>>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.

> I was watching  Diana Samammatero's presentation on beneficial microflora 
> in honey bee colonies and this comment by you came to mind. Looks like it 
> could line up with your thinking in that it may be directly or indirectly 
> related.
> http://www.extension.org/pages/ABRC2010_Beneficial_Microflora_in_Honey_Bee_Colonies

Thanks for the link.  I had heard that Diana had said some  interesting 
things and took in two different talks by her at that same conference. 
Apparently this talk was one I missed.  The others were more general, 
speculative-sounding and omitted the slides of the syrup, supplement and 
pollen feeding experiments (or else I must have dozed off?).  This 
presentation as more specific and scientific.  I had been waiting for 
something more than 'may' and 'possibly', and this presentation was more 
definite, although I notice that she is careful not to suggest that we know 
much.

(I have noticed that scientists often tailor the presentation to the 
audience and have been very disappointed by a talk by a noted speaker in one 
session, then blown away in a subsequent one later the same day in a 
different session).

I guess we all know that there are microorganisms associated with pretty 
well everything, but the ecology is so complex that we have a hard time 
knowing which are beneficial and which are harmful and which are not or even 
if these value judgements can be made since the effects are so interrelated 
and may only appear under specific conditions.  Even with our high-powered 
and effective medicine, there can be side-effects which are unpredictable.

Obviously when we introduce chemicals into a bee hive, we are unhappy with 
some aspect of the current equilibrium and expect to change the balance in 
the hive in a direction we favour.  It seems, though, that as with many 
things there may be unintended consequences.

Of course, in regard the varroa bloom, I am speculating wildly.

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