Hello Richard & All,
Richard wrote:
 If the bees become Varroa resistant, how can the survive as feral bees with
 tracheal mites? So,, how do we know what is happening in the feral
population?
Most of what we have learned in recent years about feral colonies has come
from the trap lines run across the southern U.S. in a attempt to check  for
Africanized bees. U.S. bees have in many areas adjusted to tracheal mites.
Italian bees seem more likely to die from tracheal mites than other strains.
Why we are not sure but I believe the Italians are affected by tracheal
mites more than other strains.
As far as feral colonies it is impossible to know every person keeping bees
in your area in most cases. People see bees and think they are feral. If you
see a bee tree then that's different. However the swarm in the tree might
have only swarmed into the tree a week before from a local treated  hive.
Bees are still swarming . Many breeders say they can breed out swarming. The
main causes of swarming can not be bred out.
Sincerely,
Bob Harrison
Odessa, Missouri