Leptogenys borneensis Wheeler, 1919

Satria, R., Nugraha, F. A. D., Achyar, A., Zulyetti, D. & Eguchi, K., 2024, Description Of The Male Caste Of Leptogenys Borneensis (Hymenoptera, Formicidae), With Its First Discovery In Sumatra, Zoodiversity 58 (1), pp. 19-26 : 20-24

Leptogenys borneensis Wheeler, 1919 ( figs 1–3 )

Leptogenys (Lobopelta) borneensis Wheeler, 1919: 59 , worker, type locality: Malaysia (Sarawak: Kuching)

Diagnosis of the worker

Head in frontal view with its posterior margin slightly convex; mandible triangular; clypeus strongly carinate. Mesosoma in lateral view, long and slender; dorsal margin of mesothorax slightly concave; posterior margin of petiole weakly convex. Petiolar node in frontal and lateral views with a bluntly pointed apex, in lateral view with anterior slope broadly convex and posterior slope weakly convex or almost straight; subpetiolar process not developed. The body dark brown with legs and antennae paler.

ly long, tapering apically. Clypeus without longitudinal median carina; anterior margin broadly convex.

Mesoscutum in dorsal view longer than wide, widest posterior to mid-length, broadly convex in lateral view; notaulus scrobiculate; parapsidal line longer than half length of mesoscutal sulcus; transscutal line sinuous. Mesopleuron distinct and complete. Metapleuropropodeal suture present. Propodeal dorsum in lateral view straight, longer than length of declivity; propodeal declivity broadly convex; propodeal spiracle circular. Wing venation as in figs 2 , G, H, with stigma; fore wing approximately 3 times as long as wide, approximately 1.3 times as long as hind wing length; hind wing approximately 3.5 times as long as wide. Fore tibia with single spur, each middle and hind tibia with two spurs. Pretarsal claw multidentate.

Petiole in lateral view longer than height, in dorsal view longer than wide ( fig. 3 , F); lateral margin straight in dorsal view; petiolar node in lateral view subtrapezoidal, anteri- or margin inclined posterad, posterior margin slightly inclined anterad. Anterior lobe of subpetiolar process in lateral view short, with postero-ventral angle sharpened; posteri- or extension in lateral view long and low, separated from anterior lobe by shallow notch, with ventral margin broadly convex. Pygostyle digitiform with long setae on apical half ( fig. 3 , A). Abdominal sternite 9 with elongate, subtriangular apical lobe of which apex is round ( fig. 3 , B).

Genital capsule longer than broad. Gonopod apex in lateral view longer than high ( fig. 3 , C). Lateropenite in lateral view rectangular with rounded corners and long, its posterior margin as long as cuspis. Cuspis in lateral view elongate and weakly arched dorsal of lateropenite, apically slightly swollen, rounded. Apicoventral apex of valviceps strongly produced; basiventral corner of valviceps distinctly produced; ventral margin of valviceps with 13 denticles ( fig. 3 , D).

Head entirely smooth and shiny, except on area between median and lateral ocelli finely striate. Mandible and clypeus weakly sculptured. Pronotum, mesoscutum, mesopleuron, propodeum, petiole and gaster smooth and shiny; mesoscutellum with longitudinal striation.

Head, mesosoma, legs, petiole and gaster with fine dense subdecumbent to decumbent various length of hairs; hairs on head longer than other.

For color pattern see in figs 2 , A–F; body basically dark brown; clypeus, mandible, antennal scape, and legs paler.

M e a s u r e m e n t s o f t h e M a l e s (n= 3)

HW 1.54–1.56 mm, HL 1.31–1.32 mm, EL 0.82 mm, EW 0.61–0.62 mm, OL 0.18 mm, OED 0.24 mm, SL 1.17 mm, WL 3.30 mm, PTH 0.69–0.70 mm, PTL 0.80 mm, CI 84–85, SI 88, PTHI 86–87.

Remarks

Leptogenys borneensis is recorded for the first time in Sumatra Island. The colony was found in decayed wood stump along the hiking trails (ca. 1500 m a.s.l.). Workers and males were found but no queen was found from the colony.

So far, based on Forel (1913), Karavaiev (1925, 1926) and this paper, the male caste is known for the following four species and one subspecies of the genus Leptogenys from the island of Sumatra: Leptogenys diminuta (F. Smith, 1857) ; Leptogenys diminuta fruhstorferi Emery, 1896 ; Leptogenys kraepelini Forel, 1905 ; Leptogenys myops ( Emery, 1887) , including Leptogenys borneensis in the present study. However, the morphology of the male genitalia of these species remains unknown, except for L. borneensis , which is provided in this study.

The morphology of male genitalia provides useful characteristics to confirm and delimitate the species of ants, and to predict evolutionary trends in behavior and reproductive biology ( Boudinot, 2013). The important characteristic of male morphology and genitalia that used for species delimitation were highlighted in the following previous studies: in the genus Odontomachus ( Satria et al., 2015) ; in the genus Opamyrma ( Yamada et al., 2020) ; in the genus Metapone ( Wang et al., 2019) ; in the genus Pheidole ( Wang et al., 2018) ; in the genus Dinoponera (Lenhart et al., 2013; Tozetto & Lattke, 2020): in the genus Cardiocondyla ( Schmidt & Heinze, 2017) . In the case of the genus Odontomachus , where the taxonomy problems of Odontomachus rixosus complex confused the myrmecologist for decades, then it can be resolved by using the information of the morphology and genitalia of the male caste ( Satria et al., 2015). However, the study of the male genitalia in the genus Leptogenys is still limited, Trager & Johnson (1988) confirmed the status of Leptogenys elongata (Buckley, 1866) and L. manni (Buckley, 1866) . They stated that the study of male genitalia is important in future revisionary work on Leptogenys ( Trager & Johnson 1988) . Lattke (2011) used male morphology as part of his argument for synonymising L. mexicana (Mayr, 1870) with L. elongata (Buckley, 1866) .

D i s t r i b u t i o n. Indonesia: Sumatra (new record); Malaysia; Thailand; Vietnam.

Acknowledgements

We wish to thank Mr. Rudi Yuliandri, Ms. Nur Aqsha, Ms. Putri Ratna Desi, Mr. Niko, and Mr. Rezha for their helps in field research. This research was financed mostly by PNBP Research Grants of Universitas Negeri Padang for Biodiversity of Sumatra Research Group under contract No. 1750/UN35.13/LT/2022 (Team Leader: Rijal Satria), and partly by Tokyo Metropolitan University Fund for TMU Strategic Research (Leader: Prof. Noriaki Murakami; FY2020–FY2022).

Figures

Fig. 1. Leptogenys borneensis Wheeler, 1919 (worker, individual code: SEMUT13xii2021-A, colony code: RS- SAGO-02):A — head in full-face view;B — body in lateral view; C — mesosoma in lateral view; D — mesosoma in dorsal view; E — petiole in lateral view.

Fig. 2. Leptogenys borneensis Wheeler, 1919 (male, individual code: SEMUT13xii2021-B, colony code: RS-SAGO-02): habitus in lateral view.

Fig. 3. Leptogenys borneensis Wheeler, 1919 (male, individual code: SEMUT13xii2021-B, colony code: RS- SAGO-02): A — head in full-face view; B — ocelli; C — mesosoma in lateral view; D — mesosoma in dorsal view; E — petiole in lateral view; F — petiole in dorsal view; G — forewing; H — hind wing.