The common understanding of the 'introduction' of tracheal mites (Acarapis woodi) into honey bee stocks....I believe is wrong. The picture painted is that this 'new' parasite spread throughout Europe, devastating bee colonies....and some decades later found its way to North America. 
The relationship between tracheal mites and honey bees is quite sophisticated. You have an obligate parasite (i.e. one that requires a host for reproduction) and, in this case only one suitable host. Furthermore the parasite has developed the ability to identify young worker bees...a necessity for successful reproduction. The requirement for a unique host and complex behaviors necessary to reproduce successfully within that host didn't evolve overnight, within a decade or even a century, in my opinion. This was not a 'new' parasite.
I believe that there were isolated stocks of Apis mellifera in Europe that had coevolved with tracheal mites. During the eighteenth and nineteenth centuries, when a mix of bees were being imported into North America, I expect that some of those coevolved and adapted bees  were part of that movement.
Then, in Europe, in the early twentieth century some of those adapted bees, with background levels of tracheal mites were introduced into areas where non adapted bees existed...triggering what became known as the Isle of Wight outbreak. 
In North America, periodically the adapted bees with tmites intermingled with some non adapted bees causing what were documented as outbreaks of dwindling and other inexplicable regional collapses. 
In the twentieth century, decades after the ban on bee imports, those adapted bees found their way into mainstream North American beekeeping triggering our tracheal mite outbreak. The non adapted bees failed and those with resistance were propagated. 
I'm sure I'll hear all sorts of reasons why this scenario couldn't fit. In my opinion, it has more merit than the idea that this single host dependant parasite mysteriously appeared out of nowhere and by random coincidence bee stocks were 'discovered' that could coexist with it.

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