Leptogenys atra

A colony (AK221) was found under rotten wood in a grassland next to a walkway near the forest in Cuc Phuong National Park. The colony contained many virgin queens. Workers foraged and cooperatively transported a small invertebrate, which could not be identified. Some individuals grasped the legs of other individuals with their mandibles and made a small chain for collective transport of their food. This chain-making behavior is similar to that of Leptogenys cyanicatena (see the L. cyanicatena species page, Leptogenys chalybaea and Peeters & De Greef, 2015), although we did not observe any large chains consisting of several tens of workers, as can be seen in Leptogenys cyanicatena. (Arimoto and Yamane 2018)

Identification
Arimoto and Yamane (2018) - A member of the Leptogenys chalybaea species group. Mandibular basal and masticatory margins forming continuous curve; masticatory margin curved ventrad near apex. Eye length in full-face view less than one-fourth of head lateral margin length; eye distinctly interrupts lateral outline of head. Apex of clypeal median lobe with two or three peg-like setae. Anterior lobe of subpetiolar process with rounded posteroventral angle, lacking acute tooth. Body black and with blue luster. Head, mesosoma, and petiolar node striate. Gaster smooth.

Workers and queens of Leptogenys atra are easily distinguished from the other two species in the L. chalybaea group, Leptogenys chalybaea and Leptogenys cyanicatena by the body color and sculpture (Leptogenys chalybaea and Leptogenys cyanicatena in parentheses): head longitudinally striate (smooth in Leptogenys chalybaea; rugose in Leptogenys cyanicatena); body black and without metallic luster (blue and with metallic luster).

Distribution
Arimoto and Yamane (2018) - Vietnam: Bak Kan, Ha Noi, Ninh Binh, Nghe An.

Distribution based on Regional Taxon Lists
Oriental Region: Vietnam.

Nomenclature

 *  atra. Leptogenys atra Arimoto and Yamane, 2018: 9, figs. 3, 4–7, 15A, D, 16A, B (w.q.m.) VIETNAM.

Worker
(n=5, holotype in parentheses) HL: 1.95–2.10 (2.07), HLL: 1.56–1.70 (1.70), HLA: 0.70–0.80 (0.80), HW: 1.67–1.80 (1.80), CML: 0.41–0.45 (0.43), CI: 85–87 (87), CLI: 21-22 (21), SL: 2.09–2.20 (2.20), SI: 119–122 (122), EL: 0.35–0.49 (0.38), OI: 21–24 (22), PrL: 1.22–1.26 (1.26), PrH: 0.87–0.99 (0.95), PrW: 1.24–1.31 (1.30), WL: 3.12–3.26 (3.26), PeL: 0.84–0.89 (0.87), PeH: 1.12–1.20 (1.19), PeW: 0.81–0.85 (0.84), LPI: 132–143 (137), DPI: 93– 101 (96).

Head width in full-face view more than 0.8 times as long as its length. Mandibular basal and masticatory margins forming continuous curve; masticatory margin curves ventrad near apex. Eye length in full-face view less than one-fourth of head lateral margin length; eye distinctly interrupts lateral outline of head. Antennal scape surpassing posterior head margin by less than two-fifths of its length; antennomere XII approximately 3.0 times as long as wide. Clypeus without median carina; apex of clypeal median lobe with two or three peg-like setae. Pronotum in dorsal view shorter than wide. Propodeal dorsum in profile broadly convex; declivity concave, separated from dorsum by blunt angle, sometimes forming a continuous curve with dorsum; declivity three-fifths length of dorsum; propodeal spiracle elliptical. Petiole in dorsal view slightly longer than wide or almost as long as wide. Anterior lobe of subpetiolar process with rounded posteroventral angle, without acute tooth.

Head, mesosoma, and petiolar node longitudinally striate, but head vertex transversely striate. Mandible smooth, with few longitudinal striae near basal margin. Antennal scape smooth basally and becoming weakly imbricate apicad. Clypeus with oblique to longitudinal striae. Meso-metapleural and metapleuro-propodeal sutures impressed and narrow. Mesosternum finely alveolate; anterior and posterior edges transversely striate. Coxa longitudinally striate to slightly alveolate. Petiolar node with shallow scalloped depressions, which impressed anteriorly and gradually sloping posteriorly. Ventral half of petiole laterally with slight alveolate. Gaster smooth. Anterior margin of gastral segments II with a brief scrobiculate band, but often the band obscure ventrally. Body black and with blue luster. Antennal scape, mandible, clypeus, and tibia dark-red. Antennomeres II–XII and tarsi red-brown. Coxa black; femur and ventral half of petiole black tinged with red. Hairs yellow-brown. Antennal scape with dense short pubescence and sparse erect long hairs. Dorsum of head, pronotum, mesosoma, and gaster with abundant erect hairs.

Queen
(n=5). HL: 1.88–1.93, HLL: 1.52–1.57, HLA: 0.69– 0.77, HW: 1.55–1.62, CML: 0.38–0.43, CI: 81–85, CLI: 20–23, SL: 1.77–1.85, SI: 112–116, EL: 0.32–0.35, OI: 20–23, PrL: 1.01–1.10, PrH: 0.82–0.89, PrW: 1.15–1.18, WL: 2.77–2.89, PeL: 0.80–0.84, PeH: 1.33–1.39, PeW: 0.69–0.75, LPI: 158–170, DPI: 86–91.

Propodeal dorsum and declivity forming a continuous curve. Petiolar node high, trapezoidal in profile, narrowed dorsally; dorsal margin truncate. Anterior lobe of petiolar process with rounded posteroventral angle. Petiole and gaster smooth; ventral half of petiole laterally with slight alveolate.

Male
(n=5). HL: 1.39–1.50, HW: 1.31–1.39, CML: 0.48–0.52, CI: 92–97, SL: 0.39–0.45, SI: 29–34, EL: 0.68–0.76, MeL: 1.48–1.55, MeW: 1.43–1.48, WL: 3.10– 3.36, PeL: 0.70–0.78, PeH: 0.91–0.96, PeW: 0.60–0.69, LPI: 123–131, DPI: 77–94.

Head in full-face view slightly longer than wide, broader posteriorly; posterior margin of head broadly convex. Mandible without basal angle and teeth; apex rounded. Compound eye occupies half of head length. Ocelli small; maximum length of lateral ocellus distinctly shorter than minimum distance between lateral ocellus and eye. Antenna 13 segmented; scape length less than half of head width; antennomere II shortest; III shorter than scape; XIII more than 1.7 times as long as XII. Clypeus without longitudinal median carina; anterior margin broadly convex; anterior lateral margin with narrow translucent lamella. Mesoscutum in dorsal view longer than wide, widest posterior to its mid-length, convex in profile; notaulus weakly impressed; length of parapsidal line more than half of mesoscutal sulcus length; transscutal line almost straight to slightly curved. Metapleuro-propodeal suture present. Propodeal dorsum in profile straight, longer than length of declivity; declivity separated from dorsum by blunt angle, almost straight to broadly convex; propodeal spiracle circular. Forewing approximately 3.2 times as long as wide, approximately 1.3 times as long as hindwing length, with stigma. Hindwing approximately 3.8 times as long as wide. Petiole in profile higher than long; in dorsal view longer than wide; node in profile subtrapezoidal, with anterior margin inclined posterad, with posterior margin inclined anterad; lateral margin convex in dorsal view; anterior and dorsal margins convex; posterior margin almost straight. Anterior lobe of subpetiolar process in profile short, with posteroventral angle sharpened but sometimes rounded; posterior extension thick, separated from anterior lobe by shallow notch, with ventral margin straight to sinuate. Prora small, pointed ventrally, separated from anteroventral angle of gastral sternite I by distinct indentation.

Head and propodeum shallowly rugose. Posterior cephalic surface and mesonotum with shallow scalloped depressions, which impressed anteriorly and gradually sloping posteriorly. Mandible and clypeus smooth. Pronotum and propodeum finely alveolate. Anterior part of mesoscutum, mesopleuron and petiole slightly alveolate. Posterior part of mesoscutum costulate and becoming regulate posterad. Mesoscutellar disc rugose. Scutoscutellar sulcus and oblique mesopleural sulcus scrobiculate. Gastral segments I–III finely alveolate; constriction between segments I and II scrobiculate; segments IV and V almost smooth but becoming slightly alveolate posterad; segment VI smooth.

Body black and with blue luster; mandible, antenna, and tarsi red-brown. Coxa and femur black; tibia black tinged with red. Hairs yellow-brown, erect. Antennal scape with dense short pubescence and erect long hairs; antennomeres II–XIII with dense short pubescence and erect long hairs. Erect hairs of gastral sternites denser than those of tergites.

Type Material
Holotype: Worker, Cuc Phuong National Park, Nho Quan District, Ninh Binh Province, North Vietnam, 10–11 VIII 1998, Seiki Yamane leg. ; LCA001.

Paratypes: (101 workers, 7 virgin queens, 20 males). 1 worker, Ba Be National Park, Bak Kan Province, North Vietnam, VIII 2003, T. Uchiumi leg. ; LCA002; 6 workers (VN01-SKY-74), Ba Vi National Park, Ba Vi District, Ha Noi City, North Vietnam, 21°03’ N, 105°22’ E, 400–550 m, 11 XI 2001, Seiki Yamane leg. [SKYC; LCA003 to LCA008]; 1 worker, same place as the former, 11 XI 2001, Seiki Yamane leg. [SKYC; LCA009]; 6 workers (Eg02-VN-059), same place, 800 m, 20 IV 2002, Katsuyuki Eguchi leg. [SKYC; LCA010 to LCA015]; 14 workers (Eg99-VN-086), same place, 400–600 m, 11 XI 1999, Katsuyuki Eguchi leg. [SKYC; LCA016 to LCA029]; 4 workers, same place as the holotype, 10 VIII 1998, Hirofumi Ȏkido leg. [SKYC; LCA030 to LCA033]; 2 workers, 1 virgin queen, same place, 11 VIII 1998, Hirofumi Ȏkido leg. [SKYC; workers: LCA034, LCC035; virgin queen: LCA036]; 6 workers, same place, 10–11 VIII 1998, Seiki Yamane leg. [SKYC; LCA037 to LCA042]; 1 worker, same place, 10–12 VIII 1998, Seiki Yamane leg. [SKYC; LCA043]; 2 worker, same place, 11–13 VIII 1998, Seiki Yamane leg. [SKYC; LCA044, LCA045]; 1 worker, same place, 10 XI 2001, Seiki Yamane leg. [SKYC; LCA046 ]; 45 workers, 4 virgin queens, 20 males (AK221), under rotted wood, same place, 20.35° N, 105.60° E, 440 m, 8 VIII 2016, Kôichi Arimoto leg. [VNMN; workers: LCA047 to LCA091; virgin queens: LCA092 to LCA095; males: LCA096 to LCA115]; 10 workers, 2 virgin queen (VN9902), frontier, Pu Hoat, Nghe An Province, Middle Vietnam, VI 1999, Bui Tuan Viet leg. [SKYC; workers: LCA116 to LCA125; virgin queens: LCA126, LCA127]; 1 worker (Code 011), primary forest, Lung Khung, Pu Hoat Nature Reserve, Nghe An Province, Middle Vietnam, 640 m, 20 XI 1999, Bui Tuan Viet leg. [SKYC; LCA128]; 1 worker (Code 012), primary forest, Pu Hoat Nature Reserve, Nghe An Province, Middle Vietnam, 750 m, 22 XI 1999, Bui Tuan Viet leg. [SKYC; LCA129].

Etymology
From the Latin ater, meaning black, refers to the black body.

References based on Global Ant Biodiversity Informatics

 * Arimoto K., and S. Yamane. 2018. Taxonomy of the Leptogenys chalybaea species group (Hymenoptera, Formicidae, Ponerinae) from Southeast Asia. Asian Myrmecology 10: e010008.