Metallactus octoguttatus D. Sassi 2019, n. comb.
Creators: name: Sassi, Davide
Publisher: name: Zenodo
Year: 2019
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Chrysomelidae
Metallactus
Metallactus octoguttatus

description: Metallactus octoguttatus (Burmeister, 1877) n. comb.
(Figs 12; 29)
Griburius octoguttatus Burmeister, 1877: 65; Clavareau, 1913: 90 (catalogue); Blackwelder, 1946: 640 (catalogue); Agrain et al., 2017: 57 (annotated checklist).
Metallactus albopictus Chamorro, 2013: 201, fig. 8; 204, fig. 26 (taxonomic study).
Types. Burmeister did not mention the number of specimens under study but two specimens housed in MACN match the original description. The typification has been made as follows, in order to stabilize the epithet. LECTOTYPE (by present designation): ♀, pinned, not dissected // “ Parana Jan.” [green label, printed] // “ Griburius octoguttatus Burmeister 1877 Syntypus ” [red label, handwritten] // “ Griburius octoguttatus Burmeister, 1877 LECTOTYPUS D. Sassi des.” [red label, printed] // “ Metallactus octoguttatus (Burmeister, 1877) D. Sassi det. 2019” [white label, printed] // (MACN). PARALECTOTYPE: 1 ex. sex undet. // “ Griburius octoguttatus Burmeister 1877 Syntypus ” [red label, handwritten] // “ Griburius octoguttatus Burmeister, 1877 PARALECTOTYPUS D. Sassi des.” [red label, printed] // “ Metallactus octoguttatus (Burmeister, 1877) D. Sassi det. 2019” [white label, printed] // (MACN).
Type locality. Paranà (Entre Ríos, Argentina).
Further material examined. ARGENTINA: Saenz Pena Chaco (2, BMNH); Estancia la Noria Rio San Javier Santa Fè G. E. Bryant (14, BMNH); S. Antonio Reimoser (2, NMV); T. N. Formosa Loc. Gran Guardia XI.1953 (2, NHMB); Chaco de Santa Fé Las Garzas borde du rio Las Garzas 20 Km l’O d’Ocampo E. R. Wagner 1903 (1, MNHN); Resistencia Balzan 188[...] (1, MSNG); La Merced Reimoser (1, NMV). PARAGUAY: San Luis Reimoser (1, NMV); Dep. Cordillera, Pirareta 12/ 15.X.2010 S25 29’ W56°56’ Leg. U. Drechsel (1, UDPC).
Distribution. Argentina, Paraguay. New to Paraguay.
Diagnosis. A Metallactus of small-medium size. It belongs to a subgroup of four species (M. albopictus, M. octoguttatus, M. madefactus and M. abditus) distinguished by a pronotal V-shaped yellow spot just in front of scutellum. Among these species, M. octoguttatus is characterized by the shape of the aedeagal median lobe, the apicoelytral spots generally separated from each other, and the completely yellow clypeus. Also, the median longitudinal spot on the pronotum is generally shorter and stouter than in M. albopictus, particularly in males, while the pronotal lateral spot is more salient along the posterior margin (C-shaped). The species is also more robust than M. albopictus and shows a lighter pronotal punctation, approaching more to M. abditus in these two last characters. M. madefactus can be distinguished for the different shape of the apicoelytral spots and the more extended yellow color on frons.
Overall, in the studied material the dorsal color pattern of the four species of this subgroup almost always seems to offer enough information for the diagnosis. However, the chromatic differences might not be adequate dealing with a larger number of specimens. For example, in some of the 14 specimens from Estancia la Noria (BMNH) the yellow elliptical spots tend to expand and coalesce, masking the “typical” habit of M. octoguttatus. Furthermore, a specimen, male, from Formosa has mostly yellowish legs, together with part of the ventral surface. The aedeagal shape could therefore prove to be necessary in many cases for a correct identification.
Description of male. Habitus in Fig. 12 a–b (LT). BL = 3.9–4.1 mm, BW = 2.4 mm, PL = 1.3–1.4 mm, PW = 2.2 mm. Interocular distance 12.8–14.6% of BL.
Head black with two almost trapezoidal yellow spots along upper section of inner ocular rim, coalescent along midline; clypeus yellow as well. Labrum brownish. Vertex quite dull, almost bare with sparse rather coarse punctures to almost impunctate. Frontoclypeal area with sparse pale setae and quite coarse punctation. Mid-cranial suture short, well impressed so that surrounding surface distinctly swollen. First five antennomeres yellowish, sublucid, the subsequent ones totally darkened, dull and more diffusedly setose.
Pronotum black with lateral margin and outer part of anterior and posterior margins covered with a single Cshaped yellow spot; a median V-shaped (almost elliptical in one paratype) yellow spot close to posterior margin just in front to scutellum; a smaller elliptical median one, yellow as well, close to anterior margin. Pronotal shape relatively short-elliptical with lateral margins thin, barely visible from above, regularly curved with maximum width slightly behind the middle. Posterolateral impressions obliterated. Surface moderately lustrous with scattered, feebly impressed punctation, slightly sparser and shallower on disc.
Scutellum black, moderately raised, apex truncated in a straight line. Finely setose and minutely punctured.
Elytron surface black with four yellow spots lined up along suture. First spot, rounded, beside scutellum; second one, rounded as well to moderately elliptical, at middle; third one, transverse, on apical clivus; fourth one, smaller and roughly rounded, at apex. A further C-shaped, yellow spot surrounding humerous and extended on outer part of anterior margin and epipleuron. Elytral outline parallel-sided to sides slightly convergent posteriorly, only weakly flattened on disc. Postscutellar area very weakly raised. Humeral callus moderately prominent, impunctate. Surface moderately shiny with shallow punctures arranged in irregular rows, perceptible on elytral apex too. Intervals not raised.
Pygidium yellow, with a brownish spot on apex, smooth, matt, with sparse, shallow punctures and whitish setae.
Inferior parts of thorax totally black to widely yellowish, covered with sparse setae and shallowly punctured. Prosternal process coarsely punctured with long setae, Abdominal ventrites black with large yellow margins to almost completely yellow, shallowly and sparsely punctured, with sparse setae. Legs totally black to largely yellowish on femora and basal section of tibiae.
Median depression on fifth abdominal ventrite shallow, matt and almost bare. Posterior margin of fifth abdominal ventrite perceptibly notched. Median lobe of aedeagus (Fig. 12 c–e) cylindrical, with smooth surface and apex scarcely separated from the rest of aedeagus, short. In lateral view apex faintly bent ventrally. Hairy dents barely impressed, scarcely delimited, bearing rather short, dense setae. Aedeagal ventral surface not swollen in lateral view, devoid of particular structures. Endophallus (Fig. 12 f–g) with sclerite I well sclerotized with denticle strongly developed, blunt, pointing upwards and barely sticking out laterally. Dorsal spicule rather short, pointed and fairly pigmented. Sclerite II long, regularly bent towards base and gradually tapered towards apex. Arch of sclerite III high, fairly projecting upwards, straight, slender. Apex of sclerite III straight, regularly tapered, fairly expanded on its proximal half, so that the sclerite looks like the head of a grebe. Branches of sclerite IV shorter than sclerite III in the folded-up structure, perceptibly curved, with slightly asymmetrical, microdenticulate apex and surface moderately sculptured, consisting of small wrinkles.
Female. BL = 4.8–5.3 mm, BW = 2.9–3.4 mm, PL = 1.6–1.8 mm, PW = 2.6–2.9 mm. Interocular distance 14.6–17.0% of BL.
Fifth abdominal ventrite in females with quite large, transverse, shallow pit. Bottom of pit bald, matt, impunctate but covered with tiny wrinkles. Vasculum of spermatheca (Fig. 12h) slender, scarcely pigmented with straight proximal branch fairly and asymmetrically swollen at base, long distal branch and long, pointed apex markedly bent downwards. Ampulla fairly 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 thick, almost regularly arranged. Distal not coiled portion of duct long, completely straight on its terminal section. Insertion on bursa copulatrix lengthened, straight, barely swollen and well pigmented.
description: Published as part of Sassi, Davide, 2019, Revision of the Metallactus hamifer species-group (Coleoptera: Chrysomelidae: Cryptocephalinae), pp. 201-245 in Zootaxa 4657 (2) on pages 230-232, DOI: 10.11646/zootaxa.4657.2.1, http://zenodo.org/record/3763876