(SOUNDBITE OF BEE SMOKER BELLOWING) DUSTIN REEDER: This is a smoker, and smoke has a calming effect on the bees. KLEIN: Dustin Reeder is a commercial beekeeper in Terra Bella, California.

This year, commercial beekeepers in the U.S. lost about 60% of their bees – more than double average losses. What do those losses mean for beekeepers, and what do we know about the cause?