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Moscow region, 27 apr, 5-6mm, on birch jus.
I think - Chaetorellia, but inside genus I can't choise species.

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Hi!

It's Chetostoma stackelbergi!

By change I collected one of these from Lohja in southern Finland a few days ago. The species was found in Finland for the first time only a few years ago, but since then several new finds have surfaced from several sites in southern and central parts of this country. It may be an authentic new arrival here. I have trouble believing that the old masters would have missed such a large (for a tephritid) and boldly patterned fly. The flying time is mid-spring in Finland (ie. right now), making it twice as conspicuous among the otherwise rather dull spring fauna. Perhaps the gradual climate change with earlier springs in N Europe has allowed this beautiful and biologically interting species to expand it's distribution.

According to Merz's book on Central European tephritis this species is rare everywhere and usually found only as single specimens. It's definitely a good find! Hooray for BlackB)

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I'm idiot. When I see Black's fly it came to my mind that I've seen somewhere illustration of this very fly. And soon I found it in Diptera of Europ. Part of Russia. It was Chetostoma stakelbergi, but the illustration was placed inside key for genus Chaetorellia. One Chaeto-something and another Chaeto-samething. Of course, searching in genus Chaetorellia lead me to nothing. Even size was abnormaly large for all Chaetorellia.
Thank you Kahis. Black may be sure that he is author of unic live photo of Chaetostoma stakelbergi! So does my Rosfoto collection!
Nikita

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Wow, it's nice to learn that I've found something rather unusual.

This specific specimen was not only drinking birch sap but also flying around and maybe laying eggs (it was actually a fresh stump, just 20m off a railroad embankment). It quickly left when disturbed (by my shadow I suppose) but returned soon.

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Dear Black, Nikita and Kahis,

This is a really great encounter!
As Merz (1994) states this species is really rare all over.
Moreover nothing is known on its biology, the same counts for most other species of Chetostoma. It is thought that the European species are connected with Lonycera, presumably in the fruits. Its charming sisterspecies C. curvinerve is found more often recently in western Europe. But also for this species it is not known where the larvae live. For this latter it is however known that the adults hibernate trough winter and can be found in autumn and (early) spring up to June. Perhaps this is the same with C. stackelbergi?? In any case do either of you know wether Lonycera was near the place you found the specimen? For it is unlikely that she would have laid here eggs in a birch stump, she was probably only feeding on the sapruns.

Cheers,

John

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To John Smit: As regards Lonicera, the answer's yes there definitely grows Lonicera xylosteum.

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Hi Black,

Thanks. That more or less confirms yet another rumour!

John