I've heard it mentioned more than once before:
"These queens are treatment free. They will thrive without treatments. But if you do treat, you'll destroy the genetics and they'll never be able to be treatment free again."
How true is that?
If a certain strain of bees is genetically pre-dispositioned in some way to be treatment free (either hygienic, VSH, grooming behavior, high tolerance to mite spread viruses, ect.), how would a change in environment over a short period of time affect those genetics? While some treatments can be very harsh, I can't say any of them affect bees on a genetic level. And with the life span of a worker bee being about 4 weeks in the summer time, theoretically if you treat, and let all the bees be replaced, the current work force should still be just as genetically treatment free as the previous work force.
I can see how over a long period of time if you treat that hive, and they replace their queen from new genetics and mate with other hives near by that are treated, you would be allowing weaker genetics to combine into the mix. But that's long term, over a series of years. Not short term, as in within one season.
I'm aware that some will say "well, if they are treatment free, why treat at all?" Often times in treatment free situations, you have high mite counts, or borderline mite counts, where it's a coin flip as to whether or not the hive will be able to overcome the mites on their own or whether they will crash and die. Assuming allowing them to die is not an option, if you were to treat to help reduce the mite loads (and further spread their potentially partially mite resistant genetics) and keep the colony alive, the apiary might be better off for it (if two partially mite resistant stocks breed together, some might have no mite resistance, others might have super mite resistance, and by allowing it to die the year before you loose that possibility).