Vockeroth, J.R. (1969) A revision of the genera of the Syrphini (Diptera: Syrphidae). Memoirs of the Entomological Society of Canada 62, 176 pp.
Citrogramma quadricornutum Vockeroth
Very distinct species with face entirely yellow and large male genitalia. Unique Citrogramma species with metasternum bare, and it also has scutellum with a broad defined black macula, scutum with two metallic bluish vittae, and 2nd, 3rd, 4th and 5th abdominal terga with posterior bluish metallic dark vittae. In general, C. quadricornutum is a small species with the most extensive bluish metallic areas in its body, on frons, scutum, pleuron and abdomen.
Adapted from original description (Vockeroth 1969).
Head: Facial tubercle rather broad, weak, indistinct above and below. Face, front, gena, and about lower fifth of occiput yellow; face and front with a broad, non-pollinose, somewhat translucent median vitta, face laterally densely pollinose; gena with a broad black anterior vitta from eye to oral margin, sometimes obscurely darker behind this vitta. Occiput otherwise black, black pilose on upper fifth, otherwise white-haired, grey pollinose, with denser grey pollen behind eyes on about median 2/3. Vertical triangle black, subshining, black pilose. Front, and face immediately beside antenna, black pilose; remainder of face, and gena, white pilose. Antenna yellow-orange, basoflagellomere brownish dorsally; arista black.
Thorax: Scutum with disc opaque black with two broad subshining steel blue vittae; laterally with broad entire pale yellow vitta, not broader than postpronotum and only slightly broader than notopleuron; from just before posterior end of notopleuron yellow vitta is separated from scutal margin by a narrow opaque blackish-brown vitta. Scutellum yellow with blackish-brown opaque basal triangle which is basally as broad as dark scutal marking, the yellow margin much broader laterally than medially, the extreme anteroventral angles of scutellum brown. Pleura black, subshining, faintly greyish pollinose, the extensive yellow areas much as in notiale except that the anepimeron is entirely black on the anterior half and brownish on the posteroventral fourth. Scutal pile on dark portion of disc and on postalar callus black and rather sparse and coarse, on yellow margin yellow, on brown lateral vitta brownish. Scutellar pile black, coarse and sparse, those on the margin almost bristle-like. Pleural pile yellowish white. Subscutellar fringe black, very sparse, absent on median 1/3 to 1/4, of only four or five hairs on each side. Dorsal katepisternal pile patch triangular, restricted to dorsal half of katepisternum, very broadly separated from the very small ventral patch. Hypopleuron (meron) without hairs in front of spiracle. Metasternum bare. Wings with alula very slightly narrowed, of uniform width throughout most of its length. Membrane with small bare areas as follows: most of cell R in front of spurious vein, less than anterior half of cell BM, extreme anterior margin of alula. Stigma dark brown; costal and subcostal cells, and extreme wing base, pale brown. Legs: Pro- and mesolegs irregularly yellow-brown, the procoxae yellow, the femora sometimes darkened above, the tarsi almost black; metacoxa and trochanter yellow, rest of metaleg blackish-brown to brown. Pile of legs rather short and sparse, a short posteroventral row near apex of metafemur rather bristle-like, pile otherwise not distinctive.
Abdomen narrower than thorax, almost parallel-sided, very slightly broadened beyond tergum 2, with a weak but broad margin only on tergum 5. Tergum 1 blue-black, shining, narrowly yellow laterally. Tergum 2 shining blue-black anteriorly, with a narrowly divided yellow fascia on anterior half, each half triangular, transverse posteriorly, broadened laterally, produced narrowly forward laterally to base of tergum, yellow fascia followed by an opaque black transverse fascia and a shining blue-black transverse fascia, each of which occupies about 1/4 of tergum. Tergum 3 with successively a very narrow blue-black shining fascia, a very narrow opaque black fascia, a slightly broader yellow fascia, a still broader opaque black fascia, and a somewhat narrower blue-black shining fascia. Terga 4 and 5 similar to 3 but the anterior shining band very reduced, the yellow band sometimes very narrowly divided and, on tergum 5, extremely narrow.
Terminalia reddish, sternite 8 partly dark and shining. Sternites yellowish, without distinct markings. Terminalia greatly enlarged, sternites 5 to 8 with only a very few short hairs but with micro pubescence long. Sternite 8 normal in shape. Tergite 9 with two very stout, subcylindrical, slightly tapering, apically rounded, posterodorsal processes which are curved slightly ventrad near apex, are of almost the same shape, and are joined basally behind the apices of the cerci, and with two anterodorsal processes which are very unequal in length, of almost uniform width throughout, truncate apically, convex and evenly sclerotized ventrally, concave and membranous dorsally, and of which the longer right process is directed slightly, and the shorter left process strongly, toward the left; micropubescence of tergite longer than usual. Cerci asymmetrical, the right slightly longer than the left. Surstylus articulated along anterior part of lower margin of tergite 9 below base of dorsal process, very irregular in outline, with a large rounded posteroventral emargination and with a large sub quadrate flattened lobe arising along the middle of the outer surface and curving sharply ventrad laterad of the posteroventral emargination; right surstylus slightly different in shape, with the lateral lobe extending farther forward and with outline rounded rather than subquadrate; surstyli rather thin, with sparse erect setae which are most abundant on both surfaces of dorsal half and on inner surface of lateral lobe. Sternite 9 with broad shallow posteroventral emargination, ventral surface in front of emargination rather weakly sclerotized, and bearing just above its lower margin a broad, rectangular, truncate, posteroventrally directed, minutely pilose process with slightly convex anteroventral surface and concave posterodorsal surface; apicolateral process of sternite curved dorsomediad to join the very short surstylar apodeme. Superior lobe subrectangular, directed ca.udad, rather short, compressed except basally, with obliquely truncate apex and with a few moderately long setae on outer surface. Aedeagal base in the form of a very short uniformly sclerotized cylinder, broadened toward apex and slightly compressed anteroposteriorly, with a slender tapering acute ventrally directed process at each anteroventral corner. Distal portion of aedeagus broad, of almost uniform width throughout, strongly depressed, sclerotized at extreme base and with sclerotization produced as a triangle on about basal 2/5 of posterior surface, with a slender tapering acute anteroventrally directed lateral process on each side at base, with anteroventral margins weakly spiculate on about median third, and with apex posteriorly weakly but distinctly sclerotized and slightly produced as a pair of asymmetrical subtriangular lobes.
From Mengual (2011).
Very similar to male: face yellow, medially shiny and laterally white pollinose; gena yellow, with a black macula on genal groove; frons yellow with medial broad black vitta narrowing dorsally, with bluish metallic iridescence, not reaching ocellar triangle, black laterally on eye margin on dorsal 1/2, forming a narrow inverted V-shaped yellow macula; antenna orange, basoflagellomere dark dorsally; lunule yellow. Pleuron mostly yellow, except katepisternum black with dorsal yellow macula, posterior anepisternum black on anterior 1/2, meron black, anterior anepimeron black, and katatergum black posteriorly. Metasternum bare. Scutellum yellow with dorsal broad dark macula reaching anterior margin. Coxa and trochanter yellow; pro- and mesolegs yellow except tarsi dark; metaleg black. Same scutum and abdominal pattern as in male, with yellow fasciae narrower and two triangular yellow maculae joined medially on 2nd tergum. Abdomen a bit broader.
Body length: 7.6 to 7.8 mm.
Species found in Papua New Guinea, Morobe Province.