Polyrhachis delicata

This species is an arboreal nester, using silk to join the leaves of various lowland rainforest trees and shrubs (Kohout 1999, 2000; Robson & Kohout 2005, 2007; Kohout, 2012).

Identification
As indicated by Kohout (1994), the most obvious differences between P. delicata and Polyrhachis queenslandica are their colour and the orientation of their propodeal spines. However, due to a high degree of variability, notably within Queensland populations of both species, these characters can be unreliable and, while both species are usually separable, no single character is universally diagnostic. The propodeal spines in P. delicata are generally more strongly upturned, but the actual angle of elevation varies between specimens, even those of the same nest series. The propodeal spines in P. queenslandica are distinctly less elevated with only a small amount of variation between the specimens examined. The colour of the body appears to be a more reliable character to separate the species but only in fully pigmented specimens. A mostly red or reddish-brown mesosoma, gaster and appendages, contrasting with a darker head (almost black in some specimens) characterises P. delicata, while the body in P. queenslandica is mostly uniformly black or very dark reddish-brown. The sculpturation of the head and mesosoma in P. delicata is rather distinctly reticulate-punctate and opaque, while it is markedly more finely and closely punctate in P. queenslandica. The petiolar node in P. delicata is relatively slim and distinctly narrows dorsally in lateral view, with the anterior face smoothly curving onto the petiolar dorsum in an uninterrupted line that incorporates the anterior edge of the dorsoposteriorly elevated median spine. In contrast, the petiolar node in P. queenslandica is distinctly thicker in lateral view, with the anterior face curving onto a virtually flat dorsum and the median petiolar spine dorsoposteriorly elevated at a distinctly steeper angle. The latter character does not serve to separate the queens of the two species, however, the median petiolar spine in the queen of P. queenslandica is simply pointed, while its apex is clearly emarginated in P. delicata.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Polyrhachis delicata is known from two disjunct populations, one in the Northern Territory around Darwin and the other in northern Queensland, ranging from about Coen on Cape York Peninsula south to Cairns. The specimens of the type series of the junior synonym P. lysistrata were allegedly collected ‘near Townsville’ by F.P. Dodd on 30.iv.1902, however, I have seen no other specimens of this species collected that far south.

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

Nomenclature

 *  delicata. Polyrhachis delicata Crawley, 1915b: 238 (w.) AUSTRALIA. Kohout, 2012: 51 (q.). Junior synonym of queenslandica: Crawley, 1921: 96. Revived from synonymy and senior synonym of lysistrata: Kohout, 1994a: 135.
 * lysistrata. Polyrhachis (Myrmothrinax) lysistrata Santschi, 1920a: 569 (w.) AUSTRALIA. Junior synonym of delicata: Kohout, 1994a: 135.

Worker
Kohout (2012) - (syntype cited first): TL c. 6.55, 5.39-6.90; HL 1.62, 1.43-1.72; HW 1.40, 1.22-1.47; CI 84, 82-93; SL 2.06, 1.84-2.15; SI 147, 142-153; PW 0.92, 0.78-0.97; MTL 2.18, 1.84-2.28 (37 measured).

Anterior clypeal margin with wide median truncation flanked by small teeth. Clypeus with median carina; straight in profile, posteriorly rounding into moderately impressed basal margin. Frontal triangle distinct. Frontal carinae sinuate with margins only weakly raised at midlength; central area almost flat with poorly indicated frontal furrow. Sides of head in front of eyes converging towards mandibular bases in virtually straight line; behind eyes sides widely rounding into convex occipital margin. Eyes convex, in full face view clearly breaking lateral cephalic outline. Ocelli lacking; position of lateral pair indicated by shallow punctures in sculpturation. Pronotal dorsum often with poorly defined median longitudinal depression; pronotal humeri angular with lateral margins converging posteriorly into distinct promesonotal suture. Dorsum of mesosoma with lateral margins converging posteriorly in weakly sinuate line; metanotal groove well defined. Lateral margins of propodeum subparallel, terminating in strongly upturned, weakly diverging, acute spines. Petiole with anterior and posterior faces almost straight, converging dorsally in lateral view; petiolar dorsum a flat, posteriorly rising platform, armed with two widely diverging, short lateral spines and a long, acute, dorsoposteriorly elevated median spine. Anterior face of first gastral segment distinctly higher than full height of petiole, widely rounding onto gastral dorsum.

Mandibles finely longitudinally striate with numerous piliferous pits; sculpture finer and rather polished towards masticatory borders. Clypeus more-or-less longitudinally reticulate-striate. Intensity of sculpturation increasing posteriorly, with vertex, mesosoma and petiole distinctly reticulate-punctate. Gaster very finely shagreened, highly polished.

Mandibular masticatory borders with numerous, semierect, golden hairs and very short, closely appressed hairs towards bases. Clypeus with relatively short setae lining anterior margin and several relatively short, paired hairs near anterior and basal margins. A few slightly longer, semierect hairs along frontal carinae and on vertex, very few erect hairs on front coxae. Pubescence almost completely absent from mesosoma and petiole. Gastral venter and apical gastral tergites with numerous, relatively long hairs. Dorsum of gaster with very short, closely appressed, much diluted golden pubescence.

Colour. Body mostly medium to dark reddish-brown, often variously blotched light orange or red; head in fully pigmented specimens distinctly darker, usually very dark reddish-brown or black, with mandibles, except masticatory borders, middle portion of clypeus and central area along frontal carinae usually distinctly lighter; appendages mostly light to medium reddish-brown, with distal funicular segments progressively lighter towards antennal apex. Mandibular masticatory borders, anterior clypeal margin and frontal carinae narrowly lined with brown.

Queen
Kohout (2012) - TL c. 8.11-8.67; HL 1.93- 1.96; HW 1.61-1.65; CI 83-84; SL 2.28-2.34; SI 139- 144; PW 1.59-1.68; MTL 2.43-2.59 (5 measured). Apart from sexual characters, closely resembling worker except: pronotal humeri obtusely angular. Mesoscutum about as wide as long, lateral margins converging anteriorly and forming moderately rounded anterior margin; median line distinct; parapsides flat. In profile, anterior face of mesoscutum widely rounding onto virtually flat dorsum. Mesoscutellum weakly convex, moderately raised above dorsal plane of mesosoma, strongly rounding into distinctly impressed metanotal groove. Propodeal dorsum with lateral margins indistinct; propodeal spines somewhat flattened dorsally, shorter than distance between their bases, oblique to main axis of body; their inner margins continued medially and forming an open ‘U’ in anterior view. Petiole with anterior and posterior faces converging dorsally; spines shorter and thicker than in worker; median spine only marginally longer than lateral pair with its apex more-or-less emarginated.

Type Material
Polyrhachis delicata type material.

Syntype workers from Darwin, Northern Territory, Australia, 16.iv.1913 (G.F. Hill) (examined by Kohout, 2012).

Polyrhachis lysistrata type material.

Syntype workers from Townsville, Queensland, Australia (F.P. Dodd) (examined by Kohout, 2012).