Oxyepoecus bidentatus

Oxyepoecus bidentatus
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hymenoptera
Family:	Formicidae
Subfamily:	Myrmicinae
Tribe:	Solenopsidini
Genus:	Oxyepoecus
Species:	O. bidentatus
Binomial name
	Oxyepoecus bidentatus; Delsinne & Mackay, 2011

The fact that workers were extracted from leaf litter (Winkler method) or were collected in pitfall samples, while no gynes were found, suggests that this species nests in the soil, but workers forage in the leaf litter when abiotic conditions are favorable. Localities where the species was found have a mean annual rainfall and temperature ranging from 593 to 887mm and from 23 to 25◦C, respectively. (Delsinne et al. 2012)

Identification

Delsinne et al. (2012) - Its worker morphology places this species within the rastratus species-group. The reticulate-costulate dorsal surface of the head and the well-defined subpostpetiolar process, forming a pair of prominent blunt teeth, separate O. bidentatus from all the other species of Oxyepoecus.

Oxyepoecus bidentatus is the only species of the genus to have both the dorsal surface of the head entirely covered by sculpture and a bidentate subpostpetiolar process. The anterior subpostpetiolar process of Oxyepoecus bruchi of the vezenyii species-group is also prominent and bidentate, but the dorsal surface of the head is mainly smooth and shining except for two patches of fine, longitudinal rugulae which do not reach posteriorly to the vertex margin nor laterally to the compound eye. Criteria separating O. bidentatus from other species of the rastratus species group are the mesopleuron and lateropropodeum covered by longitudinal costae (and not reticulate as for Oxyepoecus myops, Oxyepoecus rosai, and Oxyepoecus reticulatus), and the presence of a reticulate-costulate sculpture on the dorsal surface of the head reaching posteriorly to the vertexal margin and laterally to the compound eye.

Key to Oxyepoecus of Paraguay

Keys including this Species

Distribution

Oxyepoecus bidentatus was found in three localities of the Paraguayan dry Chaco. Because the maximal distance between localities was 340 km, O. bidentatus is suspected to be widely distributed in xeromorphic Chacoan forests, even if rarely found.

Latitudinal Distribution Pattern

Latitudinal Range: -21.21° to -23.36666667°.


North Temperate	North Subtropical	Tropical	South Subtropical	South Temperate

Source: AntMaps

Distribution based on Regional Taxon Lists

Neotropical Region: Argentina, Paraguay (type locality).

Distribution based on AntMaps

Distribution based on AntWeb specimens

Check data from AntWeb

Countries Occupied

Number of countries occupied by this species based on AntWiki Regional Taxon Lists. In general, fewer countries occupied indicates a narrower range, while more countries indicates a more widespread species.

Estimated Abundance

Relative abundance based on number of AntMaps records per species (this species within the purple bar). Fewer records (to the left) indicates a less abundant/encountered species while more records (to the right) indicates more abundant/encountered species.

Biology

Explore Overview of Oxyepoecus biology

The following account is modified from Kempf (1974) and Albuquerque & 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 (details provided here). 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).

Castes

The gyne and male are unknown.

Nomenclature

The following information is derived from Barry Bolton's Online Catalogue of the Ants of the World.

bidentatus. Oxyepoecus bidentatus Delsinne & Mackay, in Delsinne, et al. 2011: page, figs. 2, 3 (w.) PARAGUAY.

Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.

Description

Worker

Measurements of holotype, paratypes (n = 2) between parentheses: TL 1.94 (1.86–1.90), HL 0.52 (0.51–0.55), HW 0.44 (0.42–0.46), EL 0.07 (0.06-0.07), SL 0.32 (0.32–0.35), PL 0.07 (0.07–0.11), PW 0.17 (0.19–0.23), PPL 0.09 (0.08–0.12), PPW 0.22 (0.25–0.28), WL 0.63 (0.60–0.64), CI 85 (83-84), and SI 62 (63-64).

Lateral clypeal teeth are well developed, directed anteriorly; eye small, about 16–18 ommatidia, five ommatidia in greatest diameter; scape in repose failing to reach posterior border of head by about two maximum widths; sides of head nearly straight, parallel; frontovertexal margin slightly convex; pronotal shoulder gently angulate, marked with striae; notopropodeal (=metanotal) groove indistinct; propodeal angles developed, with two medium-sized acute teeth; subpetiolar process well-developed, lobe-like, directed ventrally; subpostpetiolar process well-developed, forming pair of blunt teeth, directed ventrally; nodes of petiole and postpetiole high and dorsally rounded, compressed anteroposteriorly; in lateral view, petiolar node higher than postpetiolar node; as seen from above, postpetiole much broader than petiole.

vertex sculpture
detail of petiole and postpetiole
detail of the bidentate subpostpetiolar process

Long erect hairs abundant on clypeus, vertex, dorsum of mesosoma, petiole, postpetiole, all surfaces of gaster; mandibles, antennae, legs, and dorsal surface of head with abundant shorter semierect hairs.

Mandibles smooth and shiny, with few scattered punctures; head dorsum reticulate-costulate, lateral costulae attain compound eye and posteriorly vertexal margin; dorsopronotum and mesonotum longitudinally costate; dorsopropodeum transversely costate (about 10–12 costae on dorsal face), anterior half of the lateropronotum mostly smooth and glossy, sometimes with faint longitudinal costae; posterior half of the lateropronotum, mesopleuron and lateropropodeum covered by sparse longitudinal costae; nodes of petiole and postpetiole transversely costate; gaster smooth and glossy with sparse punctures.

Body Color. Concolorous Reddish Brown.

Type Material

Holotype worker. Paraguay: Presidente Hayes: Rio Verde, Lat: S 23.22, Long: W 59.20, 15-16.X.2003, Delsinne T., 24-hour pitfall sample (specimen number 29272, SIDbase, RBINS). Images of the holotype are available at http://projects.biodiversity.be/ants.

Paratype workers. Paraguay: Presidente Hayes: Rio Verde, Lat: S 23.22, Long: W 59.20, 15-16.X.2003, Delsinne T., one worker, 24-hour pitfall trap, specimen number 32013, MCZC; Boqueron: T. Enciso N.P., Lat: S 21.21, Long: W 61.66, 03–05.XI.2001, Leponce M., five workers in three Winkler samples, RBINS, INBP, specimen numbers 7598, 7683, 7684, 7698, and 32605 (scanning electron microscope (SEM) pictures of the specimen number 7684 are available at http://projects.biodiversity.be/ants); Boqueron: Garrapatal, Lat: S 21.45, Long:W61.49, 05-06.XI.2001, Leponce M., one worker, Winkler sample, specimen number 24606, RBINS.

Etymology

From Latin, bidens, referring to the subpostpetiolar process forming a pair of well-defined teeth.

References

Delsinne, T., Mackay, W., Wild, A., Roisin, Y., Leponce, M. 2011. 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).