Key to Indian species of the genus Eristalinus (males and females)

Eristalinus quadristriatus (Macquart, 1846) is excluded from this key because no reliably identified specimens have been available for examination, and its original description is too brief to allow a confident assessment of its diagnostic characters.

1. Metafemora distinctly incrassate and arcuate, yellow with a median brown ring; metatibiae firmly compressed and carinate on basoventral ⅓ (Fig. 12A–B) (subgenus Merodonoides) ....................... ............................................................................................... Eristalinus fasciatus (Macquart, 1834)

– Metafemora at most slightly incrassate, not arcuate; metatibiae neither compressed nor carinate on basoventral ⅓ (other subgenera) (Fig. 12C–D) ................................................................................ 2

2. Eyes fasciate and maculate (subgenus Eristalodes) (Fig. 13A) ....................................................... 3

– Eyes maculate (subgenus Eristalinus) (Figs 2B, 5A) ...................................................................... 4

3. Scutum dull yellowish grey with four indistinct black vittae; tergum II with a broad uninterrupted yellow fascia bordered narrowly with black anterior and posterior margins (Kondo et al. 2024: fig. 2a) ................................................................................ Eristalinus taeniops (Wiedemann, 1818)

– Scutum pale yellow with four distinct black vittae (Fig. 13B); tergum II mostly black, with a narrow creamy white fascia interrupted medially (Fig. 13C) ....................... Eristalinus paria (Bigot, 1880)

4. Abdomen metallic green, without markings (Fig. 14A) ................................................................... 5

– Abdomen with coloured markings, at least on tergum II (Figs 5C, 6D, 14B–C) ............................. 6

5. Abdomen uniformly aeneous green, entirely covered with pale yellow pile and without markings (Fig. 14A); male holoptic ........................................................... Eristalinus aeneus (Scopoli, 1763)

– Abdomen mostly dull black, with pale yellow pile only on lateral and posterior margin of each tergum; terga II–III with aeneous maculae (Kahanpää, 2021: figs 1a, 3); male dichoptic ................. .......................................................................................... Eristalinus sepulchralis (Linnaeus, 1758)

6. Scutellum unicoloured (Figs 1A, 3A, 4A, 6A, 9A, 11A) ................................................................. 7

– Scutellum, at least partly from yellow to translucent (Fig. 15) ...................................................... 10

7. Terga mainly black, always with creamy white maculae (Ka­Lun, 2022: figs 11–12) ....................... ................................................................................................. Eristalinus tarsalis (Macquart, 1855)

– Terga differently coloured, without creamy white markings (at most tergum II with orange/yellowish brown maculae) (Figs 2D, 3D, 5C, 6D, 10D, 11D) .......................................................................... 8

8. Terga II–IV with conspicuous orange maculae, a black fascia posteriorly, and sometimes with median black vittae (Figs 2D, 3D, 10D, 11D) ............................................................................................... 9

– Only tergum II with yellowish brown maculae (more distinct in males), rest of the terga with shiny blueish grey maculae and arcuate black fascia posteriorly (Figs 5C, 6D) .......................................... ................................................................. Eristalinus sapphirinus Roy, Naskar & Banerjee sp. nov.

9. Males: scutum uniformly shining black without pruinose vittae, mesonotal pile long, dense and black; tergum III with distinct median black vitta; wing with a distinct brown infuscation (Fig. 1A–C). Females: indistinct pruinose vittae may present laterally on scutum (Fig. 3A) ................................. ....................................................................... Eristalinus brunettii Roy, Naskar & Banerjee sp. nov.

– Scutum with four distinct, pruinose vittae in both sexes (Figs 9A, 11A); Males: mesonotal pile short, sparse, and yellowish brown; tergum III with median black vitta indistinct or absent; wings nearly hyaline (Fig. 9A–C) ......................................................... Erisalinus polychromata (Brunetti, 1923)

10. Terga with obliquely placed creamy white markings (Fig. 15A–B) ................................................... ........................................................................................... Eristalinus obliquus (Wiedemann, 1824)

– Terga with transversely placed creamy white markings (Fig. 15C–D) ...........................................11

11. Scutum with longitudinal, strongly contrasting and continuous four shining black and five light yellow pruinose vittae (Fig. 14B–C) .............................................................................................. 12

– Scutum tawny with dull black vittae distinctly interrupted behind the transverse sulcus (Mutin 2020: fig. 1) ................................................................................... Eristalinus arulans (Wiedemann, 1824)

12. Femora mainly yellowish brown or orange (Fig. 16A–B) ... Eristalinus arvorum (Fabricius, 1787)

– Femora all black except at the extreme apex (Fig. 16C–D) ........................................................... 13

13. Abdomen short, ovate-conical (Fig. 17A–B); tarsi predominantly pale yellow, with apical 4–5 tarsomeres black (Fig. 16C–D) .................................. Eristalinus quinquestriatus (Fabricius, 1794)

– Abdomen long, elongate-conical (Figs 14C, 17C); tarsi predominantly black, with only basitarsomere pale yellow on basal ¼–½ (Fig. 18C–D, F) ................................................................................... 14

14. Males: tergum II with arcuate creamy white fascia (Smit et al. 2017: pls 10, 12). Females: fascia on tergum II not tapering laterally, attaining its maximum width sublaterally and reaching the lateral margins (Figs 14C, 18E) ................................................... Eristalinus tabanoides (Jaennicke, 1867)

– Males: tergum II without arcuate creamy white fascia (Fig. 17C). Females: fascia on tergum II tapering laterally, attaining its maximum width at middle, and not reaching the lateral margins (Fig. 18A–D) ...................................................................... Eristalinus megacephalus (Rossi, 1794)