Polyrhachis alphea

Polyrhachis alphea appears rather uncommon with a patchy distribution extending across New Guinea and neighbouring islands to the extreme tip of Cape York Peninsula. A single colony, including a dealate queen, and several alate queens collected at light trap represent the only Australian records of P. alphea.

Identification
Kohout (2012) - Australian specimens differ slightly from those from New Guinea, notably in the intensity and density of sculpturation. The coarse rugosity of the head is somewhat less pronounced in Australian specimens and confined mostly to the front of the head, with the vertex only reticulate-punctate. The rugosity is also weaker on the sides of the mesosoma and petiole. The petiolar spines in New Guinean specimens, when viewed from the front, form a rather narrow ‘U’ with the tips of the spines weakly turned inwards. In contrast, the petiolar spines in Australian specimens are straight, more slender and distinctly diverging. The legs of Australian specimens are generally darker, reddish-brown, while in the holotype and most other New Guinean specimens examined, they are relatively light, yellowish-brown. However, in spite of these differences, the Australian and New Guinean specimens are very similar and I am reluctant to consider them separate species. Until more New Guinean material, including nest series, becomes available, I consider both forms to represent different populations of a single species.

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

Castes
Immature stages (eggs, larvae and pupae) in QM spirit collection. (Kohout 2012)

Nomenclature

 *  alphea. Polyrhachis alpheus Smith, F. 1863: 14 (w.) NEW GUINEA. Kohout, 2012: 45 (q.). Combination in P. (Myrmatopa): Emery, 1925b: 180.

Worker
Kohout (2012) - TL c. 5.14-6.75; HL 1.34-1.68; HW 1.06-1.31; CI 77-82; SL 1.79-2.18; SI 161-174; PW 0.75-0.94; MTL 1.81-2.25 (12 measured).

Anterior clypeal margin truncate medially; truncate portion widely and shallowly emarginate and flanked by blunt angles. Clypeus with short, median carina, flat in profile, posteriorly rounding into moderately impressed basal margin. Frontal triangle distinct. Frontal carinae sinuate with distinctly raised margins; central area relatively narrow, deeply concave; frontal furrow poorly indicated. Sides of head in front of eyes converging towards mandibular bases in virtually straight line; behind eyes sides rounding into convex occipital margin. Eyes relatively large, strongly convex, in full face view clearly exceeding lateral cephalic outline. Ocelli lacking. Mesosomal dorsum distinctly laterally marginate. Pronotal dorsum flat; humeri with rather short, acute, anterolaterally directed spines; pronotal spines mostly horizontal, but distinctly upturned in some specimens, with lateral edges continuous with weakly rounded pronotal margins. Promesonotal suture distinct. Mesonotum posteriorly with weakly raised lateral margins that converge towards rather shallowly impressed metanotal groove. Propodeal dorsum marginally wider than long, lateral margins terminating posteriorly in short, transverse ridges that appear as upturned teeth in profile; ridges continued medially for a short distance with propodeal dorsum between them descending into oblique declivity in medially uninterrupted curve. Petiole with anterior face very low, posterior face convex and distinctly higher; dorsum armed with pair of relatively long, more-or-less diverging, dorsoposteriorly directed, acute spines; dorsum between them narrowly rounded or with indication of intercalary teeth or tubercles in some specimens. Anterior face of first gastral segment flat at base, widely rounding onto dorsum.

Mandibles finely longitudinally striate with numerous piliferous pits. Head rather coarsely sculptured, deeply irregularly rugose with superimposed small punctures; sculpture somewhat less intense on clypeus and on vertex near occipital margin. Dorsum of mesosoma and petiole, except spines, coarsely reticulate-punctate with sculpture on pronotum more-or-less longitudinally directed. Gaster finely shagreened, highly polished.

Mandibles with several curved, golden hairs near masticatory borders. Anterior clypeal margin with one longer median seta and fringe of relatively short setae laterally. A pair of longer, erect or semierect hairs near anterior clypeal margin and along frontal carinae; fore coxae with several relatively long, semierect hairs; somewhat shorter, single hairs on venter of trochanters and femora. Gaster with several golden, semierect hairs lining dorsoposterior margins of apical segments; distinctly longer hairs on gastral venter. Appressed, golden or off-white, rather diluted pubescence on dorsum of gaster, virtually absent from other body surfaces.

Colour. Black. Mandibles dark reddish-brown at bases, distinctly lighter apically with dark teeth. Antennal scapes and basal funicular segments dark reddish-brown, subsequent segments progressively lighter; base of scapes and apical antennal segments orange. Legs, including coxae generally reddish-brown; fore coxae usually darker or almost black in some specimens. Gaster dark reddish-brown, with posterior margins of segments lined with dark brown or black.

Queen
Kohout (2012) - TL c. 8.32-8.87; HL 1.93-2.09; HW 1.50-1.59; CI 75-79; SL 2.43-2.56; SI 158-169; PW 1.65-1.87; MTL 2.65-2.81 (9 measured). Apart from sexual characters, very similar to worker except: distinctly larger; pronotal humeri with somewhat flattened acute teeth. Mesoscutum as long as wide, with lateral margins strongly converging anteriorly, forming distinctly narrowly rounded anterior margin; anterior face of mesoscutum low, with dorsum forming continuous, moderately convex line in lateral view; median line flat anteriorly, weakly raised dorsoposteriorly; parapsides distinct, weakly raised posteriorly. Mesoscutellum not raised above dorsal plane of mesosoma, flat anteriorly, widely rounding posteriorly into deeply impressed metanotal groove. Propodeal dorsum with blunt lateral margins terminating posteriorly in short, upturned, transverse ridges. Petiolar spines virtually identical to those in worker. Sculpturation, pilosity and colour as in worker.

Type Material
Holotype worker from Waigeo Island, New Guinea (A.R. Wallace) (examined by Kohout, 2012).

Polyrhachis alpheus

Holotype worker in. Labelled “Wag.” (= Waigeo I., New Guinea) and with a Donisthorpe type-label. Gaster of holotype is missing.