The Furst paper cited in the first post (and the Genersch paper from '96 on deformed wings in Bombus) are routinely cited as evidence of damaging overspill to non-Apis pollinators. These often lack key controls - for example, demonstrating replication of DWV in "symptomatic" Bombus.
When I heard this, I was questionning as I could not get visual proof. I mean if I can see physical DWV on honeybee, I would easily see it on my wild bumblebee nests.
Now, I'm fully convinced that wild populations of Bombus get DWV as I have seen Bombus crawling from nest located in soil 20 m away from my hives. How do they get contaminated ? I don't know ; a few of them show evidence of DWV. I see in February that some queen bumblebee tries to enter hives, looking for honey. According to my observation, I see they have no success getting in honeybees defend the entrance. But it may happen. Is it from visiting flowers ? I don't know. See picture attached taken June 24th 2020.
I keep different nests of solitary bees in addition of my hives, and regarding solitary bees, I have not yet seen this problem. . I have only noticed it on bumblebee, may be because the number of foragers is larger and it is easier to spot.
Georges France

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