Posted by Kahis on 14-12-2006 20:48
#2
Forget about the colour characters; S. sibirica varies from all-yellow to almost-all black. The 1st sternite is a good character and van Veen illustrates it well on page 207: All other Sphegina species has a well-developed chitinous plate on the ventral side of the base of abdomen (the vaguely 2-lobel thing in fig. 732). S. sibirica has no such plate as shown in fig. 733.