Diagnosis. Male adult: only extant species of Atrichopogon (Meloehelea) from Patagonia with one subapical tooth in the gonostylus and aedeagal-parameral complex with posteromedial portion slightly notched. Female adult: only extant species of Meloehelea from Patagonia with very strong mandibular teeth.
Description. Male adult: Head: Dark brown (Fig. 1 A). Ommatidia without interfacet pubescence, abutting medially for length of 3 ommatidia. Antenna brown; with plume well developed; flagellomeres 5–8 at least partially fused; flagellomere 9–10 with plume setae, 10–13 elongated; flagellomere 13 with apical projection slightly basally constricted; AR 1.00. Maxillary palpus brown (Fig. 1 B); third segment slightly swollen at midlength, with well-developed pit located at midlength; segments 4, 5 separate; PR 3.00. Proboscis short, mouthparts length 0.20 mm; head width/mouthparts length 2.00. Thorax: dark brown (Fig. 1 C); scutellum slightly paler than scutum; scutum with setae arising directly from surface; paratergite with 1 seta. Anepisternum well developed, sharply bilobed posteriorly. Legs light brown; hindtibia slightly expanded at apex; hindtibial spur length less than width of hindtibia at midlength; hindtibial comb with 8 spines; prothoracic TR 3.20; mesothoracic TR 3.00; metathoracic TR 2.50; claws curved, bifid at tip, empodia present. Wing (Fig. 1 D) without pattern of pigmented membrane, with macrotrichia apically on r 3, wing length 1.40 mm; breadth 0.46 mm; CR 0.64. Halter white. Abdomen: tergites uniformly brown. Sternites more or less similarly rectangular shaped. Genitalia (Fig. 1 E): segment 9 about equal in width to segment 8, tergite 9 short, extending midlength of gonocoxite, posterior margin rounded. Sternite 9 with posterior margin slightly concave, with single row of 10 setae. Gonocoxite without medial lobe, moderately stout, 1.7 times longer than greatest breadth; gonostylus 0.75 as long as gonocoxite, nearly straight, apex gently curved, pointed, subapical stout tooth. Aedeagal-parameral complex broad; posterodorsal projection tapering to cap-like process; posteroventrally broad, posteromedial portion slightly notched. Cercus elongate, barely extending beyond apex of 9 th tergite.
Female adult: As for male, with following differences. Head: antenna dark brown, with flagellomeres 1–8 compressed, slightly broader than long; flagellomeres 9–13 elongate, proportions as shown in Fig. 2 A, flagellomere 13 with apical nipple, slightly constricted basally; AR 2.47 (2.06–2.86, n= 5). Maxillary palpus with third segment bearing sensory pit slightly beyond midlength; PR 2.95 (2.50–3.22, n= 5); mouthparts length 0.20 (0.16– 0.22, n= 5) mm, head width/mouthparts length 1.78 (1.63–1.96, n= 5). Mandible well developed (Fig. 2 B), with 18 (15–20, n= 5) strong teeth (Fig. 2 B). Laciniae with pale indistinct teeth, without spicules. Thorax: Legs (Fig. 2 D) light brown; hind tibia slightly expanded at apex; hindtibial spur length less than width of hind tibia at midlength; hindtibial comb with 8 spines; prothoracic TR 3.18 (3.00– 3.40, n= 5); mesothoracic TR 2.81 (2.61–2.92, n= 5); metathoracic TR 2.48 (2.39–2.57, n= 5); empodia present. Wing (Fig. 2 C) without pattern of pigmented membrane, with macrotrichia very abundant in r 3 and m1, 15– 30 in m2, 1– 8 in cua 1, and 0–3 in anal cell; radial cells with broad lumen, second 4 times longer than first; wing length 1.50 (1.36–1.64, n= 5) mm; breadth 0.63 (0.58–0.68, n= 5) mm; CR 0.71 (0.69–0.73, n= 5). Halter white. Abdomen (Fig. 2 E): tergites uniformly brown. Sternite 8 without elongate, curved setae. Two subequal ovoid spermathaecae, each with elongated neck, measuring 69 x 49 µm, neck 10 µm, and 73 x 54 µm, neck 11 µm. Cercus brown.
Distribution and bionomics. Atrichopogon macrodentatum inhabits Nothofagus forests within the Valdivian forests of Argentina and Chile, at elevations of 791– 950 m. The dominant species in these forests are N. pumilio (lenga) and N. antarctica (ñire).
Specimens examined. Types: Holotype male, Argentina, Parque Nacional Nahuel Huapi, arroyo Neuquén-Co, 40 º 28 ’ 48.3 ”S 71 º 36 ’ 44.1 ”W, 809 m, 23.i/ 4.ii. 2008, A. Garré – F. Montes de Oca, Malaise trap. Allotype female, same data except CDC light trap (MLP). Paratypes, 4 females, as follows: same data as holotype, 1 female (MLP); Argentina, Parque Nacional Nahuel Huapi, Puerto Blest, Estación Biológica, 41 º01’ 34.4 ”S 71 º 48 ’ 55.7 ”W, 791 m, 6 / 13.i. 2007, A. Garré – F. Montes de Oca, 2 females, at light (MLP); Chile, Cautín Prov., Lago Conguillio, 6.xii. 1984, J. A. Downes, 1 female (1661 / 8 / 1) (CNCI).
Taxonomic discussion. The female of this new species is easily distinguished from their congeners of the subgenus Meloehelea by the very strong mandibular teeth. The male have only one tooth in the gonostylus. Other characters to distinguish this species from the remaining Patagonian species may be found in the key.
Derivation of specific epithet. A reference to the strong female mandibular teeth.