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It seems to me that this fly is not Urophora cardui. This one was less (4-5mm). Moscow region, july.

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Dear Nikita,

You 're absolutely right! It's not Urophora cardui, which has a different wing-pattern. The species with the kind of wing-pattern as photographed are abundant in the Palearctic, and very difficult to identify. To be sure you should extract the aculeus of the female and look at its apex, the last 0,1 mm!
One of the most common species, at least here in Europe, with this kind of wing-pattern is U. solstitialis. But since I can't have a look at the aculeus, you'll never be sure about it.

Best wishes,

John Smit

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Thank you John. But one more question. How did you distinguish genus Urophora from Rhagoletis ?

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Hi Nikita,

By sight! ;)
There is a marked difference, but you'll need a good magnification of the wingbase. The genus Urophora belongs to the subfamily Myopitinae which is characterised by the convex closed Anal cel, whereas all other subfamilies have a more or less pronounced triangular distal extension at the bottom side of the anal cel.
But as I said you'll need a good magnification of the wingbase, in your picture here it's impossible to tell.

Best wishes,

John

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John, thank you for your patient explanation.
Photografers who send me images on www.Rosfoto.ru and me myself thought that a fly with such unusual wing colour have to be easyly identified till species.
If I know the limit of my current knowledge - it is a good step forward too.
So, thank you once more.
Nikita