Polyrhachis debilis

Donisthorpe (1938): "taken in a nest of leaves woven together with silk at Mafulu, 4000 ft., Papua by Miss L. E. Cheesman, xii. 1933. Miss Cheesman swept off herbage a number of workers of the same species at Kokoda." Nothing more is known about the biology of Polyrhachis debilis.

Identification
Kohout (2006) - Polyrhachis debilis is similar to Polyrhachis yorkana. Both species both display considerable variability in the development of the propodeal spines which range from inconspicuous tuberculae to short spines. However, they differ in numerous characters, including the shape of the head, which in P. debilis is as wide or even wider than long (CI 100-103), while in P. yorkana it is distinctly longer than wide (CI 96-98). In full face view, the eyes of P. debilis do not reach the sides of the head, while in P. yorkana they clearly break the cephalic outline. In lateral view, the pronotum is distinctly convex in P. debilis and rather ﬂat in P. yorkana. In dorsal view, the pronotum in P. debilis is relatively narrow with evenly rounded shoulders, while in P. yorkana the pronotum is distinctly widest just behind the shoulders and, in the majority of specimens examined, the pronotal humeri are subangular or distinctly angular. They also differ in their relative size, with P. debilis distinctly smaller (HL 1.34-1.47 verus HL 1.56-1.62).

Leong et al. (2015) Taiwan: There are currently 2 species of Polyrhachis (Cyrtomyrma) known from Taiwan, Polyrhachis rastellata and Polyrhachis debilis. Polyrhachis debilis can be distinguished from P. rastellata by the small pair of denticles on the propodeum and the furrowed, narrowly rounding fronto-clypeal suture.

Distribution
Papua New Guinea to the islands of eastern Indonesia.

Polyrhachis debilis previously recorded from Australia (Kohout, 2000) belong to Polyrhachis yorkana. Although the type locality of Polyrhachis debilis (Fly River, Papua New Guinea) is situated just across Torres Strait from Cape York Peninsula, it apparently does not occur in Australia. (Kohout 2006)

Distribution based on Regional Taxon Lists
Indo-Australian Region: New Guinea. Palaearctic Region: China.

Nomenclature

 *  debilis. Polyrhachis laevior var. debilis Emery, 1887a: 240 (w.) NEW GUINEA. Donisthorpe, 1938c: 266 (q.). Combination in P. (Cyrtomyrma): Emery, 1925b: 208. Raised to species: Donisthorpe, 1938c: 265. See also: Kohout, 2006b: 124.

Worker
Leong et al. (2015) - TL: 7.5; HL: 1.5; HW:1.5; CI: 1; SL: 1.8; SI: 1.2; PW: 1.2; MTL:2.1.

Body color light black; the anterior of trochanter, femur, and tibia light to medium reddish-brown; coxa, trochanter and tarsi distinctly darker. Fronto-clypeal suture has a furrow, narrowly rounding. Eyes with weakly convex anterior, and flat posterior face; Ocellus lacking; Shoulders of pronotum rounded. Promesonotal suture obvious and smooth, metanotal groove absent. Propodeum with a pair of small denticles, propodeal declivity descending in a circular curve; petiole with weakly convex anterior, and flat posterior face; dorsum armed with four acute spines, dorsal pairs slightly longer and slenderer than lateral pairs, radian between dorsal spines smaller than between dorsal and lateral spines. Subpetiolar process angulate anteriorly, widely rounded posteriorly. Anterior face of first gastral segment weakly concave at base.

Mandibles fine with numerous pits and hairs. Head, mesosoma and gaster rough with sides of pronotum and mesoand metapleurae reticulate to reticulaterugose. Mandibles with many curved, short setae, direction of setae similar with that of the teeth. Short setae distributed evenly on margin of clypeus. Single pair of relatively long, anteriorly directed setae in the middle, anterior clypeal margin. Several pairs of relatively short hairs arising near anterior and basal clypeal margins, along frontal carina and on vertex. Coxae, trochanter and the end of the femora have some hairs. Posterior of gaster with some hairs at the apical segments. Whole body with numerous shallow punctures.

Differisce dal tipo della P. laevior per le spinette del metanoto ridotte a piccolo denti, talvolta appena sensibili. Sono nel dubbio se riferirla alla P. laevior o alla rastellata, perche connette intimamente le due forme; percio credo che la P. laevior debba essere considerate come razza della rastellata.

Queen
Similar to worker, but the shoulders are more rounded,the teeth of the epinotum reduced to small tubercules, those of the scale blunter. Wings yellowish; pterostigma and veins light yellowish brown. (Donisthorpe 1938).

Male
Donisthorpe (1938) reported males were taken with a nest series but this caste remains undescribed.

Type Material
NEW GUINEA, Fly River, col. L.M. D’Albertis; INDONESIA, Aru Island, col. O. Beccari. Syntype workers, , , – as reported by Kohout (2006).