Polyrhachis trispinosa

Specimens have been collected from fogging samples in cacao.

Identification
A member of the Polyrhachis aequalis species group.

Kohout (2008) - The workers of P. trispinosa closely resemble those of Polyrhachis subtridens from Mentawei I. and Polyrhachis solivaga from the Philippines. All feature a shallow, longitudinal, median depression on the pronotal dorsum and an almost identical configuration of the petiolar spines, featuring rather short lateral spines and a rudimentary middle spine. They differ in several characters, including the width of pronotal dorsum, the length of the mesosoma and the colour of the body. In P. subtridens and P. solivaga the pronotal dorsum is wider with its sides rounded and the median depression rather distinct. The propodeal declivity is steeply oblique and the lateral petiolar spines range from short to rudimentary within single populations. In contrast, the narrower pronotal dorsum in P. trispinosa specimens has sides ranging from weakly rounded to almost straight and has a less distinct median depression. In addition, the mesosoma of P. trispinosa is distinctly more slender and longer with the propodeal declivity less steeply oblique. The colour of the body in P. subtridens and P. solivaga specimens is generally medium reddish-brown, while it is distinctly darker, virtually black, in most P. trispinosa specimens.

Distribution based on Regional Taxon Lists
Indo-Australian Region: Indonesia, Sulawesi.

Castes
The holotype queen of P. trispinosa  (OXUM) is undoubtedly conspecific with a queen collected by M.M. Bos at Lore Lindu National Park. Bos also collected a short series of distinctly smaller queens that also closely match the holotype but have proportionally wider pronotal dorsums and more widely rounded anterior margins of the mesoscutum. However, the smaller queens share the characteristic configuration of the petiolar spines found in the holotype, and I consider them microgynous queens of P. trispinosa.

Nomenclature

 *  trispinosa. Polyrhachis trispinosus Smith, F. 1861b: 40, pl. 1, fig. 11 (q.) INDONESIA (Sulawesi). Kohout, 2008a: 313 (w.). Combination in P. (Myrmothrinax): Emery, 1925b: 184.

Worker
Kohout (2008) - TL c. 6.45-7.66; HL 1.56-1.81; HW 1.22-1.43; CI 78-80; SL 1.96-2.18; SI 149-163; PW 0.84-0.90; MTL 2.15-2.59 (8 measured).

Anterior clypeal margin with wide, medially notched truncation, flanked by acute teeth. Clypeus with blunt median carina that is less distinct anteriorly; clypeus weakly convex in profile, narrowly rounding into moderately impressed basal margin. Frontal triangle poorly indicated. Frontal carinae sinuate with margins weakly and narrowly raised; central area relatively wide, weakly raised medially with shallowly impressed frontal furrow. Sides of head in front of eyes converging into mandibular bases in almost straight line; behind eyes sides broadly rounding into convex occipital margin. Eyes weakly convex, in full face view exceeding lateral cephalic outline. Ocelli lacking, positions indicated by shallow pits in cephalic sculpture. Mesosomal dorsum laterally marginate, rather narrow and slender. Pronotal dorsum with shallow, longitudinal median depression; humeri subangular; promesonotal suture distinct. Mesonotal dorsum with posteriorly raised lateral margins; metanotal groove distinct. Propodeal dorsum longer than wide with lateral margins terminating posteriorly in upturned, acute teeth; propodeal dorsum descending into oblique declivity in medially uninterrupted line. Petiole relatively low, with anterior face widely rounding onto dorsum; posterior face almost straight; dorsum of petiole armed with three spines; lateral pair longer and acute, somewhat dorsolaterally and weakly posteriorly directed; middle spine very short, broad-based and tooth-like, rudimentary in some specimens; position of middle spine variable, situated well behind lateral spines and clearly visible in side view in most specimens but situated more anteriorly and virtually hidden by lateral spines in some specimens. Anterior face of first gastral segment flat, widely rounding onto dorsum.

Mandibles very shallowly, finely longitudinally reticulate. Head, mesosoma and petiole very closely, mostly irregularly reticulate-punctate with sculpturation slightly more coarse on sides of mesosoma. Gaster very finely shagreened, rather polished.

Mandibles with a few, rather short, mostly erect, yellowish-golden hairs at masticatory borders and extremely short, closely appressed hairs towards bases. Anterior clypeal margin with a fringe of short setae lining margin medially and laterally. Clypeus with numerous, relatively long, erect hairs and a few pairs of somewhat shorter erect hairs lining frontal carinae. Anterior and posterior faces of fore coxae with a few, relatively long hairs; mid and hind coxae with a few shorter erect hairs ventrally. Femora with a few, medium length, erect hairs on ventral surfaces. Gaster with a few short, erect hairs along apical segments dorsally; more abundant, longer hairs on gastral venter. Extremely short, closely appressed, silvery or pale golden pubescence very scarcely distributed over all body surfaces, a little more abundant on dorsum of first gastral segment.

Colour. Mostly black or very dark reddish-brown; mandibles dark reddish-brown with teeth black and narrow yellowish band at masticatory borders; clypeus and gastral segments blotched dark reddish-brown; basal funicular and tarsal segments black with subsequent segments progressively lighter; five apical segments of funiculi and terminal segments of tarsi, including claws, very light yellow.

Queen
Kohout (2008) - (holotype queen cited first, compared queen second, 3 microgynous queens last): TL 9.88, 9.88, 7.56-7.81; HL 2.21, 2.15, 1.72-1.78; HW 1.72, 1.72, 1.34-1.40; CI 78, 80, 77-80; SL 2.62, 2.71, 2.12-2.18; SI 152, 157, 156-158; PW 1.81, 1.78, 1.50-1.62; MTL 3.18, 3.12; 2.37-2.43.

Queen very similar to worker with usual differences indicating caste; mesosoma rather slender as in worker; configuration of petiolar spines indentical to worker with lateral spines short and acute and median spine very short or rudimentary.

Type Material
Kohout (2008) - Holotype queen. INDONESIA, SULAWESI, Tondano (A. R. Wallace), (examined).

Polyrhachis trispinosus

Holotype dealate queen in. Labelled “Tond.” (= Tondano, Sulawesi) and with a Donisthorpe type-label.

References based on Global Ant Biodiversity Informatics

 * Chapman, J. W., and Capco, S. R. 1951. Check list of the ants (Hymenoptera: Formicidae) of Asia. Monogr. Inst. Sci. Technol. Manila 1: 1-327
 * Emery C. 1886. Saggio di un catalogo sistematico dei generi Camponotus, Polyrhachis e affini. Memorie della Reale Accademia delle Scienze dell'Istituto di Bologna 5: 363-382
 * Emery C. 1901. Formiciden von Celebes. Zoologische Jahrbücher. Abteilung für Systematik, Geographie und Biologie der Tiere 14:565-580.
 * Kohout, R. J. 2008. A review of the Polyrhachis ants of Sulawesi with keys and descriptions of new species (Hymenoptera: Formicidae: Formicinae). Memoirs of the Queensland Museum 52:255-317.
 * Smith F. 1861. Catalogue of hymenopterous insects collected by Mr. A. R. Wallace in the islands of Ceram, Celebes, Ternate, and Gilolo. [part]. Journal and Proceedings of the Linnean Society of London. Zoology 6: 36-48.