Polyrhachis dohrni

The neotype was collected from a nest inside a dry hollow twig on a living tree in the grounds of the Lowland Agricultural Experimental Station, Kerevat (04º20’S, 152º02’E, c. 50m).

Identification
Kohout (2007) - P. dohrni is apparently limited to the Bismarck Archipelago: New Britain, neighboring islands and low altitude localities along the coast of New Ireland. It is similar to Polyrhachis abdita from Lelet Plateau, but differs in several characters. The eyes of dohrni are moderately convex and in full face view break the lateral outline of the head, if only marginally. The mesosomal dorsum is more slender and the pronotal humeri armed with broad-based, more anteriorly directed, acute teeth. The propodeal margins terminate posteriorly in blunt distinct processes that appear as minute teeth in profile. The anterodorsal margin of the first gastral segment is not raised above its dorsal face in lateral view but, viewed from behind, the margin appears medially produced. The legs, notably the proximal halves of the femora, and apices of antennal scapes are distinctly lighter reddish-yellow and the dorsal gastral pubescence is more golden. In contrast, P. abdita has distinctly flattened eyes that do not reach the lateral outline of the head in full face view. The mesosoma is somewhat wider posteriorly. The pronotal teeth are less produced, more angular and the greatest pronotal width is at its midlength. The lateral propodeal margins are only narrowly rounded posteriorly, not dentiform. The anterodorsal margin of the first gastral segment, when viewed from behind, is smoothly rounded, without any indication of a median process. The antennal scapes and femora are more-or-less uniformly medium to dark reddish-brown and the relatively abundant pubescence, including that of the gaster, is silvery or silvery-gray.

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

Nomenclature

 *  dohrni. Polyrhachis dohrni Forel, 1901b: 34 (w.) NEW GUINEA (Bismarck Archipelago). Kohout, 2007a: 198 (q.). Combination in P. (Aulacomyrma): Emery, 1921e: 17.

Worker
Kohout (2007) - TL c. 4.74-5.80 (5.44); HL 1.22-1.37 (1.34); HW 1.09-1.23 (1.23); CI 86-92 (92); SL 1.25-1.43 (1.40); SI 113-121 (114); PW 1.06-1.25 (1.18); MTL 1.15-1.37 (1.37) (9 measured).

Anterior clypeal margin arcuate with shallow notch medially. In profile clypeus virtually straight with very weakly impressed basal margin that is laterally indicated by a hairline break in cephalic sculpture. Frontal carinae sinuate, with laminate lobes. Frontal triangle indistinct. Sides of head weakly convex. Eyes moderately convex, in full face view usually breaking lateral cephalic outline. Mesosoma marginate along entire length; pronotal humeri armed with broadly-based, acute teeth that are laterally continuous with posteriorly converging, uninterrupted, pronotal margin. Promesonotal suture distinct; metanotal groove lacking dorsally, position marked by shallow emargination of lateral margins. Mesonotal margins posteriorly converging; propodeal margins subparallel, terminating in blunt processes that appear as minute teeth in profile. Propodeal dorsum descending abruptly into weakly concave propodeal declivity. Petiole scale-like, biconvex, with sharp dorsal margin, its apex higher than anterodorsal margin of first gastral segment; lateral petiolar spines directed outwards and slightly curved backwards from bases. First gastral segment concave medially, accommodating posterior face of petiole; anterodorsal margin not elevated above dorsal face of segment in lateral view, however, when viewed from behind, appearing somewhat medially produced. Mandibles finely, mostly longitudinally, striate-rugose. Sculpture of body consisting of more-or-less regularly spaced striae, mostly longitudinal on head, pronotal dorsum and sides of gaster; V-shaped on mesonotal and propodeal dorsa, oblique on sides of mesosoma. Petiole and dorsum of gaster finely, microscopically, shagreened.

Entire body with numerous semierect to erect, off-white to pale-yellow hairs, that do not exceed greatest diameter of eye in length. Silvery appressed pubescence fairly abundant, but not concealing underlying sculpture, except on propodeal dorsum, where it curves towards midline. Gastral pubescence rather abundant, silvery at sides and along posterior borders of segments, becoming distinctly golden on dorsal aspect of first gastral segment. Black; mandibular masticatory border, apices of antennal scapes, funiculi, distal parts of femora and tarsi medium to dark reddish brown, with funiculi and tarsi becoming lighter apically. Tibiae distinctly lighter, except proximal and distal ends, that are very narrowly dark, reddish brown.

Queen
Kohout (2007) - Dimensions: TL c. 6.50-6.95; HL 1.53-1.56; HW 1.34-1.40; CI 87-90; SL 1.47-1.56; SI 109-112; PW 1.37-1.47; MTL 1.56-1.59 (4 measured).

Very much like worker with usual characters identifying full sexuality, including three ocelli and complete thoracic structure with wings. Sculpture, pilosity and color as in worker except eyes more prominent, clearly breaking cephalic outline in full face view. Lateral petiolar spines distinctly shorter.

Type Material
Kohout (2007) - Type locality: BISMARCK ARCHIPELAGO, Credner I. (F. Dahl), ? - (holotype apparently lost).

The holotype of this species should be lodged in the MNHU, together with other specimens collected by Friedrich Dahl from the Bismarck Archipelago. Extensive searches by Dr Frank Koch and the author failed locate it there or in any other collections examined and it is considered lost. Forel (1901: 35) stated that the specimen was taken from the stomach of a bird Pachycephala melanura on Credner I., 7.viii.1896. Because of considerable damage to the specimen (“Pro- und Mesothorax stark defekt”), Forel was apparently uncertain about the caste and in the original description listed the specimen as a worker with a question mark. However, further on he wrote: “... drei deutliche Punktaugen (♀ ??)”. Because dohrni workers do not possess ocelli, the specimen Forel described was undoubtedly a queen.

To establish the nomenclatural stability of the species, I have designated, in accordance with Article 75.3.5. of the International Code of Zoological Nomenclature (Fourth Edition), a worker specimen as the neotype of Polyrhachis dohrni Forel. The specimen was selected from a colony of 5 workers and 2 alate queens collected from a nest inside a dry hollow twig on a living tree in the grounds of the Lowland Agricultural Experimental Station, Kerevat, East New Britain Province, 04º20’S, 152º02’E, c. 50m, rf. edge, 14.vii.1984, R.J. Kohout acc. 84.67. The locality is situated only about 35km SW of Credner Islands, the type locality of P. dohrni. The neotype has been deposited in.