For the $14 billion agricultural industry, honeybees are a linchpin. But the insects have been under attack, their numbers decimated by the mysterious and devastating colony collapse disorder, or CCD. Scientists have focused on several possible causes in their search for what’s driving CCD, including deadly pathogens, neonicotinoid pesticides, and a lack of natural habitat. The latest suspect is something akin to an intraspecies plague.
Recently, the U.S. Department of Agriculture noticed during an unusual pathogen a routine check of commercial honeybees. It was tobacco ringspot virus, a plant disease that’s common in an number of crops, including soybeans. What made this one unique was the fact it was now infecting—and spreading among—the honeybees.
Geoffrey Mohan, reporting for the Los Angeles Times:
[F]urther study revealed the RNA virus was replicating inside its Apis mellifera hosts and spreading to mites that travel from bee to bee, according to the study published online Tuesday in the journal mBio.
The discovery is the first report of honeybees becoming infected by a pollen-born RNA virus that spread systematically through the bees and hives. Traces of the virus were detected in every part of the bee examined, except its eyes, according to the study.
Researchers report that the virus’s genetic diversity is what leads to its high mutation rate. It acts as a “quasi-species,” replicating quickly in an attempt to evade the host’s immune response. Similar behavior may be able to explain the dogged persistence of avian and swine flu, as well as HIV.
The virus may or may not be a major driver of CCD—there are too many factors for them to say for certain yet. Plus, they still have to learn more about the virus, how spreads, and how to stop it. It’s possible that varroa mites play a role in the disease’s spread, too, as they were found carrying, but not succumbing, to the virus. Their bites could spread the disease from one bee to the next. The parasites have long been associated with CCD, though their exact role is debated.
Scientists caution that they still don’t know the exact cause of CCD—it could be any one of a long list of suspects or a deadly combination of them. But given the discovery of this virus, and its interaction with the varroa mite, the latter is looking more and more likely.