Small, slender species with abdomen almost parallel-sided. Species with wing infuscated, scutellum yellow with triangular black macula reaching anterior margin, and legs dark brown except pro- and mesofemur yellow basally. C. robertsi has abdomen with very narrow yellow fasciae, and male frontal triangle yellow with posterior margin with a narrow black vitta, character not shared with other species like C. pendleburyi, C. vockerothi, C. circumdatum, C. hervebazini and C. solomonense.
Citrogramma robertsi Wyatt, 1991.
Wyatt, N.P. (1991) Notes on Citrogramma Vockeroth (Diptera: Syrphidae) with descriptions of five new species. Oriental Insects 25, 155-169.
Adapted from original description (Wyatt 1991).
FEMALE.
Head: Face yellow with a rather narrow black median vitta, even at greatest width narrower than yellow lateral areas of face. Tubercle fairly large and broad, most of lower part of face swollen. Frons black except far a striking orange inverted Y-shaped area, caused by convergence of lateral pale vittae, which then extend upwards to the ocellar triangle. Lateral pile of face mostly dark, but with some pale pile on lower part. Antennae dull orange, darkened dorsally on pedicel and basoflagellomere.
Thorax with pale median area of scutum almost uniformly grey dusted with a vague metallic iridescence, this area separated from the lateral yellow vitta by a sharply defined black area. Pile of scutum pale yellow on median and lateral pale areas, otherwise black. Pleurae with large continuously yellow area, extending ventrally to dorsal parts of the katepisternum and meron. Scutellum with large sharply defined black basal triangle, covering most of scutellar disc with only a narrow yellow margin. Halteres pale yellow, squamae whitish on anterior half, otherwise intensely blackened. Legs mostly blackish, but pro- and mesofemora extensively pale yellow basally; trochanters and coxae of these legs also pale yellow. Pile of legs mostly black, but pale on the yellow areas. Wing membrane faintly sooty-brown, mare intensely so near wing-tip; stigma and subcostal cell intensely blackish-brown. Membrane entirely microtrichose.
Abdomen mostly blackish with narrow yellow fasciae on terga 2 to 5, that on tergum 2 narrowly interrupted; also shining black fasciae along hind margins of these terga.
unless otherwise stated