> I'm also wondering, though, if I picked up a more virulent strain of
> varroa recently.

I pushed for CCD research funding to explore but did not happen.
A more virulent strain would explain many things.

> If there are differing strains, that could explain why bees that seem
> varroa resistant in one region don't show resistance in another and why
> some people can get away without treating and others cannot.

My opinion is simple.
Russian genetics, varroa tolerant genetics (SMR & VSH)
have been introduced.
AHB genetics has been in the U.S. over two decades. it used to be a hive
without the above would survive (not in a commercial setting) two years.
With the introduction of the above plus hygienic bees the above bees are
surviving better.

However as Kirk & I point out little has changed for the commercial
beekeeper. When you push your bees varroa becomes your top problem. We
demand hives at maximum strength. We need uniformity and can not afford to 
take chances.
We check and treat if needed. ( usually is!)

When you grow brood you grow varroa. maybe research could come up with a
market for varroa, SHb grubs & wax moth grubs ? On second thought I would 
not want
to raise SHb grubs! Smells like vomit!

bob

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