There is no one single thing responsible for colony collapse disorder, a phenomenon seen over the better part of the last decade where honeybees mysteriously disappear from their hives. Scientists believe there are a number of factors, including climate change, air pollution, pesticides, and viruses that are contributing to the issue, which threatens modern agriculture as we know it (some of the tastiest crops are pollinated by bees). But every couple months, it seems that scientists get a little closer to figuring out exactly what’s going on.
Most recently, scientists at the U.S. Department of Agriculture’s Agricultural Research Service discovered something called the Tobacco Ringspot Virus (TRSV) during a routine screening of bees for viruses. The virus, spread by pollen, causes soy crop blight. It replicates inside honeybees, which can transmit it from plant to plant. Scientists already have known that for awhile.
The recent TRSV discovery, shared in the journal mBio, is the first time that scientists have found evidence that honeybees can be infected throughout their bodies by virus-contaminated pollen. In other words, honeybees don’t just spread the virus, they become infected themselves. That’s a big problem.
From PhysOrg, an explanation of why RNA viruses like TRSV are particularly worrisome:
Notably, about 5% of known plant viruses are pollen-transmitted and thus potential sources of host-jumping viruses. RNA viruses tend to be particularly dangerous because they lack the 3′-5′ proofreading function which edits out errors in replicated genomes. As a result, viruses such as TRSV generate a flood of variant copies with differing infective properties.
One consequence of such high replication rates are populations of RNA viruses thought to exist as “quasispecies,” clouds of genetically related variants that appear to work together to determine the pathology of their hosts. These sources of genetic diversity, coupled with large population sizes, further facilitate the adaption of RNA viruses to new selective conditions such as those imposed by novel hosts. “Thus, RNA viruses are a likely source of emerging and reemerging infectious diseases,” explain these researchers.
Scientists have found that colonies plagued by viruses, like Israel Acute Paralysis Virus and Kashmir Bee Virus, have less of a chance of surviving the winter than colonies that are virus-free. The researchers in the TRSV study write: “The increasing prevalence of TRSV in conjunction with other bee viruses is associated with a gradual decline of host populations and supports the view that viral infections have a significant negative impact on colony survival.”
TRSV isn’t the sole cause of colony collapse, but it’s almost certainly making the problem worse.