Let's say that 1 colony out of 10 collapses in an area.  A late-summer collapsing colony can contain 30,000 mites.  If only half those mites drift to the other 9 hives, that would be, on average, roughly 1700 mites invading each of the other hives.  That number could easily tip colony health of the other hives.

30,000 mites? Am I missing something?  A big colony would be 30k bees,  at a 25% level the hive is done, spotty brood and DWV has wreaked havoc for weeks already,  that would put the number a lot lower than 30k?  A collapsing colony would have less than 10k bees?  3 mites per bee?  And 1/2  manage to bail to another hive??   

I done a lot of mite washes (nowhere what you have)  never seen anything over 50 on the extreme end of a hive?  







A November collapse involves a smaller number of mites per hive--perhaps 13,000.  Using the same parameters as above, that could cause the drift of an average of 722 mites to each of the surrounding hives, a post-treatment addition that could easily put many of them over the tip point for winter survival.



A November collapse for most of the country results in Zero emigration. By November most of us are in winter and little to zero flights.  Agreed warmer climates may have different problems!  But that’s never part of the discussion.  What most forget (and I understand why) is probably 80% of our mite losses here in the Midwest are in deep winter. Yes,  there is some fall collapse,  but about never in the Aug time frame I hear mentioned a lot.


As mentioned both your math cases assume 1/2 the mites manage to move to another hive, then stopping them from moving should be a big target.  If they are that mobile, then maybe that’s where we should actually be looking.

I would have bet the actual number would be less than 10%.  When that hive collapses,  the majority of those bees don’t move,  they die afield.  By the time robbing comes into play your typical down to a few hundred bees in this part of the country.

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