February 16, 2012
Researchers at a California university have found a parasitic fly which causes honeybees to become disoriented and abandon their hives before dying, behavior which made one of the researchers compare them to zombies. Scientists believe this may be a contributing factor to Colony Collapse Disorder, which has decimated honeybee populations, affecting the honey market and the pollination of crops as well as raising concern about environmental toxins.
The insect version of a horror movie
The parasitic flies were discovered by chance when John Hafernik, professor of biology at San Francisco State University, collected some dead bees, found under a light on campus, as food for a praying mantis he had just captured. “Being an absent-minded professor, 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 flies were later identified as Apocephalus borealis. The female A. borealis fly deposits its eggs into the bee’s abdomen, and about a week later, mature fly larvae emerge from the host’s head and thorax. Infected bees move their limbs in a jerky limb fashion and walk in circles. They leave their hives and seek bright lights as if they were moths rather than bees. They die shortly afterwards and as many as 13 parasite fly larvae may then crawl out from the body of their host.
One member of the research team, biology graduate student and study co-author Andrew Core, observed that the bees “kept . . . falling over. It really painted a picture of something like a zombie.” The researchers found that bees which leave the hive to forage at night, rather than those that forage by day, seem most likely to become infected. In addition, the researchers believe the parasitic flies may multiply within a hive, infecting other members of the swarm, even pregnant queen bees.
The research team analyzed several hives in the both the Central Valley and Bay areas of Northern California and also some hives from South Dakota. Seventy-seven percent of the hives they sampled contained evidence of A. borealis. The scientists believe this may be a recent change in the behavior of this particular species of fly. The A. borealis fly has been known in the past to be a parasite of bumblebees and paper wasps but has not previously been known to inject its eggs into honeybees.
Double parasites, viruses and more
The researchers’ findings add another clue to the mystery of CCD but also reveal how complicated the origins of that disorder are. Infected bees and their fly parasites were found to hold genetic traces of another parasite, Nosema ceranae. Analysis also revealed both parasite and host have a virus which causes wing deformities. These findings suggest that A. borealis may weaken hives in multiple ways.
The research team plans to use video monitoring and tiny radio tags to monitor hives for further research. Since they have so far only sampled hives from two states, they want to learn if the new parasitic behavior of A. borealis occurs in other areas. They hope to learn whether the “zombie bees” choose to leave the hive or if other members of the group sense their disease and drive them away to protect the swarm. They also hope to pinpoint the location in which bees become infected “We don’t know the best way to stop parasitization, because one of the big things we’re missing is where the flies are parasitizing the bees,” stated Hafernik.
“We don’t fully understand the web of interactions,” said Hafernik. “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.” Hafernik and Core’s study was published in early January 2011 in the open access science journal PLoS ONE.
This article was posted: Thursday, February 16, 2012 at 4:52 am