Acerocnema Becker, 1894

Chagnon, Marie-Eve & Sinclair, Bradley J., 2021, Revision of Nearctic species of Acerocnema Becker (Diptera: Scathophagidae), Zootaxa 4952 (3), pp. 523-539 : 524

Acerocnema Becker, 1894

Acerocnema Becker, 1894: 154 . Type species, Cordylura breviseta Zetterstedt (original designation).

Pachystyla Lioy, 1864: 1005 . Type species, Cordylura macrocera Meigen (original designation). Preoccupied by Pachystyla Moerch, 1852 (Mollusca) .

Diagnosis. Small-bodied flies with body colour either yellow or black and shiny ( Figs 15–22 ). Overall species are weakly bristled. Head is rounded with a variable number of setae. Arista pubescent to bare; length of arista as long as first flagellomere. Postpedicel generally much longer compared to other species of Scathophagidae . Palpus spatula-shaped. Setae on head and body yellow or black. Scutal setae are variable in appearance and number, notopleurals, supra-alar, postalar and dorsocentrals distinct. Scutum also with fine soft hairs among the setae. Scutellum always with strong apical and lateral setae. Vein R 1 usually bare, if setulae present confined to distal portion. Legs with a few extremely weak setae. Abdomen with fine hairs over surface. Male sternite 5 enlarged, deeply bilobate posteriorly, apical lobes narrow to broad. Epandrium on dorsal surface of abdomen, surstylus, cercus and tergite 5 all jutting out from ventral surface of abdomen. Surstylus flattened, slender and at times broadened apically ( Figs 1–8 ). Cerci fused basally with deeply divided process underneath. Female terminalia ( Fig. 14 ) very similar to Gimnomera . Segments beyond 6 compressed; terminal segments strongly sclerotized and compressed, with spine-like projections.

Remarks. DNA barcode data is available for two identified Nearctic species of Acerocnema ( merga , fasciventris ) and an additional unidentified species ( Fig. 27 ) (see Discussion section for further details).

Figures

FIGURE 27. Neighbour-joining tree of 12 specimens of Acerocnema with COI sequences, including unique voucher number (numbers starting with CCDB are from this study), sequence length and GenBank accession number.

FIGURES 15–18. Acerocnema male species, habitus lateral views. 15. A. fasciventris (Malloch); 16. A. merga sp. nov.; 17. A. rufula (Curran); 18. A. vanga sp. nov.

FIGURES 19–22. Acerocnema female species, habitus lateral views. 19. A. fasciventris (Malloch); 20. A. merga sp. nov.; 21. A. rufula (Curran); 22. A. vanga sp. nov.

FIGURES 1–4. Male terminalia of Acerocnema. 1. A. fasciventris (Malloch), posterior view; 2. same, lateral view; 3. A. merga sp. nov., posterior view; 4. same, lateral view.Abbreviations: an—anus; cerc—cercus; d sec cerc—dorsal section cercus; epand—epandrium; hypd—hypandrium; pgt—postgonite; sur—surstylus; v sec cerc—ventral section cercus.

FIGURES 5–8. Male terminalia of Acerocnema. 5. A. rufula (Curran), posterior view; 6. same, lateral view; 7. A. vanga sp. nov., posterior view; 8. same, lateral view. Abbreviations: cerc—cercus; d sec cerc—dorsal section cercus; pregt—pregonite; sur—surstylus; v sec cerc—ventral section cercus.

FIGURES 9–14. Male and female Acerocnema. 9. A. fasciventris (Malloch), male sternite 5, ventral view; 10. A. merga sp. nov., pregonites and postgonites, lateral view; 11. A. merga sp. nov., male sternite 5, ventral view; 12. A. rufula (Curran), male sternite 5, ventral view; 13. A. vanga sp. nov., male sternite 5, ventral view; 14. A. fasciventris (Malloch), female abdomen, lateral view. Abbreviations: cerc—cercus; epiph—epiphallus; epiprct—epiproct; hyprct—hypoproct; pgt—postgonite; ph—phallus; pregt—pregonite.