Isn't it also true that maladies like varroa are progressive over a long
time?  I mean, can a colony with early varroa infestation look good for one
or two years and do well, until the mites get so bad that the colony
finally declines??  Last spring I started to see the loss of colonies due
to varroa.  This was after overwintering fine and during buildup period.
Say 7 out of a dozen colonies in a typical yard just started to peter out,
while the others carried on apparently fine.  That's when I first saw the
mites on the bees.
 
My point is, mites were no dou bt present in the "good" colonies, too.
Perhaps mites just weren't up to high enough levels to stunt colony
development (?).  If I bred queens from the good colonies, presuming some
resistance, I'd then be wasting my time.  There would be no "resistance,"
and it would be just a matter of time til the remaining colonies were done
in.
 
What I did was unite the dying colonies (pairs) and got the Apistan strips
in all hives.  The crop was good; too bad I didn't have full quota of
strong colonies for it.  The united sick colonies took all season to build
up again, but each produced 1-1.5 supers surplus.
 
Thanks.