Image 1 - Parasitic Fly Likely Culprit in Bizarre ‘Zombie’ Bee Behavior
January 4, 2012

Parasitic Fly Likely Culprit in Bizarre ‘Zombie’ Bee Behavior

Scientists suspect that a parasitic fly that preys on honey bees could be the cause behind the alarming phenomenon known as colony collapse disorder (CCD), in which thousands of worker bees exhibit bizarre behavior before suddenly vanishing from their colony.

Since the problem was first observed in the U.S. in 2006, experts have been attempting to explain the strange ℠zombie-like´ behavior in usually robotically predictable worker bees. European scientists have also joined in to solve the mystery as affected colonies have also been observed in increasing numbers across western Europe in recent years.

In a number of the studied cases, colonies died out entirely as up to 90 percent of its worker bee abruptly abandoned their hives and died, causing a collapse of the hive´s rigidly structured division of labor.

Previously, scientists had focused their research efforts on investigating various viral and fungal infections as well toxic chemicals in pesticides as potential causes behind the bees´ abnormal and ultimately destructive behavior.

Experts now believe, however, that a tiny parasitic fly called Apocephalus borealis may in fact be the culprit behind these large-scale hive suicides.

A. borealis has long been known to attack bumble bees, and recently discovered evidence indicates that they may now be exploiting their close cousin the honey bee as hosts as well.

Exhibiting a macabre life cycle typical of many insect parasites, the tiny flies first lay their eggs in the abdomens of the unsuspecting worker bees. Shortly thereafter, the infected bees appear to go mad and exhibit what scientists have described as ℠zombie´ behavior, abandoning their colony to seek out and swarm around light sources.

Eventually, the crazed hymenoptera die and A. borealis´ tiny larvae begin to emerge from the abdomen of the carcass.

In an interesting twist to this gruesome natural drama, geneticists studying the phenomenon have recently discovered that both parasite and host insects are often infected with a mutated virus that causes wing deformation as well as a parasitic fungus called Nosema ceranae.

Scientists had previously suspected either the virus or the fungus as a possible cause of CCD, and some still think that there may be a yet undiscovered link.

One current problem is that researchers haven´t yet been able to detect exactly when and where the bees are being preyed upon by the deadly parasite.

“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,” explained entomologist John Hafernik, a honey bee expert and professor at San Francisco State University.

“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,” he 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.”

The results of the recent study were published in this week´s online version of the journal Public Library of Science ONE.


Image 2: These are images of Apocephalus borealis and honey bees. (A) Adult female A. borealis. (B) Female A. borealis ovipositing into the abdomen of a worker honey bee. (C) Two final larvae of A. borealis exiting a honey bee worker at the junction of the head and thorax (red arrows). Credit: Natural History Museum of Los Angeles County


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