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Wild Bees Harbor Honeybee Viruses Without Apparent Effects on Mortality

NEW YORK (GenomeWeb) – Common honeybee viruses appear to be widespread in wild bees from some sites in the US, suggesting such viruses may not enhance mortality in wild bees from non-honeybee species.

Researchers from Iowa State University and the University of Iowa collected more than 150 samples from four bee families at sites in Iowa in 2013. They used RT-qPCR to test for and quantify levels of five viruses detected in honeybees in the past. As they reported today in PLOS One, they uncovered one or more viruses in the majority of the wild non-honeybees tested.

Even so, the team saw low levels of the viruses in wild bees relative to honeybees collected in apiaries. And follow-up experiments hinted that at least two wild bee species appear capable of withstanding infection by such viruses, which have been linked to honeybee losses in the past.

"There has been recent concern that common honeybee viruses can spread to other bee species, contributing to their declines," senior author Amy Toth, an ecology, evolution, and organismal biology researcher at Iowa State University, and her co-authors wrote. They noted that "exposure of wild bee species to emerging pathogens from the managed honeybees, and the potential threat such viruses pose to wild bees, needs investigation."

To explore these questions, the researchers started by collecting nearly 300 bee samples at three remnant tallgrass prairie sites, one restored tallgrass prairie site, and one commercial soybean field site in Iowa between mid-May and early August 2013. These included representatives from five bee families, 11 genera, and more than two-dozen species.

After focusing in on genera represented by five or more individuals, the team was left with 148 wild bees and 21 wild honeybees, together spanning four families and eight genera. It tested these samples with RT-qPCR using primers corresponding to the black queen cell virus, Israeli acute paralysis virus, deformed wing virus, sacbrood virus, and Lake Sinai virus.

Just over 80 percent of the non-honeybees harbored one or more of these viruses, albeit at low levels in most cases. The deformed wing virus turned up most often, in more than half of these bees. The sacbrood virus was close behind, in 45 percent of the non-honeybees. Just 3 percent of the non-honeybees carried black queen cell virus.

Though the wild bees all appeared healthy, the researchers decided to take a closer look at wild bee responses to inoculation with a concoction of the common honeybee viruses. They did not see any discernable changes in mortality in solitary, commercially reared Megachile rotundata bees or in field collected Colletes inaequalis bees, but observed detrimental effects in Apis mellifera honeybees.

"Although the findings here may appear to reduce concern about the detrimental effects of viruses on wild bees, it is premature to dismiss the issue, as our data do not yet rule out the possibility that some honeybee viruses can infect and harm some species of wild bees," the authors cautioned. "Many more species of bees and pathogens need to be tested, and longer-term studies are needed to test potential effects of pathogens on lifespan, behavior, or reproduction."