Caucasian Honey Bees (Apis mellifera caucasica) originated in the mountain range and valleys of the Caucasus. The climate varies considerably and the local strains have adapted to suit.
Caucasians have the reputation for having the longest tongues of the Western honey bee sub-species, but it doesn't seem to have given the bees much benefit. They are also reputed to be great collectors and users of propolis. Bearing in mind the recent discoveries about heavy propolis collectors being healthier, Caucasians are said to have poor resistance to nosema (probably N apis), although accounts vary.
Brood rearing is reckoned to start late, with low swarming tendency. They are no longer as popular as they once were. In my early years I handled what I was told were Caucasians, but I haven't seen any pure ones for some time.
Caucasian queens were imported into the U.K in large numbers by Mr Abbott (possibly Arthur) of Mountain Grey Apiaries, Brough, Yorkshire (liquidation 4 November 1966) from 1926 onwards. I remember them still advertising later than that when a man called J.E. (Eddie) Eade was involved, so I assume he bought the assets from the liquidator.