>>What exactly is the mechanism by which the oxalic acid in the 
trickle method kills mites?

I've heard mixed opinions with most theorizing that bees ingest the 
solution during the clean-up after trickling.

>>...whether to crack the boxes in two box hives, which is fairly 
intrusive to a nicely sealed and tightly clustered unit.

I avoid having to separate my hive bodies - I also overwinter in 2 
deeps - by cracking the bottom deep lose from the bottom board and 
inverting the 2-deep combo on a fork lift lowered to the ground.  
With the bottom deep now facing up, I can trickle the OA solution 
into the bottom deep.

>>How would ingestion work???

The theory (I am not aware of conclusive research) is that the 
ingested solution makes the bees' blood pH more acidic.  Tolerable to 
the bees but too acidic to the mites.  When the mites feed on the 
treated bees' blood, they drop dead.

>>...even strong colonies did not not have many "lines of bees".

I believe this is all right.  The bees are concentrated and just 
about all will be exposed to the solution.

>>I understood that oxalic trickle could be done at cold 
temperatures.  Is that correct???

As others have said, the ambient temperature is not a significant 
factor.  The warm temperature in the clusters should allow for a good 
distribution of the solution among the bees as long as the solution 
gets passed the outer layer of bees...  I am thinking: in the cold 
temps the cold solution may kill some outer-layer bees although this 
kill may be insignificant.

Waldemar

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