The quest to figure out what’s behind honeybee deaths has become as much a political question as a scientific one. Recent data show that honeybee populations have recovered from outbreaks of colony collapse disorder that began to draw attention in 2006. Managed bee colonies continue to grow—globally they are at record numbers. In April, the Sierra Club noted in a blog post:
…honeybees are at no risk of dying off. While diseases, parasites and other threats are certainly real problems for beekeepers, the total number of managed honeybees worldwide has risen 45% over the last half century. “Honeybees are not going to go extinct. says Scott Black, executive director of the Xerces Society. ‘We have more honeybee hives than we’ve ever had….’
Although there is no ‘bee-apocalypse as many environmentalists have claimed, bee health issues are real, and there are many claims being made about the challenges to these important pollinators. Among them:
- Some critics maintain that CCD continues today and say, mistakenly, that honeybee populations are dropping.
- Others argue that glyphosate, neonics, genetic engineering or other agricultural technologies are claiming the lives of bees.
- Beekeeping practices and hive hygiene have been called into question.
- Others point to the role of Varroa mites.
Now, we can add one more suspect to the list: viruses.
The science blog/news page Science 2.0 recently posted a story entitled “Bees: it’s the viruses that are the problem.” The story pokes at environmental groups that “raise millions of dollars insisting they will get targeted pesticides (e.g. neonicotinoids) banned to save bees that aren’t really in peril,” while, “At the top of the list is not pesticides, it’s nature.”
Specifically, the article cites a recent study at Pennsylvania State University that applied high-throughput next-generation sequencing techniques to discover a host of new viruses that have something to do with Apis mellifera, the European honeybee. They found about 127 “contigs,” new genetic configurations that could translate into distinct viruses, to be exact.
But even the study doesn’t arrive at the same conclusion as the Science 2.0 headline. The Penn State group really was showing that next-generation sequencing is proving to be a valuable technique for uncovering viruses that may have a role in bee health. On other hand, those viruses may just be harmlessly—or at least non-pathologically—in the same environment.
When CCD broke out in the mid-2000s, another group led by Columbia University virologist Ian Lipkin also looked at one type of virus, that had been discovered in Israel and seemed to be associated with colony deaths in Australia and other parts of the world. Responsibly, Lipkin said that this correlation was not cause:
“We haven’t proven this is the cause. It is a candidate for being a trigger for CCD,” Lipkin told Scientific American.
And since those days (which predated what’s now called “NGS”), the field of bee virology is exploding. As for which virus (if any) causes bee deaths? Get in line.
In 2007, about 18 RNA and DNA viruses that impacted honeybees somehow were identified. Since, next generation sequencing techniques have reached even more than the 127 identified by the Penn State study.
Common viruses now include: Israeli acute paralysis virus (the one discovered in 2007 by Lipkin’s team), Kashmir bee virus, acute bee paralysis virus, black queen cell virus, deformed wing virus, kakugo virus, Varroa destructor virus-1, sacbrood virus, and slow bee paralysis virus. Researchers all observe that thanks to advanced genetic identification, many more will follow. And no single virus has been uniquely tagged to colony collapse disorder and bee health.
But do they all harm bees?
Probably not. But a few might.
In a recent paper in Current Opinion in Insect Science, Montana State University researchers Alexander McMenamin and Michelle Flennikin observed that one key indicator of impact is the ability to replicate in honey bees. If a virus doesn’t, it isn’t as likely to be harmful to bees. This is due to viral behavior; viruses don’t replicate all by their lonesome. Instead, they invade a host cell and use that cell to reproduce, producing both more viruses and disease.
Some viruses so far have been “passively” associated with honey bees, and don’t replicate in the animal. These include two plant viruses from Spain, the Turnip ringspot virus and Turnip yellow mosaic virus.
Sometimes viruses can only become pathogenic when linked with the right vector. For the honeybee, this was a mix of two aliens: the European honeybee, and Varroa destructor, which originated in Southeast Asia. Distorted wing virus (DWV) is now seen as a major contributor to bee deaths, but only became so once it was transmitted by V. destructor. Before, the virus was associated with non-symptomatic infections in bees.
As more bee-linked viruses are discovered and characterized, and their behavior known (including the ability to attach to a host vector like Varroa), scientists will be able to better predict the ecological conditions that result in bee infection. Until then, it’s a search for about a million needles in a haystack.