Honey bees can become the unwitting hosts of a fly parasite that causes them to abandon their hives and die after a bout of disoriented, “zombie-like” behavior, San Francisco State University researchers have found.

The phenomenon, first observed on the SF State campus, may help scientists learn more about colony collapse disorder (CCD). This mysterious ailment has drastically increased honey bee colony losses across the United States since its discovery in 2006.

So far, the fly parasite has only been found in honey bee hives in California and South Dakota, said SF State Professor of Biology John Hafernik. But the possibility that it is an emerging parasite “underlines the danger that could threaten honey bee colonies throughout North America, especially given the number of states that commercial hives cross and are deployed in,” Hafernik and colleagues write in the January 3, 2012 issue of PLoS ONE.

Hafernik, who also serves as president of the California Academy of Sciences, didn’t set out to study the parasitized bees. In 2008, he was just looking for some insects to feed the praying mantis that he had brought back to SF State’s Hensill Hall after an entomology field trip. He scrounged the bees from underneath the light fixtures outside the biology building. “But being an absent-minded professor,” Hafernik joked, “I left them in a vial on my desk and forgot about them. Then the next time I looked at the vial, there were all these fly pupae surrounding the bees.”

The fly

The fly, Apocephalus borealis, deposits its eggs into a bee’s abdomen. Usually about seven days after the bee dies, fly larvae push their way into the world from between the bee’s head and thorax. But it’s the middle part of this macabre story that may be the most scientifically interesting to those studying the dramatic and mysterious disappearance of honey bees.

After being parasitized by the fly, the bees abandon their hives in what is literally a flight of the living dead to congregate near lights. “When we observed the bees for some time—the ones that were alive—we found that they walked around in circles, often with no sense of direction,” said Andrew Core, an SF State graduate student from Hafernik’s lab who is the lead author on the study.

Core won first place at the 2011 California State University Research Competition and the Geraldine K. Lindsay Award for excellence in the natural sciences at the annual meeting of the Pacific Division of the American Association for the Advancement of Science for his presentation of the bee research.

Bees usually just sit in one place, sometimes curling up before they die, said Core. But the parasitized bees were still alive, unable to stand up on their legs. “They kept stretching them out and then falling over,” he said. “It really painted a picture of something like a zombie.”

Bees that left the hives at night were more likely to bear the parasite than those who foraged during the day, the researchers found. Genetic tests of parasitized hives also showed that both bees and flies were often infected with deformed wing virus and a fungus called Nosema ceranae.