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1/2 Inch Fly Nectaring - Polybiomyia macquarti - male

1/2 Inch Fly Nectaring - Polybiomyia macquarti - Male
Victoria, Victoria County, Texas, USA
July 18, 2017
Size: 1/2 inch
I kept trying to see this as a wasp till I forced myself to just look at field marks. For a size reference the blooms are 1/8 inches across. I do bees and wasps so my best shot is this is a Genus Physocephala in the thick-headed fly family. Thanks for any help. Paul M.

Moved from Cerioidini.

Likely ID: Polybiomyia macquarti...a new species for BugGuide
From the relatively short frontal prominence (i.e. projection on the head, at base of antennae) the MND(1) indicates this is either Polybiomyia or Sphiximorpha.

Trying to run this photo through the Sphixomorpha key in Thompson(2)(2012) one is led somewhat tentatively to S. willistoni...but there are discrepancies and contradictions here in navigating through couplets 5 and 7 in that key [e.g. microtrichia of the wings & markings on the face are not visible here...and the yellow at the base of the 2nd abdominal segment is not ≤ 1/5 its length].

Furthermore, a careful reading of the detailed original description of S. (=Ceria) willistoni, as well as study of its images on BugGuide, indicates additional descrepancies with the post here in the following significant characters:

1) S. willistoni lacks the pair of large, yellow, prescutellar (="directly anterior to the scutellum") spots seen here;
2) the "petiolate" aspect of the 2nd abdominal segment here is more elongate & narrowly constricted than in S. willistoni images on BugGuide (in my experience, this appears to be a generic distinction between Polybiomyia and Sphiximorpha...though it's not mentioned in the keys of Shannon(1925), the MND(1), nor the MCAD(3));
3) S. willistoni typically has distinctive (though sometimes subtle) pairs of fine, "sideways U"-shaped, yellow markings located laterally on the 3rd and 4th abdominal segments:


...although, uncharacteristically, the current Texas posts on BugGuide lack these "U"-shaped markings;
4) in S. willistoni the antennae are entirely dark (typically black) beyond the reddish basal portion of the first segment, whereas in the post here the terminal portion of the antenna has a clear and relatively bright reddish hue.
In contrast to all the above, if we run the post here through the Polybiomyia key in Shannon (1925), it goes unequivocally to P. macquarti and agrees very well with original description of that species under its earlier synonym Ceria scutellata Williston, 1887.

Note that this is a male, from the holoptic (i.e. touching along top of head) eyes. And, per Shannon's treatment, the two yellow (approximately!) "parallel" & "trapezoidal" spots just anterior to the scutellum are diagnostic of the male in P. macquarti. Shannon also notes that in females of P. macquarti (which have eyes dichoptic, or "well-separated"), the pre-scutellar spot takes the form of a single trapezoidal spot. (Which is consistent with Williston's description of the female...note he did not describe the male.)

This "Nomenclator" page gives the range of P. macquarti as Texas and Mexico. Shannon (1925) gave a specimen record from Brownsville, TX on June 5, 1904; while Hull(1930) gave an August 30th, 1928 specimen record from Beeville, TX (~55 miles sw of location for this post).

Good find, Paul!!

Moved from Syrphid Flies.

Moved for expert attention
Moved from ID Request.

Very cool! I'm pretty sure this belongs here. The Conopids aren't this boldly patterned. I'm thinking Tribe Cerioidini, but I'm not finding a match in the Guide.

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