Honeybees Infected By Plant Virus
January 21, 2014

Plant Virus Infects Honeybees, May Be Responsible For Colony Collapse

Brett Smith for redOrbit.com - Your Universe Online

A virus that typically infects plants has been found to infect honeybees and could be responsible for the widespread collapse of honeybee colonies around the world, according to a new report in the journal mBio.

The study team said they made their discovery when conducting routine screenings of bees for common and atypical viruses. The screenings “resulted in the serendipitous detection of Tobacco Ringspot Virus, or TRSV, and prompted an investigation into whether this plant-infecting virus could also cause systemic infection in the bees," said study author Yan Ping Chen from the Department of Agriculture's Agricultural Research Service (ARS) laboratory in Beltsville, Maryland.

"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 study author Ji Lian Li, from the Chinese Academy of Agricultural Science in Beijing.

"We already know that honeybees, Apis melllifera, can transmit TRSV when they move from flower to flower, likely spreading the virus from one plant to another," Chen added.

TRSV is an RNA virus, which tends to be particularly dangerous because they lack a function that edits out genetic errors. As a result, these viruses produce a flood of varying copies – many with differing infective characteristics.

One outcome of such high reproduction rates are clouds of genetically-related RNA variants that can work in concert to establish the pathology of their hosts. This genetic diversity, combined with large populations, facilitates the adaption of RNA viruses by novel hosts.

"Thus, RNA viruses are a likely source of emerging and reemerging infectious diseases," the study researchers said.

In the study, the research team looked at bee colonies they considered either "strong" or "weak" and found TRSV infections, as well as other viral pathogens, were more frequently found in the weak colonies than they were in the strong ones. The researchers also found that the overall health of bee populations with elevated levels of viral infections began declining in late fall and completely collapsed before February. Those colonies with lower viral infection rates generally survived through the winter months.

The study team also picked up TRSV inside the bodies of Varroa mites, a parasite that has been known to transmit viruses among bees as it feeds on their blood. Mite-associated TRSV was found to be restricted to the tiny arthropod’s gastric cecum – indicating that the mites probably spread TRSV within the hive without catching it themselves. Study researchers suspected that TRSV could also be passed vertically from the queen mother to her offspring.

"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 study team wrote.

The researchers noted that 5 percent of recognized plant viruses are pollen-transmitted and called for insect-pollinator management programs to investigate potential host-jumping events as a part of their strategy.