Drift and robbing can move mites around.  Absconding does happen, but  
its causes and frequency are hard to document and probably highly  
variable- certainly variable when comparing European and African  
derived bees.  Mite reproduction leads to "exponential" growth of  
populations inside susceptible colonies.  How much do all of the above  
contribute to "mite bombs" or to constant pressures from varroa on the  
average colony out there?

It is hard to piece all of the above into one coherent evidence-based  
package of understanding.  "Treatment free" beekeepers and those who  
fail to control mites clearly are a problem for neighbors.  Is that  
the primary source of mite pressure on colonies?  Experiments with  
isolated vs. grouped colonies indicate that the cumulative number of  
mites acquired by colonies from outside sources is relatively small  
compared to the numbers that can potentially be produced by  
reproduction within colonies.  How frequently do infested colonies  
abscond, and how frequently do these absconding colonies move into low  
infestation colonies, and how many mites are in an absconding swarm?   
If one is measuring "number of mites" in a colony by density of mites  
on adults, that "number" can dramatically increase when brood  
production decreases or stops in the fall.  One can play with numbers  
to demonstrate all kinds of outcomes to fit a number of hypotheses.   
Ultimately that is only useful as a guide.

There may also be regional and geographic differences in how all of  
these factors play out.  I get a sense that in "the south" of the US  
"unexplained" surges of mites in colonies are not very frequent,  
whereas in other areas they may be more common, or at least more  
detrimental.

Evidence, experiments, experience to help sort all of this out?



  

             ***********************************************
The BEE-L mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software.  For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html