Unusual weather -- more than a still-mysterious condition called colony collapse disorder -- appears to be the main culprit behind honeybee deaths this winter, according to several apiarists in Western Pennsylvania.

While debate continues over causes, many beekeepers agree that mortality rates are higher.

North Hills beekeeper Bob Jenereski reported higher-than-normal losses at the hives he has visited in Allegheny, Butler and Lawrence counties.

Characteristics of colony collapse disorder, which has been reported in more than half the states across the country, include the disappearance of adult bees from hives. Its cause remains unknown.

Mr. Jenereski, who lives in Marshall, maintains about 350 hives. He has visited about half his colonies so far this spring, and he has found plenty of dead bees, most of which appear to have starved to death.

Bad weather is the most likely culprit, he said.

A warm January tricked many queens into laying larger numbers of eggs, he speculated. When February arrived, bringing with it weeks of below-freezing temperatures, the adult bees faced the challenge of keeping a bigger-than-normal "brood nest" at a toasty 95 degrees. The bees do that by flexing their wing muscles to generate body heat that keeps the center of the hive warm.

Mr. Jenereski took apart one of his dead colonies, taking out the wooden frames on which the bees build their honeycombs. Once the adult bees had eaten the honey from the combs nearest the "brood nest," they couldn't move to the next frame because they would have left the eggs, larva and pupa exposed to the cold.

"They starved to death even though there was more food just an inch away," he said.

It costs at least $75 to restart a colony with a new queen and about 12,000 new bees, he said.

The presence of so many dead bees in his hives was one pretty definitive sign that he was not seeing colony collapse, he said.

"These are nothing like the conditions migratory beekeepers are facing," he said.

Migratory beekeepers are those who transport their hives from location to location so their bees can pollinate farm crops and orchards. Some crops, such as almonds in California and apples in Pennsylvania, rely almost exclusively on honeybees for pollination needed to produce fruit.

It is those traveling colonies that appear to have been most heavily affected by colony collapse, according to the Mid-Atlantic Apiculture Research and Extension Consortium.

In late February, however, some nonmigratory beekeepers in the Mid-Atlantic states and in the Pacific Northeast began reporting colony losses.

Mr. Jenereski said he could see no pattern in deaths among his hives. In one area, he found live bees in only seven of 28 hives; in another yard -- the term beekeepers use for multiple hives -- 12 of 12 colonies survived.

Wampum beekeeper Bob McMillin estimated he has lost 150 of his 250 hives. The Lawrence County resident said he believes about one-third of his losses represent colony collapse disorder, which is characterized by abandoned hives still containing large amounts of honey.

"The bees seemed to be under a lot of stress last fall," he said. "That made them nasty. When you took the top off a colony, they would go for you."

Like Mr. Jenereski, he sees no obvious pattern in the insect deaths. In one yard, only three of 48 hives survived, while in another, 26 of 28 are still buzzing. "There is not one thing you can point to as a cause," Mr. McMillin said.

Jim Stein, who is president of the Beaver Valley Beekeepers Association, said he is hearing reports of higher-than-normal losses.

He pointed out that many things may have contributed to the deaths: the March cold snap that sent temperatures back into the teens, mite infestations and a hot, dry summer that reduced the amount of plant nectar available for food-making.

He and many other beekeepers are awaiting guidance from state agricultural officials, he said, before trying to repopulate their dead colonies.

The latest information on colony collapse disorder, including a list of frequently asked questions, is available at the Mid-Atlantic Apiculture Research and Extension Consortium Web site, maarec.org.