Oxyepoecus reticulatus

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Oxyepoecus reticulatus
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Solenopsidini
Genus: Oxyepoecus
Species: O. reticulatus
Binomial name
Oxyepoecus reticulatus
Kempf, 1974

Oxyepoecus reticulatus casent0178101 profile 1.jpg

Oxyepoecus reticulatus casent0178101 dorsal 1.jpg

Specimen labels

A typical Oxyepoecus ant; rarely collected and little is known about its biology.

Identification

In the rastratus species-group, O. reticulatus workers present exclusively the integument almost entirely covered by irregular somewhat undulate costulae on the head disc, mesosoma and dorsal petiolar peduncle (Albuquerque and Brandão 2009).

Keys including this Species

Distribution

Parguay and south and southeastern Brazil from Minas Gerais to Santa Catarina states.

Distribution based on Regional Taxon Lists

Neotropical Region: Brazil (type locality), Paraguay.

Distribution based on AntMaps

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Distribution based on AntWeb specimens

Check data from AntWeb

Biology

Typically collected in berlesates of forest floor cover in relatively dry forests.

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 (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

Males have not been collected.

Nomenclature

The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.

  • reticulatus. Oxyepoecus reticulatus Kempf, 1974b: 502, figs. 23-26 (w.q.) BRAZIL. See also: Albuquerque & Brandão, 2009: 303.

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

This tiny species is very close to Oxyepoecus plaumanni, the worker differing as follows: head entirely sculptured on dorsum, i. e. the sculptured area touches the eyes and the side of the head and reaches posteriorly the occiput; laterotergite of pronotum horizontally costulate, not smooth; sides of thorax heavily reticulate-punctate, costae at best vestigial; dorsum of thorax with strong interstitial punctulae, the latter masking in part the longitudinal rugae or costulae on pronotum, eliminate them altogether on mesonotum, and also render the transverse costulae on basal face of propodeum indistinct or absent; petiolar node a little more compressed antero-posteriorly.

The queen differs from that of plaumanni in sculpture of the cephalic dorsum and laterotergite of pronotum, as stated for the worker, and in the longitudinally costulate mesonotal scutum.

The differences from rastratus (worker and female), another very close species, have already been given while treating this species above.

Description

Worker

Kempf 1974 Oxyepoecus fig 23-30.jpg

(holotype). Total length 1.9 (1.9-2.3) mm; head length 0.51 (0.48-0.56) mm; head width 0.41 (0.38-0.44) mm; scape length 0.31 (0.29-0.35) mm; maximum diameter of eyes 0.07 (0.05-0.07) mm; Weber's length of thorax 0.57 (0.51-0.62) mm; maximum width of pronotum 0.31 (0.27-0.32) mm; hind femur length 0.33 (0.29-0.37) mm; petiole width 0.15 (0.13-0.15) mm; postpetiole width 0.23 (0.16-0.23) mm; cephalic index 82 (77-84). Chestnut brown; mandibles, antennae and legs lighter, yellowish brown. Mandibles, antennae, gular face of head, declivous face of propodeum, legs, petiole, postpetiole and gaster shining, smooth to very superficially and indistinctly sculptured. Remaining parts of the insect opaque with the following sculpture: cephalic dorsum finely, longitudinally costulate with fine, but very distinct and usually more conspicuous interstitial punctulae; the sculptured area attains laterally the eyes and posteriorly the occiput; pronotum longitudinally costulate above and on sides, the interstitial punctulation being weak to obsolescent on sides (laterotergite), strong on dorsum, nearly masking the longitudinal costulae; mesonotum and remaining part of sides of thorax reticulate-punctate; coarser costulae on bottom of metapleura; basal face of propodeum with the transverse rugulae more evident yet not becoming the marked transverse costulae of the other species; declivous face vestigially transversely costulate on upper half, but quite shining. Hairs very abundant on head, curved mesad dorsally on disc, forward on sides; standing and moderately abundant on dorsum of thorax, petiole and postpetiole, and on gaster, the latter also with shorter, recurved hairs; oblique to subappressed on antennae and legs.

Head. Mandibles subtriangular, not strikingly elongate, the basal border not much longer than the chewing border, basal tooth separated from the subbasal tooth by a shallow diastema. Median apron of clypeus, as usual in the genus, protruding forward and bicarinate; clypeal teeth and denticles well developed. Frontal area impressed, more or less smooth and shining. Frontal carinae short, subparallel, little expanded laterad, the maximum width between their outer edges less than one third of head width. Eyes very small, scarcely convex, with about 4-5 facets across the greatest diameter, the total number of ommatidia not reaching 20. Antennal scapes failing to reach the occipital corner by a distance which exceeds the maximum thickness of the scape. Funicular segment I longer than VIII and IX taken individually, as long as II-V combined; segments II-VII decidedly broader than long, VIII and IX about as long as broad.

Thorax. Promesonotum gently convex in both directions, immarginate in front, shoulders marked, yet not tuberculate, sides of pronotal dorsum indistinctly marginate; antero-inferior angle of pronotum obtuse but rounded. Metanotal groove not impressed, metanotal suture indistinct. Propodeal armature consisting of a pair of small but pointed teeth. Sides of declivous face subcarinate.

Petiole strongly pedunculate, node high and dorsally rounded, somewhat compressed antero-posteriorly yet not conspicuously expanded laterad; subpetiolar process in the form of a small tooth. Postpetiole much broader than petiole; conspicuously expanded laterad, the posterior surface of node without distinct transverse costulae.

Variation. Six workers, from sifted leaf mold near halfway down the coastal range on the old São Paulo-Santos road (Caminho do Mar), are lighter, yellowish brown in color, and have slightly larger eyes (6-7 facets across the greatest diameter). Another lot of 2 workers, also from sifted forest floor cover, taken alongside the São Paulo - Curitiba highway (BR-116) near Juquitiba, São Paulo State, by myself is even more discrepant and is not listed as type. These specimens have the costulae on cephalic dorsum very feebly developed, the entire thorax, including the laterotergite of pronotum and the declivous face of the propodeum reticulate-punctate with practically no trace of costulae. Also the petiole and postpetiole are superficially reticulate-punctate. They might represent still another not yet recognized species, but we need more material to check up on the constancy of these characters.

Queen

(paratype). Total length 2.5 mm; head length 0.55 mm; head width 0.45 mm; scape length 0.33 mm; maximum diameter of eyes 0.11 mm; Weber's length of thorax 0.71 mm; maximum width of pronotum 0.40 mm; hind femur length 0.37 mm; petiole width 0.17 mm; postpetiole width 0.27 mm; cephalic index 83. Similar to the worker with the distinctive characters of the caste. Cephalic dorsum finely, longitudinally, costulate, with conspicuous interstitial punctures, the sculpture attaining both the occiput and the eyes, as in worker. Eyes with about 10 facets across the greatest diameter. Laterotergite of pronotum, catepisternum of mesonotum and remaining parts of sides of thorax with horizontal costulae, the interstitial microsculpture superficial to obsolete, hence quite shining. Pronotum entirely declivous in the middle, the dorso-lateral portions finely, obliquely costulate. Mesonotal scutum and scutellum longitudinally costulate, opaque. Basal face of propodeum with about 10 transverse rugulae, the interstitial punctulae weak. Propodeal teeth short but pointed; the distance between their tips subequal to width of petiole. Posterior surface of postpetiole with several transverse rugae or costae. Although a completely developed female in all regards, this specimen never had wings.

Type Material

BRAZIL, Santa Catarina State: Nova Teutônia, VIII-1952, F. Plaumann leg. 39 workers (holotype and paratypes; TB n. 5954); Chapecó, V-1957, VI-1960, VII-l960, F. Plaumann leg. 12 workers (WWK; paratypes); Concórdia, VII-1958, F. Plaumann leg. 1 worker (WWK; paratype); Linha Facão, V-1957, F. Plaumann leg. 25 workers (WWK; paratypes); Passo Bormann, XII-1957, F. Plaumann leg. 1 worker (WWK; paratype); Paraná State: Guaragi, V-1964, F. PIaumann leg. 2 workers (WWK n. 4008, 4560; paratypes); Rio Azul, 1000 m, X-1959, F. Plaumann leg. 1 worker (WWK n. 3188; paratype); Rolândia, 6-IV-1955, W. W. Kempf leg. 2 workers (WWK n. 1414; paratypes); Mariópolis, without date, F. Plaumann leg. 1 female (TB; paratype) ; São Paulo State: Agudos, 25-III-1955, 17-IV-1955, 4-1-1956, 8-1-1956, W. W. Kempf leg. 15 workers (WWK n. 1405, 1430, 1552, 1560; paratypes); same locality, XI-1959, C. Gilbert leg. 1 worker (WWK n. 3218; paratype); Campos do Jordão, 16-X-1956, W. W. Kempf leg. 1 worker (WWK n. 1601; (paratype); Caminho do Mar, meio da serra (old São Paulo-Santos highway), 8-VIII-1960; W. W. Kempf leg. 3 workers (WWK; paratypes).

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
  • Kempf, W. W. 1974b. A review of the Neotropical ant genus Oxyepoecus Santschi (Hymenoptera: Formicidae). Stud. Entomol. 17: 471-512 (page 502, figs. 23-26 worker, queen described)