Diacamma scalpratum

Peeters, Heraty & Wiwatwitaya (2015) excavated four complete colonies of D. scalpratum from northern Thailand. Colonies were plentiful and easy to find in a small patch of pine forest. Excavation continued to a depth of 90cm in one colony. These four colonies yielded 151±109 workers (mean number ±SD) and 69±38 cocoons (range 47-101). Only one worker had gemmae in each colony, and dissections confirmed that this was the gamergate (i.e. mated and egg-laying). All workers dissected had 16-20 ovarioles, and this number is diagnostic among closely related species (e.g. another species with large workers from Thailand has 8 ovarioles).

Identification
Laciny et al. (2015) - Very large, slender species (TL ca. 16.4–18.5 mm). Trunk black; frontal lobes and clypeus often, subpetiolar process and gaster tergites and sternites at posterior margins always reddish brown; mandibles and tibiae dark reddish brown. Standing setae on trunk short. Trunk strongly striate on mesosoma and petiole, weaker on head. Head, mesosoma, and petiole with very dense microreticulation, matt. Head elongated, sides posteriorly of eye moderately convex. Striation posterior of eyes meeting narrow, slightly concave occipital margin; ridges slightly narrower than interspaces; occipital margin laterally slightly widened and terminating in very short, blunt projections. Eyes small, not protruding. Clypeus finely, very densely punctured, except for anterior margin with larger and sparser puncturation; anteromedially with widely rounded apex. Striae on pronotum transversely elliptical. Striation on mesosoma sides slightly oblique, upcurved on propodeum. Petiole strongly compressed, dorsally not striate, but with crest posteriorly forked up to the closely spaced, long teeth; dorsolaterally with striation oblique relative to dorsal outline of node, ventrolaterally with reduced striation and almost smooth; subpetiolar process prominent, strongly concave, posterior corner longer than anterior one. Gaster tergite 1 without striation, but with fine puncturation, shiny as the following tergites.

As in the Diacamma intricatum species group (see notes for Diacamma magdalenae), the D. scalpratum group possesses a compressed petiole, but the striation of the head is longitudinal like in all species treated in the following. We place in this group three described species, D. scalpratum, Diacamma violaceum, and Diacamma longitudinale. The latter one is known from Vietnam and Laos (Emery 1889, Santschi 1920, 1924) and is readily distinguished by its longitudinal striation of the pronotum (compare also Diacamma palawanicum). Closest to the D. scalpratum group are two endemic species of Palawan (Philippines), D. palawanicum and Diacamma concentricum. They differ by several characters of the petiole.

Distribution based on Regional Taxon Lists
Oriental Region: Bangladesh, India, Myanmar, Pakistan.

Biology
Different immature stages and adults of the wasp Schizaspidia diacammae (Chalcidoidea: Eucharitidae) were found inside several ant cocoons ([[Media:Peeters, C., Heraty, J. & Wiwatwitaya, D. 2015. Eucharitid wasp parasitoids in cocoons of the ponerine ant Diacamma scalpratum from Thailand.pdf|Peeters et al. 2015]]). Wasp larvae were feeding on ant pupae, while other host cocoons yielded five wasp pupae as well as both male and female adults. Parasitized cocoons are cut in a distinct manner by the wasps when they exit, and this feature can be used to assess the prevalence of parasitism. Dissection of the ovaries of one recently emerged physogastric wasp female revealed thousands of eggs ready to be laid. Among 9 families of wasps parasitic on ants, only Eucharitidae (56 genera) specialize in attacking the immature stages of ants.

Nomenclature

 *  scalpratum. Ponera scalprata Smith, F. 1858b: 84, pl. 6, figs. 21, 22 (w.) INDIA. Emery, 1889b: 496 (m.); Wheeler, G.C. & Wheeler, J. 1952c: 610 (l.). Combination in Diacamma: Mayr, 1862: 718. Senior synonym of compressum: Dalla Torre, 1893: 29; Emery, 1911d: 65.
 * compressum. Diacamma compressum Mayr, 1879: 660 (w.) INDIA. Junior synonym of scalpratum: Dalla Torre, 1893: 29.

Worker
Laciny et al. (2015) - Lectotype Diacamma compressum: TL 18.07; HW 2.82; HL 3.85; EL 0.76; SL 4.76; PH 2.48; PL 1.79; PW 1.28; SpD 0.50; SpL 0.45; WL 6.13; MTL 3.95. Indices: CI 73; SI 169; PI 72; SpDI 40; SpLI 36; EI 27. Paralectotype of D. compressum: TL 17.67; HW 2.74; HL 3.78; EL 0.77; SL 4.70; PH 2.48; PL 1.70; PW 1.29; SpD 0.51; SpL 0.45; WL 5.71; MTL 3.78. Indices: CI 72; SI 171; PI 68; SpDI 40; SpLI 35; EI 28. non-type (n = 6): TL 16.37–18.46; HW 2.64–2.84; HL 3.65–3.91; EL 0.76–0.82; SL 4.50–4.89; PH 2.32–2.51; PL 1.67–1.85; PW 1.11–1.35; SpD 0.42–0.60; SpL 0.47–0.59; WL 5.51–6.13; MTL 3.52–3.85. Indices: CI 72–76; SI 164–174; PI 69–77; SpDI 35–47; SpLI 36–51; EI 26–30.

Structures: Head elongated; sides long and parallel in front of eyes, moderately convex behind eyes. Eyes small, not protruding. Striation posterior of eyes divergent, meeting the narrow, medially slightly concave occipital margin; ridges matt, densely microreticulated, slightly narrower than interspaces. Occipital margin laterally slightly widened and terminating in very short, blunt projections. Clypeus finely, very densely punctured, except for anterior margin with larger and sparser puncturation; anteromedially with widely rounded apex. Mandible with obliterate fine striation, setae on masticatory margin very long. Mesosoma with coarse striation, especially on pronotum. Striae on pronotum transversely elliptical. Striation on mesosoma sides slightly oblique, upcurved on propodeum, reduced on mesopleura. Posterior face of propodeum separated from sides by strong carinae.

Petiole strongly compressed, with narrow dorsal crest posteriorly forked up to the closely spaced, long teeth; at sides the ridges as wide or slightly narrower than interspaces; subpetiolar process prominent, with strongly concave ventral outline, posterior corner longer than anterior one, anteriorly marginate. Gaster tergite 1 lacking striation, but with fine puncturation, shiny as the following tergites and sternites.

Pilosity: Standing setae on trunk short, those on head, pronotum, and abdominal apex slightly longer. Short appressed pilosity of trunk well developed, but on matt surfaces less obvious than on the shiny gaster where it is longer and velvety. Standing setae on scape very short, on legs short, slightly longer on flexor sides of femora.

Colour: Trunk black, without metallic shimmer. Clypeus and frontal lobes often reddish; subpetiolar process and broad stripes at posterior margins of gaster tergites and sternites pale reddish brown. Mandibles, femora and tibiae more or less extended red, other leg parts strongly infuscated. Colour of antennae variable.

Type Material
Laciny et al. (2015) - Mayr (1879) described D. compressum from two workers from “Sind in Ostindien im k. k. zoologischen Hofcabinete [old name for ] in Wien”; the type locality is attributed to Sindh in southern Pakistan. Both specimens are still in the collection of NHMW. One of them bears Mayr’s original identification labels whereas the second specimen bears a label “Collect. G. Mayr” and a label “scalpratum det. G. Mayr” which were both attached by the former curator, Anton Handlirsch. It is speculative why the specimens were differently labelled. Possibly the second specimen was kept by G. Mayr who changed the identification after Dall a Torre (1893) synonymized D. compressum with D. scalpratum in his catalogue.



Ponera scalprata

Holotype worker in. Labelled “N. Ind. 54/16.” Acc. Reg.: “1854 no. 16. N. India (Sikkim, Him.) From Dr Hooker’s collection. Collected by Dr Hooker during his travels in n. India. A few of the insects were from Khasya Hills.”

A second scalprata specimen is in, but here the usual data label is missing and has been replaced by a white card square with, “Phil. N. India.” The half-written then deleted Phil (= Philippines) raises the possibility that this specimen may not be from the original type-series.

Determination Clarifications
Laciny et al. (2015) - Records of D. scalpratum from Thailand (Antweb 2015: CASENT0173639, CASENT0173640; Peeters et al. 2015) refer to an undescribed species which will be a subject of further investigations.