If a coloney is left compleetly to its own devices, seeley says 8 years and still going. Even if the question may seem to be left to their own device, it may really mean, left to thier own devices as far as mites are concerned. There are plenty of studies on this that do not make three years the end result or 1000 mites the death threshold. On an island of managed bees they were regularly living with over 40 percent mite threasholds. There is a lot more to do with it then it only works one way. Location, the bees, the virus load, etc etc.
There are bees and places where it also works just like LJ says. You don't know with your bees untill they are tried. When trying they may die just like they die in some places up to 80 percent even when treating. There are alway exceptions to the rules on all sides. There are studies on all sides. The only way to know for sure where you are is to try and to adjust to what ever your bees tell you after trying.
LJ is correct on what the mite modles people have come up with but there are other factors that can effect those modles.
Some of those factors are understood and some are not.
There is antidoltal evidence that people do better then that and are happy with the results they obtain. Somebody else may look and say that I would not be happy with that. It is probly not a good ideal to allow other people to decide what makes you happy. I bought the only bees I have ever bought from a guy who has had bees for 20 years and does not treat for mites. I was told that if I kept those bees like the guy I bought them from, I should have the same success he has. The question then becomes and I happy with that level of success?
It does not work the same every where cause you can not control all the external things that are around you. LJ's advice is probly good more then not but is not the only advice for every place out there. I may or may not be best where you are. In the end, I still say you don't know till you try.
I am starting my third year. I start it knowing and even expecting my bees to die. They are alive right now and looking good. If I was in seeleys forrest, I would be expecting some of the established hives to die but not all of them.
Cheers
gww
Ps There is a need to get unstuck on some definition of what does treatment free mean and get more stuck on the definition of what does personal success mean.