> Dan, the bee stocks in the U.S. were established from stocks that
apparently had not been exposed to tracheal mite

I'm less sure of this. Think about it. I believe that the sole known host for tracheal mites is Apis mellifera. Over what period of time do you think a parasite, such as the tmite and its host require to become so uniquely tied that the parasite is totally dependent on that particular host? It isn't as though such a dependent parasite/host relationship mysteriously appeared in 1921. In fact, there is pretty good evidence that the Isle of Wight disease was not actually caused by tracheal mites.  I would suggest that some US stocks were descended from tmite coevolved Europeans....and some not.  Those that were tolerant survived and were propagated.  
All the same....I think we're all guessing....at best..... but I think it may be misleading to make such an oversimplified comparison.

             ***********************************************
The BEE-L mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software.  For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html