In this video expert beekeeper David Heaf clearly explains why many natural beekeepers do not treat their bees with acids, sugar dusting or pesticides to counter Varroa mites. I know many conventional beekeepers are also no longer treating.
Of the many untreated colonies I know, wild or managed, it appears that tolerance to varroa in bees is not rare, but the journey to getting a tolerant apiary is not easy. Some of these untreated colonies are more than 10 years old.
I like to think that in their 20 million years of evolution, bees have encountered similar problems before and many retain the genetic answers to the problem, but only if we do not interfere with the natural process.