Further to the discussion. Even if a species is resistant due to
grooming and so on, it is unlikely ever to be totally free of a parasite
like varroa. Apis Cerana the original host species co-exists with Varroa
it does _not_ eradicate it. The problem with Apis Mellifera it that it
doesn't even recognise Varroa as a threat, so it doesn't (unless the
rumour is true) even try to groom it out. If one treats Apis Cerana with
Apistan one will get Varroa knockdown, even though Apis Cerana is
resistant!
 
Buckfast bees _are_ pretty resistant to tracheal mites as are most UK
origin bees (although Buckfasts are now bred in the Canary Islands).
 
Incidently, I use some New Zealand/U.K. cross bees and find them very
nice to keep, prolific and good workers if a little hungry in the winter.
I haven't used American bees (yet?) because of recent import restrictions
into the UK due to Varroa. The NZs I've used have been susceptible to
tracheal mite which is somthing of a down side.
 
        Regards, Gordon.