Parnassius apollo subspecies

For online resources, perhaps the best known is Parnassius of the World goran.waldeck.se/ but it hasn't been updated since 2009.

If you have access to them, there are the series of books on Parnassius by Dietz (P. apollo was published in 2000 so is even older) and Parnassiinae of the World (Weiss part 4, 2005 and Rose & Weiss part 5, 2011).

Of course, validity of subspecies is often subjective, particularly in Parnassius apollo.

Adam.