I am quite certain that varroa resistance or tolerance has evolved numerous times around North America, but economic pressures and movement of bees and queens repeatedly dilutes or outcompetes the varroa tolerant strains.
Also, bees that are tolerant or resistant may not have the characteristics that commercial or hobby beekeepers seek and may not produce much honey. They may be culled or replaced by beekeepers who do not recognize them as such.
Recognizing these qualities in individual hives in an operation requires much more thorough and frequent testing than most beekeepers are likely to want to do.
Ask Randy.
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