Diptera.info

Posted by nielsyese on 25-05-2021 08:53

Good morning,
I'm struggling with the difference between Diasemocera marginella and D. roederi. I have the key from Zatwarnacki (2018) Solving the puzzle of taxonomic position of the petroleum fly by resurrection of Diasemocera from Psilopa (Diptera:Ephydridae) with proposed specific and generic synonymies.

It says:
Wing hyaline in cell cua1->D. marginella
Wing darkened in cell cua1, posteriorly to vein M4 -> D. roederi

The problem is that I don't know where to find cell cua1 and vein m4? Can anybody explain this? The photo's don't look quite different to me either.:|

Edited by nielsyese on 25-05-2021 08:57

Posted by Tony Irwin on 25-05-2021 09:59

Neils-Jan - I think it's best to ignore Tadek's key, and compare his figs 49 and 50. If you don't have them, let me know and I'll send them to you. (Cell cua1 is posterior to the one you have marked on your drawing.)

Posted by nielsyese on 25-05-2021 12:01

I'm not quite sure I understand it. I have the photos of Zatwarnicki.

If I understand it well now, I don't have to look for a darkening like as dark as the spots in the wings, but the difference is about the slightly dark tinge in the cell on the picture, with the red arrow ? (picture taken by Ludwig Jansen on https://waarnemingen.be/observation/149474722/)

There are a few Dutch records of Psilopa marginella on waarneming.nl, for example:
https://waarnemin...188840005/
https://waarnemin...187296566/
https://waarnemin...187333977/

These might be P. roederi then, or is it impossible to say?
I'm sorry for the questions, maybe it is a bit silly I don't understand it well, even with the pictures of Zatwarnicki in fornt of me.:S

Posted by Tony Irwin on 25-05-2021 14:04

I think that this wing is marginella, based on the angle of crossvein M-Cu and that the dark spot over crossvein R-M does not extend into cell bm/dm (that is the pale cell with crossvein M-Cu at its distal end). It does not help that many individuals of marginella have abbreviated wings, which can affect the venation and markings. Using the male genitalia to check the identification is sensible.
The specimens photographed in the field are more difficult to assign, but I suspect they are all roederi, as it appears that the dark spot over R-M extends across cell bm/dm.