Honeybees colonies afflicted with CCD, or Colony Collapse Disorder, have significantly higher pathogen loads than healthy hives, according to a new study by researchers from Penn State's College of Agricultural Sciences, other universities, and the U.S. Department of Agriculture's Agricultural Research Service.
The researchers collected samples of adult bees, wax comb, pollen and brood (developing larvae) from 91 colonies in Florida and California. Scientists then quantified more than 200 variables, including the presence of parasites such as varroa and tracheal mites; infection by bacteria, viruses and fungi; pesticide levels; nutritional factors; and bee physiology. No single factor was found consistently only in those colonies suffering from CCD.
No single pathogen infected CCD colonies at a higher rate than non-CCD colonies. However, CCD colonies were co-infected with a greater number of pathogens -- viruses, bacteria and microparasites such as Nosema. For instance, 55 percent of CCD colonies were infected with three or more viruses, compared to 28 percent of non-CCD colonies.
The study may have also excluded some suspected factors as causes of CCD. Beekeepers and environmentalists, for example, have speculated that pesticide use may be to blame, at least in part, for the mysterious disorder. But the Penn State study found that certain pesticides were actually present at higher levels in the non-CCD colonies.
The study's findings, which were published in the online journal PLoS ONE, illustrate the complexity of solving the CCD problem, according to lead author and Penn State entomologist Dennis vanEngelsdorp. "Our results suggest that this condition may be contagious or the result of exposure to a common risk factor that impairs the bees' immune systems, making them more susceptible to pathogens," said vanEngelsdorp.
VanEngelsdorp noted that higher pathogen loads are likely to have caused CCD symptoms, but what causes the bees to become infected with so many pathogens is still not known. "Although pathogens seem likely to play a critical role in CCD, that role may be secondary, much like AIDS patients die from secondary diseases," he added.
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