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The Cause of Colony Collapse Disorder, As a Crime Drama

A new study has fingered a villain and her henchman. Here's what investigators have learned about the mysterious illness that's affected U.S. honeybees.


Scientists have discovered key clues in their investigation into the cause of colony collapse disorder, the disease that in recent years has cost U.S. beekeepers as much as 40% of their bees, and caused widespread concern about the future of roughly one-third of food crops that need pollination.

Previous attempts to define the cause of the disease, characterized by hives that mysteriously empty of bees while overwintering, have suggested causes as various as viruses, fungi and parasites, both new and old; pesticide poisoning; stress and malnutrition – or, most likely, some combination. Some early diagnoses proved wrong, and others at least taught beekeepers valuable lessons about keeping their hives healthier.

Now, after three years of collaboration, a team of scientists say they have a smoking gun, or as close to a smoking gun as has yet to emerge: the hives affected by colony collapse disorder tend to be infected with a virus that is new to beekeepers, and a fungus, that is well-known.

The team identified the new virus using a technique called spectrometry-based proteomics, a test modified by the U.S. military to test for bioterror attacks and the like. Think of it like a very accurate police lineup: By comparing how different viruses glow under testing, investigators can tie a specific virus to the scene of the crime.

bee cartoon

The new virus they found in bee hives is an "insect iridescent virus" – called so because it infects insects and because when scientists subject it to testing, it glows with an iridescent bluish-green or purple color. Scientists refer to these viruses by an acronym, IIV, but since she's our villain, let's just call her "Ivy" to make things easier to follow. It's an appropriately evil-sounding name for an evil-doing lifeform: A virus, after all, replicates by inserting her genetic material into a host's cell, co-opting that cell's genetic machinery, and then exploding the host cell so she can infect more cells.

Ivy is a mysterious villain, but she comes from a big family of iridescent insect viruses (at least two dozen are known to science). Some of her cousins cause minor insect illnesses, while other are lethal – some so lethal that they've been co-opted and enlisted as biopesticides against pests like mosquitoes. We know Ivy is unique among bee viruses that scientists have fingered as possible causes of colony collapse disorder (she's a DNA-virus, as opposed to an RNA-virus). Ivy might be the cousin of a similar bee virus discovered 20 years ago in India, and she may be related to a moth virus. She may have come recently to bees, having started her criminal career infecting other insects, or she may have started her career overseas and only recently found her way to U.S. bees. She thrives in cool, wet conditions, which makes sense, since those weather conditions have accompanied some of the worst colony collapses. Whatever her background, she's only recently started her crime spree on U.S. bees.

Scientific investigators are still trying to find out exactly who she is (what strain) how she got here (viruses generally don't carry passports) – and who she's working with. Scientists looking at the crime scene hives also found evidence of a fungal parasite of the genus Nosema. In police parlance, this guy is "known to" beekeepers. He's been infecting hives for a long time. The collapsed hives that Ivy infected were also riddled with Nosema.

Investigators, then, have only come as far as fingering the likely subjects in a police lineup. What's next?

Labeling Nosema a henchman is premature. It could be that Nosema works with Ivy. It could be that one weakens the hive, making way for the other. Or it could be that hives weakened by colony collapse disorder are more susceptible to both villains. Scientists will work to isolate the specific strain of the Ivy virus affecting bee hives, and see how it works, alone and in consort with Nosema.

Investigators will also try to identify ways beekeepers can protect themselves. Beekeepers have ways to detect and treat Nosema infestations. But right now, there's no easy way to identify Ivy; once there is, beekeepers can weed out infected colonies before the virus spreads, and imported bees can be quarantined or, if infected, destroyed. Like any good villain, she has vulnerabilities: Viruses like her can't replicate at very high temperatures (above about 85 F). Keeping bees in dry, sunny locations may help.

And investigators will look, like a movie studio plotting a sequel, for more villains. Another villain well-known to beekeepers is the Varroa mite, which may act as a vector for the dispersal of the virus, just as mosquitoes transmit West Nile virus or malaria to humans. An insect iridescent virus was seen in Varroa mites that prey on bees some years ago after a collapse of bees in the U.S. Northeast. Varroa is known to increase damage caused by other viruses, and beekeepers who fail to control varroa levels are likely to sustain high colony losses.

So Ivy may be the ringleader, or part of a crime syndicate. The search goes on.

For an entirely more scientific description of this study, and a list of all the investigators, look to the scientific journal PLoS ONE, where you'll find Iridovirus and Microsporidian Linked to Honey Bee Colony Decline.

This story was reported by Kim Flottum and written by Dan Shapley.

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