A N N A L E S Z O O L O G I C I (Warszawa), 2016, 66(1): 35-42 AENICTUS SELETARIUS, A NEW SPECIES OF HYPOGAEIC ARMY ANT FROM SINGAPORE, WITH AN UPDATED KEY TO THE AENICTUS MINUTULUS SPECIES GROUP (HYMENOPTERA: FORMICIDAE: DORYLINAE) FROM SOUTHEAST ASIA MARK K. L. WONG1 and BENOIT GUÉNARD2, * 1National Parks Board, Singapore Botanic Gardens, 1 Cluny Road, Singapore 2School of Biological Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong; e-mail: [email protected] *Corresponding author Abstract.— A new species of the army ant genus Aenictus (Hymenoptera: Formicidae: Dorylinae) is described. Aenictus seletarius sp. nov., belonging to the Aenictus minutulus species group, was discovered from a single subterranean pitfall trap in Singapore. Like A. subterraneus and A. changmaianus in this species group, A. seletarius displays substantial variation in body size within the worker caste. An updated key to the Aenictus minutulus species group from Southeast Asia is presented. ± Key words.— Aenictus, army ant, body size variation, Malay Peninsula, Singapore INTRODUCTION Guinea and Australia (Fig. 1; also see www.antmaps. org). Globally, Southeast Asia supports the greatest Among all 18 genera of the monophyletic army ant diversity of Aenictus species, with a total of 118 spe- cies (antmaps.org) comprising all twelve species subfamily Dorylinae (Brady et al. 2014), the genus groups that have been established for the genus (Jai- Aenictus Shuckard, 1840 is the most diverse, compris- trong and Yamane 2011). ing a total of 184 valid species including the present The Aenictus minutulus species group includes addition and 30 valid subspecies (Bolton 2015). Most relatively small-sized species, measuring 1.80–3.20 mm Aenictus species are specialized predators of other in total body length. Based on the latest revision by ant genera (Gotwald 1995, Shattuck 2008, Jaitrong and Jaitrong and Hashimoto (2012), the group is restricted Yamane 2011, Jaitrong et al. 2012, Hashimoto and to Southeast Asia where it is represented by six spe- Yamane 2014), although the remains of spiders, flies cies: Aenictus changmaianus Terayama et Kubota, and woodlice have been recorded in the nests of Aenic- 1993 (Vietnam, Thailand and Cambodia), Aenictus tus gracilis Emery, 1893 (Hirosawa et al. 2000). Like minimus Jaitrong et Hashimoto, 2012 (Vietnam), Ae- other army ants, members of Aenictus are obligate col- nictus minutulus Terayama et Yamane, 1989 (Thai- lective foragers and utilise strategies of mass raiding land, Sumatra and Java), Aenictus peguensis Emery, to attack and overpower their prey. The genus Aenic- 1895 (Vietnam and Myanmar), Aenictus subterra- tus is widely distributed throughout the Old World neus Jaitrong et Hashimoto, 2012 (Borneo) and an tropics and subtropics, from Africa to the Middle East, undescribed morphospecies Aenictus sp. 56 of WJT India and Pakistan, South China, Southeast Asia, New (Borneo and Java). Here we describe Aenictus PL ISSN 0003-4541 © Museum and Institute of Zoology PAS doi: 10.3161/00034541ANZ2016.66.1.002 36 M. K. L. WONG and B. GUÉNARD seletarius sp. nov. from Singapore, a new addition to WL – Weber’s Length of Mesosoma. Maximum diago- the A. minutulus species group that displays substan- nal distance in lateral view, from base of anteri- tial variation in the body size of its worker caste, from or slope of pronotum to metapleural lobe; four individuals collected in a single subterranean pit- PNH –Pronotum Height. Maximum height of prono- fall trap. We describe A. seletarius from the worker tum, measured in profile from the posterior caste and provide an updated key to Southeast Asian base of the lateral sides of pronotum, where species of the A. minutulus group. procoxa is attached, to the highest point of the pronotum; PNW –Pronotal Width. Maximum width of pronotum MATERIAL AND METHODS measured in dorsal view; PTL –Petiole Length. Maximum diagonal length of Abbreviations of the type depositories and other petiole, measured in lateral view, from most material are as follows: anteroventral point of the peduncle, at or below LKCNHM – Lee Kong Chian Natural History Museum, the propodeal lobe, to most posterodorsal point Singapore. of tergite; SBSHKU – Insect Biodiversity and Biogeography Lab- PTH – Petiole Height. Maximum height of petiole, oratory, School of Biological Sciences, The measured in lateral view, from the highest University of Hong Kong, Hong Kong SAR. (median) point of the node, orthogonally to the Photographs of specimens were obtained with an ventral outline of the node; incorporated digital camera, Leica DFC450, mounted PTW – Petiole Width. Maximum width of the petiole in on a Leica M205C dissecting microscope through the dorsal view; Leica Application Suite V4 software. A total of 14 to 45 PPL –Postpetiole Length. Maximum length of post- images were taken and stacked together. Measure- petiole, measured in lateral view; ments of specimens were taken in mm (accurate to PPH –Postpetiole Height. Maximum height of post- 0.001 mm and rounded to the nearest 20.01 mm for petiole, measured in lateral view from the high- presentation) with the Measure Tools function of the est point of the node; Leica Application Suite V4 software on imaged speci- PPW – Postpetiole Width. Maximum width of the post- mens after proper placement for each body part meas- petiole in dorsal view; ured. Measurements and morphological terminology CI – Cephalic Index. Calculated as: HW / HL × 100. follow: Jaitrong and Hashimoto (2012) for HW, HL and SI – Scape Index. Calculated as: SL / HW × 100; SL; Fischer et al. (2014) for PNH and PTH; Baroni MaI – Mandibular Index. Calculated as: MaL / HW × Urbani (1977) for PI and PPI. 100; PI – Petiolar Index. Calculated as: PTW / PTL × 100; The abbreviations used for the measurements and PPI – Postpetiolar Index. Calculated as: PPW / PPL × indices are as follows: 100. HW – Head Width. Maximum width of head in full-face view; HL – Head Length. Maximum head length in full-face SYSTEMATICS view, measured from the anterior clypeal mar- gin to the midpoint of a line drawn across the Aenictus minutulus species group posterior margin of head; MaL – Mandible Length. Maximum length of mandible Diagnosis. The A. minutulus species group was from the anterolateral margin of clypeus at out- established by Jaitrong and Hashimoto (2012) from er side of mandibular insertion to mandibular their redefinition and renaming of the Aenictus pier- apex; cei species group (Jaitrong and Yamane 2011). From SL – Scape Length. Maximum measurable length of the A. piercei species group, Jaitrong and Hashimoto scape, from the proximal point of scape shaft to removed two species (Aenictus piercei Wheeler et the distal end of scape, excluding the basal of Chapman, 1930; Aenictus lifuiae Terayama, 1984) constriction and condylar bulb; and added two new species and one undescribed mor- TL –Total Length. Maximum length of specimen phospecies (see synoptic species list of A. minutulus measured from the tip of the mandibles to the species group below). Jaitrong and Hashimoto (2012) tip of the abdominal segment VII, not including define the A. minutulus species group as follows: sting. Due to the position of the specimen, total “Head in full-face view with occipital corner con- length was measured as the sum of head length vex, and posterior margin almost straight to shallow- + thorax, petiole and postpetiole length + ly and broadly concave; occipital margin lacking col- gaster length; lar. Antenna 10-segmented; antennal scape short, A NEW SPECIES OF AENICTUS (HYMENOPTERA: FORMICIDAE: DORYLINAE) FROM SINGAPORE 37 reaching only midlength of head. Anterior clypeal mar- –. In full-face view posterior margin of head almost gin roundly convex, lacking denticles. Mandible subtri- straight or feebly concave; propodeal junction angular; its masticatory margin with a large apical roundly angulated; smaller species (TL 2.10–2.15 tooth, medium-sized subapical and basal teeth, and 2–6 mm; HW 0.48–0.50 mm) (Borneo) . denticles between them; basal margin of mandible with . A. subterraneus Jaitrong et Hashimoto conspicuous denticles. Frontal carina short; para- 4. Basal margin of mandible with 1–2 small denticles frontal ridge absent. With mesosoma in profile prome- next to large basal tooth and followed by a larger sonotum convex dorsally and sloping gradually to the denticle (North Vietnam) . propodeum; metapleural groove present or absent . A. minimus Jaitrong et Hashimoto (mesonotum and propodeum fused); propodeal junc- –. Basal margin of mandible with 3–5 denticles that tion angular. Subpetiolar process well developed, trian- gradually reduce in size toward base of man- gular or subrectangular. Head and first gastral seg- dible . 5 ment entirely smooth and shiny. Body yellowish brown 5. Head square-shaped and almost as wide as long (CI to reddish brown; typhlatta spot absent. Size variation 91–96); antennal scape relatively short (SI 61–64); occurs among individuals from single colonies.” polymorphic worker caste with largest individuals exceeding 3.10 mm in TL (Singapore) . A. seletarius sp. n. Synoptic species list of A. minutulus species –. Head longer than wide (CI < 90); antennal scape rel- group from Southeast Asia atively long (SI 67–72); relatively smaller species (TL < 2.60 mm) . 6 Aenictus changmaianus Terayama et Kubota, 6. Metapleural gland bulla relatively large; distance 1993 (Vietnam, Thailand, Cambodia); between propodeal spiracle and metapleural gland Aenictus minimus Jaitrong et Hashimoto, 2012 bulla shorter than or almost as long as spiracular (North Vietnam); diameter (Thailand, Vietnam and Cambodia) . Aenictus minutulus Terayama et Yamane, 1989 . A. changmaianus Terayama et Kubota (Thailand, Sumatra, Java); –. Metapleural gland bulla relatively small; distance Aenictus peguensis Emery, 1895 (Vietnam, Myan- between propodeal spiracle and metapleural gland mar); bulla clearly longer than spiracular diameter (Thai- Aenictus seletarius sp. nov. (Singapore); land, Java and Sumatra) . Aenictus sp. 56 of WJT Jaitrong et Hashimoto, 2012 . A. minutulus Terayama et Yamane (Borneo, Java); Aenictus subterraneus Jaitrong et Hashimoto, 2012 (Borneo). DESCRIPTION OF NEW SPECIES Updated key to A.