FRESNO, Calif. - As the cold slowly loosens its grip on California's Central Valley, the pink and white flowers on fruit and nut trees are just beginning to blossom and growers are scrambling for a dwindling supply of bees to pollinate their fields.

Harsh weather across the country, pesticides and mites are blamed for killing off billions of bees needed to pollinate just about every crop throughout the year - oranges in Florida, apples in Washington, blueberries in Maine and California's $1.4-billion-plus almond crop, according to some preliminary research by scientists with Pennsylvania State University and the U.S. Department of Agriculture.

“It's startling. We were just starting to get information through word-of-mouth from beekeepers in the east a couple months ago and we thought about what it was going to mean once it got time for them to travel to California,” said Dennis vanEngelsdorp, a bee expert with the Pennsylvania Department of Agriculture.

The frigid temperatures were compounded by droughts, which meant less food for bees, vanEngelsdorp said.

“One thing, like weather, will not kill them,” he said. “But if there's already one thing making them weak, than the added stress of a mite or a chemical makes life harder for them.”

The number of commercial honey bee colonies is less than half of what it was 25 years ago, said Maryann Frazier, a bee expert at Penn State's College of Agricultural Sciences. A colony is defined as a queen bee and thousands of her workers.

Scientists were in California this week gathering bee samples to study what's killing them off.

At stake are crops, especially huge industries like California's almonds, which account for 80 percent of the world's almonds, according to the state Department of Food and Agriculture.

Soon, half of the commercial bees available nationwide will get busy in California, transporting pollen from flower to flower on their legs. The blooming season that paints large squares of the valley in warm pastels lasts through mid-March.

“I wish we had more answers than questions right now,” said Jeff Pettis, a researcher at a USDA honey bee lab in Maryland who was in California this week. “This couldn't be happening at a worse time.”

California farmers began to worry after a cold snap swept over the West earlier this year followed by plummeting temperatures in the Midwest because it takes more energy for bees to stay alive in the cold, said Steve Park, a second generation beekeeper in Northern California.

The already feeble bees may not be strong enough to handle a cross-country trek, though beekeepers have made the annual migration to California for at least 60 years, vanEngelsdorp said.

Meanwhile, farmers stand by, hoping enough bees are available during the late winter window when pollination is possible.

“It's kind of wait-and-see right now,” said farmer George Miller.