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Photo#1059423
Acrocera sp.? - Acrocera melanderi - female

Acrocera sp.? - Acrocera melanderi - Female
Harris Grade Road, Santa Barbara County, California, USA
April 24, 2015
Size: ~4mm
Found in bishop pine woodland habitat

Images of this individual: tag all
Acrocera sp.? - Acrocera melanderi - female Acrocera sp.? - Acrocera melanderi - female

Moved to Acrocera melanderi
Moved from Pterodontia misella (...where this was temporarily moved by accident!)

Comparing the tangential and oblique dorsal views in this post to Alice's other post, I'm fairly convinced this is indeed A. melanderi. The nearest other candidate from the keys in Sabrosky (1948) and Cole (1919) would be A. bakeri...in which females have nearly the entire dorsum of the abdomen yellow (see Cole's Fig. 34 here). That's certainly not the case here!

Moreover, Sabrosky (1948) provides two figures for the abdominal dorsum pattern in A. "steyskali" (= melanderi)...the first of which (Fig. 1) agrees better with Alice's earlier post; and the second (Fig. 1a) agrees better with this post. The point being that the degree of variation recorded for A. melanderi seems sufficient to accomodate what appears to be the lack of small yellow spots on tergite 2 here (note that tergite 1 is mostly hidden from view under the scutellum in Acrocera).

Oops!
(Inadventently tagged and moved these with some other posts. Trying to do too much at once...please ignore this comment)

Yet another nice find Alice :-)
Moved from Small-headed Flies.

This is definitely Acrocera, from the dainty antennae at top of head; bare eyes; and "obsolete" (i.e. imperceptible) mouthparts.

I wish there were a more recent key and treatment for nearctic Acrocera...but I ran this through the best I know of, Sabrosky(1) (1948). And it was a dej√° vu...Acrocera melanderi:

 

It would be nice to have a more complete view of the pattern of black-on-yellow/orange for the dorsum of the abdomen. But I'm pretty sure that's what this is.

PS: Randy found also found an acrocerid the day after we met with you...caught it "by hand" on the summit of Indian Knob (the high point in the hills south of San Luis Obispo).

 
ID
Thanks Aaron, I was wondering if they were the same. I'm afraid this was the best I could do in terms of dorsal. Do you think this one is a male?

These are always a treat to find! There were Araneus detrimentosus and a Metepeira sp. in the vicinity that could have been potential hosts?

 
Distinguishing males & females in Acrocera
Is this one a male or a female? Good question!

Sabrosky (1944) states on pg. 386 that in Acrocera:

"The abdomen of a male ends bluntly in a fairly large subglobular structure; the female abdomen ends in an elongate tapered ovipositor well illustrated by (Fig. 32 and) Fig. 32a of Cole (1919)."
He also states (on pg. 396):

"...the males and females are distinctly different in appearance, the males being somewhat smaller and having a great deal more yellow to orange color on the dorsum of the abdomen."
And scouring Cole(1) (1919), I found he stated that in Acrocera females have projecting genitalia that are the most conspicuous among all genera in the family. In particular, in Cole's Plate IX, Figs. 27 and 27a show males of A. bulla with a relatively rounded posterior tip; while 27b shows the female genitalia as pointed and projecting.

But (somewhat annoyingly), in the majority of his excellent habitus drawings, Cole did not clarify whether a male or female was being depicted. However, a careful reading of his species discussions indicates most the specimens available to him for examination were females. Indeed, Sabrosky (1944) noted that roughly 3/4's of the nearctic Acrocera previously described were based on females, and sexual dimorphism was a significant point of confusion (with some conspecific males and females being describes as different species). Sabrosky's papers often refer to the excellent drawings Cole's 1919 paper, and clarified the sex for a number of them. If you browse Cole's plates IX through XIII (starting at this link) you'll find most the habitus images depict females...in particular: Figs. 28, 30, 31, 32, 33, 34, 37, and 38. It seems the only male habitus drawings are Figs. 27 and 29. But Fig. 36a indicates the female genitalia of A. obsoleta are (anomalously) small and short (note though that the epithet refers to the obsolete wing venation in this species, rather than the small female genitalia).

The upshot of the above is that male Acrocera have a relatively rounded derière; while females generally have those flattened projecting structures with conspicuous cerci (their ovipositors, or clasping organs, or ??).

In particular, I think it's now clear that your post here is of a female...due to the projecting terminalia and conspicuous cerci.

 
More acrocerids in our area
Alice, I'm glad you delight in finding acrocerids (and are good at it :-)!

FYI, a boatload of Pterodontia johnsoni were collected around Oso Flaco Lake between June and July in the 1950's and 60's.

And a number of other species of Acrocera have been recorded in CA (i.e. bakeri, bulla, convexa, orbicula, subfasciata and perhaps unguiculata.(1)).

Then there are the other genera occuring in our area: Eulonchus, Ocnaea, Ogcodes, and Turbopsebius.

Hope you have the good fortune to run into some more of these and get nice photos in the future! :-)

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