Other than three years where I tried treating for Varroa, I've never treated for anything since 1974 and I haven't treated any hives for anything since 2003. I treated those three years because the causes of my 100% losses were obviously Varroa. Some winters I have really high losses, but they are the same percent as the people who treat around me. A really cold winter is a hard winter. I do post mortems on my lost hives and I don't see hardly any Varroa. But bees have certainly gotten harder to keep alive since Varroa arrived.