Two new species of the Aenictus wroughtonii species group (Hymenoptera, Formicidae, Dorylinae) from Thailand

Abstract The Aenictus wroughtonii species group is widely distributed in Asia. The members of this group are characterised by a slender body, long legs, anterior clypeal margin with 5–10 denticles and a weakly-developed subpetiolar process. Twelve worker-based species of this group have been recorded from Asia. Herein, two new species from Thailand (Aenictus nuchiti sp. n. and Aenictus samungi sp. n.) are added to this group. A key to the Asian species of this group is provided.


Introduction
The Aenictus wroughtonii species group was established by Wilson (1964) based on the external morphology of the worker caste. Subsequently, Jaitrong et al. (2010) and Jaitrong and Yamane (2011) redefined the species group and listed seven worker-based species from the Oriental region. Recently, Sharaf et al. (2012) and Staab (2014) described new species of the group from Saudi Arabia and Southeast China, respectively.
To date, 10 species have been recorded in the A. wroughtonii group from Greece, Turkey, Iran, Israel, India, Sri Lanka, Southeast China and Taiwan to Southeast Asia (Aktaç et al. 2004, Jaitrong and Yamane 2011, Sharaf et al. 2012, Staab 2014.
During our survey of the Asian Aenictus, two unidentified species belonging to the A. wroughtonii group were found from Thailand. After carefully examining specimens of these two species under a stereomicroscope and comparing them with the type material of closely related species, it was concluded that both species are new to science. In the present study, the two new species are described and a key for the Asian species based on the worker caste is provided.
Multi-focused montage images were produced using NIS-Elements-D-[Sequence6*-Focused] from a series of source images taken by a Nikon Digital Sight-Ri1 camera attached to a Nikon AZ100M stereoscope. Type specimens of each species were measured for the following parts using a micrometer (accurate to 0.01 mm).
The abbreviations used for the measurements and indices are as follows: HL Maximum head length in full-face view, measured from the anterior clypeal margin to the midpoint of a line drawn across the posterior margin of the head. HW Maximum head width in full-face view. ML Mesosomal length measured from the point at which the pronotum meets the cervical shield to the posterior margin of the metapleuron in profile. PH Petiolar node height, measured in profile, the maximum vertical height of the petiole from summit to lower most part of subpetiolar process. PL Petiole length measured from the anterior margin of the peduncle to the posteriormost point of the tergite in profile. SL Scape length excluding the basal constriction and condylar bulb. TL Total length, axial length of body, summed HL (including mandibles) + ML + PL + postpetiole length + gaster length. The general terminology for the worker caste of the ants follows Hölldobler and Wilson (1990) and Bolton (1994). The studies of Jaitrong et al. (2010) and Jaitrong and Yamane (2011) have been referred to for the important characteristics of the genus Aenictus.

Aenictus wroughtonii species group Figs 1A, 3A
Diagnosis. (modified from Jaitrong and Yamane 2011). Head narrow, oval or elliptical; occipital margin lacking collar (distinct carina). Antenna short or long, comprising 10 segments; scape short, attaining mid-length of head or longer attaining or extending beyond the posterolateral corner of head. Anterior clypeal margin roundly convex with 5-10 denticles. Mandible triangular, with masticatory margin bearing 8-12 minute inconspicuous denticles in addition to a large apical tooth with a sharp apex; basal margin of mandible lacking denticles. Frontal carina short; parafrontal ridge feeble and incomplete. Mesosoma narrow and elongate. Legs very slender. Propodeal junction in profile angulate (Fig. 1A) or rounded (Fig. 3A). Subpetiolar process weakly developed or almost absent. Head and gaster entirely smooth and shiny. Body yellow, yellowish brown to dark brown; typhlatta spot absent.
Distribution. Greece, Iran, Israel, Turkey, Saudi Arabia, India, Sri Lanka, Southeast China, Taiwan, Vietnam, Thailand, Malay Peninsula (West Malaysia), Sumatra, Borneo (Sabah, Sarawak, and Brunei) and Philippines (Negros and Luzon) (Aktaç et al. 2004, Jaitrong and Yamane 2011, Sharaf et al. 2012, Staab 2014. Currently valid names. Aenictus arabicus Sharaf & Aldawood, 2012, A. artipus Wilson, 1964A. biroi Forel, 1907;A. camposi Wheeler WM & Chapman, 1925;A. gutianshanensis Staab, 2014, A. nuchiti sp. n., A. rhodiensis Menozzi, 1936, A. sagei Forel, 1901 Fig. 1). Head in full-face view elliptical, clearly longer than broad with slightly convex sides and almost straight posterior margin. Antennal scape short, extending beyond the mid-length of the head but not reaching the posterolateral corner of the head; antennal segment II slightly longer than III-VI; the last (X) almost as long as VIII and IX combined and as long as II and III combined. Frontal carina thin and short, not extending beyond level of posterior margin of torulus. Clypeus short, with its anterior margin roundly convex, bearing 7 denticles. Mandible with an apical tooth large and curved, followed by a medium-sized subapical tooth and a series of 10-12 minute teeth on masticatory margin. Mesosoma in profile with pronotum strongly convex dorsally, demarcated from mesonotum by a shallow transverse groove; mesonotum convex, sloping gradually to metanotal groove; mesopleuron demarcated from metapleuron by a shallow groove. Propodeum in profile lower than promesonotum, with a weakly convex dorsal outline; propodeal junction angulate; declivity of propodeum widely and shallowly concave, encircled by a thin rim. Petiole in profile slightly longer than high, with a dorsal outline convex; seen from above relatively narrow with sides almost parallel; subpetiolar process present, its ventral outline convex, without angle or tooth; postpetiole slightly shorter than petiole but seen from above slightly broader than petiole; its node short, clearly shorter than high.
Body with relatively sparse standing hairs mixed with sparse short hairs over surface; longest pronotal hair 0.10-0.13 mm long. Head, mesonotum, propodeum and gaster dark brown; pronotum, waist, antennae and legs reddish brown.
Description of Queen. (Paratype, Fig. 2). Head in full-face view subrectangular, posteriorly narrow and gradually widening anteriorly, slightly shorter than broad, with sides weakly convex and posterior margin concave; upper frons weakly concave. Antennal scape flat, relatively short, about half as long as head, basally narrow, widening considerably apicad; flagellum of antenna missing (for this specimen). Frontal carina indistinct. Parafrontal ridge absent. Anterior clypeal margin concave, without denti- cles. Mandible half as long as head length, with a slender, inner margin that is convex while lateral margin weakly concave; masticatory margin without denticles. Mesosoma elongate; in profile, pronotum convex dorsally; mesonotum weakly concave; propodeal dorsum almost straight; seen from above pronotum and propodeum broader than mesonotum; propodeal junction low, roundly convex; propodeal declivity weakly convex, not encircled by a rim. Petiole longer than high, with its dorsal outline slightly elevated posteriorly, with petiole in profile posterodorsal corner bluntly angulate; seen from above petiole with a distinct longitudinal furrow running from anterior face to posterior face; subpetiolar process large, subtriangular, with its apex pointed downwards. Gaster large and elongate; first tergite narrower and shorter than second, its anterior slope weakly concave; second tergite largest; third as long as first; tip of gaster missing in this specimen. Legs relatively long and slender; femora and tibiae clavate.
Entire body smooth and shiny, with relatively dense standing hairs; hairs slightly shorter on pronotum than on head, mandible and antennal scape; longest pronotal hair 0.08 mm long. Head dark brown; lateral and ventral faces of head and mandible reddish brown; scapes and legs yellowish brown. Mesosoma with ground colour reddish brown; lateral faces of pronotum and mesonotum, entire mesopleura and propodeal declivity dark brown. Petiole with ground colour reddish brown; lower portion of petiole, posterior slope of petiole and subpetiolar process dark brown; gaster with ground colour dark brown; lateral faces of second tergite reddish brown.
Etymology. The species is named after Mr Supachai Nuchit (Royal Forest Department, Thailand) who kindly helped us with ant collecting at Pa Omkoi National Forest, Chiang Mai Province.
Distribution. Northern Thailand (Chiang Mai Province). Comparative diagnosis. Aenictus nuchiti sp. n. is most similar to A. biroi, A. camposi, A. gutianshanensis and A. vieti in having dense punctures on the mesosoma and an angulate propodeal junction. However, A. nuchiti is much smaller than the latter four (TL 2.24-2.41 mm, HW 0.38-0.43 mm in A. nuchiti; TL > 2.6 mm, HW > 0.43 mm in the latter four). It has a short antennal scape that reaches only two-thirds the head length (in contrast, reaching or extending beyond the posterolateral corners of the head in the latter four). This species can be distinguished from A. gutianshanensis and A. vieti by the configuration of the subpetiolar process (ventral outline roundly convex and without anterior angle in A. nuchiti; ventral outline with anterior angle in A. biroi, A. gutianshanensis and A. vieti). Aenictus nuchiti is similar to A. biroi and A. camposi in the unarmed subpetiolar process. In A. nuchiti, however, the body size is much smaller than that of A. biroi and the head is clearly longer than broad in A. nuchiti (almost as long as broad in A. biroi). The body colour is dark brown in A. nuchiti, whereas it is entirely yellow in A. camposi. The propodeal declivity is broader and widely rounded above in A. nuchiti but is narrow and tapers distinctly above in A. camposi.  Description of Worker. (holotype and paratypes; Fig. 3). Head in full-face view clearly longer than broad, with its sides weakly convex and posterior margin almost straight or feebly concave. Antennal scape short, only slightly extending mid-length of head; antennal segment II (pedicel) clearly longer than each of III-VI; X longer than VII, VIII and IX combined. Frontal carinae fused at level of anterior margin of torulus, extending beyond level of posterior margin of torulus. Clypeus short, with its anterior  margin bearing 7 denticles. Mandible subtriangular, with apical tooth large and curved, followed by a medium-sized subapical tooth, 4-5 minute teeth and a medium-sized basal tooth on masticatory margin. Mesosoma in profile almost flat dorsally; metanotal groove distinct. Propodeum in profile with a nearly straight dorsal outline; propodeal junction rounded; propodeal declivity weakly convex, not encircled by a rim. Petiole including subpetiolar process shorter than high, with its dorsal outline convex; subpetiolar process rather developed, with its ventral outline roundly convex, without angle or tooth; postpetiole shorter than petiole and shorter than high, in profile slightly elevated posteriorly.
Body with relatively sparse standing hairs mixed with sparse short hairs over surface; longest pronotal hair 0.07-0.08 mm long. Head, mesosoma, waist, gaster, antennae and legs yellowish brown; mandible dark brown.
Etymology. The species is named after Mr Yuthana Samung (Faculty of Tropical Medicine, Mahidol University, Thailand) who kindly helped us in taking pictures of Thai ants, including the two new species discovered in the present study.
Distribution. Western Thailand (Tak Province). Comparative diagnosis. Aenictus samungi sp. n. can be easily distinguished from the other members of the A. wroughtonii species group by the following characteristics: smallest species of the group (HW 0.31-0.33 mm in A. samungi; HW > 3.7 mm in other members); petiole shorter than high (as long as or longer than high in other members); promesonotum with almost flat or straight dorsal outline (convex and sloping gradually to metanotal groove in other members); antennal scape short only just reaching mid-length of the head (at least two-thirds of the head length or beyond the posterolateral corner of the head in other members). Both Aenictus nuchiti sp. n. and A. samungi sp. n. have small bodies and short antennae, but can be easily separated from each other by the different conditions of the propodeum (Figs 1A vs. 3A).