MINNEAPOLIS – Researchers nationwide are trying to solve a growing agricultural mystery: Where are all the bees?

While picnickers may cheer their demise, the rapidly shrinking bee population threatens the pollination and survival of a multitude of commercial crops.

A hint of the problem first arose five months ago in Florida where beekeepers said they found whole hives abandoned by adult bees who left behind food and bee larvae, the young who develop inside the hive.

“We’re at a tipping point but we don’t know what’s caused the tip,” said Kevin Hackett, a bee expert with the U.S. Department of Agriculture.

The problem now has a name – colony collapse disorder – but no explanation. It concerns one type of bee, the European honey bee, or apis mellifera. Bumble bees and any of the 1,500 other species of bee found in the United States are not in danger, but neither are they a replacement for the honey bee.

It’s the nation’s workhorse when it comes to pollination, handling the work necessary to create many commercial crops.