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Hello Siggi,

yes, it appears that there's a complex now including C. intermedium, lessonae and cisalpinum.

The following is an excerpt of van Veen's key at home.hccnet.nl/mp.van.veen/KEYS/Chrysotoxum/chytox_key.html, which seems to be no mare available:

3.a. Abdominal margin of tergites entirely yellow; antennae: segment 3 of equal length as segment 1+2 together [frons yellow] -> Chrysotoxum cisalpinum Rondani
Note: A marked character of specimens in the Zoological Museum Amsterdam (with abdominal margin entirely yellow and the antennal segment lengths as given above) is that they have a partly yellow frons in both male and female. This would make an easy characteristic against C. intermedium and C. lessonae. Seguy (1961) is cryptic about the male (antennal knob black), but describes for the female that there is a broad yellow band above the antennae. Sack (1932) describes the frons for both sexes as black. To complicate the matter further, some specimens in the ZMA are very close to typical C. cisalpinum, but their abdominal margin is black at the front of each tergite. They have a partly yellow frons. A study of type material is needed to check if both sexes of C. cisalpinum have a partly yellow frons and if the coloration of the abdomenal margin is more variable than assumed by Sack (1932) and Seguy (1961).

3.b. Frons black; abdominal margin black and yellow; antennae: segment 3 distinctly longer than segment 1+2 together -> 4

4.a. Tergite 2: spots form stripes that increase only little in width towards side margin -> Chrysotoxum intermedium Meigen
Jizz: blackish Chrysotoxum, yellow bands run from hind corner of side margin to front middle.

4.b. Tergite 2: spots triangular, increasing in width to cover almost the entire length of the side margin, margin itself black in front, yellow in hind part -> Chrysotoxum lessonae
Note: Addition of C. lessonae in this key is provisional. Sack (1932) is not very clear on this species and the above is also based on collection material of the ZMA.

(In van Veen's Hoverflies of Northwest Europe of 2010 C. lessonae is not listed.)