This Virus Pushes Struggling Bee Colonies Over the Edge

More bad news for bees: A virus passed from plants to honeybees could play a role in colony collapse disorder, further complicating the picture as to why entomologists have seen a massive die off in the species worldwide.

It’s called tobacco ringspot virus, and it’s seen more commonly in bee colonies classified as “weak,” leading researchers at the USDA to suggest that the virus may play an important role in colony collapse disorder, a phenomenon that began showing up around 2006 that has stumped scientists ever since. That’s a big deal, because bees pollinate roughly $14 billion worth of crops in the United States each year, and scientists aren’t exactly sure why a third of commercial bee colonies in the country died off last year.

There’s likely lots of things contributing to the phenomenon, including “polluted scents” due to pesticides, massive use of fungicides and other chemicals, parasites, and a “toxic viral cocktail” that appears to include tobacco ringspot virus (TRSV), which had previously only infected plants.

“Our study provides the first evidence that honeybees exposed to virus-contaminated pollen can also be infected,” said Ji Lian Li, lead author of the study published in mBio Monday.

In plants, TRSV causes leaf browning and a loss of production, and is particularly a problem in soybeans and tobacco, obviously. In bees, the virus damages the nervous and muscular system.

While there are plenty of viruses and pathogens that infect bees (that diversity is one of the reasons why experts are having trouble identifying the cause of colony collapse disorder), TRSV appears to be an important one: The virus was found in each part of a bee’s body besides its eyes, and can seemingly be passed from insect to insect, because it has been found in Varroa mites, a bee parasite that has been blamed for colony declines all around the world.

The virus is believed to impair a honeybee’s nervous and muscular system, and Li found reason to suspect “systematic spread” of the virus through a colony. Li notes that “increasing prevalence of TRSV in conjunction with other bee viruses in infected colonies is associated with gradual decline of host populations and winter colony collapse.”

The virus’s mechanism of action is also somewhat rare: Plant viruses are often spread from plant to plant by bees or other pollinating insects, but they rarely mutate enough to actually infect the insect itself.

Though scientists have long suspected that diseases play some role in colony collapse disorder, the USDA researchers weren’t searching for TRSV, and instead were doing a routine screening for other viruses that normally show up in honeybees. This new finding just makes the goal of controlling the health of commercial bee colonies even more difficult. The authors note that “the phenomenon of viral host range spanning the plant and animal kingdoms adds an additional layer to the already complex plant-pathogen-pollinator interactions.”