?> After a few years without treatment something changes where the mites 
seem less virulent.

Just very anecdotal and not all scientific:

I had an interesting thing happen this year.  In the last few years, I have 
been splitting as much as a I can with the goal of producing bees and 
avoiding producing honey.  Each fall, I treated with a single drizzle of 
oxalic acid and had sufficient control that my mite levels were in the 5% 
level or less each fall at the end of brood rearing.

At the end of last year I noticed that AFB was creeping up on me and this 
spring I treated all hives with tylosin as recommended, then, later treated 
with OTC since OTC hits things that tylosin misses. The bees looked good 
after that, and AFB was totally gone.  Patterns which had been getting 
spotty improved. (I had been adding hygienic and supposedly varroa tolerant 
stock).

This fall, I noticed what looked like EFB. while filling feeders at the end 
of a day.  "That is strange", I thought, since EFB is usually a spring 
condition around here, and I can't recall having seen it in my bees ever.  I 
did not bother to take a very close look, since I was feeding and had a yard 
to finish and figured if it was EFB an OTC dusting would fix it.  EFB 
responds to OTC well.

Then about two weeks? later, I noticed that a powerful hive collapsed since 
last visit.  It was the one where I had seen the 'EFB', and I realised that 
maybe I was seeing something else.  I got out the shaker and got high 
numbers -- 15-1/2%, 12%, and 22% in nearby hives.  I quit testing at that 
point and started dialling for Apivar.

Anyhow, every season is different: last year I made honey in spite of 
myself.  This year I did not.  This year I split a bit more drastically and 
the weather in August turned out to be bad.  There are other things, too, 
BUT I'm wondering if this one thing, treating with antibiotics somehow 
tipped the balance in favour of the varroa.  Maybe varroa mites have 
bacterial enemies.  Maybe tylosin is a growth promoter for varroa, just as 
it is for hogs.  Maybe the antibiotics resulted in less hygienic action by 
the bees.  Maybe tylosin had nothing to do with anything except the better 
patterns and absence of AFB.

Anyhow, I wonder if there is a relationship.  If so it should not be hard to 
prove., unless it only shows up where AFB is also present.

I know, Peter.  Don't bother saying it :) 

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