Chalybion, Dahlbom, 1843

Pham, Phong Huy, Ohl, Michael, Nguyen, Anh Thi Tu & Nguyen, Dinh Thi, 2025, Taxonomy of the genus Chalybion Dahlbom, 1843 (Hymenoptera: Sphecidae) from Vietnam, with description of a new species, Zootaxa 5679 (4), pp. 573-584 : 574-575

Key to the Vietnamese species of Chalybion

Females

1. Anterior margin of clypeus with broadly projecting median lobe; antenna ferruginous; petiole wholly yellow; legs partly yellow; metasoma black; pubescence of head and mesosoma black (subgenus Hemichalybion )........ C. sumatranum ( Kohl, 1884)

- Anterior margin of clypeus with three or five teeth medially; antenna black and blue or green; metasoma, petiole and legs wholly blue or green, pubescence of head and mesosoma white (subgenus Chalybion )............................... 2

2. Lower metapleuron with conspicuous carina above midcoxa; area between antennal sockets with transverse carina; tarsi with plantulae............................................................................................ 3

- Lower metapleuron without conspicuous carina above midcoxa; area between antennal sockets without transverse carina; tarsi without plantulae..................................................................................... 5

3. Mesosoma less than three times as long as high; petiole longer than hind basitarsus; forewing hyaline.................................................................................................... C. gracile Hensen, 1988

- Mesosoma elongate, more than three times as long as high; petiole shorter than hind basitarsus; forewing light brown...... 4

4. Clypeus with longitudinal carina ( Fig. 7 ); inner eye margin conspicuously curved dorsally ( Fig. 7 ); vertex behind posterior ocelli conspicuously sloping ( Fig. 8 ); occipital carina lowered far from apical area ( Fig. 8 ); sterna III and IV largely covered with dense, brown micro-pubescence ( Fig. 10 ); apical edge of fourth sternum not depressed ( Fig. 10 ); terminal metasomal sternum somewhat curved apically ( Fig. 10 ); body dark blue ( Fig. 11 ); head and mesosoma not iridescent ( Figs 7–9 )................................................................................... C. dolichothorax ( Kohl, 1918)

- Clypeus without longitudinal carina ( Fig. 18 ); inner eye margin conspicuously curved at middle ( Fig. 18 ); vertex behind posterior ocelli moderately sloping ( Figs 19, 20 ); occipital carina highly raised near apical area ( Figs 19, 20 ); sterna III and IV not covered with brown micro-pubescence ( Fig. 23 ); apical edge of fourth metasomal sternum conspicuously depressed ( Fig. 23 ); terminal metasomal sternum widely flat apically ( Fig. 23 ); body dark green ( Fig. 24 ); head and mesosoma iridescent ( Figs 18–21 )................................................................... C. iridescens Pham & Ohl , sp. nov.

5. Metasomal sternum VI flat and wide, broadly truncate at apex.................................................. 6

- Metasomal sternum VI not markedly wide, rounded at apex.................................................... 7

6. Both forewing and hindwing brown distally, hyaline proximally; petiole moderately curved...... C. malignum ( Kohl, 1906)

- Both forewing and hindwing light brown; petiole markedly curved.................... C. tanvinhense Pham & Ohl, 2019

7. Propodeum without tomentum anterolaterally; petiole markedly curved................... C. japonicum ( Gribodo, 1882)

- Propodeum with tomentum anterolaterally; petiole moderately curved................... C. bengalense ( Dahlbom, 1845)

Males

Males of C. sumatranum , C. dolichothorax , C. iridescens sp. nov., and C. gracile are unknown and not included.

1. Anterior margin of clypeus without teeth; flagellomeres VIII and IX with placoids; petiole markedly curved....................................................................................... C. tanvinhense Pham & Ohl, 2019

- Anterior margin of clypeus with five teeth; placoids varied; petiole moderately to markedly curved.................... 2

2. Anterior margin of clypeus with five rather small teeth; both forewing and hindwing brown distally, hyaline proximally.................................................................................... C. malignum ( Kohl, 1906)

- Anterior margin of clypeus with five broad teeth; wings uniformly coloured....................................... 3

3. Flagellomeres VII or VIII to IX with placoids; propodeum without tomentum anterolaterally; petiole conspicuously curved.............................................................................. C. japonicum ( Gribodo, 1882)

- Flagellomeres V or VI to IX with placoids; propodeum with tomentum anterolaterally; petiole moderately curved..................................................................................... C. bengalense ( Dahlbom, 1845)

Figures

FIGURES 7–11. Chalybion dolichothorax (Kohl, 1918), ♀. 7. Head, in frontal view; 8. Head, in lateral view; 9. Mesosoma, in lateral view; 10. Metasoma, in ventral view; 11. Habitus, in dorsal view.

FIGURES 18–24. Chalybion iridescens Pham & Ohl, sp. nov., holotype, ♀. 18. Head, in frontal view; 19. Head, in dorsal view; 20. Head, in lateral view; 21. Mesosoma, in lateral view; 22. Forewing; 23. Metasoma, in ventral view; 24. Habitus, in dorsal view.