>
> >Doing a very rough conversion, assuming steady-state and using a 100-day
> mite time to live, that gives us a 5000 mite number, mostly phoretic at that
> date, I assume.


Allen, I feel that your total mite estimate is likely a bit high.  I checked
with various conversions, e.g.,
https://secure.fera.defra.gov.uk/beebase/public/BeeDiseases/varroaCalculator.cfm

and come up with estimates of 2500-3500.

>
> >Anyhow, this is very rough, so take the 5,000 and a late October
> population of 30,000 (8 lbs. of bees) and we get 5/30=17%.


So phoretic infestation level may well be as little as half  of your rough
calc, or 8%.  However, your estimate of 30,000 bees may also be high, which
would then raise the infestation percent (this is one reason that I prefer
alcohol wash to natural mite drop).

>I think that any commercial beekeeper could have saved him the effort, and
most would halve that number or quarter it.

He wasn't trying to see determine a threshold, that figure simply came out
of the data from the control and non miticide treated hives.  Below 50
mites, a substantial number survived and made grade in almonds.  Above that,
you might as well save yourself effort and walk away from them.

>
> >Seems we calculate differently.  I'd be interested in how 20-30 converts
> to 3%. in your situation.  I gather we are using different assumptions.


See above.


> > I checked the drop against washes in my outfit last year and got a good
> fit with my method and timing, albeit on a small sample.


I have done on a larger scale, and came up with a coefficient of correlation
near zero!  Really surprised me.  That was when I gave up on natural mite
drop as being meaningful if not taken over a long series.

>
> > I guess that answers my questions about history and location.
>

This was separate from Frank's trial.  His was  in southern California
hills, well south of Bakersfield.

>
> >One huge caveat in this is the use of packages.  They are a special case,
> and seem to have less vulnerability to varroa collapse than overwintered
> colonies, possibly due to different virus profiles (which is confirmed
> anecdotally).  I suppose that may explain why most of us would think hat 50
> is twice too high and maybe 4X.
>

Sorry if I misled.  Eischen's data was separate from the CAP project, which
was packages.  Eischen's was with commercial migratory hives.  However, I
agree with you on the virus issue!

Randy Oliver

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