APPENDIX 1. Key to species of M. ruficornis species group

Males

1. Two wart-like prominences present in the middle of the posterior margin of sternum 4. Metatrochanter with small obtuse process; metafemur with distinct ventral protuberance; apex of metatibia with lamellar outer anteroventral spur and curved inner posteroventral spur (Fig. A1 A–B).............................. Merodon papillus Vujić, Radenković et Pérez-Bañon

- Sternum 4 without these prominences..................................................................... 2

2. Metafemur with long protuberance ventrally, as long as or longer than the process on metatrochanter (Fig. A7)........... 3

- Metafemur without or with shorter protuberance ventrally (Fig. A6 C: pf)......................................... 6

3. Metafemur strongly thickened and swollen (Fig. A7 B). Cercus with characteristic shape; posterior surstyle lobe rectangular (Fig. A8 C: pl).................................................................. Merodon hoplitis Hurkmans

- Metafemur less thickened............................................................................... 4

4. Metafemur with extremely long ventral protuberance (more than one half of its width) (Fig. A9 A); metatibia with two apical spurs, one outer anteroventral pointed vertically and another inner posteroventral directed horizontally.................................................................. Merodon ilgazense Vujić, Marcos-Garcìa, Sarýbýyýk et Ricarte

- Protuberance on metafemur shorter (less than one half of its width).............................................. 5

5. Protuberance on metafemur distinctly longer than process on metatrochanter; inner posteroventral apical spur on metatibia long and pointed (Fig. A7 C). Thorns on anterior surstyle lobe and inner side of posterior surstyle lobe strong (Fig. A8 A–B: al, pl)..................................................................... Merodon gallicus Vujić et Radenković

- Protuberance on metafemur shorter or the same length as process on metatrochanter; inner posteroventral apical spur on metatibia shorter (Fig. A7 A). Thorns on anterior surstyle lobe and inner side of posterior surstyle lobe shorter and less distinct (Fig. A8 D–E)..................................................................... Merodon trebevicensis Strobl

6. Metafemur with distinct protuberance ventrally (as on Fig. A3 A–B)............................................. 7

- Metafemur without protuberance ventrally................................................................ 14

7. Metatrochanter with very long calcar (0.7 width of metafemur) (Fig. 1A, B); metatibia with two distinct apical prolongations (as in Fig. 1A)........................................................................................ 8

- Metatrochanter with shorter calcar (as in Fig. 1D); metatibia with one distinct apical prolongation (as in Fig. 1D)......... 9

8. Metatibia with twisted distinct, inner, posteroventral spina (Fig. 1E: marked with arrow); metafemur with indistinct ventral tubercle (Fig. 1B: marked with arrow)............................... Merodon acutus Vujić et Radenković sp. nov.

- Metatibia with narrow, pointed, inner, posteroventral spina (Fig. 1A); metafemur with distinct ventral tubercle (Fig. 1A: marked with arrow)..................................................................... Merodon armipes Rondani

9. Anterior spur at the apex of metatibia directed backwards (as on Fig. A3 A)..................................... 10

- Anterior spur at the apex of metatibia pointed forwards or upwards (as on Fig. A6 E)............................... 11

10. Spur at the apex of metatibia triangular, thorn-like (Fig. A3 A). Thorns on anterior surstyle lobe and inner side of posterior surstyle lobe short, almost indistinct (Fig. A4 A: al, pl).................................. Merodon ruficornis Meigen

- Spur at the apex of metatibia rounded (Fig. A3 B). Thorns on anterior surstyle lobe and inner side of posterior surstyle lobe distinct (Fig. A4 C–D)..................................................... Merodon abruzzensis Van der Goot

11. Lamella behind the apical spur of metatibia with undulated fold (Fig. A6 D: lm).................................. 12

- Lamella behind the apical spur of metatibia with straight ventral margin (Fig. A6 E). Posterior surstyle lobe rounded; thorn on anterior surstyle lobe indistinct (Fig. A5 B–C: al, pl).......................... Merodon ponticus Vujić et Radenković

12. Tibiae at both ends and basal three tarsomeres pale.......................................... Merodon auripes Sack

- Legs predominantly dark. Basal metafemur strongly curved (as on Fig. A12 A)................................... 13

13. Process on metatrochanter shorter and more pointed (Fig. A12 A–B). Posterior surstyle lobe rounded (Fig. A11 C: pl).......................................................................... Merodon ovaloides Vujić et Radenković

- Process on metatrochanter longer and broader (Fig. A13 A–B). Posterior surstyle lobe hook-like (Fig. A14: pl)........................................................................................... Merodon planiceps Loew

14. Legs dark.......................................................................................... 15

- At least basal two (three) tarsomeres pale................................................................. 21

15. Spur at the apex of metatibia small, triangular, lamella indistinct; process on metatrochanter small and pointed; ventral margin of metafemur without long and dense pile (Fig. A6 B); margin of anterior surstyle lobe with very strong dorsal extension (Fig. A11 B)................................................................. Merodon nigripodus Vujić et Hayat

- Spur at the apex of metatibia larger, lamella present (as on Fig. A10 A).......................................... 16

16. Metatibia with distinct inner posteroventral spina (Fig. 15E; marked with black arrow).............................................................................................. Merodon trispinus Vujić et Radenković sp. nov.

- Metatibia with much smaller or indistinct inner posteroventral spina (as in Fig. 15F)............................... 17

17. Posterior surstyle lobe rounded and with indistinct inner thorn (Fig. A11 C: pl). Process on metatrochanter small and pointed; anteroventral spur at the apex of metatibia with innerly curved apical extension (Fig. A12 A–C); metafemur can be with trace of ventral protuberance.................................................. Merodon ovaloides Vujić et Radenković

- Posterior surstyle lobe with more or less flat dorsal margin................................................... 18

18. Anteroventral apical spur of metatibia extended more than anterodorsal end of metatibia (Fig. A10 A); posterior side of apex of metatibia without small spur........................................................................... 19

- Anteroventral apical spur of metatibia not extended more than anterodorsal end of metatibia (Fig. A15 A–D), posterior side of apex of metatibia usually with small spur (as on Fig. A15 D–E)................................................ 20

19. Process on metatrochanter wide and strong; pile on ventral side of metafemur two times shorter than its width (Fig. A10 A–B); cercus oval (Fig. A11 A: c)....................................................... Merodon loewi van der Goot

- Process on metatrochanter narrower; pile on ventral side of metafemur long and dense, at least two thirds of its width (Fig. A13 A); cercus rectangular (Fig. A14)..................................................... Merodon planiceps Loew

20. Long pile on trochanters predominantly black; metafemur anteriorly covered with mostly black pile; terga 3 and 4 with pollinose fasciae clearly visible from lateral view; apical spur at posterior side of metatibia bigger (Fig. A15 D–E)................................................................................... Merodon portschinskyi Stackelberg

- Long pile on trochanters predominantely pale; metafemur anteriorly covered with mostly pale pile; terga 3 and 4 without pollinose fasciae (some specimens have traces of pollen on terga, but there are invisible from lateral view); apical spur at posterior side of metatibia small, in some specimens almost indistinct......................... Merodon turcicus Vujić et Hayat

21. Metatibia with anteroventral apical plate-like lamella (Fig. 8A, B: marked with white arrow), not extended more than the anterodorsal end of metatibia (Fig. 8A, B: marked with gray arrow).............................................. 22

- Metatibia with anteroventral apical prolongation (Fig. 8C: marked with white arrow) extended more than the anterodorsal end of metatibia (as in Fig. 8C: marked with gray arrow)........................................................ 23

22. Metatrochanter with very small calcar (Fig. 8B: marked with black arrow)....... Merodon lamellatus Vujić et Radenković

- Metatrochanter with medium sized calcar (Fig. 8A: marked with black arrow)................................................................................................. Merodon fulvitarsis Vujić et Radenković sp. nov.

23. Lamella behind apical spur of metatibiae with straight ventral margin (Fig. A6 A); posterior surstyle lobe rectangular (Fig. A5 A)............................................................................. Merodon alexandri Popov

- Lamella behind apical spur of metatibiae with rounded ventral margin (Fig. A10 A); posterior surstyle lobe hook-like (Fig. A11 A)........................................................................... Merodon loewi van der Goot

Females

1. Tergum 4 with transversal depression (Fig. A2 B–C: td)....................................................... 2

- Tergum 4 without transversal depression (Fig. A2 A), tarsi dark, at least dorsally............................................................................................. Merodon papillus Vujić, Radenković et Pérez-Bañon

2. Tergum without pollinose fasciae..................................................... Merodon alexandri Popov

- Tergum 2–4 with clear pollinose fasciae................................................................... 3

3. Sternum 4 with strong thorn-like protuberance (Fig. A2 C: pp)............................ Merodon armipes Rondani

- Sternum 4 without protuberance......................................................................... 4

4. Metafemur with protuberance ventrally.................................................................... 5

- Metafemur without protuberance........................................................................ 13

5. Pile on metafemur short, adpressed, especially in apical third (Fig. A9 C). Mediotergite entirely dusted. Distribution: Adriatic mountains..................................................................... Merodon hoplitis Hurkmans

- Pile on metafemur longer (Fig. A9 B). Mediotergite postero-medially shiny. Some other range........................ 6

6. Basal three tarsomeres of all legs pale..................................................................... 7

- Tarsi darkened at least dorsally......................................................................... 12

7. Apex of metatibia rounded (Fig. A3 C).................................................................... 8

- Apex of metatibia angled (Fig. A12 D)................................................................... 10

8. Tergum 5 with a pair of deep lateral depression (Fig. 15)... Merodon ilgazense Vujić, Marcos-Garcìa, Sarýbýyýk et Ricarte

- Tergum 5 with a pair of weaker depression................................................................. 9

9. Distribution: Italy, Abruzzi Mountains.......................................... Merodon abruzzensis van der Goot

- Distribution: rest of Europe....................................................... Merodon ruficornis Meigen

10. Metatarsus of metaleg without or with only few black bristles................................................. 11

- Metatarsus of metaleg with black bristles. Distribution: western of Alps to Caucasus area..... Merodon trebevicensis Strobl

11. Distribution: Turkey and Azerbaijan ....................................... Merodon ponticus Vujić et Radenković

- Distribution: France ..................................................... Merodon gallicus Vujić et Radenković

12. Distribution: western of Alps to Caucasus area. Metatarsus of metaleg with black bristles..... Merodon trebevicensis Strobl

- Distribution: France. Metatarsus of metaleg without or with only few black bristles... Merodon gallicus Vujić & Radenković

13. Three basal tarsomeres pale, at least of metaleg............................................................ 14

- Tarsi darkened at least dorsally......................................................................... 21

14. Apex of metatibia rounded (as on Fig. A3 C).............................................................. 15

- Apex of metatibiae angled (as on Fig. A12 D).............................................................. 17

15. Distribution: Europe.................................................................................. 16

- Distribution: Turkey ................................................... Merodon lamellatus Vujić et Radenković

16. Distribution: Italy, Abruzzi Mountains......................................... Merodon abruzzensis Van der Goot

- Distribution: rest of Europe....................................................... Merodon ruficornis Meigen

17. Pile on ventral surface of metafemur long (the longest ones at least two thirds width of metafemur)................... 18

- The longest pile on ventral surface of metafemur shorter, usually one half width of metafemur (Fig. A10 C)............ 19

18. Distribution: Turkey and Azerbaijan ....................................... Merodon ponticus Vujić et Radenković

- Distribution: Europe.................................................................. Merodon auripes Sack

19. Metatrochanter angled (as in Fig. 7B).................................................................... 20

- Metatrochanter rounded (Fig. 7C)........................................ Merodon lamellatus Vujić et Radenković (females of M. alexandri with faciate maculae on terga 2–4 also keyed here; distinction between females of these two species is based on distribution)

20. Metatibia curved in apical third (Fig. 7B).......................... Merodon fulvitarsis Vujić et Radenković sp. nov.

- Metatibia not curved in apical third (Fig. 7F)......................................... Merodon loewi van der Goot

21. Apex of metatibia rounded (as on Fig. A3 C).............................................................. 22

- Apex of metatibia angled (as on Fig. A12 D)............................................................... 23

22. Distribution: Italy, Abruzzi Mountains.......................................... Merodon abruzzensis van der Goot

- Distribution: rest of Europe....................................................... Merodon ruficornis Meigen

23. The longest pile on ventral surface of metafemur short, usually one half of width of metafemur (Figs. 7D, 7F)........... 24

- Pile on ventral surface of metafemur long (the longest ones at least ⅔ of width of metafemur) (Fig. 7E)................ 25

24. Tergum 4 with distinct transverse depression (Fig. 3B)................. Merodon trispinus Vujić et Radenković sp. nov.

- Tergum 4 with less distinct transverse depression (as in Fig. 3A: marked with arrow).......... Merodon loewi van der Goot

25. Apex of metatibia with distinct lamella (Fig. A12 E–F: lm).......................... Merodon turcicus Vujić et Hayat

- Apex of metatibia with smaller lamella (Fig. A13 C)........................................................ 26

26. Tergum 5 and sternum 5 predominately pale pilose (a few black pile may be present) (Fig. 11A)...................... 27

- Tergum 5 and sternum 5 with numerous black pile medially (Fig. 11B).......................................... 28

27. Apical third of metafemur dorsally with shorter and adpressed pilosity (Fig. 7A).................................................................................................. Merodon acutus Vujić et Radenković sp. nov.

- Apical third of metafemur dorsally with longer and less adpressed pilosity (Fig. 7E)..................................................................................................... Merodon ovaloides Vujić et Radenković

28. Frons with narrow lateral pollinose vittae along eye margins (Fig. 11C); distribution: Caucasus, Georgia ........................................................................................ Merodon portschinskyi Stackelberg

- Frons with broader pollinose vittae along eye margins (Fig. 11D); distribution: Italy, Greece (Rhodes) and Turkey ........................................................................................ Merodon planiceps Loew