Trevor Weatherhead said:

> But A. cerana is also able to tolerate V. destructor
> and A. mellifera is in the situation where V. jacobsoni will not
> reproduce on.

> Nor will V. destructor reproduce on A. cerana that is the natural
> host of V. jacobsoni and V. jacobsoni will not reproduce on the
> A. cerana that is the natural host of V. destructor.

> Why will V. destructor reproduce, quite successfully, on A. mellifera
> whereas V. jacobsoni will not?

There has been much confusion.  This should help clear up some of it.
Here's results from actual hands-on experiments by someone who:

a)  Knew up front that he was dealing with
     two very different mites and two very
     different bees

b)  Took an approach completely free of
     fuzzy thinking

c)  Explained himself and his tests in plain English.
     (Overall, excellent work.  I don't know the fellow,
     but we each owe him at least a beer.)

http://www.agralin.nl/wda/abstracts/ab3010.html

Which says, in part:

  "Differential reproduction of mites in both host-species,
   A. cerana and A. mellifera, seems to be a key factor in
   susceptibility of honey bees to Varroa (Buchler, 1994;
   Rosenkranz & Engels, 1994).

   In European A. mellifera colonies mites reproduce in
   both worker and drone brood and mite numbers increase
   rapidly.

   In colonies of... A. cerana, mites invade both types of
   brood cells but refrain from reproducing in worker cells
   (Boot et al., 1997).

   Thus, in A. cerana mite numbers can only increase when
   drones are being reared. In African and africanised A.
   mellifera races a high percentage of mites that invade
   worker brood also refrain from reproducing (Camazine, 1986;
   Ritter, 1993).

   Therefore, like A. cerana, African and africanised honey bees
   are less susceptible to Varroa.

   I studied whether refraining from reproduction in worker brood is
   due to a trait of the honey bee or due to a trait of the mite (Chapter 6).
   By transferring Varroa mites originating from A. mellifera colonies to
   A. cerana worker brood and vice versa there appeared to be two distinct
   mite populations with a different reproductive strategy.

   Mites originating from A. mellifera reproduced in worker brood in both
   species of honey bee, whereas mites originating from A. cerana
   reproduced in drone brood only. Later, genetic studies of Varroa mites
   (Anderson & Trueman, 2000) made clear that the two [mite] populations in
   fact belong to different species. The mites that parasitise Western honey
   bees originate from Korea and Japan and were erroneously called V.
   jacobsoni and have been recently named V. destructor (Anderson &
   Trueman, 2000).

Regardless, the entire question is more than a bit of a non-sequitor.
While mites (including V. destructor) may carry diseases, they are
not a disease in themselves.  The original question attempted to
apply a theory about microbiological forms of life (viruses, et al) to
macrobiological forms of life (bees and mites).

Viruses and other microbiological forms of life can go through a
"generation" in the time it takes you to read this sentence.
Therefore, they can mutate, "adapt", and "evolve" much much more
quickly than mites and/or bees.

How long have bees remained essentially unchanged?  Longer than
most living things currently on the planet.  Did bees somehow learn
to "adapt" to tracheal mites?  No.  Bees had to be cross-bred to
create even slight advantages.

        jim

        farmageddon