>It could be attributed to the widespread use of miticides against varroa.
As I recall, tracheal mite was not much affected by amitraz, but is killed
by formic vapors.  Most commercial stocks are alive due to amitraz, not
formic.

>Why would resistance to tracheal mites spread rapidly and comprehensively
while resistance to varroa has not given
similar time frames?

After breeding stock that was strongly resistant to AFB and then tracheal
mite (following Steve Taber's lead), I expected that it would be just as
easy for varroa.  I was wrong.
Resistance to tracheal might be as simple as elongating the setae
protecting the thoracic spiracles.  As Dick points out, this would perhaps
require only selection for a single allele.  Add to this the strong
selective pressure upon the breeding population, due to the high winter
mortality rate due to tracheal mite infestation. This very quickly did the
selection process for the queen producers.

Randy Oliver
Grass Valley, CA
530 277 4450
ScientificBeekeeping.com

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