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Bee mystery not over yet

News reports overstate recent findings

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Ambushed on his way to the cafeteria one recent Wednesday after giving a talk, bee biologist Jeff Pettis proved remarkably gracious to this entomology paparazzo with a burning question.

On opening day at the 10th annual conference of the North American Pollinator Protection Campaign, Pettis allowed himself to be stopped for a chat in an echoing, block-long corridor in the U.S. Department of Agriculture’s central hive in Washington, D.C.  Asked whether the recent media buzz over a fungus-virus pair of bee pathogens means science has finally figured out why bees are vanishing in a mysterious illness called colony collapse disorder, he replied directly.

“We have not,” Pettis said, sounding a bit wistful.

A recent scientific paper made news by suggesting that a newly discovered virus and a long-lamented fungus might be combining to hammer the bees. Pettis, of the USDA Bee Laboratory in Beltsville, Md., rates the headlines as “overblown.”

Other bee researchers too have been saying “wait and see” since the latest fungus-virus hypothesis appeared in a PLoS ONE paper online October 6. The cautious chorus even includes the scientist who led the study that caused the fuss, Jerry Bromenshenk of the University of Montana in Missoula. Excited as he sounds about his research, he’s not ready to claim that he has found the cause of colony collapse disorder.

What he and his colleagues say they have found is a link between the disorder and a pair of pathogens. All 45 of the collapsing or collapsed colonies the researchers sampled showed what look like signatures of infections by both a Nosema fungus, already well established in apiarists’ nightmares, and some form of what’s called an iridescent virus. Using a stand-in iridescent virus from moths, the researchers also found that combining the fungus and the virus did more damage to bees than either did alone.

The idea that a Nosema strain pairs up with another pathogen to cause colony collapse disorder is not new. As Science News’s Eva Emerson reported from the American Society for Microbiology meeting in June, Jay Evans of the USDA Bee Research Laboratory has also linked colony collapse disorder with a Nosema-plus-virus infection. He, however, was looking at several small RNA-based viruses.

What Bromenshenk’s team has not done, Bromenshenk himself explains, is meet the traditional standard for proving that a particular pathogen causes a disease, a set of criteria known as Koch’s postulates. Basically the team will have to isolate the honeybee pathogens, demonstrate that healthy honeybees inoculated with them get colony collapse disorder, and then recover the same pathogens from them.

The moth-virus inoculation that they have performed didn’t even reveal whether worker bees would fly away from their hives to die, the hallmark of colony collapse disorder. The lab setup kept the bees from flying much of anywhere, says coauthor and chemical ecologist Colin Henderson, also at Montana.

He and the bee team are eagerly hoping to work through Koch’s postulates, Henderson says. The tests could resolve some odd spots in the data. For example,the iridescent virus showed up not only in the collapsing colonies but in nine of the 13 apparently healthy ones. “Bee colonies are messy,” Henderson says.

The virus’ appearance in healthy colonies doesn’t automatically dash the fungus-virus hypothesis. An iridescent virus can lurk in an insect and not cause a fatal disease — at least in other species — says study coauthor Trevor Williams of the Institute of Ecology AC in Xalapa, Mexico. The new research is only the second report of one of these viruses in honeybees, Williams says, and he’s eager to see some actual infected material.

Lethal infections of these viruses in other insects create an iridescent sheen in the victim that can be quite pretty, in a sense, says Diana Cox-Foster of Pennsylvania State University in University Park. She, like Pettis, is waiting for more information. Neither she nor her colleagues have noticed iridescent viruses in hundreds of collapsing colonies examined in recent years.

The basic idea of combined menaces does make sense though, Cox-Foster says. She is investigating a different one-two combination: Pesticide exposure, she says, can substantially encourage the proliferation of viruses.

Citations

J.J. Bromenshenk et al. Iridovirus and Microsporidian Linked to Honey Bee Colony Decline. PLoS ONE. [Go to]
Further Reading

E. Emerson. Honeybee death mystery deepens. Science News, Vol. 13, June 19, 2010, p. 15. Available online: [Go to]

S. Milius. No one villain behind honey-bee colony collapse. Science News On the Scene blog, December 15, 2009. [Go to]

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