Mecodema dux Britton, 1949

Seldon, David S. & Buckley, Thomas R., 2019, The genus Mecodema Blanchard 1853 (Coleoptera: Carabidae: Broscini) from the North Island, New Zealand, Zootaxa 4598 (1), pp. 1-148 : 44-46

Mecodema dux Britton, 1949 .

Figure 26 .

Diagnosis: Distinguished from other North Island Mecodema species by: 1, the overall pronotal shape being ovate; 2, numerous punctures between pronotal foveae; 3, elytral striae 1–4 with obsolescent punctures, striae 5–8 with punctures more impressed; 4, the distinctive shape of the apical portion of the penis lobe ( Fig. 26 PL).

Description: Length 19–24 mm, pronotal width 5–6 mm, elytral width 6–7.1 mm. Colour of entire body dark reddish-brown to matte black, coxae and legs reddish-brown.

Head: Narrow and convex ( Fig. 14D ). Vertex with short, deep wrinkles and punctures; vertexal groove narrow, defined by punctures that extend onto posterior frons area ( Fig. 26 ); supraorbital puncture large bearing 2 setae; 5–6 moderately defined supraorbital grooves extend onto lateral area of frons; frons medially convex with a large and shallow depression anteriorly each side of midline; frontoclypeal suture ( Fig. 9 ) narrow, well-defined the entire length, tentorial pits indistinct; anterior area of clypeus with deep grooves laterally and medially, 1 large setose puncture each side bearing 2–3 setae. Labrum lobate, anterior edge outwardly curved, very slightly emarginated medially with 2 proximate central setae, 2 setae each side evenly spaced. Mentum lobes rounded ( Fig. 12F ), median process broad and short, moderately angled upward (30°), strongly indentate ( Fig. 12A ); mentum setae absent. Submentum sclerite constriction narrow with 6 evenly-spaced setae along constriction. Stipes with 2 basal setae. Gula pits small, suture poorly defined, gula slightly convex with very fine transverse lines. Gena with rugose transverse wrinkles across entire area.

Prothorax: Prothoracic carina narrow the entire length, moderately crenulated with 7–10 setae each side ( Fig. 26 ), extended beyond anterior angle; posterior lateral sinuation indistinctly carinate, angled inward; pronotum narrow and deflected laterally giving pronotum an almost ovate shape; midline ( Fig. 11 ) indistinct, anterior medial triangular impression and posterior medial diamond-shaped impression present, transverse rugose wrinkles across entire disc, numerous punctures between foveae; pronotal foveae narrow and shallow; anterior edge inwardly curved, posterior edge inwardly curved medially ( Fig. 26 ). Prosternum flat with fine transverse lines and central depression; proepisternum with numerous punctures. Procoxal setae absent; protibia distally expanded and shovellike ( Fig. 10B ).

Elytra: Narrow and deflected; humeral angle anteriorly convergent ( Fig. 6A ); basal margin curved and bevelled to base, interval 1 extended to margin, a few punctures along base; lateral carina narrow, broadened in posterior ⅓, extended to humeral angle; humerus with 2–3 setose proximate punctures anterad; suture impressed but no more so than striae; striae with small, regularly spaced, asetose punctures that increase in size laterally; striae 1–4 with obsolescent punctures, striae 5–8 with punctures impressed (some punctures star-shape); intervals 1–4 weakly convex, intervals 5–8 moderately convex, interval 9 strongly convex; intervals with fine wrinkles; 7 th strial setal pattern with 2 setose punctures in anterior ½, 5–6 setose punctures in posterior ½ ( Fig. 26 ), setose punctures small; some specimens with setose puncture at the junction of the basal margin and interval 2.

Ventral surface: Mesepisternum with short grooves and punctures; metepisternum grooved; setose punctures present on mesocoxa (1) and metacoxa (2). All abdominal ventrites lineate, ventrites 1 and 2 ( Fig. 2 ) may have a few scattered punctures; ventrites 3–5 with 1 setose puncture present each side of midline; ventrite 6 setae present: ♂ with a single seta each side, apical edge a rounded curve, ♀ with 2–3 pairs (may have 1–2 more pairs) of setae each side, apical edge with a rounded, narrow point; lateral foveae absent. Anterior metaventrite process a short triangle with a well-defined and broad carina the entire length.

Male genitalia: Apical portion of penis lobe asymmetrically hooked with a moderate deflection to right of vertical axis (VV) ( Fig. 15B ); ventral process formed by short, sharp angle to form a rounded point that is pushed forward of vertical centre ( Fig. 3 ), apex symmetrically curved upward to form dorsal process that is short, very rounded but flattened (half discus-shaped) with a brief curve back to the shaft, posterad the vertical axis ( Fig. 26 PL); penis lobe shaft narrow at apex gradually broadened to base, shaft of penis lobe straight (VV); overall length of penis lobe moderately curved ventrally (LV) ( Fig. 16B ). Structures of the endophallus ( Fig. 4 ): lateral form of the apex of the central spicule pointed; dorsal form of the apex of the central spicule long and narrow; setal (scales) coverage of the apical plate moderate (26–75%); size of left setose flange small; size of right setose flange large. Left paramere basal lobe rectangular with very low dorsal hump forming a definite (60°) slope to arm; arm very short and narrow, terminal lobe not distinct from arm; very sparse, medium length setae form an apical tuft ( Fig. 26 LP); ventral edge setal distribution from apical tuft, a short gap, then a medium to long-lengthed comb of setae to basal lobe-arm junction ( Fig. 26 LP); ventral edge straight. Right paramere a long and narrow triangle with a double row of long setae extending along apical ¾ of ventral edge ( Fig. 26 RP); apical ½ of arm inwardly curved toward penis lobe.

Female genitalia: Basal gonocoxite 1 ( Fig. 5 ) short and broad especially apically, ventral surface with a few wrinkles, internal dorso-lateral carina with a single short seta at terminal end and inner edge of carina at base of gonocoxite 2. Gonocoxite 2 a rounded triangle, with apical portion slightly curved outward. Ramus long and narrow, broadened posterad.

Comments: Mecodema dux can be found throughout the Ruahine Ranges, there can be some morphological differences, and slight variation in the apical portion of the aedeagus among populations. These variations are more pronounced between populations on either side of the ranges, i.e. eastern and western populations.

Distribution: New Zealand, North Island, Ruahine Ranges, Hawke’s Bay, Rangitikei, Taupo.

Holotype: NZAC male labelled [card mounted, genitalia exposed (on card)]. Type [round label, outer red circle] / Oio, N.Z., 20.I.36 F. Gardener [hw] / HOLOTYPE Mecodema dux sp.n E.B.Britton. det. 1946 / E.S. Gourlay Acc. 1970 Ent. Div. / NZAC 04011194 .

Material examined: 1♀, NEW ZEALAND RI Ruahine SFP, Rangitane Rd end, Kawhakau Base , 25.II–1.III.1995, Larivière. Larochelle / 700m moist, drained Nothofagus-horopito forest, rich-litter, big logs, pittraps ( NZAC) ; 1, NEW ZEALAND, HB, eastern Ruahine Range , Swamp Loop, 11 Dec 2012 – 8 Jan 2013, D.S. Seldon & D. Brown DSS081 / pitfall traps in kahikatea-beech canopy, S39°47’38.2, E176°11’48.8, 627m ( NZAC); 1, NEW ZEALAND, HB, eastern Ruahine Range , Swamp Loop, 11 Dec 2012, D.S. Seldon & D. Brown DSS082 / underlogs in kahikatea-beech canopy, S39°47’37.0, E176°11’45.0 ( NZAC) .

Figures

FIGURE 2. Ventral view of a Mecodema specimen showing specific morphological structures, excluding taxonomic structures indicated in detail figures, used in the species descriptions. ƑLF = ventrite lateral foveae; ƑSP = ventrite setose punctures; MTC = metacoxa; MTƑP = metaventrite process; MSC = mesocoxa; PC = procoxa; PS = prosternum; G = gena; PES = proepisternum; MSE = mesepisternum; MTE = metepisternum; Ƒ1–Ƒ6 = ventrites 1-6 (ventrites 1-3 may be fused); M = midline (dashed line, not a taxonomic structure).

FIGURE 3. Detail of the apical portion of aedeagus (male genitalia) with parameres removed showing taxonomic structures, vertical and horizontal planes that are referred to in the species descriptions and redescriptions: aedeagus shaft width (ASW); vertical central line (ƑCL) [dashed line, not a structure]; horizontal central line (HCL) [dashed line, not a structure].

FIGURE 4. An Environmental Scanning Electron Microscope (ESEM) photograph of the four main structures of the apical plate of the endophallus within the penis lobe. This is an example from Mecodema haunoho showing the central spicule (c.s), left (l.s.f) and the right setose flange (r.s.f), and microtrichial field (m.f). These structures are variable among species but within a species, they are very consistent, even over distant geographical ranges. The microtrichial field can be covered in flattened scales as in photo above, or with elongated setae-like scales.

FIGURE 5. The entire female reproductive tract (ventral view) including taxonomic structures (for all other abbreviated structure names see Seldon et al. 2012). However, for this revision only the following structures are important: HS = helminthoid sclerite; G1 = gonocoxite 1; G2 = gonocoxite 2; TDC = transverse dorsal carina; R = ramus.

FIGURE 6. Detail of the three different forms of the elytral humeral angle: (A) = anteriorly convergent (M. parataiko), (B) = evenly convex (M. oconnori), (C) = subangulate (M. atuanui).

FIGURE 9. Dorsal view of head with detail of the morphological structures used in the species descriptions. Ƒ = vertex; SPS = supraorbital puncture setae; SP = supraorbital puncture; F = frons area; FCS = frontoclypeal suture; C = clypeus; M = mandible; LS = labrum setae; L = labrum; ACM = anterior clypeal microsculpture; CSP = clypeal setose puncture; TP = tentorial pit; SG = supraorbital grooves; E = eye; ƑG = vertexal groove.

FIGURE 10. The protibia form is a character used mainly to determine between genera, except for one species in Mecodema where the difference between (A) greatly distally expanded (M. antarctica) and (B) expanded distally (all other Mecodema species) is used.

FIGURE 11. Detail of pronotum showing the taxonomic structures used in the species descriptions. PPC = posterior pronotum constriction; PS = pronotal setae; PAA = pronotum anterior angle; AE = anterior edge; PC = pronotal carina; ML = midline; PF= pronotal foveae; PPS = pronotum posterior sinuation; PE = posterior edge.

FIGURE 12. Ventral view of the mentum with a number of different character states. Illustrations A–D are the different forms of the indentation in the apex of the median process: (A) distinctly indentate (M. manaia); (B) moderately indentate (M. pluto); (C) slightly indentate (M. infimate); (D) indentation notched (M. parataiko). Illustrations E–G are the three general forms (i.e., hashed lines) of the mentum lobes: (E) triangular; (F) rounded; (G) squared.

FIGURE 14. Diagrammatic cross sections that represent the width and convexity of head or deflection of pronotum (frontal view): (A) broad and flat; (B) broad and convex; (C) narrow and flat; (D) narrow and convex.

FIGURE 15. The penis lobe in ventral view showing the relative deflection to right of vertical: (A) distinctly deflected (M. regulus); (B) moderately deflected (M. haunoho); (C) slightly deflected (M. oregoides). Scale bars = 1 mm. Structures of penis lobe indicated are: base (B); lateral edge (LE); apical portion (AP); ventral edge (ƑE).

FIGURE 16. Relative strength of the ventral curve over the length of the penis lobe (lateral view): (A) slightly curved (M. oblongum); (B) moderately curved (M. ponaiti); (C) distinctly curved (M. manaia). Scale bar = 1 mm.

FIGURE 26. Mecodema dux plate with half habitus (left) and the three (detached) structures of the male aedeagus: the right (RP) and left parameres (LP), plus the penis lobe (PL). The bottom scale bar is the width across the widest point of the pronotum of the specimen used for this habitus and top scale bar equates to the half the length of the penis lobe.