> I also have doubts about Medhat's shaker for alcohol wash after I tried 
> rewashing the same samples a number of times and coming up with a 
> different result each time. At least some of the mites are trapped in 
> among the bee bodies when straining the liquid through the screen.

I'm glad you mentioned that.  I use one 48 times a day when I am inspecting, 
and I have noticed that the technique enters into the results.  So does the 
weather or the location of the planets or something.  It seems some mites 
just hold on harder some days and, as you say, it is a little tricky making 
sure the mites do not get filtered by the dead bees.

That, incidentally is an argument for using 200 bees instead of 300, and if 
you are doing your own bees often, and more than one hive, maybe just 100 
would do.  Of course your statistical accuracy drops fairly quickly with 
sample size, but I ask myself, how accurate do I have to be when the counts 
are over 3 per 100 bees?  Especially if I see that in more than one hive?  I 
can always repeat the test right away to verify or to average.

At any rate, on the job I shake the 300 bee sample several times and take 
the largest number of mites I see.  Some days every shake of the same sample 
gives the same number, sometimes not.  No matter, the result is close.  The 
lab takes the samples our field guys have shaken and marked and say that we 
see 90% of the mites.  The scatter chart that Medhat made up shows some 
variance, but it is not too bad.

> I also find it rather difficult counting mites looking up into the liquid, 
> and rather slow trying to shake and count samples in the beeyard.

We shake one minute and then count.  It takes another minute for the mites 
to settle and if you need glasses like I do some days, then the stingers, 
etc. can confuse the issue.  As I say, I shake each sample again --  
sometimes three times -- to see what kind of day this is going to be and if 
I always get the same number one minute is all it takes, BUT our samples are 
re-counted at the lab.

>I prefer taking a number of samples to be alcohol washed carefully later at 
>home, the liquid pored into a white bottomed container where mites are 
>easily seen and counted.

I guess if you want to be really accurate, but we do six hives in a yard and 
if any one of them shakes more than 6 mites, you can be pretty sure the 
beekeeper is going to do something to all hives.  Maybe not right away, but 
sometime soon and maybe do all the yards if the matter is not clear.  As my 
friend Bob will tell you, in commercial beekeeping exceptions are not 
tolerated for long.

We're dealing with big commercial guys with an average of about five 
thousand hives each and they don't fool around.  They have a few windows to 
treat and if IPM monitoring shows that there are hot spots, they don't have 
time to try to guess which hives have problems and find out later they were 
wrong, or waste precious time in a short window of opportunity.

Those with a few hives can use the same sampling technique, but may want to 
zero in on individual hives.  In that case, accuracy of individual samples 
is more important, but IMO, it all comes down to a binary output (worry or 
don't worry) that is not much affected by an error of even 20%, and, used 
properly, this tool is accurate within 15%, 95 times out of 100.

(95% of all statistics are made up on the spot). 

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