Metallactus generosus Suffrian, 1866

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 : 151-155

Metallactus generosus Suffrian, 1866

( Figs 1 ; 4a ; 5 )

Metallactus generosus Suffrian, 1866: 269 ; Clavareau, 1913: 93 (catalogue); Blackwelder, 1946: 641 (catalogue).

Material examined. Types. Suffrian did not mention the number of the specimens available for his description, but examined material from Montevideo (Clark collection), Paraguay (von Heyden collection) and Porto Allegre (Berlin collection) ( Suffrian 1866: 271). The male in BMNH appears to correspond to Clark’s material and is hereby designated lectotype, to fix the identity of this species. Seven syntypes in MNHUB were not examined in detail, but they likely belong to three different taxa (four are true M. generosus , two are probably M. argentinensis and the last may belong to an unidentified species close to M. quadrinus ( Suffrian, 1866) . The Paraguayan syntypes were in the von Heyden collection, at present in the Senckenberg Deutsche Entomologische Institut in Müncheberg. However, a thorough investigation failed to find any, so the von Heyden syntypes must be considered lost. LECTOTYPE: ♂, body, aedeagus and detached abdomen glued on the same card, endophallus glued on a separate card, // “95” [blue label, handwritten] // “ M. generosus Suf. M. Video [Montevideo]” [white label, handwritten] // “E. Coll. Laferté” [white label, printed] // “67.56” [white label, printed] // “ Metallactus generosus Suffrian, 1866 LECTOTYPUS D. Sassi des.” [red label, printed] // ( BMNH). The script “67.56” means: fifty-sixth acquisition in the year 1867, which corresponds to BMNH’s acquisition of the Clark collection. This allows the specimen to be identified as part of the type series in Suffrian’s description. PARALECTOTYPES: 1♀, pinned, // “ C. [sic] generosus ” [white label, handwritten] // “E. Coll. Chevt.” [white label, printed] // “67.56” [white label, printed] // ( BMNH); 1♂ 6♀, // “23946” [white label, printed] // “ Metallactus generosus Suffr. * ” [white label, handwritten] // “Cyclops N. Porto Allegre Sello.” [blue label, handwritten] // ( MNHUB). The label information for these last seven specimens matches the registration data from the old catalogue of the MNHUB (“23946 Metallactus generosus Suffr. * 7. Porto Allegre, Sello”). All paralectotypes labelled: “ Metallactus generosus Suffrian, 1866 PARALECTOTYPUS D. Sassi det.” [red label, printed].

Type locality. Montevideo ( Uruguay) .

Additional material examined. (11 specimens, 3 males and 3 females dissected to check genitalia). ARGENTINA: Entre Rios Santa Elena 25.I.1912 G. E. Bryant (1, BMNH) ; Entre Rios Liebig XI. 1987 Amagada leg. (1, DSPC) ; Haut Parana Tiju-Cuare Près San Ignacio E. R. Wagner III–IV.1911 (1, MNHN) . BRAZIL: “ San Palo Cipo ” [probably: São Paulo Cipó-Guaçu] V. N. Alin coll. (2, ERPC) ; São Paulo 18.X.1973 V. N. Alin (1, FSCA) ; São Paulo Mraz lgt (5, NHMP) .

Distribution. Argentina, Brazil, Uruguay. This species is newly recorded for Argentina. Unfortunately, it is not possible to confirm the presence of the species in Paraguay due to the non-availability of the syntypes from von Heyden collection.

Diagnosis. Metallactus generosus differs from its two relatives by the pronotal black patch reaching anterior half of lateral margins. It also differs from M. nigroplagiatus in having a larger black patch on elytron which is always extended to lateral margin on apical clivus. It also differs from M. argentinensis in the endophallus, the branches of sclerite IV being remarkably expanded on apex. In the four available males, the sides of pronotum tend to be slightly more convergent anterad than in the posterior half, so that the maximum width is very close to posterior angles. Conversely, male pronotal sides are more regularly arched in the other species and the maximum width is just behind midline. Besides, in M. argentinensis and M. nigroplagiatus , an ill-defined longitudinal carina is sometimes perceptible along the ventral side of median aedeagal lobe, whereas no indication of that structure is detectable in M. generosus . Hovewer, the effectiveness of these last differences needs to be tested on a higher number of specimens.

Description of male. Habitus in Fig. 1 a–b (LT). BL = 4.6–4.8 mm, BW = 2.8–2.9 mm, PL = 1.5–1.7 mm, PW = 2.5–2.6 mm. Interocular distance 9.5–10.9 % of BL.

Head black with a pentagonal yellow spot ( Fig. 4a ) extending from upper part of frons to basal half of vertex. Labrum brownish. Vertex almost impunctate, glabrous. Surface of frons dull, punctation evident, rather coarse; whitish setae quite dense just below the yellow spot. Mid-cranial suture obliterated. Ocular lines well impressed, strictly adhering to ocular rim. Ocular canthus barely punctured with short, appressed setae. Antennae ( Fig. 1h ) with first five antennomeres sublucid, yellowish, 3–5 rod-shaped, 6–11 totally darkened, dull, similar in shape to 1–5 but more diffusedly setose.

Pronotum black with two posterolateral yellow spots extending from posterior corners over posterior and lateral margins up to about mid length. Sometimes a third smaller, elliptical spot just in front of scutellum. Pronotum rath-er elongate, tronco-conical, evenly convex. Lateral margins narrow, slightly more convergent anterad, maximum width near posterior angles. Posterolateral impression almost obliterated, posterior margin not swollen toward sides. Surface moderately shiny with scattered, fairly impressed punctation, denser on sides, obliterated on disk.

Scutellum completely black, moderately raised, subquadrate. Surface rather matt, with small, scattered setae.

Elytron black with one anterolateral yellow spot in continuity with the pronotal one, thus forming a single light patch. One additional rounded yellow spot on apex, reaching posterior margin. Epipleuron yellow. Suture narrowly black between apical yellow spots. Elytral outline parallel-sided, elytral disc slightly flattened. Lateral margins rather large, visible in dorsal view to humeral calli. Postscutellar area not raised. Humeral callus prominent, impunctate. Surface rather dull with moderately impressed punctation, only partly arranged in almost regular striae, clearly perceptible up to apical clivus. Intervals flat. Epipleuron smooth, impunctate, with shallowly convex surface.

Pygidium piceous, smooth, covered by sparse, shallow punctures and pale stiff setae.

Inferior parts of thorax completely black, with sparse and scarcely apparent punctation and rather dense setosity. Only hypomera almost glabrous, shiny, with well impressed, sparse punctures. Prosternal process narrow, longitudinally grooved, covered with long setae, with apex roughly pointed and slightly raised. Abdominal ventrites completely black, shallowly and sparsely punctured, with rather dense, recumbent setae. Legs totally black.

Fifth abdominal ventrite with a shallow, glabrous, smooth, impunctate median depression and weakly notched posterior margin. Median lobe of aedeagus ( Fig. 1 c–e) cylindrical with smooth surface and apex triangular, short, fairly pointed, almost straight in lateral view. Setose depressions very shallow, barely delimited, with scattered, erected setae. In ventral view median lobe rather convex, with no sign of longitudinal carena. Ventral profile fairly swollen in lateral view. Endophallus ( Fig. 1f ) with sclerite I well developed and pigmented, denticle apparent, blunt, stemming from the middle of sclerite, slightly directed upwards. 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 almost 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 finely but distinctly serrate edge and surface minutely wrinkled.

Female. BL = 4.8–6.0 mm, BW = 2.8–3.5 mm, PL = 1.6–2.2 mm, PW = 2.5–3.2 mm. Interocular distance 14.6–16.7 % of BL.

Fifth abdominal ventrite in females with quite large, impressed pit. Bottom of pit glabrous, matt, impunctate but covered by tiny wrinkles. Vasculum of spermatheca ( Fig. 1g ) scarcely pigmented with straight proximal lobe not swollen at base, short distal lobe with a rather abruptly pointed, slightly bent apex. Ampulla perceptibly pigmented, not on midline but placed towards dorsal side of vasculum. Duct insertion and spermathecal gland insertion barely distinct from one another. Duct uniform in size, slender, coiled with coils rather loose and somewhat irregularly ar-ranged. Not coiled portion of duct near bursa copulatrix rather short, almost straight. Insertion on bursa copulatrix lengthened and barely swollen, clearly pigmented.

Remarks. Dorsal colour pattern is quite constant in the studied specimens, characterizing the species. However, two females from São Paulo, presumably of this species, remarkably differ. In one of them the two yellow patches on elytron coalesce along elytral side to form a single large stripe. In the second one elytron is totally yellow. The continuity between pronotal and elytral light pattern, typical of the species, is detectable in the first female.

Figures

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

FIGURES 1–2. Metallactus generosus Suffrian, 1866 (1), M. argentinensis Jacoby, 1907 (2): 1a–b: habitus; 1c–e: median lobe of aedeagus in ventral (c), dorsal (d) and lateral (e) view [0.8 mm]; 1f: sclerites of endophallus in lateral view [0.4 mm]; 1g: spermatheca [0.6 mm]; 1h: antenna [1.6 mm]. 2a–b: habitus; 2c–e: median lobe of aedeagus in ventral (c), dorsal (d) and lateral (e) view [0.8 mm]; 2f: sclerites of endophallus in lateral view [0.5 mm]; 2g: spermatheca [0.4 mm]; 2h: antenna [1.5 mm]. 1a–b: lectotype; 2a–b: lectotype. scI–IV: sclerites I–IV of endophallus; ds: dorsal spicule; sd: setose depression. Square brackets: length of scale segment.

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’.