No more bragging for me--one of my hives has taken a significant dip in population and I went through it today to condense them down because there was too much comb for them to take care of. Now it has 10 frames fully populated and good amount of brood, and 2 medium frames of honey and pollen, and the balance is empty frames in the medium. In combining, there was an errant piece of brood comb which I cut out and it had 5 capped drone cells on it. When I was all done with the hive I checked those 5 drone cells and 3 of 5 had mites.

The hive is about 3 feet, then 5 feet, 7 feet, from other hives. Do I need to worry about mite spread? In this small area of 5 hives I've noticed starting since last fall they are not doing as well as 5 hives about 50 feet away. The only mite checks I ever do is the drone cell check, which last fall every hive was fine. I don't treat, obviously. Any advice?
Thanks.