Honeybees Can Spread Viruses by Transporting Infected Pollen

Colony collapse disorder, the mysterious and deadly malady that is wiping out bee colonies around the world, may be linked to a viral pathogen that more commonly infects plants, according to scientists.

While conducting a routine screening of bees for frequent and rare viruses, a team that included the US Department of Agriculture's Agricultural Research Service (ARS) laboratory found the presence of TRSV, or tobacco ringspot virus, in bees.

The ARS's Yan Ping Chen called finding the virus in bees a "serendipitous" discovery amid the routine tests. Chen and his colleagues went on to investigate whether this plant virus could also cause systematic infection in bees, finding evidence that the virus was indeed widespread.

Chen said it was already known that honeybees can transmit viruses from contaminated pollen as they move from flower to flower.

"The results of our study provide the first evidence that honeybees exposed to virus-contaminated pollen can also be infected and that the infection becomes widespread in their bodies," said Ji Lian Li of the Chinese Academy of Agricultural Science in Beijing. Li was the lead author of the paper on the research published in mBio, the online open-access journal of the American Society for Microbiology.

TRSV is a virus that seeds itself in the RNA, where it can exploit a weakness in the genetic code and generate a flood of variant copies of itself with different infective properties, the researchers said, adding that "RNA viruses are a likely source of emerging and reemerging infectious diseases."

The researchers are now investigating whether there is a link between TRSV and colony collapse disorder, and there appears to be one. As the team examined bee colonies classified as "strong" and "weak," they found TRSV and other viruses were more common in the weaker colonies. Colonies with high levels of multiple viral infections were observed declining in the autumn and effectively decimated by the middle of winter. In contrast, colonies with fewer viral infections were observed surviving entire winters.

"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," the researchers said, concluding that increased colony surveillance and virus monitoring are necessary to help create more effective honeybee management programs.