No matter where you live -- in a brick Philadelphia row house, the sprawling suburbs of Dallas or an apartment in Seattle -- you depend, more than most of us know, on honeybees raised in California or Florida.
The bees have been dying in unusually large numbers, and scientists are trying to figure out why.
"One in every three bites of food you eat comes from a plant, or depends on a plant, that was pollinated by an insect, most likely a bee," said Dennis vanEngelsdorp of Penn State University's College of Agricultural Sciences.
"We're still managing to pollinate all the orchards," he said. "But we're really cutting it close out there."
It has been going on for four years. In 2009 almost 29 percent of the bee colonies in the United States collapsed, say scientists who surveyed commercial beekeepers and brokers. That's slightly less than the 36 percent loss in 2008 and the 32 percent counted in 2007, but an informal survey just finished suggests that the die-off continues.
"Something is wrong out there," said David Mendes, a commercial beekeeper near Fort Myers, Fla., who is also president of the American Beekeeping Federation. "It may be something in the agricultural environment that's making them sicker and more vulnerable to illness.
"It didn't used to be like this," he said. "I'm managing to hold my numbers, but it's hard."
In spring, as the weather warms, Mendes usually trucks the bees he's raised from Florida to Maine to pollinate plants for blueberry farmers, and then to Massachusetts to start the cranberry season. Instead, he's spending a lot of his time trying to raise more bees to make up for the ones he's lost. The numbers bounce back, but it's a lot of work.
"And it's not without cost," he said.
He said he has been buying commercial nutrients to keep his stock healthy -- an expense he has to pass on to the farmers who hire him to help pollinate their crops. Almonds and apples, soybeans and strawberries -- as well as animals that feed on pollinated crops -- may all be a bit more expensive this year because of a shortage of bees to pollinate the trees or vines.
What's going on? Is it a virus or fungus? A pesticide? Some researchers investigated the electromagnetic radiation from cell phones, wondering if the signals were disturbing the bees. But most scientists say there is probably no single answer. Honeybees are raised commercially, but scientists say wild pollinators, such as bumblebees and bats, seem to be having trouble as well.
Christopher Mullin of Penn State joined with several colleagues to take samples from beekeepers across 23 states, and found a wide variety of pesticides and other chemicals in the hives they examined. No one pesticide, they said, was strong enough to be lethal -- but they said it is possible that some of them are combining in some way that is not yet understood.
"The 98 pesticides and metabolites detected in mixtures up to 214 ppm [parts per million] in bee pollen alone represents a remarkably high level for toxicants in the brood and adult food of this primary pollinator," Mullin and his colleagues wrote in the journal Public Library of Science-One.
At an American Chemical Society meeting in San Francisco today, scientists are talking about the problem, but they say they doubt they will have a solution soon.
"All the bees we've looked at, you can't look at a single cause," said Jeffrey Pettis, research leader for the Department of Agriculture in Beltsville, Md.
Mendes, the Florida beekeeper, says he's concerned. He says he has friends whose bees died off if they were next to cultivated farmland, and he wonders if there's something spreading from them worldwide; there have been bee-population collapses as far away as Europe and India.
"In many ways we view honeybees as an indicator species," like the proverbial canary in the coal mine, he said. "We don't know what's going on. And we all share the same earth."