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Virus transmission between bee species does not lead to new variants, study finds

A new study led by researchers at the University of Minnesota found transmission of viruses between different bee species did not lead to the formation of new virus variants.

Results of the study, in Communications Biology, may be a rare bit of good news for bee pollinators, which have been in decline for over 25 years, according to the U.S. Fish and Wildlife Service.

Led by researchers in the College of Veterinary Medicine and the College of Food, Agricultural and Natural Resource Sciences, the study focused on three viruses: deformed wing virus, black queen cell virus and sacbrood virus. These are three known pathogens of the non-native Western honey bee, the most commonly kept by beekeepers and the most widespread bee species in the world.

The researchers performed genomic sequencing on samples over three years to track the Western honey bee viral landscapes and whether the viruses could infect and adapt to common native bumblebees.

They found:

• While the honeybee viruses were present in the bumblebees, they were over 98% genetically identical and did not accumulate mutations that were specific to bumblebees.
• No bumblebee-specific variants of honeybee viruses could be detected, signaling that the viruses had not established themselves within the bumblebee populations. This suggests that the bumblebee was a dead-end host and bumblebee to bumblebee transmission was not taking place.
• The bumblebee had their own distinctive virome, suggesting that these viruses were of more concern than those originating from honeybees.

Bee pollinator populations that are crucial to ecosystems and food production globally are under strain because of habitat loss, pesticides, climate change, invasive species, and pathogen-related diseases. One potential disease threat comes from the phenomenon for viral spillover to native pollinator species.

"While a concern, viral spillover from managed honeybees to wild bumblebees has of yet not resulted in the pandemic-type effects as first proposed," said lead principal investigator and corresponding author Declan Schroeder, a professor in the College of Veterinary Medicine. "Viral spillover does not appear to be a reason to limit or restrict the placement of honeybee colonies in areas occupied by wild bumblebees or bees of other species."

Protection of bumblebees of conservation concern from potential pathogen spillover from honeybees is still a valid conservation action, particularly when protecting species at risk of extinction. Low genetic diversity, which has been demonstrated in bumblebee species of conservation concern, could increase vulnerability to pathogen spillover.

"We will continue to monitor the true viral diversity found both in managed honeybees and wild bee pollinators. Having a clear understanding of the bee viral baseline will allow us to act if new or reintroductions occur," said Schroeder.

"While it is reassuring to see a lack of virus replication in this study system, there are still several reasons to minimize exposure of native bee populations to managed honeybees. While this study found that there were no new virus variants formed in bumblebee hosts, that does not mean that the spillover of honeybee viruses to other bees is without risk.

"I hope that this study can lead to more monitoring to understand the impacts of the viruses on the health of bumblebees and other wild bees," said co-author Elaine Evans, an Extension professor and researcher in the College of Food, Agricultural and Natural Resource Sciences.