#6
Hi Pierre-Nicolas.
It is in fundamental book Insecta of European part of USSR, 1970, vol.5, part2. At my experience it still works ok if you than check current name.
I have PDF copy to send, but it is in Russian.
Nikita
#8
Hi Pierre-Nicolas
The book Nikita mentions (Insecta of European part of USSR, 1970, vol.5) has been produced in an English version. I'll see if I can make a pdf of Gorodkov's key to send to you. I'm sure if this is not legal, someone will tell me!

Alternatively you may be able to get the two volumes that cover the Diptera (volume 5, parts 1 and 2) second-hand. The English version was produced by the Smithsonian in 1988. They may still have copies available.