Megasoma bollei (Dechambre, 2006) new combination

Figs. 1A–G, 2A–E

Gibboryctes bollei Dechambre 2006: 155 (original combination)

Diagnosis. Megasoma bollei is distinguished from other Megasoma species by the following combination of characters: Clypeus short, nearly three times wider than long, triangular in shape (Fig. 2A, D); mandibles rectangular, lacking teeth, truncate on apical margin (Fig. 2A); male head with short, flattened, transverse, bifurcate horn (Fig. 2A); male pronotum only with a small, forward produced tubercle near anterior margin (Fig. 1E); female head with two small tubercles on frontoclypeal suture (Fig. 2D).

Type material. Holotype male examined (Fig. 1A–C)., labeled: “Pampa Avila II.1996 Dpta Chacabuco Chaco ARGENT. S. Bolle [white label, handwritten] / HOLOTYPE [red label] / Gibbboryctes bollei n. sp. [illegible] HOLOTYPE R.-P. Dechambre det. 2006 [white label, partially handwritten] / MNHN EC8765 [white label]” (MNHN).

Non-type material examined. ARGENTINA: Chaco, Castelli, 10.i.2006, E. Abadie — 1 male, 1 female (CERPE) ; Chaco, Castelli, 20.ii.2002, R. Foerster — 1 male (EPGC) ; El Colchon, 25–30.i.2006, E. Abadie — 1 male, 1 female (EPGC) . PARAGUAY: Presidente Hayes, Escalante, (- 23.783ºS, - 60.783ºW), 27–28.i. 2003, 151 m, B. Garcete — 1 female (CERPE) .

Male redescription. (Figs. 1D–E, 2A–C). Body length: 24.6–26.0 mm. Body width: 11.2–12.1. Body: Oval in dorsal view (Fig. 1D), convex in lateral view (Fig. 1E); dorsal surface glabrous; ventral surface moderately covered with yellow setae. Color: Predominantly reddish brown; protibial outer margin dark. Head: Surface coarsely rugopunctate. Clypeus triangular, transverse, three times wider than long, slightly reflexed, acute anteriorly (Fig. 2A). Frontoclypeal suture with a transverse, bifurcate horn in dorsal view (Fig. 2A); horn short, flattened in lateral view (Fig. 1E). Frons with punctures larger compared to those of clypeus. Ocular canthus subrectangular, transverse, glabrous, slightly emarginate on anterior margin; outer corners acute. Mouthparts: Mandibles rectangular, concave dorsally, lacking teeth, truncate on apical margin (Fig. 2A). Maxilla densely setose; galea triangular, rounded at apex, lacking teeth. Mentum subparallel on sides, convergent near apex; surface covered with large, deep, setigerous punctures. Antennae: With 10 antennomeres; club as long as antennomeres 2–7 combined; lamellae 8–10 decreasing in size exclude. Thorax: Pronotum lacking posterior border; lateral margins rounded; surface densely covered with large, deep, coalescent punctures; pronotal medial line longitudinally smooth; anterior region with a small, transverse tubercle contiguous to anterior margin; tubercle slightly emarginate at middle in dorsal view, forward produced in lateral view (Fig. 1E). Scutellar shield parabolic, densely punctate on sides, smooth on middle area near anterior margin; punctures rounded, deep. Elytral surface rugose, punctate; elytral striae distinct, covered with deep punctures; interstriae finely punctate. Prosternal process short, densely setose. Legs: Protarsomeres elongate, cylindrical; tarsomere 5 subequal in length to 2–4 combined. Protibia subequal in length to protarsomeres 1–5 combined; surface densely rugopunctate dorsally; outer margin with three triangular teeth subequal in size. Mesofemur oval, transverse, densely setose. Mesotibia subtriangular, bicarinate on outer surface (one basal carina, one medial carina); each carina bordered with spinule-like setae; basal carinae sometimes absent; medial carina diagonally projected, weakly crenulate; apex truncate, glabrous. Metafemur sparsely setose. Metatibia larger than mesotibiae. Abdomen: Tergite 7 lacking stridulatory apparatus; tergite 8 transverse, subtriangular, strongly convex in lateral view; surface rugopunctate, densely setose. Ventrites 2–5 gradually increasing in length, moderately setose; ventrite 6 smooth, arched, emarginate at middle of posterior margin, sparse setae confined to posterior margin. Aedeagus: Parameres in caudal view (Fig. 2B) elongate, symmetrical, slightly arched, finely punctate, convergent at apex, with inner sides sparsely setose apically. Parameres in lateral view (Fig. 2C) dilated at basis, gradually becoming convergent toward deflexed apex.

Female redescription. (Figs. 1F–G, 2D). The female differs from the male in the following aspects: Head: Clypeus rounded anteriorly (Fig. 2D). Frontoclypeal suture lacking horn in lateral view (Fig. 1G), with two small, rounded, contiguous tubercles at middle in dorsal view (Fig. 2D). Thorax: Pronotum lacking anterior tubercle (Fig. 1G); pronotal surface coarsely, contiguously punctate; middle lateral area near margins with sparse, irregularly arranged setae. Abdomen: Tergite 8 flattened in lateral view. Ventrite 6 subtriangular, lacking apical emargination.

Remarks. Megasoma bollei was described by Dechambre (2006) who highlighted characteristics of the clypeus (triangular, short, acute) and mandibles (projected beyond the clypeus) to accommodate the species in Gibboryctes . However, the characters used by Dechambre (2006) are insufficient to justify the position within the genus, since Endrödi (1974) defined it by many more attributes, such as absence of sexual dimorphism; frons with a transverse tubercle in both sexes; bidentate mandibles with lobed teeth strongly produced; pronotum without horns or tubercles, only with a shallow concavity in both sexes; prosternal process short; tergite 7 (=propygidium) lacking stridulatory area; quadridentate protibiae; and protarsi not thickened in males. These characters are incompatible with those observed in M. bollei . Rather, the species is morphologically associated with the aspects used to define Megasoma (Hardy 1972, Lachaume 1985, Morón 2005, Prandi et al. 2020): conspicuous sexual dimorphism marked by the presence of a bifurcate, short horn on the male head (Fig. 2A), while females have only two small tubercles (Fig. 2D); male pronotum with an anterior tubercle (Fig. 1E), tubercle absent in females (Fig. 1G); mandibles without teeth (Fig. 2A); tergite 7 lacking stridulatory apparatus; tridentate protibiae (Fig. 2A); and cylindrical protarsomeres (1–5 combined subequal to protibial length) (Fig. 2D). The length of the protarsomeres relative to the protibial length supports placement of M. bollei in Dynastini rather than Oryctini (Endrödi 1976, 1985). Nineteen species are now included in the genus Megasoma (Morón 2005; Prandi et al. 2020).

Distribution. Megasoma bollei is known from Argentina and Paraguay (Fig. 2E).