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Tribe Cerioidini

Ceriini Syrphid - Ceriana tridens - male Puzzling! Not even sure it's a syrphid. Your take? - Ceriana tridens - male Syrphid - Sphiximorpha willistoni fly 151 - Polybiomyia - female   - Sphiximorpha willistoni - female Syrphidae - Ceriana tridens - male pupa - Sphiximorpha willistoni Ceriana tridens? - Ceriana tridens
Classification
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Hexapoda (Hexapods)
Class Insecta (Insects)
Order Diptera (Flies)
No Taxon ("Aschiza")
Family Syrphidae (Syrphid Flies)
Subfamily Eristalinae
Tribe Cerioidini
Numbers
4 genera in our area:  Ceriana,  Monoceromyia,  Polybiomyia, and Sphixomorpha.
The generic circumscription adopted on BugGuide is that of (1), (2),(3), and Van Steenis et. al. (2016). [Note though that all taxa treated as genera in the Guide, are treated in (4) as subgenera of a single cerioidine genus Ceriana (sensu lato).]
"Cerioidini is surely monophyletic, but the generic limits get a bit difficult on a worldwide basis." --Martin Hauser, pers. comm. to =v= 20.i.2012
Identification
The most salient character for Cerioidini is the distinct projection at the top of face (or base of the frons), called the "frontal prominence" or "antennifer" (see images here, from (1)). The frontal prominence is very long in Ceriana and Monoceromyia; but relatively short in Polybiomyia and Sphixomorpha...in the latter it can be simply a large "bump".
All Cerioidini have antennae with a terminal "style" (rather than a dorsal arista) and most also have somewhat elongate and basally constricted (i.e. "petiolate") abdomens: only very mildly so in Ceriana, but more so in most Sphixomorpha; and conspicuously so in most Polybiomyia, and especially in Monoceromyia.
The wings of Cerioidini have cross-vein "r-m" meeting the discal cell "dm" beyond its middle, and (as with all Syrphidae) a "spurious vein" (labelled "sv" in the wing venation diagram below):

In Cerioidini, females have eyes well-separated; males have eyes which touch at the middle of the top of the head.
Below are labelled images to help in referring to various parts of cerioidine flies:
         
Note that photos providing views of the sides of the thorax are helpful for species ID, since the pattern/location of (usually) yellow spots there is diagnostic.
Identification keys for Cerioidini:
Key to nearctic genera of Cerioidini in(1) begins at this couplet.Key to world-wide genera on pg. 161 of Van Steenis et. al.(2016).Key to species in Shannon(1925)...not currently available online, but the keys for "Tenthredomyia"=Ceriana and Polybiomyia appear here and here.Key to "Cerioides" species in Curran(1924) (incomplete, and some species names used there are older synonyms, but includes many spp. from Ceriana, Sphixomorpha, and Polybiomyia per current circumscription...together with fairly detailed descriptions of each species treated).Key to species of Sphiximorpha in Thompson(5)(2012).
Habitat
Larvae (and adults) found within (respectively, on) tree bark, near sap-runs. Adults also found visiting flowers, or resting nearby to them.
Food
Larvae live mostly within tree sap associated with tree wounds or "putrifying pockets of water in tree cavities" [Heiss(1938), pg. 16]. The larvae presumably feed by filtering other organisms within the sap (e.g. bacteria).
Adults feed at flowers, and some have been observed feeding on sap.
[Note: Larvae of some species found in Mexico (which could possibly also occur in the southwestern U.S.) feed on the sap of Agave spp., in particular near wounds. And larvae of at least two Australian species (C. mellivora and C. ornata) are known to feed in bee hives on larval provisions (though apparently not the bee larvae themselves)...see here and here. Such behavior is not known outside Australia.]
Life Cycle
Larvae are associated with tree sap near wounds or cavities in bark or wood (e.g. due to mechanical breakage, wood-borers, etc). Adults are often found on bark near sap-runs, where: 1) mating takes place; 2) males sometimes defend territories; and 3) females oviposit on the bark (or cracks therein). Adults also visit flowers to feed, like most syrphids.
See Also
Most often, Cerioidini are mistaken for wasps...for which they are remarkably effective mimics! That mimicry is enhanced by their: 1) unusually long and stout antennae, which...like most wasps...are geniculate (= angled at the middle); 2) relatively long and basally constricted (or "petiolate") abdomens; 3) color patterning of the body; 4) anterior darkening (infuscation) of the wings; and 5) their behavior (i.e. moving antennae up and down, waving of forelegs, etc.).   [Waldbauer(1970)]
Even when recognized by observers as being flies (e.g. from having 2 wings and halteres), Cerioidini are often mistaken for thick-headed flies of the subfamily Conopinae.
But in contrast to Conopinae, members of Cerioidini have: 1) a distinct (though sometimes short) projection at the top of face (the "frontal prominence"); 2) males with eyes touching in the middle; and 3) distinctly different wing venation...including the "spurious vein" characteristic of Syrphidae (though many conopinae also have a "spurious vein").
Additionally, Conopinae will not typically be found lingering on tree bark.
Print References
Adams, C. F. (1904). Notes on and descriptions of North American Diptera. Univ. of Kans. Sci. Bulletin 2: 447 (Full Text - Orig. Desc. of "Sphiximorpha" snowi, now Ceriana)
Coquillett, D. W. (1902). New cyclorhaphous Diptera from Mexico and New Mexico. Canad. Ent. 34: 195-202. (Full Text - Orig. Desc. of "Sphiximorpha" ancoralis, now Ceriana)
Curran, C. H. (1921). Genus Ceria pp. 174-176 in: New species of Syrphidae. Canad. Ent. 53: 15:171-176 (Full Text)
Curran, C. H. (1924). Subfamily Cerioidinae, Genus Cerioides in: Contribution to a monograph of the American Syrphidae from North of Mexico. Univ. of Kansas Sci. Bull. 15:77-216 (Full Text)
Curran, C. H. (1941). Genus Cerioides pp 243-247 in: New American Syrphidae (Diptera). American Museum Novitates, 519 (Full Text)
Davidson, W. M. (1926). A new Californian syrphid (Diptera). Ent. News 37:40-42. (Full Text - Orig. Desc. of "Ceriodes" durani, now Sphiximorpha)
Heiss, E. M. (1938). A classification of the larvae and puparia of the Syrphidae of Illinois exclusive of aquatic forms. Univ. Ill. Bull. 36: 1-142. (Full text)
Hull, F. M. (1930). Some Notes and Descriptions of Cerioidine Wasp-waisted Flies (Syrphidæ, Diptera). Psyche 37(2):178-181 (Full Text)
Hull, F. M. (1935). Some mimetic flies, with description of two new species from North America (Syrphidae: Diptera). Psyche 42: 99-102. (Full Text)
Ichikawa, T. & O’Hara, K. (2009). Adult behaviors in two species of cerioidine flies, Primocerioides petri (Hervé-Bazin) and Ceriana japonica (Shiraki) (Diptera, Syrphidae). Technical bulletin of the Faculty of Agriculture, Kagawa University, 61, pp. 1-10 (Translation from Japanese into English here, sans figures)
Kahl, P. H. (1897). New species of the syrhpid genera Mixograster Macq. and Ceria Fabr., with notes. Kansas University Quarterly, 6:137-146. (Full Text)
Loew, H. (1853). Neue Beiträge zur Kenntniss der Dipteren. Berlin. E. S. Mittler & Sohn. (Full Text)
Loew, H. (1864). Díptera Americae septentrionalis indigena. Centuria quinta. Berlin. Ent. Ztschr. 8: 49-104. (Full Text)
Loew, H. (1872). Diptera Americae septentrionalis indígena. Centuria decima. Berlin. Ent. Ztschr. 16: 49-115. (Full Text)
Ricarte A., Marcos-García M., Rotheray G., Hancock E. (2007). The early stages and breeding sites of 10 Cerioidini flies (Diptera: Syrphidae). Ann. Ent. Soc. Am. 100: 914-924 (Full text)
Rotheray, G.E., Hancock, E.G., & Maier, C.T. (1998). Two Ceriana species (Diptera: Syrphidae) breeding in exuded tree sap. Entomologist's Monthly Magazine, Vol. 134: 223-228 (Full Text)
Shannon, R.C. (1922). A Reclassification of the Subfamilies and Genera of the North American Syrphidae. Bull. Brooklyn Entomol. Soc. 17: 30-42. (Full Text)
Shannon, R.C. (1925) The syrphid–flies of the subfamily Ceriodinae in the U.S. National Museum Collection. Insecutor Inscitiae Menstruus, No. 13, 48–65.
Snow, W. A. (1895). Diptera of Colorado and New Mexico. Syrphidae. Kans. Univ. Quart. 3: 225-247. (Full Text - Orig. Desc. of "Ceria" townsendi, now Polybiomyia)
Thompson F.C. (2012). Fabulous flower flies for famous fly fanatics (Diptera: Syrphidae). Can. Entomol. 144: 1-16
Van Steenis, J., Ricarte, A., Vujic, A., Birtele, D., & Speight, M. (2016). Revision of the West-Palaearctic species of the tribe Cerioidini (Diptera, Syrphidae). Zootaxa 4196(2):151-209 (Full Text)
Waldbauer, G. P. (1970). Mimicry of hymenopteran antennae by Syrphidae. Psyche 77:45-49. (Full Text)
Williston, S. W. (1886). Ceria on pp. 259-265 in: Synopsis of North American Syrphidae. Bull. U.S. Natl. Museum, 31:1-335 (Full Text)
Williston, S. W. (1892). Ceria. Biol. Centr.-Amer., Dipt., Vol III, pp. 76-78 (Full Text)
Works Cited
1.Key to the genera of nearctic Syrphidae
Miranda G.F.G, Young A.D., Locke M.M., Marshall S.A., Skevington J.H., Thompson F.C. 2013. Can. J. Arthropod Identification 23: 1-351.
2.Manual of Nearctic Diptera Volume 2
Varies for each chapter; edited by J.F. McAlpine, B.V. Petersen, G.E. Shewell, H.J. Teskey, J.R. Vockeroth, D.M. Wood. 1987. Research Branch Agriculture Canada.
3.Manual of Central American Diptera
Brian V. Brown et al. 2009. NRC Research Press.
4.Skevington J.H. (2014) Nearctic Syrphidae checklist
5.Fabulous flower flies for famous fly fanatics (Diptera: Syrphidae). A tribute to the dipterists of the CNC
Thompson F.C. 2012. Can. Entomol. 144: 1-16.