Scientists discovered a mysterious phenomenon that has decimated honey bee populations across US and Western Europe, which could be linked to a “zombifying” parasitic fly.

Colony collapse disorder (CCD) is marked by the sudden disappearance of worker bees from a colony.

CCD was first recognized as a serious problem by U.S. beekeepers in 2006, but has also affected bee colonies across Western Europe.

In some of the recorded cases, bee losses have reached levels of up to 90%.

Viral and fungal infections and toxic chemicals in pesticides have all been suggested as possible explanations for CCD.

The new theory involves the parasitic fly Apocephalus borealis, which is already known to attack bumble bees.

Evidence has now emerged of the fly targeting honey bees.

Apocephalus borealis lays its eggs in the abdomens of bees, which start displaying “zombie” behaviour, abandoning their hives en masse to congregate near lights.

Finally they die, and the fly larvae emerge from their bodies.

U.S. scientists noted that hive abandonment is a primary feature of CCD.

Genetic tests also showed that both bees and flies were often infected with deformed wing virus and the fungus Nosema ceranae.

Both infections have previously been cited as possible causes of CCD, suggesting a link.

Professor John Hafernik, from San Francisco State University, said: “We don’t know the best way to stop parasitisation because one of the big things we’re missing is where the flies are parasitizing the bees.

“We assume it’s while the bees are out foraging because we don’t see the flies hanging around the bee hives. But it’s still a bit of a black hole in terms of where it’s actually happening.”

The research is published today in the online journal Public Library of Science ONE.

Analysis of the parasites confirmed they were the same flies that have been infecting bumblebees. The fly could be an emerging and potentially costly new threat to honey bees, say the scientists.

Prof. John Hafernik added: “Honey bees are among the best-studied insects in the world. So at one level, we would expect that if this has been a long-term parasite of honey bees, we would have noticed.”