BAKERSFIELD, Calif. - A mysterious malady appears to have expanded drastically in the past year, wiping out 40 percent or even 50 percent of the honeybee hives needed to pollinate fruits and vegetables.
A conclusive explanation for colony collapse disorder has escaped researchers and beekeepers since it first surfaced eight years ago. But experts say there is growing evidence that a powerful new class of pesticides incorporated into the plants themselves - known as neonicotinoids - could be an important factor.
The pesticide industry disputes that, but its representatives also say they are open to further studies to clarify what, if anything, is happening.
"They looked so healthy last spring," said Bill Dahle, 50, who owns Big Sky Honey in Fairview, Mont. "We were so proud of them. Then, about the first of September, they started to fall on their face, to die like crazy. We've been doing this 30 years and we've never experienced this kind of loss before."
In a show of concern, the Environmental Protection Agency recently sent its acting assistant administrator for chemical safety and two top chemical experts to the San Joaquin Valley of California.
In the valley, commercial beekeepers who only recently were losing a third of their bees to the disorder say the past year brought far greater losses.
The U.S. Agriculture Department is to issue its own assessment in May. But in an interview, the research leader at its Beltsville, Md., bee research laboratory, Jeff Pettis, said he's confident that the death rate would be "much higher than it's ever been."
Following a now-familiar pattern, bee deaths rose swiftly in autumn and dwindled as operators moved colonies to faraway farms for the pollination season.
Beekeepers say the latest string of deaths has dealt them a heavy blow.
Bret Adee, who is an owner, with his father and brother, of Adee Honey Farms of South Dakota, the nation's largest beekeeper, described mounting losses.
"We lost 42 percent over the winter. But by the time we came around to pollinate almonds, it was a 55 percent loss," he said in an interview here this week.
"They looked beautiful in October, and in December they started falling apart, when it got cold."
Dahle said he had planned to bring 13,000 beehives from Montana - 31 tractor-trailers full - to work the California almond groves. But by the start of pollination last month, only 3,000 healthy hives remained.
TRACKING THE DISORDER
Annual honeybee losses of 5 percent to 10 percent once were the norm for beekeepers. But after colony collapse disorder surfaced around 2005, the losses approached one-third of all bees despite beekeepers' best efforts to ensure the insects' health.
The effect is not limited to beekeepers. The Agriculture Department says a quarter of the U.S. diet, from apples to cherries to watermelons to onions, depends on pollination by honeybees. Fewer bees means smaller harvests and higher food prices.
Bee shortages pushed the cost to farmers of renting bees to $200 per hive at times, 20 percent above normal. That, too, might translate into higher food prices.
Precisely why last year's deaths were so great is unclear. Some blame drought in the Midwest, although Dahle lost nearly 80 percent of his bees despite excellent summer conditions. Others cite bee mites that have become increasingly resistant to pesticides. Still others blame viruses.
But many beekeepers suspect the biggest culprit is the growing soup of pesticides, fungicides and herbicides used to control pests.
While each substance has been certified, there has been less study of their combined effects. And many critics say that scientists have not sufficiently studied the effect of neonicotinoids, the nicotine-derived pesticide that European regulators implicate in bee deaths.
The explosive growth of neonicotinoids since 2005 has roughly tracked rising honeybee deaths.
Neonics, as farmers call them, are applied in smaller doses than older pesticides. They are systemic pesticides, often embedded in seeds so that the plant itself carries the chemical that kills insects that feed on it.
Older pesticides could kill bees and other beneficial insects. But while they quickly degraded - often in a matter of days - neonicotinoids persist for weeks and even months.
Beekeepers worry that bees carry a summer's worth of contaminated pollen to hives, where ensuing generations dine on a steady dose of pesticide that, eaten once or twice, might not be dangerous.
"Soybean fields or canola fields or sunflower fields, they all have this systemic insecticide," Adee said. "If you have one shot of whiskey on Thanksgiving and one on the Fourth of July, it's not going to make any difference. But if you have whiskey every night, 365 days a year, your liver's gone. It's the same thing."
Research to date on neonicotinoids "supports the notion that the products are safe and are not contributing in any measurable way to pollinator health concerns," said the president of CropLife America, Jay Vroom. The group represents pesticide producers.
A coalition of beekeepers and environmental and consumer groups sued the EPA last week, saying it exceeded its authority by conditionally approving some neonicotinoids. The agency has begun an accelerated review of their effect on bees and wildlife.
The European Union has proposed barring their use on crops frequented by bees. Some researchers have concluded that neonicotinoids caused extensive bee deaths in Germany and France.