>
> >I think the thresholds are the same for the Minnesota sugar shake and for
> alcohol wash if they are done correctly.


In my experimentation, I found it hard to recover as many mites by sugar
shake as by alcohol wash--usu. about 70%, so I'd use a lower threshold for
sugar shake.


> >I've done a lot of alcohol washes and mite drops and have to say that any
> one reading may not have any direct relationship to another from the same
> hive or to the true situation in any one hive.


As a result of our discussion on this subject some months ago, I've been
collecting data to compare the two of late--natural 24-hr drops vs alcohol
washes of 1/2 cup of bees taken from the first non brood frame next to the
broodnest (to lessen the chance of getting the queen)--paired measurements
from each hive.  Data from 16 hives over the month of August, when mite
levels were high (mite washes of up to 63/300 bees, or 21% infestation),
each colony sampled 4 times over that time period.

Have plotted all out over time.  Mite washes were very steady in all but 3
hives, in which the counts increased steadily over the last two washes.
 Natural drops, on the other hand, jogged up and down, often changing by a
factor of 2.

When I plotted all pairs of mite infestation measurement (n = 48), there
was scant correlation (r sq = 0.06).  The problem was that in many cases,
there was virtually no natural mite drop from seriously infested colonies
(e.g. wash of 63 mites, drop of 13 mites).

All colonies were actively rearing brood, so can't blame on lack of
broodrearing.

Nine of the 48 natural drops were 13 or fewer mites--the OMFA threshold for
August is 12 mites.
Only 1 of the alcohol washes was under 3 mites per 100 bees (8/300)--the
OMFA threshold.

I'll be publishing all data at some point, but thought that it would be of
interest to the List.  The take home to me was that I couldn't count on
natural drop to reliably indicate severe mite infestations.  I also found
that mite washes were generally consistent  week to week for any hive
 during August.

>It also suggests a threshold that makes me shudder: The Minnesota poster
> says "If your colony has over 10-12 mites/100 bees, you should consider
> treatment.
>

That figure would be a calculated figure if brood were present--doubling
the value of the sugar roll, so a sugar roll of 5-6 mites per 100 bees.
 This is the level at which I see DWV start to go epidemic in the brood
(not necessarily and deformed wing bees)..

>
>  > where I live, in my opinion and the opinion of successful beekeepers I
> know, the Minnesota recommendation would, with great probability, lead to
> disaster in a large outfit -- especially if that was a spring count, and
> far less so if that count was found after all brood had hatched in fall.
>

I'm in agreement!
-- 
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com

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