into the respiratory systems, that have been introduced. And I would emphasize that the honey bee is not native to North America either. So it's primarily biological organisms.
The other one is actually maybe things like climate change, where the bees aren't setting down as well. We get very mild winters, so they use up a lot of honey because it's warmer, and then they get weaker because they're more active, whereas they were supposed go into suspended animation, per se.
So there are many factors. To my knowledge, pesticides is not one of them. It's mainly biological organisms like tracheal mites and varroa mites that are causing the problems.