I don't think you can determine anything about a swarm's varroa resistance or tolerance, or if ithey carrying AFB spores , SHBs or any number of brood diseases. The safe thing to do is isolate the bees in an out yard until you can figure out what you have. The mythology that feral colonies are out there surviving on superior genetics makes for entertaining bee talk, but one of our state entomolgist's (CT) who spent months looking for them in Yale's isolated forests never found any.
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