Monomorium denticulum

Distributed in a surprising variety of habitats but colonies appear to be very rare, being represented by a handful of workers. These have been collected in pitfall traps or from sifted litter in Uapaca woodland, tropical dry forest, spiny forest and rainforest. (Heterick 2006)

Identification
Heterick (2006) - A member of the M. schultzei complex in the M. monomorium species group. Monomorium denticulus is the only member of the otherwise exclusively Afrotropical Monomorium schultzei species complex represented in Madagascar. This ant is smaller than M. schultzei and is separable from other members of the complex by virtue of its shallow metanotal groove with short cross-ribs, its pinhole-like propodeal spiracle and its distinct clypeal denticles. The elongate mesosoma bears a superficial resemblance to that of Monomorium exiguum. This ant can be yellow or brown.

Distribution based on Regional Taxon Lists
Malagasy Region: Madagascar.

Nomenclature

 *  denticulum. Monomorium denticulus Heterick, 2006: 114, figs. 17, 50 (w.) MADAGASCAR.

Worker
HEAD: Head rectangular; vertex planar; frons shining and smooth except for piliferous pits; pilosity of frons a mixture of well-spaced, distinctly longer erect and semi-erect setae interspersed with shorter decumbent setae or setulae. Eye large, eye width 1.5× greater than greatest width of antennal scape; (in full-face view) eyes set at about midpoint of head capsule to set below midpoint of head capsule; (viewed in profile) eyes set around midline of head capsule; eye elliptical, curvature of inner eye margin may be more pronounced than that of its outer margin. Antennal segments 12; antennal club three-segmented. Clypeal carinae always well-defined; anteromedian clypeal margin emarginate or straight, clypeal carinae terminating in small denticles; paraclypeal setae moderately long and fine, curved; posteromedian clypeal margin extending slightly beyond level of posterior margin of antennal fossae. Anterior tentorial pits situated nearer antennal fossae than mandibular insertions. Frontal lobes straight, parallel. Psammophore absent. Palp formula 2,2. Mandibular teeth three, plus minute, basal denticle or angle; mandibles with sub-parallel inner and outer margins, smooth (except for piliferous pits); masticatory margin of mandibles approximately vertical or weakly oblique; basal tooth a small to minute denticle or angle, much smaller than t3 (four teeth present).

MESOSOMA: Promesonotum shining and mainly smooth, vestigial striolae, if present, confined to lower anterior mesopleuron; (viewed in profile) promesonotum broadly convex anteriad, convexity reduced posteriad; promesonotal setae greater than twelve; standing promesonotal setae a mixture of well-spaced, distinctly longer, erect and semi-erect setae which are curved distally and often paired, interspersed with much shorter, incurved, decumbent setae; appressed promesonotal setulae very sparse or absent. Metanotal groove strongly impressed, with distinct transverse costulae. Propodeum shining and smooth, with a few weak striolae on metapleuron; propodeal dorsum convex; propodeum smoothly rounded or with indistinct angle; standing propodeal setae consisting of one prominent pair anteriad and a less prominent pair posteriad, smaller, decumbent setae few or absent; appressed propodeal setulae very sparse or absent; propodeal spiracle nearer metanotal groove than declivitous face of propodeum to equidistant from metanotal groove and declivitous face of propodeum. Vestibule of propodeal spiracle absent or not visible. Propodeal lobes present as rounded flanges to present as vestigial flanges or small strips of cuticle only.

PETIOLE AND POSTPETIOLE: Petiolar spiracle lateral and situated within anterior sector of petiolar node; node (viewed in profile) conical, vertex tapered, or, conical, vertex rounded; appearance of node shining and smooth throughout; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) between 4:3 and 3:4; anteroventral petiolar process absent or vestigial; ventral petiolar lobe present; height ratio of petiole to postpetiole between 3:2 and 4:3; height–length ratio of postpetiole between 4:3 and 3:4; postpetiole shining and smooth; postpetiolar sternite without anterior lip or carina, or this structure vestigial.

GASTER: Pilosity of first gastral tergite consisting of well-spaced, erect and semi-erect setae interspersed with a few appressed setulae.

GENERAL CHARACTERS: Color yellow to brown. Worker caste monomorphic.

Type Material
HOLOTYPE: worker, Prov. Mahajanga, P. N. Ankarafantsika, Ankoririka, 10.6 km 13º NE Tsaramandroso 16º16′S, 47º3′E 210 m, 9–14.iv.2001 E. Rabeson et al. BLF 3664/ sifted litter tropical dry forest/ CASENT 0470359 3664(11). PARATYPES: Prov. Mahajanga (all specimens with same collection data as holotype, one worker with collection code 3664, three workers with collection code 3662): 1 worker ; 13 workers.

Etymology
Latin dim. of ‘dens’ (masc. ‘tooth’).

References based on Global Ant Biodiversity Informatics

 * Heterick B. 2006. A Revision of the Malagasy Ants Belonging to Genus Monomorium Mayr, 1855 (Hymenoptera: Formicidae). Proceeding of the California Academy of Sciences (PCAS) 57: 69-202