Acerocnema merga, Chagnon & Sinclair, 2021

Chagnon, Marie-Eve & Sinclair, Bradley J., 2021, Revision of Nearctic species of Acerocnema Becker (Diptera: Scathophagidae), Zootaxa 4952 (3), pp. 523-539 : 527-529

Acerocnema merga sp. nov.

( Figs 3, 4 , 10, 11 , 16 , 20 , 24 )

urn:lsid:zoobank.org:act:1973FD2A-C8F3-4077-AF37-3981721EF4E0

Type material examined. HOLOTYPE ♂ labelled: “Herschel I., Y. T./ 7-16 July 1971 / W. R. M. Mason ”; “ HOLOTYPE / Acerocnema / merga / Chagnon & Sinclair [red label]”; “ CNC/ 1589603 ” ( CNC) . PARATYPES: CANADA. Nunavut: Cambridge Bay, 69.1193° -105.42065°, Repl.1 mesic, Malaise, 7–11.vii.2011, NBP Field Party (1♂, LEM); same data except, 69.1277° -105.41688°, Repl.1 wet (1♂, LEM); 69.12177° -105.41688°, Repl.1 wet, Malaise, CCBD-21325-G12 (1♀, barcode associated, LEM); same data except, 69.12070° -105.42582°, Repl.2 mesic, 11–15.vii.2011 (1♂, LEM); Cambridge Bay , 69.0943°, -105.445°, 13.vii.2018, CBG Team 1, CHARS00072 -F06 (1♂, barcoded, CBG). Yukon: mi 87 [km 140] Dempster Hwy [ca. 64°34′N 138°15′W], 16–17.vii.1973, G. & D.M. Wood (1♀, CNC) ; km 155 Dempster Hwy [ca. 65°37′N 138°10′W], 11–12.vii. 1981, 950 m, D. Lafontaine & G. & M. Wood (1♀, CNC) ; British Mts. [69°13′N 140°05′W], 27.vii.1956, R. E. Leech (1♀, CNC) ; British Mts. , 69°13′N 140°05′W, 21–25.vi.1984, G. & M. Wood & D. Lafontaine (1♀, 3♂, CNC) ; British Mts., tributary to Firth River [69°13′N 140°05′W], 20–28.vi.1984, G. & M. Wood (1♂, CNC) ; Dempster Hwy km 140, 65.0319° -138.1779°, 900 m, swp nr pond in forest, 13.vii.2013, S. Rochefort (1♂, LEM) ; Firth River [68°50′10.9″N 140°36′00.9″W], 13.vii.1956, R. E. Leech (1♂, CNC) ; Herschel Is. [69°34′45.7″N 138°54′19.2″W], 7–16.vii.1971, W. R. M. Mason (4♀, 3♂, CNC) ; same data except, 24–28.vii.1971 (2♀, CNC) . USA. Alaska: Cape Thompson [68°08′38.1″N 165°58′39.4″W], 23.vii.1961, R. Madge (2♀, CNC) ; Deering [66°04′32.5″N 162°43′20.0″W], 30.vii.1969, J. Matthews (1♀, CNC) .

Possible additional material. Cambridge Bay , 69.11993° -105.42065°, Repl.1 mesic, Malaise, 7–11.vii.2011, NBP Field Party, CCBD-21325-G11 (1♀, barcoded [failed], LEM) .

Diagnosis. This species is distinguished by the brightly yellow postpedicel in males, with at least base of postpedicel pale in females and pair of shiny scutal vittae on posterior half.

Description. Male. Body primary colour grey/black matt; pleura grey/black matt; scutum grey/black with pair of shiny vittae starting anterior to suture; entire body pruinose. Setae on head yellow.

Head with face and gena yellow; genal width more than half eye height; postgena yellow; postocellar triangle brown. Frontal vitta dark yellow, darker than gena; fronto-orbital plate yellow transitioning to black towards ocellar triangle; parafacial yellow. Fronto-orbital plate with 3–5 inclinate frontal setae, 1–2 proclinate and 1 lateroclinate orbital setae, 1 pair of lateroclinate ocellar setae, 1 pair of short divergent postocellar setae, 1 long inclinate inner vertical seta and 1 long lateroclinate outer vertical seta. Vibrissa strong, with 2 short supravibrissal setae and 1–3 short subvibrissal setae, all yellow. Antenna with postpedicel yellow sometimes spotted black, about 5 times as long as pedicel; scape and pedicel black; arista black and bare, not longer than postpedicel. Palpus yellow with pale setulae over surface and slightly flattened at tip.

Thorax with scutal setae yellow; acrostichal setae biserial, finer than dorsocentrals; 1 presutural and 2 postsutural dorsocentral setae; 2 posterior postpronotal setae; 1 presutural intra-alar seta; 2 notopleural setae; 0 postsutural intra-alar setae; 2 postsutural supra-alar setae; 2 postalar setae; 2 pairs of scutellar setae. Pleura with 2 yellow proepisternal setae and many yellow proepimeral setulae; many yellow posterior anepisternal setulae; 1 yellow posterodorsal katepisternal seta; anterior half of anepisternum and anepimeron without setulae; katepisternum with setulae ventrally.

Wings (length 3.8–4.0 mm) clear, lightly infuscate, R 1 bare; CuA+CuP not reaching wing margin. Halter yellow to white.

Legs entirely yellow; setae yellow. Fore femur with white ventral pile. Fore tibia with 1 preapical ventral seta; 1 anterodorsal seta on apical 1/2. Mid femur with white ventral pile. Mid tibia with 1 preapical posterior, 1 preapical anterior, 1 preapical anteroventral, 1 preapical ventral seta; 1 anterodorsal seta on apical 1/2. Hind femur with 2 ventral setae on apical 1/4. Hind tibia with 1 preapical anteroventral and 1 preapical posteroventral seta; 1 anterodorsal and 1 posterodorsal seta on apical 1/2; 1 anterodorsal seta on apical 3/4. Tarsi with short, white ventral pile.

Abdominal tergites shiny black, with pale setulae over surface. Abdominal sternites yellow/brown. Sternite 5 enlarged and yellow, subtriangular with 2 narrow divergent apical processes; processes with short setulae ( Fig. 11 ).

Terminalia ( Figs 3, 4 , 10 ) with epandrium black; surstylus yellow, with apical perimeter black; cercus dorsally black, ventrally yellow; hypandrium black. Epandrium on dorsal surface of abdomen, surstylus, cercus and tergite 5 all jutting out from ventral surface of abdomen. Surstylus long, apical end flattened slightly into rounded rectangular paddle shape with apical notch; inner surface with thick setae; surstylus not meeting beneath cercus, wrapping around cercus, partially covering. Cercus composed of two sclerotized sections connected via membranes: dorsal section with sclerotized oval sclerite, clothed with many long wavy, dorsally directed setae; ventral section comprising 3 processes with forked, finger-like middle process; ventral sections joined medially by swollen triangular lobes densely clothed in minute setae. Pregonite deeply branched ( Fig. 10 ), both branches slim, anterior branch 2/3 length of posterior branch; posterior branch with apical setae, half length of branch. Postgonite slim with apical end slightly enlarged, subequal in length to posterior pregonite branch. Epiphallus digitiform, slightly shorter than postgonite, slightly arched.

Female. Very similar to male; postpedicel sometimes spotted black, at least base yellow; terminalia as in generic diagnosis.

Distribution. This species is confined to the northwestern high arctic ( Fig. 24 ).

Etymology. This species name is derived from Latin merga (two-pronged fork), in reference to the shape of the lobes on sternite 5.

Remarks. This new species is very similar to the Russian species, A. arctica Ozerov , based on yellow postpedicel, black postocciput, pruinescent scutellum and also including a similarly shaped sternite 5, surstyli and long brush of cercal setae. This new species has a distinct notch on the apex of the surstylus (uneven apex in A. arctica ) and the lower process of the male cercus is forked (apparently unforked in A. arctica ) (see Ozerov 2013, figs 24–29).

Figures

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 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.

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 23–26. Known distribution of Acerocnema. 23. A. fasciventris (Malloch); 24. A. merga sp. nov.; 25. A. rufula (Curran); 26. A. vanga sp. nov.