University Park, Pa. -- Colony Collapse Disorder, diseases, parasitic mites and other stressors continue to take a devastating toll on U.S. honey bee populations, but Pennsylvania beekeepers on average fared better than their counterparts nationally during this past winter, according to apiculture experts in Penn State's College of Agricultural Sciences.
A recent survey by the Apiary Inspectors of America found that losses nationwide topped 36 percent of managed hives between September 2007 and March 2008, compared to a 31 percent loss during the same period a year earlier.
Pennsylvania fared better, with losses of about 26 percent, compared to nearly 48 percent the previous year. "About 70 percent of the state's losses this year were not related to Colony Collapse Disorder," said Dennis vanEngelsdorp, acting state apiarist for the Pennsylvania Department of Agriculture and a Penn State senior extension associate in entomology.
He said the state's lower overall bee-mortality rate may be due to greater awareness of bee health issues and beekeepers' diligence in controlling varroa mites, nosema and other threats. He pointd out that weather conditions also may have been more favorable for winter survival.
vanEngelsdorp noted that the state's comparatively lower losses meant that beekeepers this spring were able to meet the pollination demands of Pennsylvania's $61 million apple industry, which is the fourth largest in the country. Apples are completely dependent on insects for pollination, and 90 percent of that pollination is accomplished by honey bees.
"However, the cost of pollination has risen dramatically," he said "This year, apple growers paid about $65 per colony, compared with $35 to $45 in the past." A typical apple orchard requires one colony per acre to achieve adequate pollination. Last year, apple growers harvested about 21,500 acres.
Later this year, pumpkin growers may pay $95 to $105 per colony, compared to $55 to $65 last year, vanEngelsdorp said.
Meanwhile, Penn State researchers are making progress in pinning down the cause or causes of Colony Collapse Disorder (CCD), a mysterious ailment that threatens the beekeeping industry and the crops and native plants that rely on honey bees for pollination.
In fall 2007, a team led by Diana Cox-Foster, professor of entomology, reported a strong correlation between CCD and the presence of Israeli acute paralysis virus, making the pathogen a prime suspect in the disease. Since that time, researchers have introduced IAPV to healthy honey bee colonies in a controlled greenhouse environment in an effort to induce a collapse.
"Within one week of introducing the virus, we observed dramatic bee mortality, with bees dying outside the colonies across the room in the greenhouse," said Cox-Foster. "Bees were found on the floor with paralytic-type movements, and guard bees were observed removing paralytic bees from colonies and flying across the room. The majority of these 'twitcher' bees were found to have IAPV."
Cox-Foster noted that within a month, infected colonies had declined to small clusters of bees, many of which had lost their queens. "These data indicate that IAPV is a highly pathogenic virus," she said. "But they do not yet support a finding of IAPV as the sole cause of Colony Collapse Disorder. We still suspect that additional stresses are needed to trigger CCD."
Among the potential triggers being investigated are environmental chemicals. Penn State scientists analyzing pollen, wax, adult bees and brood (larvae) have found the presence of dozens of chemicals, including pesticides used by agricultural producers to protect crops and by beekeepers to control hive pests such as parasitic mites.
"This raises several complicated questions," said Maryann Frazier, senior extension associate in entomology. "Some of these compounds could react with each other to cause toxic effects or could combine with viruses or poor nutrition to weaken immunity and cause colony collapse. We also need to do more research to understand these chemicals' sub-lethal effects on bees."
Though the role of chemicals in Colony Collapse Disorder is still unknown, Frazier noted that beekeepers need more options for controlling varroa mites so they can reduce their reliance on chemicals. "With the sheer number of compounds we're finding in hives, it's hard to believe that pesticides aren't contributing to the general decline in bee health," she said.