Bob asked for fossil proof of varroa mite and bees cohabited for
millions of years. We don't have that, of course, but in the genes of
various creatures is the equivalent of a fossil record of how long
they have been around and to which other species they may be related.

Differences in species and differences in types within species are
reflected by differences in the genetic makeup. Comparing these
differences allows us to estimate the age of various similar species
and speculate on when they may have arisen from a common ancestor. For
example, it is assumed that the various honey bee species arose from a
common ancestor, which no longer exists. It may have been a tropical
bee in Africa which spread to other parts of the world. Not only are
there now other species in Europe and Asia but these species are
separated out into types (also known as races). Using the molecular
clock, estimates can be made as to how many thousands or millions of
years have elapsed for these changes to take place.

Similarly, varroa mites have speciated and branched into different
types. Studying the genetic information points to varroa mites being
associated with different bee types long enough to co-evolve. In other
words, bees in India are different from bees in Sumatra and the varroa
mites on them are also different, suggesting that these populations
have been separate for a very long time but also that the bees and
their mites have been together for a very long time as well. On the
other hand, European bees have acquired varroa mites only recently and
therefore they have had the devastating effect of an invasive pest. As
an example, the rate of mutation and time of separation of just the
Korean and Japanese lineages of Varroa destructor has been estimated.
The time of coexistence of varroa mites and honey bees is no doubt far
longer.

> Considering that mutations within each type have occurred in the past 50
years, and that the two types have different alleles at many loci, our data
allow estimation of the divergence time of the two types. For a large set of
parameters, estimates fall in an interval of 5000–15000 years.  -- from "The
invasive Korea and Japan types of Varroa destructor, ectoparasitic mites of
the Western honeybee (Apis mellifera), are two partly isolated clones". Proc
Biol Sci. 2005 February 22; 272(1561): 411–419.

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