Researchers identify yet another threat to hive health
A team of investigators from California have discovered a parasitic fly that may be partially responsible for the massive kill-offs of bee populations.
It started with a pile of dead bees beneath a light outside the entrance of San Francisco State University’s biology building. Professor John Hafernik was not gathering specimens, but rather fodder for the praying mantis he had brought back after a fieldtrip.
“But being an absent-minded professor,” Hafernik said, “I left them in a vial on my desk and forgot about them. The next time I looked at the vial, there were all these fly pupae surrounding the bees.”
The fly, a species known as Apocephalus borealis, has been known to parasitize bumblebees and paper wasps, but this was the first indication that it might also affect honeybees. The fly deposits its eggs in the bee’s abdomen, causing its host to abandon the hive, flying to nowhere “like a zombie,” and die. About one week later, as many as 13 larvae push their way out into the world from between the bee’s head and thorax.
A terrifying image. However, not as terrifying as what it portends for honeybee colonies and the fate the agricultural systems that depends on them.
With a team of researchers, Hafernik, who is also President of the California Academy of Sciences, took samples of honeybees around the San Francisco Bay Area and found evidence of the fly in 77 percent of hives, as well as in commercial colonies in South Dakota and California’s Great Central Valley. The results of their investigation were published last week in the science journal, PLoS One.
“It’s the abandonment behavior that’s most alarming, bees leaving their hives at night and flying toward sources of light,” says Andrew Core of the State University of San Francisco and the study’s lead author. “Hive abandonment is a prime characteristic of Colony Collapse Disorder.”
The phenomenon researchers have dubbed Colony Collapse Disorder (CCD) began in 2006, with the decimation of hundreds of thousands of colonies in the United States. Globally, billions of honeybees have since died, though scientists remain at a loss as to the cause.
Possible explanations include parasites, mites, and bacterial and viral infections, though increasingly researchers believe that its causes are more complex than initially anticipated. “Colony Collapse Disorder is not caused by a single pathogen or parasite,” says Hafernik. “It’s a combination of factors that pushes hives to their tipping point.”
While there is no consensus on what is driving this phenomenon, researchers concede that the techniques of modern agriculture likely play a role.
In the US, as in Britain and other countries where agriculture takes place on an industrial scale, commercial beekeepers haul their hives from one pollination site to the next, often traversing hundreds, if not thousands of miles.
“Bees that are trucked around are placed under a lot of stress,” says Hafernik. Stress can deplete a bee’s immune system, making it more susceptible to infections and illness. “They also pick things up and bring them back to the hive. It’s hard these days to find a hive that’s clean.”
Scientists have also identified agricultural chemicals as a potential culprit in harming bees’ immune function. The World Organisation for Animal Health cited the “irresponsible use of pesticides” as a major source of damaging hives.
“Many chemicals are highly toxic to bees,” says Hafernik. “Pesticides and bees certainly don’t mix very well.”
The presence of CCD in Britain is a controversial subject. The agricultural ministry, Defra, denies the presence of CCD in Britain, despite reports of annual losses of up to 20 percent of hives.
Norman Carreck of the International Bee Research Association suggests that the classification of CCD in the UK may be a technical issue. “Certainly there have been colonies that have collapsed in this country, but colony losses can be due to different conditions.”
Whether termed CCD or not, the decline of honeybee populations poses a major threat to agricultural systems in the US, the UK and around the world. According to a March 2011 report from the UN Environment Programme: “The way humanity manages or mismanages its nature-based assets, including pollinators, will in part define our collective future in the 21st century. The fact is that of the 100 crop species that provide 90 per cent of the world’s food, over 70 are pollinated by bees.”
Since publishing their study last week, Hafernik and his colleagues have been contacted by beekeepers around the country reporting similar patterns of nighttime abandonment, suggesting that the parasite is an emerging threat. “We should pay attention to this,” says Core. “Any new threat to bees – especially a parasite that kills its host every time – should be researched extensively.”Tagged in: honeybees, John Hafernik, nature
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