> do you have any method to relate the 3 day mite drop numbers to the 
> average number of mites per bee for the colony ? The mite drop numbers 
> will depend greatly on the size of the colony whereas they should be 
> independent of colony size for the sugar roll or alcohol wash methods.

Good points.  Any time I checked natural drop against the wash, I have seen 
"good enough" correlation.

Personally, I just use 100 days for an estimated varroa average natural 
lifespan and estimate the colony population by looking at the frames of bees 
and considering the ambient temperature and did a little math.

It helps to know how much brood is in the colony, and whether they are 
cleaning out drone brood as well as other things which might affect the 
drop.

I discussed this on Sept 26, 2009 at
http://www.honeybeeworld.com/diary/2009/diary092009.htm
and other places on my website, since at one time, when I was running 
thousands of hives, it was my sole monitoring method.

I think the most important thing to keep in mind is why we are estimating 
the varroa load, and what accuracy we actually require.  For my personal 
purposes in my own yards, I am just looking for potential disasters and plan 
to use oxalic on all.  A formic flash treatment or two might not hurt 
either, but I have not done that for years.

I like drop boards simply because they show that mites are dropping and are 
another way, along with eyeballing bees for DWV and  riders, to keep an eye 
on things non-destructively.  As mentioned before, the Apinovar bottoms look 
to me to be a very elegant solution for the small beekeeper.  The links 
below have some good info.

http://www.apinovar.com/
http://www.apinovar.com/articles/FAQ_APINOVAR_en.pdf
 

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