[Syrphidae] Sphegina

[Anne Vallet]

I want first to apologize for my english. I will try to explain as clear
as possible my problem.
You know that in December 1999, a storm damaged an important part of the
forest in France. The Forest Office tries to save a maximum of trees and
set up special areas to keep trunks safe. To prevent xylophagous and
mycophagous attacks, they sprinkle permanently water on it.
Last June, I have been call on one of this area because the neighbours
complain about insects. I put a Malaise trap to check which insects are
presents. I was really surprise when I check the bottle: half of it was
Sphegina sp. I start to count it. I trapped around 4000 females (for
more that 2/3 of it, you can see eggs inside the abdomen) and “only” 150
males. With the genitalia, I can say that most of them are S. clunipes
but I have some others species.
I heart about Syrphidae pullulement only with Episyrphus balteatus and
Scaeva pyrastri. Is it a common phenomenon? Is somebody already notices
Sphegina pullulement in other habitat?
May be men create a new habitat for this species….