If an infested colony contained say 40,000 bees at 50% infestation rate of the adult bees (reasonable for a collapsing colony), then that hive would contain 20,000 infested adult bees.  If 5% of them drifted during 2 weeks, that would be 2000 mites being transferred to other colonies by drifting alone (not counting robbing).

2000 mites being transmitted to adjacent colonies over a 2 week period of time is still a lot of immigration.


Yup  2000 would be a lot,  but unless things are a lot different there,  Here you would never see  a 40 k hive at 50%   if you did a 40 k hive does not get robbed out!

The math doesn't work.  Lets say  We use your numbers  20k mites  And 5% drift.   First you have to cut the 20k  down to 10  as only half of your 5% are infested.  That gets you to 2.5% of the drifters are infected.    Also need to factor in that roughly only 1/3 of those are actually foragers likely to drift.  Numbers drop again.  Realistically the possible drift number is much closer to 500  max.   Now you assume they all go to the same hive!    


Here in the Midwest,  typically mite collapse hits in fall,  numbers drop in the hive,  and overwinter losses abound as the hives are small and unhealthy.  Fall/ summer collapse does happen,  but rarer,  follows the same path.  Hive numbers drop as replacement brood is not surviving.  Robbing is usually not a big problem as the hive has dwindled down to nothing over the period of a few weeks.  Stores are low,  brood nonexistent.  Here in MANY MANY cases  beetles get you long before this point.

Typical collapsing hive here will have far less than 10k bees.  At a 30% or infestation.  Most mites end up on the dead bees,  not out and about.  Also normally Mites are on nurse bees not foragers.   What is eluded to is that mites suddenly decide to go "walk about" and change from nurse bees to foragers en mass.  And then  apparently   those infected foragers decide  again, en mass  to join other hives.

I do seriously belive that one factor in the increase in mites is related to the decrease in bees...  same mites/fewer bees = higher rate.


Does some immigration occur?  Without a doubt.  Enough to tip a hive, a healthy hive??  I can't see it.

For example last year was one of the best I had for mites.  In the fall lots of really low numbers including a LOT of zeros.... (not sure why yet)....  one stands out very loudly...  12 hives on pallets in that yard (3 4 way pallets)  One hive tested at 16% in sept.   The other 11 hives  tested at zero or 1.  Literally mite free.  All hives were less than 4 feet apart.  I elected not to treat any of them.  Let the one die  and see how the others did.    Exactly what happened,  no measurable spike in the other 12,  and as predicted the 1 crashed in winter.


What set me off this time as mentioned was a article that claimed a 4 fold increase from immigration.   What we do with that  (besides its not even close to right) is lead people to believe its "not their hive"  but the neighbors problems....bad idea....

Not to mention we may be missing a real potential issue in mite control.  If we understood the fall increase  we might be able to exploit it.

Charles

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