If a trait is really useful in Nature it is not likely to be lost. If human, breeder selection produces queens with useful traits, those bees will also need to have all the other traits that make them suited to the environments in which we keep them. If not, we will be in a constant cycle of needing to buy new queens from those special sources. I know that approach already suits many people, but some of us would prefer to be able to sustain our own stocks of bees.
I agree with all that.
Treatment is limiting, slowing down or obstructing the acquisition of resistance to mites, but it isn't preventing it.
Its not easy to set this out... but...
If/where bees gain no benefit from adapting to varroa, they won't adapt. The required behaviours take time and energy (not much, but evolution is very into fine-tuning - waste can be a matter of life or death).
So what are the circumstances under which isolated, treated apiary bees might gain resistance? One way would be light treatment that would expose the less capable, but...
... that would only have the required effect under a program of replacing poor queens with queens from strong hives.
You need that positive breeding (or letting nature do that for you) and it must be, always, always, be a continuous process. (To be able to do that of course you need to be able to distinguish the more from the less resistant. Systematic treating will blind you to that.)
In that way, you are pressing in the right direction. (Find, and then 'make best from best' as the husbandryman's maxim goes)
But in the absence of that ongoing process, the only way treated bees will gain resistance is from local adapted free living drones. And if there are too many treated bees around there probably won't be any of those!
That's roughing things out. In reality is a case of 'the more this, the less that'.
