I suspect the same shift happens when a varroa infested colony swarms.   I've seen some heavily infested captured swarms.  And I've seen bees vacate a colony when heavily infested with mites.

             ***********************************************
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