"It boggles your mind to think how important the northern Plains region is to almond pollination in California," bee researcher Chris Heintz said.

She and other experts spoke at the annual conference of the Almond Board of California. It drew about 2,000 people to Modesto Centre Plaza over two days.

Nearly two-thirds of the nation's 2.5 million commercial hives are trucked to Central Valley almond orchards each February. By spreading pollen from bloom to bloom, the bees make it possible for the nuts to emerge and for several thousand people to work in farming and processing.

Beekeepers have contended for half a decade with a problem called colony collapse disorder. It has caused losses of roughly 30 percent of the bees over each winter, double the natural rate, though it has not cut deeply into almond production.

Researchers say one or more causes could be at work, including viruses, mites, pesticides and poor nutrition.

Bees have a variety of food sources, including the flowers of crops and wild plants, along with supplements provided by beekeepers.

North Dakota and nearby states have become important beekeeping areas because they grow bee- friendly crops such as sunflower, canola and alfalfa in summer. These crops are less extensive than corn, wheat and soybeans, which are not so good for bees.

Ned Euliss, a federal research biologist in North Dakota, said bees ideally would have a variety of food and water sources within their 2.5-mile flight radius. This could include crops, native prairie and wetlands, as well as grasses and legumes planted as part of soil conservation programs.

A crop grower still can make a living while providing food for the bees that summer nearby, said Euliss, who works out of a wildlife research center that is part of the U.S. Geological Survey.

He said the increasing use of corn to produce ethanol could reduce the summer habitat for bees.

Heintz manages pollination research for the Almond Board, which has helped fund studies on the bee trouble.

"Guess what? There's no answer," she said. "We can't find the smoking gun for colony collapse disorder."

Despite this, the state's almond crop is projected at a record 1.95 billion pounds this year. This happened even with a pollination season that was mostly cold and wet, which tends to discourage bee flight.

Dan Cummings, an almond grower and beekeeper near Chico, said 2011 seemed to have an extra-long bloom that allowed the bees to get the job done. He also cited improved hive management in recent years.

But almond industry people warn that their good fortune might run out, and a poor pollination season will lead to a shortage of almonds for the booming global market.

The disorder has contributed to an increase in the cost of renting a colony for almond pollination. It averaged $151 this year, more than triple the 2002 rate, according to a survey by the California State Beekeepers Association.

Growers typically use two colonies per acre. If almond acreage continues to grow beyond the current 750,000 acres, a shortage of bees could develop.

"We want healthy bees," Heintz said. "We want more bees and decent rental prices for California almonds."