STATE COLLEGE - Fewer beekeepers are reporting evidence of a mysterious ailment that had been decimating the U.S. honeybee population.
But losses due to colony collapse disorder remain high enough to keep beekeepers on edge, and longtime stresses on bees such as starvation and poor weather add to the burden.
A survey of beekeepers for the January issue of the Journal of Apicultural Research found that the percentage of operations reporting having lost colonies but without dead bees in the hives - a symptom of colony collapse disorder, or CCD - decreased to 26 percent last winter, compared to 38 percent the previous season and 36 percent the season before that.
Also, the percentage of colonies that died that displayed the CCD symptom was 36 percent last winter, down from 60 percent three winters ago, the survey found.
The earliest reports of CCD date to 2004, and scientists still are trying to find a cause.
''The story is really complicated. We thought we'd have a simple explanation,'' said Dennis vanEngelsdorp, Pennsylvania's acting state apiarist. ''CCD drew our attention, but there are lot of things'' affecting the bees.
More than 90 crops, from almonds to tomatoes, rely in large part on bees for pollination.
Richard Adee, who owns one of the largest commercial beekeeping operations in the country, Adee Honey Farms, based in Bruce, S.D., has bees in California now ready to pollinate the almond crop. At peak season, during the summer, he has about 80,000 hives for honey production in the Midwest.
He said that after losing 40 percent of his colonies over the winter of 2008, losses are down to a more expected 12 percent.
''We're not seeing as big a hit,'' Adee said, ''but I still talk to beekeepers who are losing bees.''
Bees rely on stored honey to survive the winter. Beekeepers can wrap colony boxes to provide extra warmth or try to provide sugar syrup for food if supplies are light, but they generally don't work with bees in the cold.
That means the winter months can be worrisome for some beekeepers, such as beekeeping hobbyist Tom Jones, of Carlisle.
''I don't know what's going to happen this year, but I'll be anxious to see ... when I go check them,'' Jones, 66, said before his demonstration at the Pennsylvania Farm Show in Harrisburg earlier this month.
This winter has been particularly brutal, with storms producing record snowfalls and chilling winds in many parts of the country. Freezing temperatures that swept in on an Arctic front from Canada plagued as far south as Florida.
Despite the apparent decline in colony collapse losses, the industry continues to be hit hard - an estimated 29 percent of all U.S. colonies died last winter, about 11 percentage points higher than what beekeepers consider normal, acceptable losses, according to the survey.
Colony collapse was ranked as the eighth most important cause of bee mortality last winter, down from fourth the previous winter.
''Losses are shifting. There are fewer operations with CCD, though they still lost a lot of colonies,'' said vanEngelsdorp, the lead author on the study. ''But other factors are killing bees.''
Starvation, typically a top cause of mortality, was first, followed by poor quality queen bees and weather. The percentage of beekeepers citing weather as a leading winter concern jumped from 9 percent to 18 percent.
The study noted many of the top causes of mortality can be countered with better management, such as wrapping colonies over the winter or providing supplemental food.