I grew up on a farm on which the apiary and all connected with it was a major part of the farm's output. Honey, beeswax, nukes (a queen and 10K or so worker bees as a starter colony, sold to other apiaries in the spring if they'd had too many winter losses), fertilizing services (drop a couple colonies off at a berry farm after dark, pick the colonies up two weeks later, profit!) and other products.

It's been over ten years since I spent any serious time with bees, but the bees themselves did a great job on the varroa mites. Sentinel bees at the hive entrance would pick the mites off the incoming bees. The problem was if the colony had a solid floor the mites would just climb back onto the next bee that passed nearby. If the solid colony floor was replaced with a mesh, the mites would fall through to the ground below while the bees could still go about their business.

We would still sometimes treat for varroa, but making it easier for the bees to handle varroa how they had evolved to was the first line of defence.

This was Canada, regular Italian bees, hard winter kills of whatever wasn't properly winterized.