Parasitic fly could explain bee die-off

Northern California scientists say they have found a possible explanation for a honey bee die-off that has decimated hives around the world: A parasitic fly that hijacks the bees’ bodies and causes them to abandon hives.

Scientists say the fly deposits its eggs into the bee’s abdomen, causing the infected bee to exhibit zombie-like behavior by walking around in circles. The bee leaves the hive at night and dies. The symptoms mirror colony collapse disorder, in which all the adult honey bees in a colony suddenly disappear.

The disease is of great concern, because bees pollinate about a third of the U.S. food supply. Its presence is especially alarming in California, the nation’s top producer of fruits and vegetables, where bees play an essential role in the $2 billion almond industry and other crops.

The latest study, published in the science journal PLoS ONE, points to the parasitic fly as the new threat to honey bees. It’s another step in ongoing research to find the cause of the disease.

Researchers haven’t been able to pin down an exact cause of colony collapse or find a way to prevent it. Research so far points to a combination of factors including pesticide contamination, a lack of blooms — and hence nutrition — and mites, fungi, viruses and parasites. Interaction among the parasite and multiple pathogens could be one possible factor in colony collapse, according to the latest study by researchers at San Francisco State University. It says the phorid fly, or apocephalus borealis, was found in bees from three-quarters of the 31 hives surveyed in the San Francisco Bay area.

The combination of a parasite, pathogens and other stressors could cause die-off, lead investigator John Hafernik said. The parasitic fly serves as a reservoir that harbors pathogens — honey bees from parasite-infected hives tested positive for deformed wing virus and other pathogens, the study found.

„We don’t fully understand the web of interactions,” Hafernik said. „The parasite could be another stressor, enough to push the bee over tipping point. Or it could play a primary role in causing the disease.”