www.ukbutterflies.co.uk

These were all taken at Stelvio Pass where warrenensis is said to fly at this time of year. I believe the majority of these are cacaliae but I do think there is at least one warrenensis among them. I have no underside shots as it was a very hot day, and they weren't at all obliging. They were all smaller than any cacaliae I have seen before, some were tiny.
Anyway, if anyone with experience of Warren's feels able to cast an opinion, here they are with altitude attached...

Checking against Matt Rowling's page on warrenensis, I believe now all except one of the above are that species. I think No 4 is cacaliae. Please put me right if anyone can though

Ok, now having seen Guy's observations in his own diary, I now think I have ONE picture here of Warren's. I would be very grateful for anyone interjecting on this soliloquy, although I think this must be the most difficult of differentiations without being in the field to see them, so understand the silence

Yes - it is very difficult without being there! I promise I will publish my thoughts, but events keep intervening ...

Guy

Not claiming to have any knowledge of these species at all but I would have thought your first photo is the only one that maybe shows something different due to the reduced chequered fringes to both wings