Aenictus minutulus

Aenictus minutulus species group

Aenictus piercei group in Jaitrong et Yamane, 2011: 9.

Diagnosis. In an earlier paper (Jaitrong & Yamane 2011) this species group was defined as follows: head in fullface view with occipital corner convex, and posterior margin almost straight to shallowly and broadly concave; occipital margin lacking collar; antenna 10-segmented; antennal scape short reaching only midlength of head; anterior clypeal margin roundly convex, lacking denticles; mandible subtriangular; its masticatory margin with a large apical tooth, medium-sized subapical and basal teeth, and 2-6 denticles between them; basal margin of mandible with conspicuous denticles; frontal carina short; parafrontal ridge absent; with mesosoma in profile promesonotum convex dorsally and sloping gradually to propodeum; metapleural groove present or absent (mesonotum and propodeum fused); propodeal junction angulated; subpetiolar process well developed, triangular or subrectangular. Head and first gastral segment entirely smooth and shiny. Body yellowish brown to reddish brown; typhlatta spot absent.

Size variation occurs among individuals from single colonies.

Remarks. This is a group of rather small species, measuring 1.80-3.20 mm in total body length. It is most similar to the A. javanus group in terms of body size and coloration, but in the former the anterior clypeal margin lacks denticles, while it has several denticles in the latter.

The Aenictus piercei group was established by Jaitrong and Yamane (2011) to include five named species occurring in Southeast Asia: Aenictus changmaianus Terayama et Kubota, 1993; A. lifuiae Terayama, 1984; A. minutulus Terayama et Yamane, 1989; A. peguensis Emery, 1894; and A. piercei Wheeler et Chapman, 1930. However, after carefully examining the type material and an associated specimen of A. piercei we concluded that this species should be removed from this group and that it is a member of the A. javanus group (A. piercei has denticles on the anterior margin of clypeus). The A. piercei group is renamed here as the A. minutulus group.

After a careful examination of the smaller specimens of A. lifuiae collected from Iriomote-jima and Okinawajima, southern Japan, we found that the mandible is almost linear, the anterior clypeal margin is straight or weakly concave, and that a gap occurs between the mandibles and anterior clypeal margin. These characteristics are used to separate the A. ceylonicus group from the other groups of the genus Aenictus, and also these specimens possess other conditions shared with the A. ceylonicus group. We transfer A. lifuiae to the A. ceylonicus group.

Checklist of species

Aenictus changmaianus Terayama et Kubota, 1993

Aenictus minimus sp. nov.

Aenictus minutulus Terayama et Yamane, 1989

Aenictus peguensis Emery, 1895

Aenictus subterraneus sp. nov.

Aenictus sp.56 of WJT

Key to species based on the worker caste

1. Promesonotum in profile with clearly convex dorsal outline; propodeum dorsally extremely lower than promesonotum (Figs 2 C, 5C, 6C).......................................................................................... 2

- Mesosoma dorsally almost flat or feebly convex (Figs 1 C, 3C, 4C).............................................. 4

2 Declivity of propodeum shallowly concave, encircled with a distinct rim (Fig. 2 C–E) (Borneo and Java)... A. sp. 56 of WJT

- Declivity of propodeum with lateral carinae, but not demarcated basally by a transverse carina (Figs 5 D–E, 6B–D)....... 3

3 In full-face view posterior margin of head convex (Fig. 5 A); propodeal junction angulated, right-angled (Fig. 5 E); larger species (TL 2.95–3.15 mm; HW 0.52–0.58 mm) (Vietnam and Myanmar).................................. A. peguensis

- In full-face view posterior margin of head almost straight or feebly concave (Fig. 6 A); propodeal junction roundly angulated (Fig. 6 C); smaller species (TL 2.10–2.15 mm; HW 0.48–0.50 mm) (Borneo).................... A. subterraneus sp. nov.

4 Basal margin of mandible with 1–2 small denticles next to large basal tooth and followed by a larger denticle (Fig. 3 E); antennal scape relatively short (SI 63–64) (N. Vietnam)............................................. A. minimus sp. nov.

- Basal margin of mandible with 3–5 denticles that gradually reduce in size toward base of mandible (Figs 1 E, 4E); antennal scape relatively long (SI 67–72).......................................................................... 5

5 Metapleural gland bulla relatively large; distance between propodeal spiracle and metapleural gland bulla shorter than or almost as long as spiracular diameter (Fig. 1 D) (Vietnam and Thailand)............................. A. changmaianus

- Metapleural gland bulla relatively small; distance between propodeal spiracle and metapleural gland bulla clearly longer than spiracular diameter (Fig. 4 D) (Sumatra and Java).................................................. A. minutulus