Onthophagus chacoensis, Rossini & Vaz-de-Mello & Zunino, 2018

Rossini, Michele, Vaz-de-Mello, Fernando Z. & Zunino, Mario, 2018, A taxonomic revision of the New World Onthophagus Latreille, 1802 (Coleoptera: Scarabaeidae: Scarabaeinae) of the osculatii species-complex, with description of two new species from South America, Journal of Natural History 52 (9 - 10), pp. 541-586 : 560-562

Onthophagus chacoensis sp. nov.

( Figures 1 (c – f), 1(i), 1(j), 1(n – p), 5(a))

Diagnosis

This species is distinguished from other species of the osculatii complex in having the metasternal disc strongly and densely punctated (punctures separated by less than one diameter). Furthermore, specimens of O. chacoensis normally have reddish spots on the humeral umbones and at the apex of the elytra. The pronotum is usually metallic green, while the elytra are dark brown with strong metallic iridescence.

Description

Body length 6.5 mm. Colour. Head and pronotum shining, metallic green with strong cupreous sheen, disc and posterior region of pronotum slightly more opaque, posteromedial region finely sericeous, elytra dark brown and opaque, with reddish spots in proximity of the humeral umbones and apex, interstriae with cupreous and green iridescence, lateral interstriae slightly shinier (VII and part of the VI), pygidium metallic green and dark, sides reddish. Forelegs and ventral side of the body dark brown, meso- and metafemurs and last abdominal sternite reddish. Tarsi, mouthparts, scape and antennal articles I – V brownish, antennal club yellow. Head. Clypeus evenly curved, margin reflexed and slightly sinuated at middle, genal margin slightly expanded beyond the clypeus, clypeo-genal junction barely indicated. Fronto-clypeal carina absent, frons with two horns beside eyes, horns weakly curved and clearly inclined backward (in lateral view), head finely and evenly punctated. Thorax. Anteromedial pronotal protuberance hump-like and rounded between cephalic horns, protuberance flanked by two wide and shallow depressions, lateral margins of pronotum evenly curved, anterior angles obtusely acuminated, border of posterior margin distinct at middle and evanescent near the posterior angles. Posteromedial region of pronotum widely and shallowly depressed, pronotal punctation very shallow and widespread across the surface, dorsal punctures of pronotum with a central pit, anterior angles with punctures very fine and simple, pronotum finely microreticulated on the posterior and central region. Elytra slightly swollen, striae distinct but very shallow, interstriae flat, punctation obsolete (only visible at high magnitude, 40× – 50×), lateral interstriae (VI – VII) with stronger punctures associated to very short and straight setae. Propleuron slightly excavated in proximity of the anterior angles of pronotum, propleural carina sinuated and thin, distal part reaches the external margin of propleuron, propleural lateral margin with strong and coarse punctures associated with long setae visible from above. Prosternum weakly swollen at middle and with few straight setae, mesosternum deeply and coarsely punctated, central region smooth and swollen. Metasternum weakly convex between mesocoxae, superior side of metasternum with stronger punctures and straight setae, metasternal disc densely and strongly punctated ( Figure 1 (e)), some punctures with a central pit, inferior side of metasternum with a shallow sulcus at middle. Abdomen. Pygidium completely bordered, with punctures of different sizes, bigger punctures with a central pit, some punctures with a short and light seta. Legs. Foretibiae slender, with four external teeth separated by small denticles, basal and external margin of protibiae serrate, internoapical margin of protibiae with a very obtuse and curved tooth, apical spur slightly curved downward, with blunt apex. Middle and hind legs unmodified. Male genitalia. In dorsal view, distal-superior area of the paramerites obtusely angled, lateral margin straight to barely excavated. In lateral view, distal-inferior area sinuate, tip of the paramerites strongly curved downward ( Figure 1 (i), 1(j)). Superior margin of the lamella copulatrix swollen on the right side, superior left lobe very narrow and slightly curved at the base, acuminate at the apex, external margin deeply and widely excavated. Inferior right lobe distinctly longer than the inferior left lobe. Secondary lamella quite narrow and elongated, curved near the base, superior margin transversally truncate ( Figure 1 (n)). Female genitalia. Ventral sclerotization of the vagina distinct, central and inferior margin distinctly curved upward ( Figure 1 (p)).

Females differ from major males by the following combination of characters: head margins evenly curved to sub-trapezoidal with clypeus barely truncated at middle, clypeo-genal junction externally not depressed, fronto-clypeal carina distinct and low, frontal carina sub-trapezoidal (from above), straight to barely curved backward at middle, head and pronotum with stronger and denser punctures, anteromedial pronotal protuberance very feebly indicated and hump-like, foretibiae unmodified and slightly larger, last abdominal sternite evenly large at middle.

Minor males can be distinguished from major males by the cephalic horns shorter, anteromedial pronotal protuberance very feeble, pronotal punctures stronger and foretibiae unmodified (like in female).

Etymology

The name of this species refers to the Gran Chaco region, extending from Bolivia to south-western Brazil, Paraguay and northern Argentina.

Distribution and ecology

Onthophagus chacoensis sp. nov. is today known from the region of the Gran Chaco: central and eastern Bolivia, south-western Brazil, north and central Paraguay and northern Argentina ( Figure 5 (a)). According to the collection data of the material examined, this species appears to be common in dry forests. However, we also examined some specimens collected in the Bolivian and Argentinian yungas (moist forests). Onthophagus chacoensis is normally collected with pitfall traps baited with human excrement.

Type specimens examined

Holotype (♂ OUMNH): 1: BOLIVIA, Dept. Santa Cruz, Santa Cruz de La Sierra, Jardin Botanico, 420m alt. 17°46 ’ 00 ” S, 63°04 ’ 13 ” W. 05-06.xi.2006, baited PF, coll. Mann & Hameli (printed on white label). 2: human faeces, baited PF 7/5, Dry semi-decid. Chiquitano Forest , Sandy /loam soils, OUMNH-2007-004 (printed on white label). 3 : HOLOTYPE, Onthophagus chacoensis Rossini , Vaz-de-Mello & Zunino, 2018 (printed on red label with black border).

Paratypes (all the specimens listed below bear a yellow label with black border that contains the following information: PARATYPE, Onthophagus chacoensis Rossini , Vaz-de- Mello & Zunino, 2018):

ARGENTINA: Jujuy: Calilegua Natural Park . 600 m . 18-28-XII-1987 (25 ♂♂, 25 ♀♀ CMNC). Yuto. X-1981 (1 ♂, 1 ♀ CMNC) . 6 Km W Yuto. INTA. 13-14-II-1982 (11 ♂♂, 21 ♀♀ CMNC) . Ledesma. XII-1986 (1 ♀ CMNC). Salta: Oran-Tablillas. II-1944 (2 ♂♂ CMNC) . Chaco: 1000 Km NW Resistencia . Chaco National Park . 12-17-XII-1990 (3 ♂♂, 4 ♀♀ CMNC; 3 ♂♂, 2 ♀♀ BGc) . BOLIVIA: Santa Cruz: Murcielago camp . Tucavaca dry forest. 18°03,5 ’ S, 59°01,6 ’ W. 420 m. X-1994 (1 ♀ BGc). Andrés Ibañez. Lomas de Arena . Forest remnant. 17°55.360 ’ S, 63°09.637 ’ W, 413m . 05-XII-2008 (1 ♂ TAMU). Bermejo. Refugio Los Volcanes. Research Station grounds . 18°06 ’ 41 ” S, 63°36 ’ 05 ” W. 1000 m. 14-XII-2004 (1 ♂ OUMNH) . Chiquitos. 20 Km NE Santiago de Chiquitos . 18°08 ’ 45 ” S, 59°16 ’ 45 ” W. 215 m . XI- 2008 (2 ♂♂, 4 ♀♀ CEMT). Parque Regional Lomas de Arena . 17°33 ’ 13 ” S, 63°05 ’ 47 ” W. 413 m . 05-XII-2008 (3 ♂♂, 4 ♀♀ CEMT). Ciudad Santa Cruz. Jardin Botanico Rio Pirai . 20-XI- 1969 (1 ♂ CMNC) . Santa Cruz Botanic Garden. 17°47 ’ 02 ” S, 63°03 ’ 47 ” W. 400 m . 07-08-XI- 2006 (20 ♂♂, 18 ♀♀ TAMU). Same locality. 17°46 ’ 00 ” S, 63°04 ’ 13 ” W. 420 m . 05-09-XI-2006 (14 ♂♂, 4 ♀♀ OUMNH). Cochabamba: Chapare. Chimore. 250 m . I-1972 (1 ♂, 2 ♀♀ CMNC). BRAZIL: Mato Grosso do Sul: Bonito . Fazenda Brasil. 21°06.274 ’ S, 56°38.148 ’ W. XI-2009 (13 ♂♂, 8 ♀♀ CEMT) . Same locality. Fazenda Palmeirinhas. 21°11.269 ’ S, 56° 33.701 ’ W. XI-2009 (1 ♂, 1 ♀ CEMT) . Same locality. Fazenda Remanso. 21°47.309 ’ S, 56° 43.737 ” W. IX-2009 (10 ♂♂, 4 ♀♀ CEMT) . Same locality. Cabanas. 21°10 ’ 15 ” S, 56°26 ’ 22 ” W. XII-2010 (6 ♂♂, 4 ♀♀ CEMT) . Same locality. Fazenda Morro Alto. 20°02 ’ 25 ” S, 56°37 ’ 47 ” W. XI-2009 (2 ♂♂, 1 ♀ CEMT) . Same locality. Fazenda Pitangueiras. 20°52 ’ 14 ” S, 56°35 ’ 19 ” W. XI-2009 (2 ♂♂, 2 ♀♀ CEMT) . Same locality. Fazenda Arco-Íris. 20°42.138 ’ S, 56°52.655 ’ W. XI-2009 (1 ♂ CEMT) . Bodoquena. Fazenda Califórnia. 20°41 ’ 06 ” S, 56°51 ’ 33 ” W. III-2011 (3 ♂♂, 8 ♀♀ CEMT) . Same locality. Cabanas. 20°41 ’ 51 ” S, 56°52 ’ 50 ” W. III-2011 (1 ♂, 4 ♀♀ CEMT) . Same locality. Ass Canaã. 20°46.267S, 56°46.038 ’ W. XI-2009 (4 ♂♂, 3 ♀♀ CEMT) . Corumbá. Passo do Lontra . XII-2005 (1 ♂, 2 ♀♀ CEMT) . Same locality. Rio Vermelho . 19° 36 ’ 44 ” S, 56°56 ’ 50 ” W (2 ♂♂, 2 ♀♀ CEMT) . Jardim Rio da Prata . 21°25 ’ 39 ” S, 56°27 ’ 04 ” W. III- 2011 (1 ♂, 3 ♀♀ CEMT) . PARAGUAY: Amambay: Pedro Juan Caballero . XI-1998 (4 ♂♂, 2 ♀♀ CEMT) .

Figures

Figure 1. Onthophagus osculatii. (a, b) Dorsal habitus of male (neotype) and female (scale bar: 1 mm). (g, h) Lateral and dorsal view of the parameres (scale bar: 0.05 mm). (k, l) Lamella copulatrix and accessory lamellae; arrow indicating the basolateral carina of the inferior left lobe of O. osculatii. (m) Female genitalia (scale bar: 0.02 mm); arrow indicating the slight medial excavation of the ventral sclerotization of O. osculatii. Onthophagus chacoensis sp. nov. (c, d) Dorsal habitus of male (holotype) and female. (e) Metasternal punctuation (scale bar: 1 mm). (f) Detail of the pronotal punctuation. (i, j) Lateral and dorsal view of the parameres (scale bar: 0.05 mm). (n, o) Lamella copulatrix and accessory lamellae; arrow indicating the deep excavation of the external margin of the left lobe of O. chacoensis. (p) Female genitalia (scale bar: 0.02 mm).

Figure 5. Geographic distribution of the species of the osculatii complex.