New research from the University of Vermont shows that domestic honeybees may be transmitting viruses to wild bumblebees. This may be one of the primary reasons for the decline of many species of wild bumblebees.

These viral infections are moving from managed bees in apiaries to nearby populations of wild bumblebees. “We show this spillover is likely occurring through flowers that both kinds of bees share,” said Samantha Alger, a University of Vermont scientists who led the new research. “Many wild pollinators are in trouble and this finding could help us protect bumblebees. This has implications for how we manage domestic bees and where we locate them.”

Although there are many reasons for the decline in wild pollinators all around the world, including land degradation, certain pesticides, and diseases. The rusty patched bumblebee, for example, has recently been listed under the Endangered Species Act because it has declined by nearly 90 percent. It was once a very successful pollinator of cranberries, plums, apples, and other agricultural plant.

The research team, consisting of three scientists from the University of Vermont and one from the University of Florida, explored 19 sites across Vermont. They found that two well-known viruses found in honeybees—deformed wing virus and black queen cell virus—were higher in bumblebees collected less than 300 meters from commercial beehives. They also found that while deformed wing virus infections were higher near the commercial apiaries, the virus was not found in bumblebees collected where foraging honeybees and apiaries were not there.

In addition, the team detected viruses on 19 percent of the flowers they sampled from sites near apiaries. “I thought this was going to be like looking for a needle in a haystack. What are the chances that you’re going to pick a flower and find a bee virus on it?” Alger said. “Finding this many was surprising.” In the good news department, though, they didn’t find bee viruses on flowers sampled more than one kilometer from commercial beehives.

The results strongly suggest that “viruses in managed honeybees are spilling over to wild bumblebee populations and that flowers are an important route,” UVM biology professor and study senior author Alison Brody said. “Careful monitoring of diseased honeybee colonies could protect wild bees from these viruses as well as other pathogens or parasites.”

“This research suggests that we might want to keep apiaries outside of areas where there are vulnerable pollinator species, like the rusty patched bumblebees,” Alger said, “especially because we have so much more to learn about what these viruses are actually doing to bumblebees.”

The study was published June 26, 2019, in the journal PLOS ONE.

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