Aenictus pachycerus (F.Smith, 1858)

Jaitrong, Weeyawat & Wiwatwitaya, Decha, 2013, Two New Species Of The Aenictus Pachycerus Species Group (Hymenoptera: Formicidae: Aenictinae) From Southeast Asia, Raffles Bulletin of Zoology 61 (1), pp. 97-102 : 98-99

Aenictus pachycerus species group

Diagnosis. — Jaitrong & Yamane (2011) defined this species group as follows: antenna long, consisting of 10 segments; scape long reaching or extending beyond posterolateral corner of head; anterior clypeal margin roundly convex in the middle, lacking denticles; mandible triangular, with very dense punctures; its masticatory margin with a large and sharp apical tooth followed by 4–12 small inconspicuous denticles, which gradually reduce in size toward basal angle of mandible; frontal carinae fused at the level of antennal base to form a single carina, and extending less than half length of head, and well developed anteriorly and poorly developed posteriorly; parafrontal ridge present, reaching less than half length of head; seen in profile its anteriormost part well developed and raised as a subtriangular process; occipital margin forming a collar or carina; promesonotum distinctly convex or very weakly convex dorsally and sloping gradually to propodeum; propodeal junction angulated; declivity of propodeum concave, encircled with a rim; subpetiolar process weakly developed.

Head entirely sculptured or smooth and shiny. Petiole and postpetiole densely punctate, at least in Southeast Asian species. First gastral segment entirely smooth and shiny, or rarely superficially shagreened, except the base of the tergite and sternite that has dense small punctures. Body black, dark or reddish brown to light or yellowish brown; typhlatta spot absent.

Remarks. — The Aenictus pachycerus group consists of relatively large species in terms of body size (TL 3.20–4.65 mm: 1.80–3.00 mm in smaller species). Wilson (1964) and Jaitrong & Yamane (2011) pointed out that this group is closely related to the A. philippinensis group, but can be distinguished from the latter by the mesonotum not visibly demarcated from the mesopleuron, and the metanotal groove almost absent or indistinct (mesopleuron clearly demarcated from metapleuron by a deep groove and from promesonotum by a distinct carina and metanotal groove relatively deep and distinct in the A. philippinensis group). This species group is also related to the Aenictus hottai group in having developed a frontal carina and parafrontal ridge but can be separated from the latter by the first gastral tergite smooth and shiny and by the weakly developed subpetiolar process (the first gastral tergite densely micropunctate and the subpetiolar process well developed in the latter; see Jaitrong & Yamane, 2011).

Key to species of the Southeast Asian Aenictus pachycerus species group based on the worker caste

1. Head entirely smooth and shiny; dorsum of mesosoma entirely smooth and shiny.....................................................................2

– Head entirely sculptured or partly smooth and shiny; dorsum of mesosoma entirely sculptured or partly smooth and shiny4

2. Promesonotum in profile with clearly convex dorsal outline; propodeum lower than promesonotum; body yellowish brown ( Philippines)............................................................. A. powersi

– Mesosoma dorsally flat or feebly convex; body reddish brown.......................................................................................3

3. Smaller species (HW 0.63–0.65 mm); propodeum in profile with feebly convex dorsal outline; longest pronotal hair 0.25–0.28 mm ( Philippines) ................................................ A. carolianus

– Larger species (HW 0.75–0.78 mm); propodeum in profile with straight dorsal outline; longest pronotal hair ca. 0.15 mm ( Philippines)................................................................ A. reyesi

4. First gastral tergite superficially shagreened ( Vietnam, Laos, and Thailand).................................................. A. paradentatus

– First gastral tergite smooth and shiny.....................................5

5. Side of head partly smooth and shiny; dorsal face of pronotum partly shiny..............................................................................6

– Side of head entirely sculpturate (punctate or reticulate); dorsal face of pronotum entirely sculptured and opaque..................7

6. Area just outside parafrontal ridge shagreened; vertex reticulate, with sparse standing hairs (less than 12); postpetiole almost as long as petiole (Sulawesi) ........ A. sulawesiensis , new species

– Area just outside parafrontal ridge with several irregular longitudinal rugulae; vertex finely punctate; vertex with denser standing hairs (more than 15); petiole distinctly longer than petiole (Java) ................................................ A. sp. 84 of WJT (see Remarks under Material examined for other species)

7. Propodeal junction in profile with protruding edge that is longer than maximum length of propodeal spiracle, very thin, acute, and far overhanging declivitous face; antennal scape longer (SI 143–152) (Malay Peninsula, Sumatra, Borneo and Java) ........ ................................................................................ A. dentatus

– Edge of propodeal junction not longer than maximum spiracle width and not overhanging the declivitous face; antennal scape shorter (SI 110 or less than)....................................................8

8. Lateral face of pronotum partly smooth and shiny or superficially shagreened with smooth and shiny interspaces; area just outside parafrontal ridge with 3–5 irregular longitudinal rugulae (Borneo)................................................. A. kutai , new species

– Lateral face of pronotum entirely sculpturate and opaque; area just outside parafrontal ridge filely punctate..........................9

9. Apical half of femora superficially reticulate with smooth and shiny bottoms; smaller species (TL 3.5–3.60 mm; HW 0.65–0.68 mm) ( Philippines, Sulawesi and Australia)............. A. nesiotis

– ntire femora finely punctate; larger species (TL 3.65–5.10 mm; HW 0.70–0.98 mm)...............................................................10

10. Petiole sessile; subpetiolar process developed, triangular; ventral outline of postpetiole almost straight or weakly convex; larger species (TL 4.85–5.10 mm; HW 0.90–0.98 mm) (S. China and Vietnam) .............................................................. A. bobaiensis

– Petiole subsessile; subpetiolar process low, its ventral outline convex; ventral outline of postpetiole feebly concave; smaller species (TL 3.65–4.20 mm; HW 0.70–0.80 mm) (Malay Peninsula, Borneo, and Buru Island) .......................... A. levior