> But it's a fair guess that if tracheal mite didn't exist in North America until around 1980
I think my original point is missed here. I won't belabor it but will make just one more run at it. North American bees' recovery from tracheal mites cannot in any way be compared to the infestation by varroa. The tracheal mite clearly has had a long term evolutionary relationship with Apis mellifera, almost certainly beginning eons before its discovery in the early twentieth century and I believe that there were already  some existing stocks of those adapted bees on both sides of the Atlantic prior to 1920.  And varroa has no evolutionary relationship Apis meillifera....except for the past century which doesn't  even constitute a blip on the evolutionary radar.

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