Diacamma caeruleum

Little is known about the biology of .

Identification
Laciny et al. (2015) - Large species (TL 12.3–14.0 mm). Trunk with strong blue metallic shimmer. Mandibles and legs blackish. Long setae abundant; fine pilosity reduced. Trunk strongly striate from genae to gaster tergite 1. Head short, sides posteriorly of eye strongly convex. Posterior of head longitudinally striate until narrowly truncated hind margin; occipital margin ventrally terminating in short, blunt teeth. Eyes rather small. Clypeus medially smooth and shiny, apex sharp, blunt. Mandible with obliterate striation. Pronotum with transverse-elliptical rugae. Striation on propodeum horizontal. Petiole very stout, its teeth relatively short and narrow; subpetiolar process shallowly concave between acute anterior and posterior corners. Gaster tergite 1 with coarse semi-circular striation.

Diacamma caeruleum is a large, metallic blue species of the Diacamma rugosum group. It is similar to Diacamma viridipurpureum and Diacamma generali. From D. viridipurpureum viridipurpureum and D. generali, but not from Diacamma viridipurpureum quezonicum, it can immediately be distinguished by strong blue iridescence. The clypeus of D. caeruleum has a strongly shiny, unpunctured midline and a blunt, but acute-angled apex, whereas the clypeus of D. generali is densely punctured and the clypeus of D. viridipurpureum is apically rounded. Moreover, in D. caeruleum the striation of the mandible is reduced.

Morphometric characters distinguishing D. caeruleum from similar species are its relatively broad petiole and smaller eyes compared to both subspecies of Diacamma viridipurpureum (EI 24–26 vs. 25–28) as well as longer petiolar spines compared to D. generali (SpLI 24–31vs. 15–27).

Distribution
Only known from the type locality in a hilly area in eastern Mindoro.

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

Nomenclature

 *  caeruleum. Diacamma caeruleum Laciny, Pal & Zettel, 2015: 128, figs. 58-63 (w.) PHILIPPINES (Mindoro I.).

Worker
holotype: TL 13.50; HW 2.38; HL 3.07; EL 0.60; SL 3.39; PH 2.02; PL 1.28; PW 1.47; SpD 0.67; SpL 0.42; WL 4.57; MTL 2.64. Indices: CI 78; SI 142; PI 63; SpDI 46; SpLI 29; EI 25. Measurements of paratypes (n = 10): TL 12.33–13.96; HW 2.20–2.46; HL 2.87–3.20; EL 0.56–0.63; SL 3.07–3.52; PH 1.83–2.07; PL 1.17–1.35; PW 1.33–1.54; SpD 0.58–0.71; SpL 0.36–0.46; WL 4.30–4.96; MTL 2.45–2.77. Indices: CI 74–78; SI 139–148; PI 60–70; SpDI 40–47; SpLI 24–31; EI 24–26.

Structures: Head moderately elongate; sides strongly convex behind small eyes. Very coarse rugae present from genae to gaster tergite 1. Posterior of eyes, longitudinal rugae reaching narrow occipital margin. On ventral side of head occipital margin ending in a small, blunt tooth. Clypeus shiny, anteromedially without punctures; anterior margin forming a sharp obtuse angle at middle. Mandibles with more or less reduced striation. Pronotum with transverse-elliptical rugae. Rugae on mesosoma sides almost horizontal. Posterior face of propodeum separated from sides by distinct carinae. Petiole stout, with rather short, very slender spines; subpetiolar process moderately concave, posterior tooth protruding, acute. Gaster tergite 1 with thick, concentric, semi-circular rugae; along posterior margin finely punctured. Gaster tergite 2 with very fine microsculpture, shiny.

Pilosity: Trunk with numerous and long standing setae. Short appressed pilosity reduced, but more distinct on head in front of eyes, hind margin of pronotum, on mesonotum, dorsal face of propodeum, petiole, hind margin of gaster tergite 1 and on following tergites. Setae on scape and legs much shorter than those on trunk.

Colour: Trunk with strong blue shimmer, tending towards violet on gaster; apex of gaster brown. Mandibles, antennae, and legs black; tarsi dark brown.

Type Material
Holotype (worker,, CASENT0915965), Philippines, Mindoro Oriental, 28 km S Calapan, environment of Balete, 100–700 m a.s.l., 27–29.XI.1992, leg. H. Zettel (#18). Paratypes: 17 workers, same locality data.

Etymology
Named after the conspicuous blue shimmer of the body.