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Photo#974154
Diplazon laetatorius - Hover fly parasite? - female

Diplazon laetatorius - Hover fly parasite? - Female
Renton, King County, Washington, USA
August 8, 2014
(Updates, mainly retitling and added comment, 11/29/17)

Was unclear whether this wasp was looking to eat aphids (almost looks like it might have one here), or whether it was doing some ovipositing (not sure that's a true word) in some of these, but at one point I saw it with it's abdomen in such a position as if it might be doing some "drilling/piercing"... did not catch the picture in time). It kept flying around nearby cattail reads that were had heavy aphid investations.

Images of this individual: tag all
Diplazon laetatorius - Hover fly parasite? - female Diplazon laetatorius - Hover fly parasite? - female

Moved
Parasitoid of aphidophagous Syrphidae, larvae of which were presumably amont the aphids.

Moved from ID Request.

 
Reconsideration...
Trying to follow-up on some Hymenoptera not originally classified to genus or species.

To me (untrained and rather unknowledgeable), I wonder if this is Diplazon laetatorius - Hover fly parasite.

I did some googling just for "aphid wasp" to see what might come up, and found another Bugguide entry for this species, then went through many of them to compare. To my eyes, looked rather similar, but somebody that knows something best look. Some pictures made it appear they might be trying to deposit eggs in aphids, or perhaps unseen hover fly larva.

Thanks.

 
I have seen rather small grub
I have seen rather small grub-like larva among the masses of aphids, although these are larger than the aphids, are white, and some appear to have a dark cap or head. One without such a feature was found moving around on one of the cattail reeds. (Maybe I will post the comparative shots - I suppose they could be one of dozens of things)

Here are the grub-live larva I refer to - posted separately.
Unidentified Larva

 
Larval Head
I expect that the larva without the black head capsule is likely that of a syrphid.