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Photo#503319
Ceriini? - Sphiximorpha - female

Ceriini? - Sphiximorpha - Female
Tucson Botanical Gardens, Tucson, Pima County, Arizona, USA
March 30, 2011
Size: ~8-10 mm
Pretty sure I have the right family (Syrphidae), and maybe tribe (Ceriini), but hoping for confirmation or maybe even a genus. Thank you.

More developments
I recently happened upon another interesting cerioidine find & photo of Eric's on Flickr...taken in the same general area as the above (a few miles away) and about 3 months later. It shows a male that's very similar looking to the female here, except it has a yellow (rather than black) scutellum. At first sight it appeared to me to have a significantly longer & narrower "waist"...but when I measured the length & (posterior) width of the 2nd tergite (from the image on screen, zoomed-in) both measurements were roughly the same.

I also bumped into another very interesting iNaturalist post by Isaac Krone from Organ Pipe National Monmument (114 miles to the WSW of Tucson). It shows a female that looks very similar to both of Eric's posts...and Isaac's female has a yellow scutellum like Eric's male post, and in contrast to the black scutellum of Eric's female here. So if they were all to turn out to be the same species, the yellow vs. black scutellum color would not be an instance of sexual dimorphism, but rather intra-species variation.

Revisiting the early key in Williston(1892), it seems all three of these posts would best go to "Ceria" meadei, and are in fair (though somewhat "iffy") agreement with Williston's 1892 description thereof. The "iffy" aspects are:

1) the ambiguity of having different-colored scutella (black in the Eric's female & yellow in the other two). Note that Williston didn't specifically mention the color of the scutellum, although he did indicate the thorax was black overall except for yellow of the humeri and sutures. And it appears his description was based on 3 males.
2) Williston described meadei as having the 3rd abdominal segment with a "biarcuate golden-pollinose band" in front of its posterior yellow band (cf. his Fig. 12 here)...whereas those golden-pollinose bands appear uniform in width in Eric's and Isaac's posts.
However, using the key to Sphiximorpha on pg. 5 of Thompson(2012), Eric's male & Isaac's female would seem to go to "S. currani" based on their yellow scutella...except that Thompson's key also indicates "currani" has yellow legs, whereas all 3 cerioidines in Eric's & Isaac's posts have black legs! [Note also that, unfortunately, "S. currani" is a nomen nudum and thus not a recognized scientific name, as explained in my comment under Isaac's iNat post. ]

Apart from the vexing issues of scutellum & leg color, the three photos discussed here look so similar it would seem they must be closely related...and (depending on how one were to go about interpreting "intra- vs. inter-species variation") perhaps the same species?

Likely Sphiximorpha meadei...a new species for BugGuide!
Just revisiting this post...following much more time, effort, and experience studying Cerioidini.

And the first thing that struck me was the very stout abdomen...in particular having 2nd segment with posterior margin appreciably wider than the length of the segment, and its basal margin quite narrowed. By now, this strikes my as a fairly consistent secondary character of Sphiximorpha...at least for nearctic Cerioidini. (And it has the advantage of being discernible without a view of the metacoxal bridge! ;-).

That prompted me to revisit the Sphiximorpha key on pg. 5 of Thompson(2012), wherein I realized this goes reasonably in that key to S. meadei (note, I actually measured the antennifer from the zoomed-in image on my screen here and, contrary to my initial visual impression, it was indeed greater than 1/3 the length of the 1st antennal segment). I'd previously discounted S. meadei here since the terminal couplet indicated "Mexico (Guerrero*)", and Guerrero is tropical and fairly far away from Tucson.

But revisiting Williston(1892) this again keys to Ceria (=Sphiximorpha) meadei, and agrees impressively well with Williston's description!

Unfortunately S. meadei appears to be a very rare species...I could find nothing substantial about it via web searches, and no specimens are listed for it in the online databases for CAS or the Essig Museum. The type is said to be at the British Museum.

Although Eric photographed this far from Guerrero, I think it may indeed be S. meadei.

PS: The eyes appear well-separated here, indicating a female.

Something new in either Sphiximorpha or Polybiomyia?
Since the frontal prominence is short here, this is presumably either Sphiximorpha or Polybiomyia. Unfortunately, as in nearly every "in-the-wild" photo like this on BugGuide, the technical character separating the two genera (membranous vs. sclerotized connective bridge between the hind coxae) is not discernible here. So what is the basis for assuming Sphiximorpha rather than Polybiomyia here?

In the most recent key for Sphiximorpha in Thompson(2012), there are only 2 species listed as occurring in Arizona: S. loewi (Williston) 1887, and S. currani Thompson 2011. Thompson's key indicates the latter has a yellow scutellum and yellow legs...while the former is described (by Williston) as also having a yellow scutellum, though it appears more rufous in the post below, which otherwise agrees quite well with Williston's original description of Ceria loewi:

   

So...since the scutellum in the photo here is black, presumably this is not one of the known species of Sphiximorpha.

On the other hand, this doesn't seem to key out well in Shannon's key for Polybiomyia either. P. engelhardti appears to be the best (though imperfect) fit, but again it's indicated to have a yellow scutellum. And the 2nd best fit, P. pedicellata has 3rd abdominal segment longer than wide (see BOLD image here), which doesn't fit here.

Thus, whether it's Sphiximorpha or Polybiomyia...it seems this may be an undescribed (i.e. "new") species.

Moved
Moved from Syrphid Flies.

Yes
Looks like a Sphiximorpha sp., but not one that's already in the guide.... Nice find Eric!
Greetings

Cropped and moved for expert attention.
Moved from ID Request.