The point was that the threshold can be much lower in
> different locations.

This is true up to a point. Randy Oliver and I were puzzled by the above. 
Then I made a correlation between nosema ceranae spore count and the hive 
crashing with what would seem a low varroa load.
Every hive crashing with what I would consider a below threshold ( by my 
standards ) had a high nosema spore count.

In my opinion the bees can handle a fairly high varroa count unless the 
nosema ceranae spore count is also high.

I must admit it took me a long time to figure out but eventually I saw a 
pattern.

Control of varroa and nosema ceranae is essential in commercial beekeeping 
today. Mainly because of feed lot beekeeping and holding yards of thousands 
of hives only feet apart.

fluvalinate varroa controls are not effective today for the most part and 
most commercial beekeepers are using formic acid. Control with formic acid 
is hard compared to the days when apistan and coumaphos worked.

Migratory beeks doing pollination do not want honey as honey makes hives 
heavy and trucks overweight.
Because many go for months without putting a super on a hive the main issue 
is health of the colony and controlling pests. Many of these beeks end up in 
the Dakotas and many of these hives are in poor shape. Too weak to gather a 
crop of honey. However by fall on strong lows they slowly rid the hive of 
poison pollen picked up in pollination. Mostly related to imidacloprid 
treated seed. One beek lost all his hives in zucchini pollination.  Being 
moved into almonds and then one pollination after another for months is hard 
on hives. Some look great when they arrive in the Dakotas but some are 
barely alive. The great ones produce honey and the others limp along and 
most build until its time to head back to California for the start of 
another season.

Those which say they can control varroa with a single dose of OA once a year 
are not doing the above. As I said in an earlier post some beeks are 
treating four times a year for varroa. In fact David Vanderdusen told us at 
the ABF convention that he recommended a miteaway treatment every four 
months in migratory operation with intense brood rearing.

I went home and tested and found in my hives five months was the most I 
could go without treating using miteaway 2  before varroa loads crashed the 
hive. *if* because of weather or another reason you did not get a good 
control with the formic treatment before one might have hives over threshold 
in less than four months. Three?

Beeks are buying miteaway 2 today by the pallet of four fifty five gallon 
barrels of pads.And who knows about the others.

bob

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