Research on Varroa in Feral Colonies
In the November 2017 issue of American Bee Journal, Tom Seeley of Cornell University reports on feral bee research he conducted recently ("How a Population of Wild Honey Bee Colonies Living in New York State is Surviving with Varroa", American Bee Journal, November 2017, p1183-1187). In the 1970's he conducted a census of beehives in the Arnot Forest near Ithaca, NY, where Cornell is located. After varroa mites invaded the area, he lost about 90% of his managed hives and assumed that the feral hives had been decimated.
In 2010-2016, he returned to the forest and did a census of feral bee colonies. The surprising results were that the number of hives was essentially the same as in the 1970's, even though the hives had varroa mites. The bees had developed the ability to coexist with the varroa.
Seeley has not published the full results of his research yet - hopefully it will be in an upcoming issue of American Bee Journal - be we can make some guesses.
It has been reported by multiple researchers that about 10% of European bee hives exhibit Varroa Sensitive Hygiene (VSH). Left alone, such as in the wild, these hives will survive and will throw off swarms. Eventually, we would expect that essentially all feral hives will exhibit VSH because any hive that does not will be destroyed by the varroa.
Think about what that means. Beekeepers who keep non-VSH bees, and treat for varroa, are maintaining and propagating the non-VSH genes. If all beekeepers would switch to feral bees with VSH characteristics, the non-VSH genes would no longer be propagated and we wouldn't have to worry about treating for varroa.
As Pogo said, "We have met the enemy and he is us."