>I don't know why this should be illogical.  Varroa mites, like all
biological
>organisms,  make up a population of widely varying individuals.  This is
>evidenced by the observation that 98% (or some such number) of varroa are
>killed by the standard Apistan treatment.  Why is it not 100%?  Because of
this
>natural variation, following the same bell-shaped curve used to describe
the
>size of leaves on a tree or the performance of students on an examination.


For the mites to breed resistance a genetic mutation must exist before, or
come into existence during a period of selection pressure (Apistan strips).
This mutation must produce a trait that will allow that subset of the
population to reproduce when the others do not. If the resistance is in the
mites genetics then introducing a different pressure (Mite-Check) could
knock down the population with the first resistant trait. However there
could be other issues.

The chemical in Apistan requires contact with the mites to work. A 98% kill
rate could mean that 2% of the bees that carry the mite will not get near
the strips. The chemical in Mite-Check advertises a lower kill ratio than
Apistan. It could therefore be the case that given the same number of bees
carrying mites come into contact with the strip, fewer of the attached mites
will die. It could be the case that more bees avoid the Mite-Check strips.

Selection can work for behavior as well as chemical tolerance. For example
mites could select for a trait that causes them to attach to bees in such a
way as to avoid contact with strips. This is along the same lines that
selects bees for hygienic behavior. It is the actions of the individual that
promote survival rather than a metabolic resistance to a chemical.

An example of this was in the roach traps that contained two simple sugars
as bait and a toxin to kill the bug that ate the bait. The roaches developed
a surviving population that were not controlled by the traps. The reason was
not that they became immune to the toxin, but that they avoided one of the
simple sugars in the trap. When the trap was redesigned to use only the
other sugar, the resistant population came back under control.

In any event since Mite-Check leaves a residual population that can start a
selection process for resistance. In this case there is no reason that the
survivors will not be resistant to both Apistan and Mite-Check.

My thoughts are that a method to deal with resistant mites should involve
pressures not related to strips. One method mentioned is the drone brood
trapping. Formic acid could become another. Who knows maybe a pheromone trap
for mites could be developed where a "fake" frame of drone brood (using the
pheromones that attract mites to drones) is inserted into the hive and 48
hours later removed along with the mites ready to lay eggs.