Thread subject: :: Chrysotoxum cautum? --> Chrysotoxum cf. verralli

Posted by HTK on 27-06-2022 23:03

Wasp-like syrphid visiting bindweed flowers on a sunny margin at the base of the renatured old mining dump at Landweiler-Reden (Saarland, Germany) on 18 June 2022. Size about 13 to 15 mm. Obviously one of the Chrysotoxum species, which are rather difficult to separate. I would suggest Chrysotoxum cautum (relative length of the antennal segments, shape and amount of yellow markings on the abdomen). Can this be confirmed? I have slightly rephrased the question, added another picture and am looking forward to your opinion.

Image 1

Edited by HTK on 07-07-2022 21:04

Posted by HTK on 27-06-2022 23:03

Image 2

Posted by HTK on 27-06-2022 23:04

Image 3

Posted by HTK on 27-06-2022 23:04

Image 4

Posted by HTK on 01-07-2022 20:26

Image 5

Posted by treebeard on 05-07-2022 13:57

Pictures are not large enough to measure antenna segments (in Ch. cautum the 3rd segment should be as large as other two segments together - it does not seem to be the case of your picture), however, my impression is Chrysotoxum verralli (yellow strips on tergites are triangular).

Ch. cautum's abdomen has a different pattern.

Best regards, Matej (not an expert)

Posted by HTK on 07-07-2022 21:01

Hello Matej,
thank you very much for your helpful comments. It's certainly no coincidence that Ball and Morris speak of the "difficult five" with the two species under discussion among them.
Kind regards,
Hans Theo

Edited by HTK on 07-07-2022 21:02

Posted by HTK on 11-07-2022 14:24

Hallo Matej,
this is to let you know that Ximo Mengual, who is a syrphid expert, in the meantime had a closer look at the pictures and confirms your view. He definitely excludes Chrysotoxum cautum. His comments:
- C. cautum has the scutellum yellow, with a transparent marking in the center; your specimen has a clear black marking on scutellum.
- C. cautum has the basoflagellomere (postpedicel) almost equal in length as scape and pedicel together; your specimen has the postpedicel shorter than pedicel+scape.
Ximo also thinks that the photographed specimen looks very much like Chrysotoxum verralli.
Best wishes,
Hans Theo

Edited by HTK on 11-07-2022 14:25