Metallactus nigroplagiatus, Sassi, 2020

Sassi, Davide, 2020, Revision of the Metallactus generosus species-group with a preliminary evaluation of the effectiveness of the endophallus morphology in distinguishing critical sibling species (Coleoptera: Chrysomelidae: Cryptocephalinae), Zootaxa 4877 (1), pp. 148-162 : 157-159

Metallactus nigroplagiatus sp. nov.

( Figs 3 ; 4c ; 7 )

urn:lsid:zoobank.org:act:EBAA17E5-7A84-4C6B-A44A-D6A6E077FFA7

Agrain et al., 2017: 58, fig. 25 (as Metallactus argentinensis ) (annotated checklist).

Types. HOLOTYPE: ♂, body, aedeagus and detached abdomen glued on the same card, // “ Argentina Tucuman 2-96 Tafi del Valle ” [white label, printed] // “ Brivio Milano ” [white label, printed] // “ Metallactus nigroplagiatus sp. nov . HOLOTYPUS D. Sassi des.” [red label, printed] // ( MSNM). PARATYPES (13 specimens, 3 males and 3 females dissected to check genitalia): 1♂ 4♀ #, same data of holotype ( MSNM, DSPC); 2♀ # // “Argentina, Tucuman, Tafi del Valle , 2000m, 14.I.1984 leg. Bordon ” [white label, printed] // ( MSMN, DSPC, MDPC); 1♂ // “Reimoser Argentinien La Merced ” [white label, printed] // ( NMV); 1♂ // “Hungarian Soil-Zool. Exp. ARGENTINA: Prov. Cordoba Fanti, Sierra de Cordoba 11.I.1966 ” [white label, printed] // “Nr. P-B. 325 Leg. Mahunka” [white label, printed] // ( HNHMB); 1♀ // “ARGENTINE PROV. TUCUMAN LAGUNITA 3000 m ” G. A. BAER I.1903 ” [white label, printed] // “ex coll. J. Achard National Museum Prague, Czech Republic” [white label, printed] // ( NHMP); 1♂ // “ Argentina N Salta Prov. Chicoana riv. W of El Carril 28.1.2009 Snizek lgt.” [white label, printed] // “ Museo Genova ex coll. M. Snizek (acquisto 2009)” [white label, printed] // ( MSNG); 1♀ // “ Pampa Grande Prov. Salta ” [white label, printed] // “ Reimoser Argentina” [white label, printed] // ( NMV); 1♀ // “ ARGENTINA Salta 11 Feb 1984 J. B. Karren ” [white label, printed] // ( BYU). All paratypes provided with additional label: // “ Metallactus nigroplagiatus sp. nov . PARATYPUS D. Sassi des.” [red label, printed] //.

Etymology. Named after the distinctive elytral colour pattern, with black patches.

Type locality. Tafí del Valle (Tucumán, Argentina) .

Distribution. Argentina.

Diagnosis. Metallactus nigroplagiatus differs from its two relatives by the elytral black pattern formed by a longitudinal median band which is usually not expanded behind midline to reach the lateral margin; for this reason the elytral side is marked by an unbroken yellow border rather than showing an anterior subrectangular patch and a rounded spot on apex as observed in the other two taxa. Metallactus nigroplagiatus also differs from M. argentinensis in the expanded apex of the sclerite IV branches of the endophallus, and from M. generosus in the pronotal black pattern never reaching anterad the lateral margins.

Description of male. Habitus in Fig. 3 a–b (HT). BL = 4.4–4.7 mm, BW = 2.7–2.9 mm, PL = 1.5–1.6 mm, PW = 2.4–2.6 mm. Interocular distance 9.1–10.6% of BL.

Head black with a subpentagonal to roughly triangular yellow spot ( Fig. 4c ) extended on vertex and upper part of frons. Labrum brownish. Vertex quite dull with few scattered punctures and rather sparse short setae. Frontoclypeal area with sparse, pale, rather long and slightly curly setae and quite coarse punctation. Mid-cranial suture short, well impressed, so that surrounding surface (in particular yellow patch) mildly swollen. Ocular lines narrow, strictly adhering to ocular rim. Ocular canthus quite shallowly punctured with short, semi-erect setae. Antennae ( Fig. 3h ) with first five antennomeres sublucid, yellowish, 3–5 rod-shaped, the subsequent ones totally darkened, dull, slender as well and more diffusedly setose.

Pronotum yellow with two rather large, slightly arcuate, windy, black stripes extended from anterior to posterior margin along median line. Anterior margin narrowly black as well. Pronotal shape tronco-conical with lateral margins thin, almost not visible from above, regularly curved with maximum width just behind half length. Posterolateral impressions obliterated. Surface almost regularly convex, moderately shiny with scattered well impressed punctation, sparser on inner part of disc.

Scutellum black, sometimes with apical margin narrowly yellow, dull, slightly raised, finely setose and minutely punctured. Apex truncated in a straight line.

Elytron yellow with a large longitudinal black stripe extended from anterior margin to apical clivus between suture and third row of punctures. Such stripe fused with the contralateral one to form a single median black patch slightly tapered backwards. Posterior two-thirds of lateral margin often very narrowly bordered of black; such pattern sometimes broadened at its anterior end to form a perceptibly spot along elytral side. These latter minor black patches never disconnect the lateral elytral yellow pattern which runs unbroken from base to apex. Epipleuron yellow. Elytral outline parallel-sided, elytral disc perceptibly flattened. Lateral margins rather large, simultaneously visible from above up to humeral calli. Postscutellar area not raised. Humeral callus prominent, impunctate. Elytral surface moderately shiny with fine punctation rather confused in anterior inner part of disc, laterally arranged in almost regular rows, rather visible on elytral apex too. Intervals flat. Epipleuron smooth, impunctate, with shallowly convex surface.

Pygidium totally black, smooth, matt, covered by sparse shallow punctures and recumbent whitish setae.

Inferior parts of thorax totally black with exception of yellow outer section of hypomera. Surface covered with punctures and rather dense whitish setae. Prosternal process slightly grooved longitudinally, covered with long setae, with a raised, bluntly triangular apex. Abdominal ventrites completely black, shallowly and sparsely punctured, with rather dense, short setae. Legs totally black.

Fifth abdominal ventrite with fairly impressed, shiny, glabrous, impunctate median depression and weakly notched posterior margin. Median lobe of aedeagus ( Fig. 3 c–e) cylindrical with apex triangular, scarcely separated from the rest of aedeagus, short, usually feebly but perceptibly bent ventrally in lateral view. Setose depressions barely to weakly impressed, scarcely separated from surrounding area, bearing few erected setae. Aedeagal ventral surface moderately swollen in lateral view, devoid of particular structures. Endophallus ( Fig. 3f ) with sclerite I well developed, rather convex and pigmented, denticle apparent, blunt, stemming from upper part of sclerite, upwards directed. Dorsal spicule rather short, with pointed apex. Sclerite II well developed, slender, almost regularly curved. Arch of sclerite III slender, rather short. Apex of sclerite III straight, regularly tapered. Branches of sclerite IV higher than sclerite III in the folded-up structure, distinctly arched towards dorsal direction, with slender basal section but remarkably expanded apically to form a crescent-shaped apex with tiny but distinctly serrate edge and surface minutely wrinkled.

Female. Habitus in Fig. xxa–b. BL = 4.8–5.4 mm, BW = 2.9–3.3 mm, PL = 1.6–1.7 mm, PW = 2.5–2.8 mm. Interocular distance 14.6–14.8 % of BL.

Fifth abdominal ventrite in females with quite small, rather deep pit. Bottom of pit, matt, impunctate, with some very short setae, covered by tiny wrinkles. Vasculum of spermatheca ( Fig. 3g ) scarcely pigmented with straight proximal lobe not swollen at base, short distal lobe and apex pointed. Ampulla mildly pigmented, slightly shifted on dorsal side of vasculum. Duct insertion and sperm gland insertion barely distinct. Duct uniform in size, slender, coiled with coils rather loose and somewhat irregularly arranged. Not coiled portion of duct near bursa copulatrix long, almost straight. Insertion on bursa copulatrix lengthened, bent, rather swollen, clearly pigmented.

Remarks. The shape of elytral longitudinal black pattern, as described above, might be considered as an effective diagnostic character to easily distinguish the present species from the otherwise very similar M. argentinensis . However, it should be taken into account that the black mark is slightly broadened posteriorly in two female specimens in study, almost reaching the lateral margin, so that the colour pattern looks quite similar to the one of several specimens of M. argentinensis .

One specimen of M. nigroplagiatus sp. nov. was figured in Agrain et al. (2017) as M. argentinensis .

Figures

FIGURE 3. M. nigroplagiatus new species: a–b: habitus (lectotype, from type locality); c–e: median lobe of aedeagus in ventral (c), dorsal (d) and lateral (e) view [0.7 mm]; f: sclerites of endophallus in lateral view [0.5 mm]; g: spermatheca [0.4 mm]; h: antenna [1.6 mm]. scI–IV: sclerites I–IV of endophallus; ds: dorsal spicule. Square brackets: length of scale segment.

FIGURE 4. Frontal view. Metallactus generosus Suffrian, 1866 (a); M. argentinensis Jacoby, 1907 (b); M. nigroplagiatus new species (c).

FIGURES 5–7. Distribution maps for Metallactus generosus species-group. M. generosus Suffrian, 1866 (5); M. argentinensis Jacoby, 1907 (6); M. nigroplagiatus new species (7). Grey square: hypothetical location for specimen labelled from ‘Brazil’.