>
> >The only one I am familiar with is the three day, divide by 3 for daily
> drop and treat if in Spring the drop is 5-10, and Fall if 50-60 (which
> seems a bit high with our new info on virus).
>

Bill, natural mite drop is dependent upon colony size and amount of
broodrearing, so difficult to come up with straight numbers.  See Figure 3
at
http://scientificbeekeeping.com/fighting-varroa-reconnaissance-mite-sampling/

Unless you have bees that are highly resistant to viruses, I'd suggest one
of the lower curves for treatment thresholds.

Even then, the threshold is for colony survival over the winter.  Any level
of mites depresses colony buildup and production.  So I hestitate to even
suggest that one allow mite levels to build up at any time of year.

-- 
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com

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