Diacamma baguiense

Notably, in contrast to other species many specimens of D. baguiense (ca. 36 % of material examined) possess intact gemmae. Cournault & Peeters (2012) observed a similar phenomenon in a hitherto undescribed Indian species of Diacamma closely related to Diacamma ceylonense. As a possible explanation a change in gemmal pheromones was postulated which may have led to a switch from mutilation to aggression-mediated monogyny in the respective colonies. (Laciny et al. 2015)

Identification
Laciny et al. (2015) - Relatively small species (TL 9.8–11.6 mm). Trunk black, without or with weak metallic shimmer. Long setae abundant, on petiole and gaster slightly longer than on mesosoma; fine pilosity abundant. Trunk striate from genae to gaster tergite 1, but striae weakly developed in front of eyes. Head elongated; sides posteriorly of eyes strongly convex. Posterior of head longitudinally striate until narrowly truncated hind margin; narrow margin ventrally terminating in short, acute teeth. Eyes moderately large, hardly surpassing lateral outline of head. Clypeus entirely punctured, but punctures more sparse at apex; apex projecting, acute or very narrowly rounded. Mandible with fine striation, in some specimens obliterate. Pronotum with coarse striation, striae transversely concentrical. Coarse striation on propodeum hardly oblique. Petiole stout, its teeth relatively short; subpetiolar process concave between acute anterior and posterior corners. Gaster tergite 1 with semi-circular striation; striae finer than those on pronotum and propodeum, semi-elliptically arranged.

Diacamma baguiense can be distinguished from Philippine congeners (described and undescribed) by the combination of moderate body size (TL 9.8–11.5), moderate eye size (EI 30–33), reduction of the longitudinal carinae of the propodeum, and distinct, but delicate striation of gaster tergite 1. We observed a strong intraspecific variability in the petiolar spine distance (SpDI 36–55) and length (SpLI 29–40). Trunk colour is black, but a weak bronze or violet-coloured shimmer is frequently present.

Distribution
This species was described from Baguio City (Benguet, northern Luzon, Philippines) and had not been recorded since. It was commonly collected by Stefan Schödl and the senior author in the mountains of Benguet and Mountain Province in the Cordillera Central, northern Luzon. In addition there is an isolated record from Mount Arayat, a volcano in Pampanga. These two workers possess slightly shorter petiolar spines (SpL 0.28 vs. 0.31–0.38) but otherwise agree well with the other populations. No records are known from other parts of Luzon. (Laciny et al. 2015)

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

Nomenclature

 *  baguiense. Diacamma baguiensis Wheeler, W.M. & Chapman, 1925: 66, pl. 2, figs. 11, 12 (w.) PHILIPPINES.

Worker
Laciny et al. (2015) - Syntype: TL 9.85; HW 1.79; HL 2.40; EL 0.60; SL 2.58; PH n.a.; PL 0.83; PW 0.91; SpD 0.47; SpL 0.29; WL 3.46; MTL 2.05. Indices: CI 75; SI 144; PI n.a.; SpDI 53; SpLI 33; EI 33. Measurements of non-type material (n = 14): TL 9.85–11.54; HW 1.73–1.89; HL 2.32–2.54; EL 0.54–0.60; SL 2.41–2.70; PH 1.37–1.61; PL 0.78–0.93; PW 0.89–1.07; SpD 0.33–0.55; SpL 0.28–0.38; WL 3.33–3.72; MTL 1.86–2.09. Indices: CI 72–77; SI 135–145; PI 56–63; SpDI 36–55; SpLI 29–40; EI 30–33.

Structures: Head elongate; sides strongly convex behind moderately large eyes. Rugae present from genae to gaster tergite 1, but differently developed. Posterior of eyes, coarse longitudinal rugae reaching narrow occipital margin. Striation on genae weakly developed. On ventral side of head occipital margin ending in a small blunt tooth. Clypeus entirely punctured, but shiny, especially anteriorly where the fine punctures are more dispersed; apex of anterior margin sharp or (rarely) narrowly rounded. Mandibles usually with fine striation, rarely more or less reduced. Pronotum with coarse transverse-elliptical rugae. Rugae on mesosoma sides coarse, moderately shiny and slightly oblique dorsally, evanescent below dense pale pilosity on pleural parts. In lateral aspect dorsal outline of propodeum evenly downcurved; posterior face of propodeum not separated from sides by carinae, or such carinae only ventrally. Petiole stout, with coarse striae and rather short spines; subpetiolar process moderately concave, anterior and posterior tooth acute. Gaster tergite 1 with distinct striation arranged in transverse-concentric, semi-elliptical rugae which are finer than those on mesosoma; along posterior margin densely punctured. Gaster tergite 2 with very fine microsculpture, shiny.

Pilosity: Trunk with numerous, rather short standing setae; those on petiole and gaster slightly longer than those on mesosoma. Short appressed pilosity abundant, scarcer on pronotum and sides of propodeum. Setae on scape clearly, those on legs slightly shorter than those on mesosoma.

Colour: Trunk black, but a weak bronze or violet-coloured metallic shimmer often recognizable; very rarely the shimmer is dark bluish. Margins of gaster tergites and apex often brownish to reddish. In few specimens clypeus reddish or brown. Mandibles, antennae, and legs variable, from dark reddish brown to black.

Type Material
Laciny et al. (2015) - 1 worker (syntype, ), “Diacamma baguiense Wh. + Ch. det. W.L. Brown”, “Bagui’o, P.I. X/24 J.W. Chapman”, “MUSEO GENOVA”