Oxyepoecus rastratus

One of the better collected species within the genus.

Identification
The exclusive character of the workers of O. rastratus in relation to other species in the group is the costulate sculpture between the frontal carinae, which reaches posteriorly the vertexal margin and laterally the compound eyes (Albuquerque and Brandão 2009).

Distribution
South (Paraná and Santa Catarina states) and Southeastern Brazil (Espírito Santo, Minas Gerais, Rio de Janeiro and São Paulo states), and Paraguay.

Distribution based on Regional Taxon Lists
Neotropical Region: Brazil, Paraguay.

Biology
The material taken by Plaumann and by myself is from berlesates of leaf-mold; a colony collected by Lenko at Serra Carac;a, Minas Gerais, was nesting in a decaying log on the forest floor, in the vicinity of Hypoponera iheringi Forel and Brachymyrmex sp. (Kempf 1974).

A Paraguay collection (A. Wild) consisted of: "seven workers and one dealate queen....nest in red rotting log; wood was too hard for a full excavation; one chamber uncovered with gyne and brood. Also "samples in the dry Chaco and in the Parana forest suggests that this species may be present in a variety of biomes" (Delsinne et al. 2012).

Nomenclature

 *  rastratus. Monomorium rastratum Mayr, 1887: 615 (w.) BRAZIL. Kempf, 1974b: 498 (q.m.); Wheeler, G.C. & Wheeler, J. 1980: 534 (l.). Combination in Monomorium (Martia): Forel, 1912g: 3; in Martia: Kusnezov, 1952h: 722; in Oxyepoecus: Ettershank, 1966: 146. Senior synonym of luederwaldti: Kempf, 1974b: 498. See also: Albuquerque & Brandão, 2009: 299.
 * luederwaldti. Monomorium (Martia) rastratum var. luederwaldti Forel, 1913l: 219 (w.) BRAZIL. Combination in Martia: Kusnezov, 1952h: 722; in Oxyepoecus: Ettershank, 1966: 146. Junior synonym of rastratus: Kempf, 1974b: 498.

Kempf (1974) - There are only two known species in the genus that share with rastratus the entirely sculptured cephalic dorsum (sculpture attaining laterally the eye and posteriorly the occiput), viz. Oxyepoecus mandibularis and Oxyepoecus reticulatus.

Workers of rastratus differ from those of mandibularis in smaller size, absence of a narrow and deep cleft between the basal and subbasal tooth of mandibles, shorter antennal scapes that decidedly fall short of reaching the occipital corner when in repose, smaller and less bulging eyes, regular and densely costulate sculpture of head and promesonotum, well developed propodeal armature, broadly expanded and antero-posteriorly compressed nodes of petiole and postpetiole.

The characters that separate rastratus workers from the same caste of reticulatus are the following: sculpture of head and promesonotum consisting of regular and dense costulae, with the punctulae either absent or feebly developed; eyes larger, with 7-9 facets in a row across the greatest diameter and over 20 ommatidia in all; antennal scape a trifle longer, its apex removed from the occipital corner by just its own maximum thickness; laterotergite of pronotum smooth and shining; basal face of propodeum sharply and densely transversely costulate; propodeal teeth well developed and protruding; petiolar node scalelike, antero-posteriorly compressed and expanded laterad. In the female caste, more or less the same differences do apply, the queen of rastratus being distinct from that of reticulatus by the head sculpture, larger eyes, smooth and shining laterotergite of pronotum, densely cross-costulate basal face of propodeum, the laterally expanded and antero-posteriorly compressed petiolar node, the absence of short, curved hairs on gaster, and the presence of well-developed wings.

Worker
Kempf (1974) - Total length 2.2-2.8 mm; head length 0.52-0.65 mm; head width 0.43-0.55 mm; scape length 0.30-0.40 mm; maximum diameter of eyes 0.09-0.13 mm; Weber's length of thorax 0.60-0.80 mm; maximum width of pronotum 0.32-0.40 mm; hind femur length 0.36-0.48 mm; petiole width 0.18-0.25 mm; postpetiole width 0.21-0.32 mm; cephalic index 76-84. Color reddish yellow to chestnut brown; mandibles, antennae, legs and tip of gaster always lighter; in darker specimens the gaster is usually infuscated. Integument smooth and shining with the ensuing exceptions: dorsum of head capsule with the exclusion of the smooth median apron of clypeus very finely and densely striato-costulate, the sculpture very regular with a silky sheen, due to minute punctulae between the costulae which attain laterally the eyes and posteriorly the occiput; dorsum of pronotum and mesonotum regularly, densely, longitudinally costulate, the interstices practically without punctulae; hence the integument appears shining, especially anteriorly on pronotum where often the costulae become very superficial or fade out completely, being visible only in certain lights and angles; basal face of propodeum densely, finely, transversely costulate, with about 20 costulae; mesopleura, metapleura and sides of propodeum mostly horizontally, the latter obliquely, costulate; a few (1-2) transverse, very faint costulae on top of declivous face of propodeum; peduncle of petiole finely and superficially punctulate above and on sides; posterior surface of postpetiole practically lacking transverse costulae or rugae. Hairs abundant, standing on dorsum of head, thorax, petiolar and postpetiolar nodes, and on gaster; on head, also more numerous and shorter hairs inclined mesad on disc and forward on sides; gaster practically without short, inclined hairs; antennae and legs with abundant, short, oblique to subdecumbent hairs.

Head. Mandibles short, subtriangular; between basal and subbasal tooth a deep yet broad incision. Posteriorly converging clypeal carinae and anterior teeth well developed, the lateral denticles subobtuse and lobelike. Frontal carinae short, subparallel, terminating at level of anterior orbit of eyes, the distance between their outer edges distinctly less than one third of head width. Eyes intermediate, feebly convex, with 7-9 facets in a row across the greatest diameter which is subequal to the distance between the anterior orbit and the mandibular insertion, total number of ommatidia well over 20. Antennal scape failing to reach occipital corner when laid back over the head by a distance that equals its maximum thickness. Funicular segment I equal to sum of II-V; segments II-VII broader than long, VIII and IX as long as broad.

Thorax. Shoulders faintly marked. Pronotum immarginate on sides of dorsal surface. Metanotal groove very faintly impressed, metanotal suture distinct. Basal face of propodeum immarginate laterally, its posterior corners with strong teeth, the tips of which point obliquely upward; the distance between the tips of the propodeal teeth less than maximum width of petiolar node. Lateral boriers of declivous face sharply marginate and faintly carinate.

Petiole and postpetiole. The former strongly pedunculate, with the subpetiolar process in the form of a small tooth; node antero-posteriorly compressed and scalelike, laterally expanded. Postpetiole much broader than long, somewhat compressed antero-posteriorly, the sides drawn out into bulky lobes. Gaster faintly excised at postpetiolar insertion.

Queen
Kempf (1974) - (undescribed). Total length 2.7-3.2 mm; head length 0.60-0.67 mm; head width 0.51-0.56 mm; scape length 0.37-0.41 mm; maximum diameter of eyes 0.13-0.18 mm; Weber's length of thorax 0.80-0.91 mm; maximum width of pronotum 0.43-0.52 mm; hind femur length 0.45-0.53 mm; fore wing length 2.6 mm; hind wing length 1.7 mm; petiole width 0.24 mm; postpetiole width 0.29-0.32 mm. Similar to the worker with the usual differences of the caste. Eyes larger, the maximum diameter with 11-13 facets in a row exceeds the distance between the anterior orbit and the mandibular insertion; the total number of ommatidia from 60 to 100. Ocelli small, their diameter equal to thinnest cross-section of the antennal scape. Pronotum with marked yet not tuberculate shoulders, entirely declivous in the middle, dorso-laterally obliquely, densely striato-costate. Mesonotal scutum and scutellum finely, densely and regularly longitudinally costulate. Basal face of propodeum transversely costulate, with about 16 costae; sides immarginate; propodeal teeth stout and prominent. Laterotergite of pronotum smooth and shining. Posterior third of mesopleura, the metapleura and sides of propodeum horizontally to obliquely costulate. Wings only slightly infuscated, venation as usual in the genus. The only winged specimen seen has a small discoidal cell, and an extra-vein arising from the junction of r-m with Rs and extending apicad between Rs and M, as shown in the wing of the male.

Male
Kempf (1974) - (undescribed). Total length 2.9 mm; head length 0.51 mm; head width (eyes included) 0.60 mm; scape length 0.12 mm; maximum diameter of eyes 0.24 mm; Weber's length of thorax 0.93 mm; maximum width of pronotum 0.60 mm; hind femur length 0.58 mm; fore wing length 2.3 mm; hind wing length 1.5 mm; petiole width 0.19 mm; postpetiole width 0.24 mm. Color fuscous brown; mandibles, antennae, apical half of tibiae, tarsomeres, tip of gaster much lighter, testaceous.

Head. Mandibles with 4 well developed teeth. Clypeus transversely strongly convex, little protruding anteriorly. Frontal carinae absent. Integument finely yet sharply reticulate-punctate, opaque. Sides of pronotum and mesopleura smooth and shining, the latter vestigially costulate on posterior border. Metapleura and sides of propodeum horizontally costulate. Mesonotal scutum nearly smooth and somewhat shining, indistinctly sculptured. Scutellum superficially, finely, longitudinally costulate-striate. Basal face of propodeum superficially reticulate-rugose, the posterior corners bluntly tuberculate, not dentate. Declivous face superficially reticulate-rugose, quite shining. Petiole, postpetiole and gaster smooth and shining. Legs, especially tibiae and tarsomeres, as well as antennae sharply punctured and opaque.

Additional References

 * Albuquerque, N. L. d. and C. R. F. Brandão. 2009. A revision of the Neotropical Solenopsidini ant genus Oxyepoecus Santschi, 1926 (Hymenoptera: Formicidae: Myrmicinae): 2. Final. Key for species and revision of the Rastratus species-group. Papéis Avulsos de Zoologia (São Paulo). 49:289-309.


 * Delsinne, T., W. Mackay, A. Wild, Y. Roisin, and M. Leponce. 2012. Distribution and Diversity of the Cryptic Ant Genus Oxyepoecus (Hymenoptera: Formicidae: Myrmicinae) in Paraguay with Descriptions of Two New Species. Psyche. 2012. DOI:10.1155/2012/594302