Oxyepoecus

These rarely collected small ants are found in South America from Columbia to Chile. The biology of the individual species is poorly know. Some species are suspected to be inquilines of Pheidole or Solenopsis. A number of Oxyepoecus are considered threatened and are listed as IUCN vulnerable species.

Identification
A unique genus within the Solenopsis genus group to combine 11-segmented antennae with a 3-segmented apical club. Most resembling Solenopsis, Oxyepoecus and Solenopsis differ mainly by the dentate propodeum, the integument always being more extensively sculptured (especially on the mesosoma pleura) and the relatively small size of gynes when compared to the conspecific workers.

Bolton (1987) - Both Ettershank (1966) and Kempf (1974) agree that Oxyepoecus is closely related to the much larger genus Solenopsis. Consistent characters separating the two genera are as follows.

Solenopsis
 * Antennal club of 2 segments in the worker and female.
 * Antennae with 10 segments in worker.
 * Propodeum unarmed in worker and female.
 * First funicular segment globular in male.
 * Mandibles with 1-2 teeth in male.

Oxyepoecus
 * Antennal club of 3 segments in the worker and female.
 * Antennae with 11 segments in worker.
 * Propodeum dentate in worker and female.
 * First funicular segment cylindrical in male.
 * Mandibles with 4 teeth in male.

Species Groups

 * Oxyepoecus species groups

Distribution
In Brazil, these ants have been found in all southeastern States (Rio Grande do Sul, Santa Catarina, Paraná, São Paulo and Rio de Janeiro, their northernmost known limit being in Goiás State (Anápolis) and northeastern Minas Gerais State (Pedra Azul), at Lat. 16°S. In Bolivia, in spite of only very few records, the genus occurs as far north as Guayaramerin (olim: Puerto Sucre, opposite to the Brazilian Guajará-Mirim, Rondônia Territory) in the northern tip of the Beni province, at Lat. 11°S. In the Argentine, the collections range from the Buenos Aires Province over Córdoba to Tucumán, giving the southern limit at Lat. 36°S, and the western limit at Long. 68°W of their presently known territory. The most widespread species is actually O. inquilinus, which occurs in northwestern Argentina, northeastern Bolivia, central and southeastern Brazil. (Kempf 1974)

Additional species and distributional data from Albuquerque et al. (2004) extend the range to include Ecuador, Peru and the Brazilian states of Piauí and Amazonas.

Biology
The following account of the biology of species within the genus is based on, and modified from, Kempf (1974) and Albuquerque and Brandão (2009).

Our knowledge of Oxyepoecus ants still rests exclusively on chance discoveries. Since about 95% of the known specimens were taken as strays in berlesates of forest floor cover, very little may be said about the biology of Oxyepoecus species except for being denizens or at least foragers in this particular habitat. The minute size of Oxyepoecus, their color and cryptic habits hamper direct observation of their habits in natural conditions (especially inside shaded forest where light rarely reaches the ground).

Oxyepoecus has been considered very rare in collections, but our studies show that they are rather common in the leaf litter of most localities where recent surveys have been conducted in the Mata Atlântica (see Comments in Albuquerque & Brandão, 2004). It is interesting to note that one of these localities we recently surveyed, Cunha, São Paulo state has four Oxyepoecus species (Oxyepoecus myops, Oxyepoecus rastratus, Oxyepoecus longicephalus and Oxyepoecus rosai), three of which were found in one square meter of leaf-litter (sample 48; all but O. rosai). In Salesópolis, SP, we recorded five of the 17 known Oxyepoecus species (O. myops, Oxyepoecus punctifrons, O. rastratus, O. rosai and Oxyepoecus vezenyii). Both Cunha and Salesópolis are localities circa 1000 m above sea level, covered by pristine evergreen dense forest.

Although Oxyepoecus samples come mostly from forested localities, workers have been less frequently collected in places with more open vegetation, as open “cerrados” (savannas). Comparing the examined material of most species, one can see that the specimens mostly come from the same localities. This is because these localities we surveyed recently, extracting ants from the leaf-litter, or localities where careful collectors lived most of their lifes (Seara, SC, for instance, where F. Plaumann worked many years).

Kusnezov (1952) put forward the hypothesis that Oxyepoecus ants are inquilines of Pheidole and Solenopsis nests. Evidence exists for their being symbiotic relationships between several Oxyepoecus species and other Myrmicinae ants (see below). Independent colonies seem to be vouched for by Oxyepoecus punctifrons and Oxyepoecus rastratus. The types of the former, collected at Rio Negro, Paraná State, Brazil, came from a nest that had over 60 workers living by themselves, but no further information is available. A few workers of the same species, at Campos do Jordão, São Paulo State, Brazil, were also found on a dead twig, between the bark and an overgrown cover consisting of lichens and mosses. The types of the var. luederwaldti (= rastratus) are from a very small colony nesting under the bark in a simple cavity within the alburnum of a tree (Luederwaldt, 1926: 275). Lenko's rastratus specimens from Caraça, Minas Gerais State, had their nest within a decaying log on the ground in a forest. A similar nesting situation was found from a more recent collection from Paraguay (col A. Wild).

The fact that Oxyepoecus workers are relatively abundant in material extracted from leaf litter samples, while dealate gynes are seldom found in the litter and larvae have never been found in litter samples, suggests that they nest in the soil, where the gynes and larvae live, but workers leave the nest periodically to search for food. Oxyepoecus has been attracted to honey or sardine baits set over the ground in different habitats, which suggests they are generalist foragers. In just one case, a gyne and two workers of O. punctifrons (Vezenyii group) were found by Rogerio R. da Silva under the bark of a the canopy branch in a recently fallen Leguminoseae (Albuquerque & Brandão, 2004).

Kempf provided the following summary regarding species associations with other ants:


 * bruchi. This species was collected once or twice in nests of Pheidole obtusopilosa Mayr at Alta Gracia and La Granja, Córdoba, Argentina. Directly observed were several dealated females. Later, among alcohol material of the same Pheidole species (same colony?) the worker was also discovered (Santschi, 1926: 7, 1929: 295). The infiltration of Ph. obtusopilosa colonies with O. bruchi does not seem to be common. Kusnezov examined 21 colonies of Ph. obtusopilosa without finding any O. bruchi or other species of Oxyepoecus (Krusnezov, 1952: 718). Yet while examining three nests of Pheidole silvestrii (= Pheidole rosae) at Tafi Viejo, Tucumán, Argentina, he found in one of them several workers of an Oxyepoecus which he described as a new species under the name of O. minutus but is a straight synonym of bruchi. The infested Pheidole colony with their guests was placed in an artificial nest and kept under observation. No hostility was observed between Ph. silvestrii and O. minutus (= bruchi), a fact which Kusnezov tries to explain by the great similarity between the workers of both species.


 * daguerrei. Here the evidence is very slim and rests solely upon the fact that the daguerrei workers were received by Santschi already mounted on the same pin with Solenopsis metanotalis var. picturata Santschi and Solenopsis tetracantha Emery, collected at Rosas, B. A., Argentina. The association between daguerrei and the two Solenopsis species, though possible, is only a surmise. O. daguerrei is known solely from the three type specimens.


 * inquilinus. The types and subsequent Argentine material (workers only) were invariably discovered in nests of Pheidole radoszkowskii. Yet inquilinus infestation is not common, since it was found only in 2 of 41 radoszkowskii colonies, prior to the description of the former. Placed together in the glass container of an aspirator, Pheidole radoszkowskii soldiers showed themselves very hostile toward the inquilinus workers by endeavoring to cut them up into pieces with their heavy mandibles (Kusnezov, 1952: 718). My own field experience, based on the hitherto known Brazilian material, suggests a similar relationship, inasmuch as several stray inquilinus workers (described under the name of turgidus, a straight synonym of the former species) were collected with Pheidole schwarzmaieri and Pheidole claviscapa workers swarming out of their disturbed nests, at Anápolis, Goiás State. A definite association, however, was not observed in nature (Kempf, 1969: 281).

Castes
The full complement of castes is known for just a few species in the genus.

Nomenclature

 *  OXYEPOECUS [Myrmicinae: Solenopsidini]
 * Oxyepoecus Santschi, 1926d: 6. Type-species: Oxyepoecus bruchi, by monotypy.
 * Oxyepoecus senior synonym of Forelifidis (and the junior homonym Martia Forel): Brown, 1955b: 68.
 * FORELIFIDIS [junior synonym of Oxyepoecus]
 * Forelifidis Smith, M.R. 1954a: 17. Replacement name for Martia Forel, 1907a: 20. [Junior homonym of Martia Ragonot, 1887: 18 (Lepidoptera).]
 * Forelifidis junior synonym of Oxyepoecus: Brown, 1955b: 68.

Albuquerque and Brandão (2009):

Worker
Monomorphic. t.l.= 1.9-3.4; h.l.= 0.46-0.79; h.w.= 0.37-0.67; s.l.= 0.23-0.57; m.l.e.= 0.05-0.16; m.w.pr.= 0.20-0.47; a.l.= 0.52-0.98; h.f.l.= 0.28-0.68; m.w.p.= 0.17-0.28; m.w.pp.= 0.20-0.36; c.i. 70-96. Mandibles triangular, short to elongate; masticatory margin with 4 teeth (dental formula 1+3; one apical, closely followed by a smaller subapical, a subbasal, and a basal tooth; the mandibular teeth separated from each other by clefts or diastemata). Palpal formula 2, 2. Clypeus with the median apron elevated, projecting forward, bicarinate, anteriorly bidentate, each tooth laterally with another small denticle; clypeal setae as in Solenopsis: median seta, first paracarinal setae and lateral setae always well developed. Anterior tentorial pits closer to frontal carinae than to genae, but not quite as close as in Solenopsis. Triangular area inconspicuous. At least the internal area of the frontal carinae with rough longitudinal sculpture. Antennal sockets not marginated by sculpture. The whole head disk may be variously covered by rough sculptures. Antennae 11-segmented with a slightly distinct 3-segmented apical club, the apical segment always longer than the two immediately preceding ones combined. Eyes small to medium sized, 6-50 ommatidia. Pronotum shoulders smooth and continuously rounded or marked by an angle. Promesonotal suture absent on dorsum of mesosoma, promesonotum continuous. Metanotal groove gently to scarcely impressed. Anepisternum and katepisternum not separated by a carina, can be distinguished one from the other by different superficial sculpture. Propodeum with the dorsal face usually transversely costulate, the posterior corners sharply angulate to dentate, the latter connected with the rounded and prominent propodeal lobes by the propodeal carinae that margin each side of the declivous face. Propodeal spiracle round, vestibulate and obliquely directed caudad. Propodeal lobes not joined above by a carina. Petiole pedunculate, node high, often antero-posteriorly compressed and laterally expanded in a scale-like fashion; subpetiolar process either simply dentiform or prolonged anteriorly into a sharp, longitudinal, sometimes somewhat elaborate, ridge; posteriorly the process may bulge ventrally. Postpetiole nodiform, not as high as the petiole, always equal to or broader than the petiolar node, laterally produced into bulky to subconical lobes; both anterior and posterior subpostpetiolar processes weak to well developed in the form of pronounced transverses ridges; the margin of first tergite of gaster not excised.

Queen
Total length 2.4-3.8 mm; not conspicuously longer than the respective worker, sharing with the latter the same general features: shape and dentition of mandibles, the carinate, dentate and projecting median apron of clypeus, the 11 – segmented antennae with a 3 – segmented apical club, the shape of the petiole and postpetiole; the latter also with a constriction behind, in front of the insertion of the gaster, and the same sculpturing pattern. Wing venation of the Solenopsis-type: fore wing with an elongate, open radial cell (Rs not reaching the anterior margin), a large cubital cell and usually a well formed discoidal cell (crossvein m-cu present).

Male
Total length about 3.0 mm; mandibles well developed, elongate triangular, meeting along the masticatory borders when mandibles are closed; masticatory margin with four distinct teeth (dental formula 1+3). Palpal formula 2, 2; labial palps geniculate. Clypeus rounded and swollen, only slightly touching the virtual transverse line that links the anterior margins of the antennal sockets; clypeal setae roughly in the same pattern as in workers and gynes. Antennae 13-segmented; scape as long as funicular segment II; first funicular segment (pedicellus) not globular, shorter than segment II; segments II-XI nearly twice as long as broad, of approximately similar length. Mesoscutum without notauli. Parapsidal furrows very faint. Middle and hind tibiae without apical spurs. Petiole either claviform or pedunculate with a differentiated and laterally expanded node. Postpetiole distinctly constricted in front of gaster, not broadly attached to the latter. Wings as in gynes.