The California winter has been a tough one on South Dakota beekeepers like Richard Adee.

Last fall he sent 155 semitrailer trucks to California loaded with hives containing bees fit and ready to pollinate the almond crop.

"We lost 40% of the hives we sent there. We sent 70,000 out and lost 28,000," said Adee, whose Adee Honey Farms in Bruce is considered the largest beekeeping operation in the nation.

"I would say overall the losses of South Dakota bees - from what I've heard - from what they started in the spring of '07 until they came out of the almonds is at least 50%. It's not good."

Now, in preparation for the honey-making season in South Dakota, he's working to get back to full strength from a mystery called colony collapse disorder.

No one's really sure what's causing the disorder, evident when adult bees abandon the hive.

It's a concern for South Dakota beekeepers, who ranked third nationally last year for honey production and for the number of colonies.

"It's very serious," said Heath Bermel, a Java beekeeper and president of the South Dakota Beekeepers Association. "There's a lot of beekeepers all over the U.S. who are losing hives."

The U.S. Agriculture Department has earmarked money and research to solving CCD because it says one-third of the human diet comes from insect-pollinated plants, and the honeybee is responsible for 80% of that pollination.

"As beekeepers we're confused and the scientific community is even more confused because they feel like they should be able to figure this out and get a handle on it, and yet there are so many variables they are just having a problem," said Adee, chairman of the legislative committee for the American Honey Producers Association.

Researchers with the Agricultural Research Service within the U.S. Department of Agriculture are chasing various theories about CCD, said Jon Lundgren, an ARS entomologist in Brookings not directly involved in the research.

Among the possible causes are parasites, a virus, or pesticides.

It may be a several factors resulting from stress on the bees, he said.

"Shipping these things across the country - that's not the way that honeybees have evolved, so we're really changing and manipulating these colonies quite a bit to suit our needs," Lundgren said.

"It's necessary if we want cheap almonds and other fresh produce, but on the flip side, by the changing agricultural landscape - both in terms of the actual landscape itself and how we approach agriculture - there's probably any number of factors that are ultimately involved in what we're seeing with CCD right now."

Without answers and a possible remedy, the financial impact will extend beyond the beekeeping business to the dinner table, said Bermel.

"It's going to hurt everything," he said. "People at the grocery store are going to see significant increases in their grocery bill."

The California almond industry covers about 600,000 acres and prefers two bee colonies per acre to do a good job during a pollinating season that lasts about six weeks.