Oxyepoecus plaumanni

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

Oxyepoecus plaumanni casent0911210 p 1 high.jpg

Oxyepoecus plaumanni casent0911210 d 1 high.jpg

Specimen Labels

Only known from Brazil.

Identification

The present species is closest to the sympatric Oxyepoecus rastratus. The worker exhibits the following diagnostic features: costulae on disc of cephalic dorsum not attaining laterally the upper orbit of eyes nor posteriorly the occipital border in full-face view; eyes smaller, with only 5-6 facets in a row across the greatest diameter and less than 20 ommatidia in all. Petiolar node not compressed nor expanded laterad. The same differences, except the eye character, hold for the females of both species, while plaumanni, in addition, has the mesonotal scutum. entirely smooth and shining.

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

Neotropical Region: Brazil (type locality).

South and São Paulo State, Southeastern Brazil

Distribution based on AntMaps

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Distribution based on AntWeb specimens

Check data from AntWeb

Biology

All the known material comes from Berlesate collections of forest leaf-mold, so nothing is known about the habits of this species, which seems to be confined to the floor cover of Araucaria forests in southern Brazil. Collections were made in in dense evergreen and drier 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.

  • plaumanni. Oxyepoecus plaumanni Kempf, 1974b: 492, figs. 27-30 (w.q.) BRAZIL. See also: Albuquerque & Brandão, 2009: 297.

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

Description

Worker

(holotype). Total length 2.1 (1.9-2.2) mm; head length 0.53 (0.48-0.55) mm; head width 0.43 (0.39-0.43) mm; scape length 0.33 (0.31-0.33) mm; maximum diameter of eyes 0.07 (0.06-0.08) mm; Weber's length of thorax 0.61 (0.55-0.61) mm; maximum width of pronotum 0.31 (0.27-0.31) mm; hind femur length 0.36 (0.35-0.37) mm; petiole width 0.14 (0.12-0.14) mm; postpetiole width 0.18 (0.16-0.18) mm; cephalic index 80 (77-81). Chestnut brown; mandibles, antennae and legs lighter, yellowish brown. Smooth and shining throughout except on frons, vertex, promesonotal dorsum and sides of thorax (excluding smooth laterotergite of pronotum), which are longitudinally costulate, and the basal face of propodeum which is very densely transversely costulate. Hairs moderately abundant; standing on body, inclined to subappressed on antennae, mandibles and legs; on cephalic dorsum and on gaster, besides the rather scarce standing hairs are other, shorter and more numerous ones inclined or curved mesad on cephalic disc, forward on cheeks, caudad on gaster.

Kempf 1974 Oxyepoecus fig 23-30.jpg
Head. Mandibles subtriangular, not strikingly elongate; basal border subequal in length to chewing border, basal tooth not separated from subbasal by a broad diastema nor by a deep cleft. Median apron of clypeus projecting forward between the two strong, anteriorly diverging carinae, forming anteriorly a pointed prominent tooth, flanked laterally and below by another small denticle. Frontal area impressed, smooth and shining, distinctly delimited. Frontal carinae short; subparallel, terminating at level of anterior orbit of eyes, moderately expanded laterad, the maximum width between their outer edges being less than one third of maximum head width. Frontal carinae, frons, and vertex finely, longitudinally costulate, the sculptured area continuous, not attaining laterally the upper orbit of eyes nor caudally the occiput in full-face view. Cheeks longitudinally striate in front of eyes. The latter comparatively small, very little convex, with about 5 (6) facets in a row across the greatest diameter, the total number of ommatidia not exceeding 20. Antennal scape failing to reach the occipital corner by a distance which exceeds the maximum thickness of scape. Funicular segment I longer than VIII and IX taken individually, as long as II-V combined; segment II-VII decidely broader than long, VIII and IX subequal in length and about as long as broad.

Thorax. Promesonotum convex in both directions, immarginate in front; shoulders faintly marked, sides of pronotal dorsum indistinctly marginate. Promesonotal dorsum finely, regularly, and superficially longitudinally costulate, but somewhat shining, especially on pronotum. Metanotal groove not impressed, metanotal suture indicated. Basal face of propodeum densely transversely costulate-rugose, with more than 15 costulae, the last costa between the small but pointed propodeal teeth not particularly prominent; declivous face of propodeum smooth and shining, with a few vestigial transverse costulae near upper limit, its sides carinate. Sides of thorax, except the smooth and shining laterotergite of pronotum, more or less regularly horizontally costulate, the costulae extending also over the prominent bulla of the metasternal gland.

Petiole strongly pedunculate, node high and rounded, not particularly compressed antero-posteriorly nor laterally expanded; subpetiolar process in the form of a small denticle. Postpetiole much broader than petiole, the node proper somewhat compressed antero-posteriorly, its posterior surface without distinct transverse costulae. Gaster smooth and shining above and below, faintly excised at postpetiolar insertion.

Queen

(paratypes). Total length 2.6-2.7 mm; head length 0.56-0.60 mm; head width 0.45-0.47 mm; scape length 0.35-0.37 mm; maximum .diameter of eyes 0.12 mm; Weber's length of thorax 0.75-0.78 mm; maximum width of pronotum 0.40-0.41 mm; hind femur length 0.40-0.43 mm; fore wing length 2.30 mm; hind wing length 1.54 mm; cephalic index 79-83. Color and pilosity as in worker, gaster occasionally somewhat infuscated. Cephalic dorsum with the same continuous patch of longitudinal costulae which do not attain laterally the upper orbit of eyes nor posteriorly the occiput. Pronotum dorsally weakly obliquely costulate, completely declivous in the middle. Mesonotal scutum smooth, scutellum longitudinally costulate; basal face of propodeum with about 10 transverse costulae; anepisternum and catepisternum of mesothorax mostly smooth and shining, at least discally; sides of metanotum and propodeum entirely costulate, the costulae being horizontal at bottom, oblique and slanting downward and forward above. Postpetiole without transverse costulae on posterior face of node. Fore wing with an open radial cell (Rs not attaining the anterior margin), a very small discoidal cell; the free abscissa of M entirely lacking in the apical field. Ocelli with the same diameter as the thinnest part of the antennal scape. Remaining characters as in worker.

Type Material

40 workers and 6 females as follows: Brazil, Rio Grande do Sul State: Erechim, VII-1960, F. Plaumann leg. 18 workers (WWK n. 8097, holotype and paratypes); Barão de Cotejipe, VII-1960, F. Plaumann leg. 1 worker (WWK n. 3765, paratype); Boqueirão, IX-1960, F. Plaumann leg. 1 worker (WWK n. 3611, paratype); Tainhas, IV-1959, F. Plaumann leg. 1 worker (WWK n. 3247, paratype); Santa Catarina State: Chapecó, VI-1960, VII-1960, VIII-1960, F. Plaumann leg. 9 workers, 2 females (WWK n. 8331, 9883, 9911, paratypes) ; Ibicaré, IX-1960, F. Plaumann leg. 2 workers (WWK n. 8178, paratypes); Nova Teutônia, VI-1960, XII-1972, F. Plaumann leg. 2 workers, 3 females ( WWK n. 8091, 8383, 8557, 8562, paratypes); Passo Bormann, XII-1957, F. PIaumann leg. 1 female (WWK s/n, paratype); Paraná State: Porto Vitória, X-1959, F. Plaumann leg. 1 worker, 1 female (WWK n. 3207, 3209, paratypes); Rio Azul, X-1959, F. Plaumann leg. 4 workers (WWK n. 3189, paratypes).

In the original description, Kempf (1974) cited a paratype from Brazil, Rio Grande do Sul state, Tainhas [29°16’S, 50°18’W], collected in April.1959, by F. Plaumann, (W.W.K. # 3247). However, although the pin and label are preserved in the MZSP collection, the specimen is missing from the triangle (Albuquerque and Brandão 2009).

Etymology

Named after its discoverer, Mr. Fritz Plaumann.

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.
  • Kempf, W. W. 1974b. A review of the Neotropical ant genus Oxyepoecus Santschi (Hymenoptera: Formicidae). Stud. Entomol. 17: 471-512 (page 492, figs. 27-30 worker, queen described)