Varroa mites never seem to be much of a problem
For the past couple of decades, here in the Marana/Picture Rocks area of Southern Arizona I have never treated, and have had very little problem with mites. Others have made some suggestions as to why this may be. After giving it lots of thought for a few years, my best hypothesis involves the fact that my bees are located on the Northern border of a very large National Park, and the nearest agriculture is at least six, or more miles away in the other direction.
I have been wondering if any other treatment-free bees have been kept in similar conditions for extended periods, and how they have responded.