Dichotomius nutans
Creators: name: Arias-Buriticá, Jorge Armando
name: Vaz-de-Mello, Fernando Z.
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Scarabaeidae
Dichotomius
Dichotomius nutans

description: Dichotomius nutans (Harold, 1867)
(Figs. 7 A–J, 8C)
Pinotus nutans Harold, 1867: page 97 (original description).
Type material: Pinotus nutans Harold Holotype (♂.): [1,square label with red border, handwritten] Uruguay P. nutans Harold. [2,square label with black line] Ex-Musaeo E. Harold [3,quadrangular and green label] Museum Paris ex Coll. R. Oberthur [4,quadrangular label, handwritten] Rio Parana [5,quadrangular label, handwritten] Uruguayanus o Reich. 1♂. [MNHN].
Additional specimens. (21♂♂. 15♀♀.): ARGENTINA: Buenos Aires: Tandil, 20/ I / 1917, Bruch, C. 1♀. [MZSP]. Tandil, André-legit. Coll. Martínez, Ene[ro], [1]954, 1♂. [CMNC]. Tandil, Bolle-legit, Coll. Martínez, 23. I. [19]54. 1♀. [CMNC]. Cordoba: Colón, Nof Cordoba W of Ascochinga Sierra de Cordoba N. 7.1. 2010 1♀. [CEMT]. BRAZIL: Rio Grande do Sul: U. S. Anna, IX/ 1927, P. Buck, 1♂. 1♀. [MZSP]. Porto Alegre, 12/ VIII / 1931, 1 ♂.; 13/ X / 1927, 1 ♂. 1 ♀.; 15/ IX / 1937, 1 ♀.; 21/ VI / 1928, 1♂.; 27/ VI / 1935, 1♂.; 3/ IX / 1941, 1♂.; 3/ V / 1938, 1♀.; 3/VIII / 1931, 1♂.; 7/IX/ 1927, 4♂. 5♀.; 7/VI/ 1928, 4♂. 4♀.; 23/X/1935, 1♂. [MAPA]. VII/1928, 1♂. [MZSP]. VII/1928, Buck, P. 1♂. 1♀. [MZSP].
URUGUAY: Rocha, Cerro de Lechihuana, Castillos 25 agosto 1995. Leg: J.R. Verdú (00023405, 000234409) 2♂ (00023407) 1♀. [CEMT].
Males: Length 18.5–26.1 mm; width 11–16.3 mm. Black color with brown setae on both sides of head and pronotum (Fig. 7A).
Head: As long as it is wide with prolonged anterior margin giving the appearance of a blunt triangle. Clypeus with a brilliant flange, without clypeal teeth. Surface of clypeus with strong and parallel wrinkles. Genae with curved and pronounced anterior edge, lateral edge straight and then curved, surface with strong wrinkles. Clypeus-genal suture evident, reaching the cephalic process. Frons with a long, sub-quadrangular central cephalic process directed backwards, dorsoventrally flattened at basal area, and compressed on the apical zone where ending with a cylindrical blunt and brilliant tip; horn surface with softer wrinkles than those of clypeus from basal to mid-region. In smaller males the horn is short and without evident final process. Posterior region of the head with elongated holes separated by one time their length.
Thorax: Pronotum twice as wide as it is long. Surface with circular punctures elongated toward the lateral edges and are separated by one time their length. Anterior region with a wide and smooth edge; there isan invaginationtowardthe anteriorregion behindthe cephalic horn, this edge then gets compressed toward the anterior angles. The anterior angle is curved. In the side view, the anterior region of the pronotum is vertical to the dorsal region, straight in the central region and curved toward the lateral zones. There are two short and curved tubercles on the central dorsal region of pronotum; from these tubercles two protuberances like humps continue toward the lateral zones, givingan appearance of an excavation in the anterior area of the pronotum. Behind and between both tubercles, there is an elongated and deep fovea that does not reach the posterior region of the pronotum. Both lateral foveae are big, deep and rounded. Hypomere with shagreened surface and dense setigerous punctures on the lateral edges with erect, long brown setae which can be seen from the dorsal view and less dense in the central region were separated by twice their diameter. In the central region the surface under the femur is smooth and brilliant with the same puncture pattern. Shagreened prosternum mid-region with corrugated surface and prolonged from its medium region until covering the antero-medial zone of mesosternum. From the posterior edge of the prosternum many yellow setae emerge directed toward the mesosternum. Elytra with strong striae, the first four of which formed by a slope with a shagreened surface, narrow in the anterior zone and becoming broader toward the middle zone before being compressed again in the final area of the elytra; the fifth to seventh striae bicarinate with uniform width through their complete length. Interstriae convex and elevated with shagreened surface and small punctures separated by three times their diameter; some of them having transverse wrinkles giving a corrugated appearance. Mesosternum strongly narrowed medially, on which there is a brilliant and smooth process that prevents the meso-metasternal suture from being seen. There is a shagreened surface toward the sides with dense setigerous punctures and yellow setae. Mesepisternum has the same surface as the lateraledges of mesosternum.Meso-metasternal sutureis erased in central areaby a mesosternum process, lateral margins evident and brilliant. Metasternum withshagreened, shiny central areawithout setae; strong carina from 1/3 of metasternum to the back ending in a deep fovea. Side edges of the anterior area shagreened with dense setigerous punctures, posterior area shagreened with large setigerous punctures. Metepisternum equal to mesepisternum.
Abdomen: Sternites shagreened with some punctures in the middle region in the 5th and 6th sternites. All sternites with dense ocellated punctures on lateral edges. 6th sternite very narrowed medially. Pygidium shagreened with elongated punctures and separated by one time their length, incomplete margin in the middle inferior region.
Male genital organ: Side view of aedeagus with sub-quadrangular phallobase, basal zone with a medium bulge on both sides, apex with a constriction of approximately 115 ◦. Parameres subtriangular with a thin at the inferior base, which continues with an invagination toward the middle zone; thin and blunt apex with flat surface setae (Fig. 7B); dorsally symmetric with enlarged base and becoming thinner toward apical zone where ending with a blunt tip; from this view, setae can be seen too. Internal region with a convex and soft invagination toward the middle of each paramere (Fig. 7C). In the ventral view parameres are thin at the basal zone with an acute prolongation described in the lateral view: blunt and flat apex where setae can be seen. Between parameres and inserted from the apical to basal zone by membrane, there are two lamellated and overlapped processes, that of the left paramere over that of the right paramere in a characteristic way running from the apical zone to beyond two-thirds of the parameres (Fig. 7D). Internal sac tubular with raspules on the basal two-thirds; in the center one big, sub-quadrangular, brown color copulatrix lamellae, with two tubular and darker lateral prolongations, entire surface covered by bristles which become longer toward the lateral margins (Fig. 7E). Apical zone with three accessory lamellae, one long and central with undefined form, in the central area more sclerotized surrounded bysemi-quitinized membrane (Fig.7F).Left lateral lamella has “C” form, with an enlarged and less sclerotized superior margin, irregular borders, inferior zone thinner and sclerotized with defined borders (Fig. 7G). Right lateral lamella has “N” form, enlarged, sclerotized, right margin wider than the left, with a semi-quitinized membrane (Fig. 7H).
Female: Length 21.5– 28 mm; width 12–16.5 mm. It differs from males due to exhibiting a four-pointed cephalic process on fron; both central tips higher, lateral tips conical and smaller (Fig. 7I). Centraltubercles of the pronotum are softer (Fig.7J). 6thabdominal sclerite not shortened medially.
Commentaries: The species is distinguished from the others of the group “ buqueti ” because the males have an only central horn on the fron and females with four-pointed cephalic process. Pronotum with two short and curved tubercles on the central region from these tubercles two protuberances like humps continue toward the lateral edges, giving an appearance of an excavation in the anterior area of the pronotum. Behind and between both tubercles, there is an elongated and deep fovea that does not reach the posterior region of the pronotum. Black elytra with strong striae where the final part of the first to the fourth are widened. This species is associated to low mountains of the Pampa biome, in extremely intervened areas, where natural vegetation is scarce.
Distribution: This species is distributed in Argentina in the Buenos Aires province, in Brazil in the Rio Grande do Sul state and in Uruguay in the Rocha department (Fig. 8).
description: Published as part of Arias-Buriticá, Jorge Armando & Vaz-de-Mello, Fernando Z., 2019, Redefinition and taxonomic revision of the " buqueti " species-group, Dichotomius Hope, 1838 (Coleoptera: Scarabaeidae: Scarabaeinae), pp. 43-52 in Revista Brasileira de Entomologia 63 (1) on pages 50-51, DOI: 10.1016/j.rbe.2018.11.002, http://zenodo.org/record/3677297