Thread subject: Diptera.info :: Chrysotoxum elegans?

Posted by Sundew on 03-07-2020 22:02
#3

Chrysotoxum is difficult for sure, especially if the pictures do not show the necessary characters... Each key, e.g. this https://books.goo...&hl=de, starts with the length relations of the three antennal segments (3 longer or as long as 1+2, or 3 shorter than 1+2). I think we have the first case here, so Ch. elegans is out. Then, we have to estimate the length of hairs on tergites 3 and 4. I cannot see them. However, "hairs very short, tergites seemingly bare" would lead us to Ch. intermedium, which looks clearly different. So we have to assume that there are "long hairs". That leads to three species: cautum, arcuatum, fasciolatum. Now again the antenna segments are important: in cautum, 3 is as long as 1+2 and 1 is shorter than 2. (Besides, the cautum female has a longitudinal membraneous strip on tergite 6 - but there is no picture of the abdomen tip.) It seems that segment 3 is longer than 1+2, so the candidates are arcuatum or fasciolatum. Size would tell them apart, but you didn't mention it. Then, the key says that fasciolatum has a dark spot in the top wing half, which your fly has, too. However, the yellow stripes look very straight in this species (https://www.galer...asciolatum), and the abdomen is more elongate. Shape and abdominal pattern of your fly would match better with arcuatum, but, as you see, there is much uncertainty!
Regards, Sundew
P.S. Never forget to tell the locality! "Living room" is not enough, country is better :D.