> I am starting to do alcohol washes in preparation for late summer
> treatment.  I washed 3 bee yards today and saw a good bit of variability
> with numbers ranging from 0 to 10.  The good news is I did not see any
> really high numbers.

What do you have for comparison?  If you have last year's numbers, and 
your survival was good -- or poor -- that might be a clue.  Also 
benchmarks may be available for your locale.

A lot depends on how well the washes were done.  I've seen a factor of 
ten difference between two samples taken in the same hive, one on a 
patch of actual brood just ready to seal, located in the bottom brood 
box, and a sample taken on what looked like a reasonable patch of brood 
comb in the upper box right above that spot, maybe ten inches away.

At this time in the north, brood rearing is at its maximum, so most of 
the mites would not show up in an alcohol wash.  Moreover drone rearing 
is peaking and there will be an explosion in mite numbers as the drones 
emerge.

A lot can happen between now and the end of summer.

I do not know your region, but up here I would be expecting trouble by 
September.

As for treating one or all, that depends on your hive numbers and 
ability or willingness to manage detail and re-test.

If using formic, a round of the whole yard would be a good idea as it 
gets the tracheal mites too, and testing for tracheal is too fiddly for 
most beekeepers, but they are there with some probability.  I seem to 
recall you use the Amrine board?  If so, that is an easy treatment and 
not too hard on the bees from what I have heard.

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