Randy said
>that varroa populations grow to
lethal levels in untreated "naive" colonies of Apis mellifera.<

One thing that I see in my small apiary is it is pretty easy to work around the varroa and not need any treatments. I wouldn't say that they are resistant more like somewhat tolerant as long as I stick with the bees' natural cycles and processes.

Last year I bought two outside nucs on June 1st to add variety to the mix. By the end of Sept they were dead due to Varroa. I have to say that I had never seen any colony collapse like these two nucs. They did come from an operation that treats for varroa. It is also my understanding that this operation sustained severe losses last winter. One of the interesting observations was one of my existing colonies robbed one of the nucs as it was collapsing. The robbing colony is as healthy now as before the robbing incident and I expect it to overwinter well.

It seemed in my limited experience that the nucs crashed because of treatments retarding brood development which in turn severely increased the exponential growth rate of the varroa. 

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