I have an opinion on this, and it is only that - an opinion. This will show a stance that is debatable, perhaps controversial, but is pretty firmly formed from years of experience and searching and researching. I will not be quoting references nor will I bother putting a flame suit on as I may need to see some heat here anyways ... There is 10in of fresh snow on the ground this morning and -10C. Yet another delay in Spring actually starting here.
imho:
Over the past 40 years since entering North America the varroa mite parasite and its vectored diseases have proven to be indiscriminate and absolutely devastating in their destruction of colonies. Other areas all around the world have the same story. To this end, there can be no actual bonafide feral colonies left. None, gone, non-existent. The colonies that are found and said as `feral`, are simply the result of cast swarms from beekeeper kept hives in the area or from a `feral` hive location that came from last years beekeeper swarms. The feral colonies, all of them, are likely dead in 3 seasons or less just like every other unmanaged colony. It is the swarming from beekeepers hives that continue to repopulate those `feral` hives locations every swarm season.
There is nothing symbiotic about the varroa mite and mellifera. The mite kills completely the colony. The only good that comes of it is that the mites die with the hive. In milder climates some mites do escape that fate by drifting or hitching the last ride out on an absconding (mite bomb) of bees from the dead/dying hive and go on to infect other colonies. In cold climates, like where I am, a fall/winter crash means all the mites die with the bees and we can be blessed with a seemingly clean slate.
When a new swarm moves into the dead-out location, the happy feral hive finder thinks that these bees here must be special mite resistant bees. What a wonderful, exceptional, and earthshattering discovery! Nope, it just an illusion possible only because all the mites died with the demise of the previous colony and the repopulating swarm that moved in did not bring many mites with them.
Now, that opinion does not say that there are not bees which seem more tolerant and able to better cope with mites and diseases than others. As beekeepers we see such traits and are doing our best to find them and promote them. Nature and divine always finds a way through turmoil. Just like many of the diseases that we are struggling with have come from apis cerena, including the varroa mite, furs`, and nosema; it is reasonable to assume that somewhere along the evolutionary tract of western honey bees there may have been a little cerena drone or two that tested their chances with a big mellifera momma in the DCA`s. Such could be a possible source of some of the traits we are seeing from time to time. A chance happening of genetic transference. Just like we know that often that weird mutt of a dog is the best at certain things and out performs its purebred ancestors in its tree; we all have some mutt queens that regularly outperform any lineage we could try to buy from some high chaired bee breeder. There may be hope for the western honeybee. Perhaps it is in the next wizbang of a well funded phd in genetic engineering, by mixing specific DNA strands of the cerena to breed-out / breed-in improved mellifera survivability with the mite.
For now what the opinion says is that at this point in time there is no such sustainable symbiotic coexistence. What we see over and over every 2 to 3 years is a cyclic story of brief periods of utopia between horrific massacres - aka a good year followed by huge colony losses. ALL unmanaged colonies are ultimately destroyed indiscriminately by the parasite and its vectored diseases. Some in their 2nd year, the rest in their 3rd. There are no supermite `feral` bees. There are only bees that have swarmed from young colonies and/or managed colonies which have repopulated feral locations. Take notice I used the term managed, not term treated. There are various ways to manage the mite, treatments are just part of it.
Where did this relationship come from? Evolution selects the fittest and the most adaptable. This mite did not coevolve with the western honeybee. It is a parasite that has switched host, probably multiple times over tens of thousands of years, and it has adapted very well each time. The mite needs to adapt to stop killing its host, and thus itself. The host needs to adapt to tolerate the parasite without completely collapsing. Both species have some evolving to do.