Key to the species of Syrphidae in French Polynesia

1. Postpronotum bare, head posteriorly strongly concave and closely appressed to thorax so that postpronotum is partly or entirely hidden (Fig. 2 B–C); male abdomen with five unmodified pregenital segments; tergum 5 visible in dorsal view (Fig. 2 A–D).............................................5

– Postpronotum pilose, head posteriorly less strongly concave so that postpronotum is clearly exposed (Fig. 5 A–B); male abdomen with four unmodified pregenital segments; tergum 5 usually not visible in dorsal view (Fig. 5 D–E, G).......................................................................................2

2. Vein R4+5 strongly sinuate (Fig. 5A); metafemur with basoventral patch of black setulae ........ ................................................................................................. Palpada vinetorum (Fabricius, 1798)

– Vein R4+5 straight or nearly so (Fig. 5C, E); metafemur without basoventral patch of black setulae...............................................................................................................................................3

3. Arista plumose (Fig. 4E); face with medial and two lateral tubercles (Fig. 4E); metafemur not enlarged, without ctenidium; entire body metallic green or purple (Fig. 4B) ................................... .......................................................................................................... Ornidia obesa (Fabricius, 1775)

– Arista bare (Fig. 4F); face carinate (Fig. 4F); metafemur greatly enlarged, with a ctenidium on posteroventral half (Fig. 5 B–E); body coloration mainly black with pale markings (Fig. 5 B–E, G–H)..................................................................................................................................................4

4. Spurious vein well sclerotized, as distinct as the neighboring R and M veins (Fig. 5C, G); ventral surface of metatibia modified, with anteroventral carina forming a prominent lamina in males, less evident in females. Male: terga 2 and 3 with a broad yellow fascia not divided medially (Fig. 5G). Female: tergum 4 with a distinct yellow fascia on posterior margin (Fig. 5D) .......... ............................................................................................... Syritta aenigmatopatria Hardy, 1964

– Spurious vein not sclerotized, appears as a shadow formed by microtrichia (Fig. 5B, E); metatibia without lamina; terga 2 and 3 with a medial black vitta forming two lateral yellow maculae (Fig. 5E) ......................................................................... Syritta oceanica Macquart, 1855

5. Face and scutellum entirely black in ground color (Fig. 4A, D); metasternum greatly reduced, with deep anterior incision on each side (as in Fig. 9C) ......... Melanostoma polynesiotes sp. nov.

– Face and/or scutellum partially pale in color, usually yellow in ground color (Figs 3F, H, 6E); metasternum entire, not reduced.....................................................................................................6

6. Face partly black, usually yellow with a medial black vitta (Fig. 3B, D, F); metasternum with at least some pile; abdomen without margin (Figs 2 A–B, 3A).......................................8

– Face entirely yellow (Fig. 3H); metasternum bare; abdomen distinctly marginated on terga 2–5 (Figs 2D, 3G, 5F)...............................................................................................................................7

7. Katepisternum without a dorsal yellow macula but densely pollinose (Fig. 5F); scutellum usually with black and pale pile; male metatrochanter without any process or projection (Fig. 6B) .......... ..................................................................................... Simosyrphus grandicornis Macquart, 1842 *

– Katepisternum with a dorsal yellow macula (Fig. 3G); scutellum with pale pile only; male metatrochanter with a ventral spine-like process or calcar (Fig. 6A) .............................................. ............................................................................................... Ischiodon scutellaris (Fabricius, 1805)

8. Scutum and scutellum entirely black (Figs 2B, 6C); abdominal terga 3 and 4 black with two small yellow maculae each, close to the lateral margin (Figs 2B, 6D) ..... Allograpta jacqi sp. nov.

– Scutum black with lateral yellow vitta (Figs 2A, 3A) and scutellum yellow with black medial macula (Fig. 2A, C); abdominal terga 3 and 4 black with a yellow fascia each (Figs 2A, C, 3A)...9

9. Wing entirely microtrichose except cell R bare anterior to spurious vein basally; costal cell bare basally, less than 1/5 .................................................... Allograpta amphotera (Bezzi, 1928)

– Wing partly bare basomedially, cell BM bare on basal ¼–½ or more, cell R bare anterior to bifurcation; costal cell bare on basal ¼ ..................... Allograpta nigripilosa (Hull, 1944)