Why are the bees dying?

So you know how honey bees have been dying a lot in the last few years, and it's a big problem for agriculture?

Discover has an article saying that it's been somewhat figure out.

Whatever the proximate cause, it increasingly appears that the bees are succumbing to a long-ignored underlying condition—inbreeding. Decades of agricultural and breeding practices meant to maximize pollinating efficiency have limited honeybees’ genetic diversity at a time when they need it the most.