Megachile (Chrysosarus) obscurior Jörgensen, 1912

Roig-Alsina, A. & Torretta, J. P., 2021, The leucografa species group of Megachile (Chrysosarus) (Hymenoptera: Megachilidae), Journal of Natural History 55 (7 - 8), pp. 457-470 : 464-466

Megachile (Chrysosarus) obscurior Jörgensen

( Figures 1 (c,f), 2(c,d), 3(a–c), 4(a–d), 5(b))

Megachile obscurior Jörgensen, 1912a: 127 , 133 (Holotype female, Argentina, Mendoza, Chacras de Coria , 11 December 1906; MLP, examined). Jörgensen 1912b: 311. Durante and Díaz 1998: 12. Durante et al. 2008: 433.

Megachile (Chrysosarus) obscurior: Raw 2007: 37 . Moure et al. 2007: 958. Ascher and Pickering 2020.

Diagnosis. Females of M. obscurior vary in the colour of their vestiture from entirely black to a pattern of black and white hairs similar to that of M. leucografa . Specimens with white hairs are more frequent in the south of the distribution, in the provinces of Mendoza and Neuquén, and black specimens are usual in the northern provinces of Tucumán and Salta, but all intergrades can be found in the same population throughout the range of the species. Specimens entirely black or with apical bands on the metasoma partially pale can be easily identified as M. obscurior , but those with complete pale apical bands on T1–T5 can be confused with M. leucografa . The hairs of the scuto-scutellar band are longer (0.6–1.1× MOD) in M. obscurior , and less plumose, so that the band is not dense and distinct as in M. leucografa . Also longer are the hairs on the dorsolateral angle of the pronotum (1.2–1.5× MOD), the hairs behind the tegula (on the posterodorsal portion of the preaxilla, 0.9–1.5× MOD), and the hairs on the disc of the scutum (up to 1.2–1.6× MOD). Females of M. obscurior also differ from M. leucografa by the colour of the appressed vestiture of T6, always black, and the pale bands of the terga, when present, are white, without yellow tints. Males are easily distinguished from those of M. leucografa and M. rancaguensis by the glabrous, rugose hypostomal area, the black hairs on the lower part of the gena, the lack of an oblique row of setae on the under surface of the forefemur, and the dark brown tuft of hairs on the inner side of the mandible not accompanied by other hairs on the lower margin of the mandible.

Redescription. Female. Body length: 9.5–12 mm (holotype 12 mm). Forewing length: 6.5–8 mm (holotype 8 mm). Colour. Integument black, except light brown base of claws. Wings weakly infuscate, with darker apices; veins and pterostigma dark brown. Pubescence. Colour variable: some specimens entirely black, others with different amount of white hairs; only palest specimens are described. Head: white hairs on gena and around antennal sockets. Mesosoma: white hairs on dorsal margin of pronotal collar; white patch on pronotal lobe and anterior part of tegula briefly continued ventrally on upper part of mesopleuron; white patch on posterolateral angle of scutum, and intermixed white and black hairs on scuto-scutellar suture; white hairs on metanotum and most of propodeum; intermixed white and black hairs on outer and lower sides of hind tibia. Metasoma: with complete apical bands of white hairs on T1 – T5 . Scopa with greyish hairs on S2–S5. Hairs on disc of scutum up to 1.5–1.6× MOD, on scuto-scutellar band 0.6–1.1× MOD, on preaxilla behind tegula 0.9–1.5× MOD, on dorsolateral angle of pronotum 1.2–1.5× MOD, on scutellum up to 2.5× MOD, and on mesopleuron below hypoepimeral area 1.2–1.5× MOD. Hairs of apical bands on T2 – T3 0.7–0.8× MOD; disc of T2 with long hairs (1.2–1.7× MOD), shorter on discs of T3 – T4 (0.7–1.2× MOD) . Sculpture. Clypeus and supraclypeal area with dense punctures, separated by shiny interspaces 0.1–0.2× PD, but supraclypeal area frequently with central area of sparse punctures (such area feebly tessellate in some specimens). Scutum and scutellum with dense punctures, separated by interspaces 0.2–0.5× PD; on most of scutum interspaces shiny, but usually feebly tessellate around admedian lines. Punctures on mesopleuron below hypoepimeral area dense, separated by 0.1–0.3× PD. Discs of terga shiny; punctures dense, separated by 0.2–0.5× PD. Morphology. Inner margin of eyes convergent below, proportion of upper to lower interocular distance 1.04. Distance between lateral ocellus and occipital margin of head 2× MOD. Clypeus 2.3× as wide as long; apical margin with median smooth emargination. Maximum width of gena 0.76× maximum width of compound eye. Proportions of scape, pedicel and first three flagellomeres 3.1:0.9:1:0.9:1; first flagellomere as long as 1.2× its apical width. Fourth mandibular tooth pointed. Hind basitarsus 2.55–2.60× as long as its maximum width. T6 slightly concave in profile, with rounded apex in dorsal view .

Male. Body length: 9.5–12.3 mm. Forewing length: 7.1–8.3 mm. Colour. Similar to that of female, except foreleg: under surface of femur and tibia, and entire tarsus yellowish brown; underside of second tarsomere with black ellipsoid spot. Pubescence. Variable in the extent of black and white hairs. Palest specimens with white hairs on most of head, except some intermixed black hairs on vertex, and black hairs surrounding the bare hypostomal area; mesosoma and most of legs with white hairs, except foreleg as described below; metasoma with entire white apical bands on T1–T4 and apical white hairs on S2–S3, remainder of metasoma with black hairs. Darkest specimens with white hairs restricted to face, pronotal lobe and medially interrupted apical bands on T1–T4. Pubescence of foreleg and mandible similar in pale and dark specimens. Mandible on lower surface with conspicuous basal tuft of dense brown hairs with white apices. Foreleg: under surface of coxa, trochanter and femur always with black hairs; femur without oblique row of setae on under surface; outer fringe of tarsus with yellowish-brown hairs (as long as 1.6–1.7× apical width of basitarsus), covered with shorter white hairs dorsally; in some specimens hairs of fringe close to tibia black; under surface of tarsus with short white hairs. Sculpture. Similar to that of female. Morphology. Vertex of head broad, distance between lateral ocellus and occipital margin of head 2× MOD. Lower margin of mandible forming distinct angle near middle. Apical margin of clypeus with median emargination, without denticles. Maximum width of gena 0.7× maximum width of compound eye. Hypostomal area glabrous, rugose. Proportions of scape, pedicel and first three flagellomeres 3.1:0.9:1:1.3:1.7; first flagellomere as long as its apical width; last flagellomere broadened. Anterior surface of forecoxa bare, with group of 6–10 ferruginous bristles up to 0.7× MOD; spine 1.0–1.2× MOD; lower outer margin of forefemur and tibia rounded. Forebasitarsus wide, flattened, proportion of lengths of basitarsus and second tarsomere along midline 1.0:0.8, basitarsus 1.4 as long as its apical width. Preapical carina of T6 medially with small median emargination, sometimes with 1–2 rudimentary teeth lateral to it. S5, S6, S8 and genital capsule as in Figure 4 (a–d).

Distribution. Argentina, provinces of Buenos Aires, Catamarca, Chubut, Jujuy, La Rioja, Mendoza, Neuquén, Río Negro, Salta and Tucumán ( Figure 5 (b)).

Material studied. Argentina. Buenos Aires: 1 M, 8 km E Carmen de Patagones , 26 December 2007, ex Larrea divaricata, A . Roig A. (MACN). Catamarca: 2 M, Campo El Arenal , 15 November 1993, A . Roig A. ( MACN) ; 1 F, Jujuil, January 1924 ( MACN); 3 F, Belén, Hualfín , 30 January 2010, ex Larrea nitida, J .P. Torretta (FAUBA). Chubut: 1 M, Biedma, Pto. Madryn , 8 February 2011, J .P. Torretta ( FAUBA) . Jujuy: 1 M, Humahuaca, Iturbe , 3 February 2010, ex Fabaceae, J .P. Torretta (FAUBA); 1 M, Salar de Olaroz, Departamento Susques , 23.2833°S 66.6345°W, 3930 m s .n.m., A. Molina (MACN) . La Rioja: 1 M, camino a Laguna Brava , 2366 m, 28 January 2006, L . Compagnucci ( MACN); 1 M, Sañogasta , 24 February 1939, Biraben and Scott, ( MLP) . Mendoza: 1 F, 3 M, Departamento Luján, Cerro Negro, ruta a Uspallata , 10 February 1999, ex Larrea cuneifolia, A . Roig A. (MACN); 1 M, Cuesta del Ternero , November 1965, A . Giai ( MACN); 1 F, Potrerillos , 17 January 1985, A . Roig A. ( MACN) . 14 F, 4 M, Villavicencio, Sitio V2 , 32.53075ºS 68.947806ºW, 1225 m, 13/ 29 November 2006, from trap nests, D . Vázquez, N. Chacoff and J. Dorado ( MACN); 2 F, Villavicencio, Sitio V2 , 32.53075ºS 68.947806ºW, 1225 m, 13 November 2006, D . Vázquez, ex Larrea divaricata (MACN) ; Villavicencio, 2 F, Sitio V1 , 32.523139ºS 68.955111ºW, 5 February 2007, 1 November 2011, D . Vázquez, N. Chacoff and J. Dorado ( MACN); 3 F, 1 M, Villavicencio, Sitio V4 , 32.538722ºS 68.9939611ºW, 20/ 23 December 2006, 22 October 2010, 11 November 2011, D . Vázquez, N. Chacoff and J. Dorado ( MACN); 2 F, Godoy Cruz, Pto . Chambón , 20 November and 1 December 1995, G . Debandi ( IADIZA); 2 F, 5 M, Uspallata , 15/ 16 December 1954, A . Ogloblin ( MLP) . Neuquén: 3 F, 3 M, entre Villa El Chocón (39.2833°S, 68.833°W) y Arroyito (39.0833°S, 68.5833°W), 14–26 November 2004, YPT, M . Tadey ( MACN); 1 F, Rinconada , 24 November 1964, A .G. Giai ( SEMC); 1 F, Co . Lotena, 18 December 1965, Schajovskoi ( MLP); 3 M, Pampa Pilmatue , 25 November 1964, Schajovskoi ( MLP) . Río Negro: 3 M, Paso Córdoba, 8 km SW Gral . Roca , 26–28 February 1998, C . and M. Vardy ( NHMUK); 1 F, Stefanelli , 8 November 1955, A .G. Giai ( SEMC); 1 F, Paso Flores , 7 February 1963, A .G. Giai ( SEMC); 4 F, 1 M, Gral . Roca , 9 November 2013, ex Cercidium praecox, H .J. Marrero (FAUBA); 3 F, Chinchinales, 24 November 1965, Schajovskoi ( MLP); 7 M, Río Colorado , November 1943, JMB ( MLP) . Salta: 1 M, Recta Tin Tin , 15 km SE Payogasta, 21 March 1990, A . Roig A. ( MACN) ; 1 F, 1 M, Recta de Tin Tin, 5 November 2004, Compagnucci and Grismado ( MACN); 1 M, Payogasta, Arroyo El Molle, 4 November 2004, Compagnucci and Grismado ( MACN); 1 F, Ruta 40, S de Cachi, 21 April 2015, R . González V. ( MACN) ; San Carlos , 2 M, 4 April 2004, Compagnucci and Grismado ( MACN); 1 M, 5 km N Cachi, camino a La Poma, 5 June 2004, Compagnucci and Grismado ( MACN); 1 F, Palo Pintado, RN 40, 4 June 2004, Compagnucci and Grismado ( MACN); 1 F, Yacochuya, 8 Km NW Cafayate, 2 January 1972, D .J. Brothers ( SEMC) . Tucumán: 2 F, 1 M, Amaicha del Valle , 3 November 1989, L . Moffatt ( MACN); 2 M, Amaicha del Valle, 2 November 2004, Compagnucci and Grismado ( MACN); 1 F, Ampimpa , 31 October 2004, Compagnucci and Ojanguren ( MACN) .

Figures

Figure 1. (a) Megachile leucografa, female, clypeus and mandibles; (b) M. leucografa, male, ventral view showing pilose hypostomal area, tuft of hairs on inner surface of mandible (‘t’), and oblique row of hairs on under surface of femur (‘r’); (c) M. obscurior, male, ventral view showing glabrous, rugose hypostomal area; (d) M. rancaguensis, male, ventral view showing pilose hypostomal area; (e) M. leucografa, female, hind tarsus; lines indicate measurements of length and width of basitarsus; (f) M. obscurior, male, dorsal view of apical metasomal terga. Scale bars: a, e = 0.5 mm; b–d, f = 1 mm.

Figure 4. Megachile obscurior, male: (a) S5; (b) S6; (c) S8; (d) genital capsule, ventral view. Scale bar: 1 mm.

Figure 5. Distribution of the species of the Megachile leugografa group. (a) Megachile leucografa (triangles); (b) M. obscurior (dots); and M. rancaguensis (stars).