Metallactus quadrinus D. Sassi 2022, n. comb.
Creators: name: Sassi, Davide
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Chrysomelidae
Metallactus
Metallactus quadrinus

description: Metallactus quadrinus (Suffrian, 1866) n. comb.
(Figs 6; 16)
Scolochrus quadrinus Suffrian, 1866: 226.
Griburius quadrinus Clavareau, 1913: 91 (catalogue); Blackwelder, 1946: 640 (catalogue).
Types. Suffrian (1866) did not mention the number of specimens under study, but he reported the name of a single collector (“Sellow”), a single locality (“Collo del Sacramento”) and a single type location (depository) (MNHUB), where a single syntype was located. A lectotype is designated as follows: lectotype (by present designation): ♀, pinned // “24007” [white label, printed] // “ quadrinus Suffr. * Col. del Sacr. Sell.” [blue label, handwritten] // “ Griburius quadrinus (S uffrian, 1866) (Sc olochrus quadrinus) LECTOTYPUS D. Sassi des.” [red label, printed] // “ Metallactus quadrinus (Suffrian, 1866) D. Sassi det. 2021” [white label, printed] // (MNHUB).
Type locality. Colonia del Sacramento (Colonia, Uruguay). Suffrian’s indications regarding the localities of the type series are often rather generic. He seems to consider “Còl. del Sàcr.” to be a Brazilian toponym. However, no evidence was found regarding the existence of a place with a similar name in southern Brazil. On the other hand, the name corresponds to a well-known Uruguayan locality. Hence, I am inclined to think that the lectotype comes from Uruguay, where the collector, F. Sello, travelled extensively (Krausch, 2002).
Additional material examined. BRAZIL: São Paulo 2.I.1974 V. N. Alin (2, FSCA); São Paulo 15.XII.1966 V. N. Alin (2, ERPC); São Paulo Mráz lgt. (3, ERPC).
Distribution. Brazil, Uruguay (new).
Diagnosis. The species was described as belonging to the genus Scolochrus (now Griburius), but the shape of the male genitalia, the morphology of the pronotal process, the ocular distance and the overall outline clearly suggest a transfer to the genus Metallactus. Among the examined species, the most similar is M. planipennis, at least based on general colour pattern. It can be distinguished from the latter by the punctation which is lighter and sparser, in particular on the pronotum, and in the pronotal outline, which is more transverse and more flattened close to the posterior margin. The aedeagal shape is quite similar, but the apical region is differently arranged in ventral view (compare Figs. 5c and 6c).
Description of male. BL = 3.4–4.3 mm, BW = 2.0– 2.5 mm, PL = 1.2–1.6 mm, PW = 1.9–2.4 mm. Interocular distance 5.9–7.0 % of BL.
Head black with triangular yellow spot on frontoclypeal area, smaller rounded one of lower part on frons. Labrum brownish. Surface with few, sparse, small punctures, short semi-erect setae. Mid-cranial suture narrow but well detectable from vertex to yellow spot on frontoclypeus. Ocular lines narrow, strictly adhering to ocular rim, marked by line of punctures departing from ocular rim just beside ocular canthus, whose surface scarcely punctate. Ocular canthus deep, rounded with few, sparse short and semi-erect setae. Antennae (Fig. 6h) brownish. First five antennomeres sublucid, 3-5 rod-shaped, 6-11 dull, flattened and more diffusely setose.
Pronotum black with two large yellow stripes covering lateral margins. Such stripes often shortly extended along posterior and anterior margins. Posterior margin at times partly yellow at middle. Pronotal outline rather transverse, elliptical, fairly flattened on disc in particular towards base. Lateral margins thin, almost not visible in dorsal view, mildly curved with maximum width just behind half length. Surface shining with scattered, finely impressed punctation, almost obliterated at middle of disc. Posterolateral impressions shallow but perceivable, delimited by slightly thickened pronotal posterior margin.
Scutellum black, distinctly raised, finely setose and very minutely punctured. Apex truncated in straight line.
Elytron black with large yellow patch on humeral region, posteriorly reaching middle of elytra. Second large rounded yellow spot covering apical clivus up to posterior margin. Yellow pattern often expanded to cover most of disc, leaving triangular or almost square black patch only, along midline. Epipleuron yellow. Elytral outline parallelsided, rather stout, elytron disc weakly flattened on posterior part. Lateral margin rather large, in dorsal view visible from apex up to humeral callus. Elytral surface shiny, covered with well impressed punctures arranged in irregular rows. Intervals slightly raised and connected here and there by faint transverse wrinkles. Postscutellar area slightly raised. Humeral callus prominent, impunctate. Epipleuron smooth, impunctate, rather convex.
Pygidium brownish, sometimes with two narrow yellow stripes along sides, smooth, matt, covered by sparse very shallow minute punctures and short setae.
Ventral parts of thorax totally dark black. Abdominal ventrites dark brown with yellow border along sides. Hypomera shiny, bare, with scarce, scattered punctures. Mesoepimera and mesoepisterna with rugulose surface, bearing scattered setae and shallow punctures. Rest of ventral surface matt, shallowly punctured, with covering of sparse, appressed setae. Prosternal process longitudinally grooved, sparsely punctured with long setae and raised short triangular apex. Legs brownish with lighter distal part of tibiae and tarsi. Apex of mid and posterior femora and anterior coxae with yellow patches.
Median depression on fifth abdominal ventrite shallow but large, fairly delimited from rest of ventrite surface, moderately shiny, bare and impunctate. Posterior margin of fifth abdominal ventrite raised, slightly notched. Median lobe of aedeagus (Fig. 6c–e) compressed laterally, with strongly expanded apex, well differentiated from shaft, roughly subpentagonal, terminated by rounded median denticle. Ventral outline convex but fairly depressed in middle. Setose depressions deeply impressed, ear-shaped, separated by wide, blunt carina. Two small ridges at bottom of each depression, distal one, bearing short setae, roughly transverse, basal one triangular, terminated with blunt apex. In lateral view such ridges looking like single, double-headed lamella.
Endophallus (Fig. 6f) with sclerite I sickle-shaped, pigmented, flattened, tapering in sharp denticle barely delimited from rest of sclerite. Dorsal spicule not detectable. Sclerite II small, stout, well-pigmented, with slender projection upwardly directed. Sclerite III sickle-shaped, with regularly curved arch and pointed apex. Branches of sclerite IV slightly shorter than sclerite III in folded-up structure, slender, distinctly arched towards ventral direction with blunt apex and smooth surface.
Female. Habitus in Fig 6 a-b (LT). BL = 4.5 mm, BW = 2.6 mm, PL = 1.6 mm, PW = 2.4 mm. Interocular distance 11.1 % of BL.
Two females were available for this study. The first one (lectotype) is black with two yellow spots on the elytra, one on the humeral region and a second one covering the apical clivus. The second specimen has the pronotum totally yellow and the elytron yellow with blurred darker patches on the anterior median section of the disc. The examined females also differ from males in a broader ocular distance.
The fifth abdominal ventrite in females has a large, rounded, impressed pit. The bottom of the pit is glabrous, covered with sparse punctures. The vasculum of the spermatheca (Fig. 6g) is moderately pigmented, S-shaped with a twisted, not swollen proximal lobe and a long, slender distal lobe, which is distally tapered with the apex almost straight. The ampulla is scarcely pigmented, short, sitting just at the basal apex of the vasculum. The duct and sperm gland insertions are perceptibly distinct. The duct is short, beside the vasculum is robust, quite rigid, forming turns more than coils, then slender and almost straight. The insertion on the bursa copulatrix is robust, conical, strongly pigmented.
description: Published as part of Sassi, Davide, 2022, Revision of the Metallactus taeniatellus species group (Coleoptera: Chrysomelidae: Cryptocephalinae), pp. 251-282 in Zootaxa 5125 (3) on pages 266-268, DOI: 10.11646/zootaxa.5125.3.1, http://zenodo.org/record/6443765