Oxyepoecus inquilinus

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Oxyepoecus inquilinus
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Solenopsidini
Genus: Oxyepoecus
Species: O. inquilinus
Binomial name
Oxyepoecus inquilinus
(Kusnezov, 1952)

Oxyepoecus inquilinus casent0006160 profile 1.jpg

Oxyepoecus inquilinus casent0006160 dorsal 1.jpg

Specimen labels

Synonyms

Despite being the most widely distributed species of the genus, Oxyepoecus inquilinus is quite rare. It is considered threatened and is listed as an IUCN vulnerable species. It is an inquiline in nests of Pheidole radoszkowskii and likely other species as well.

At a Glance • Inquiline  

Identification

Workers of O. inquilinus are distinguished by the combination of two characters: the very large compound eyes with about 50 ommatidia, and the developed spines of the propodeum (Albuquerque and Brandao 2004).

Keys including this Species

Distribution

Known from Argentina, Bolivia, Brazil, Chile and Paraguay.

Latitudinal Distribution Pattern

Latitudinal Range: -2.9667° to -26.88333333°.

   
North
Temperate 		North
Subtropical 		Tropical South
Subtropical 		South
Temperate

Distribution based on Regional Taxon Lists

Neotropical Region: Argentina (type locality), Brazil, Chile, Colombia, Paraguay.

Distribution based on AntMaps

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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.
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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.
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Habitat

O. inquilinus seems to be present both in open and closed habitats, in degraded and pristine ecosystems, and in dry and wet areas. The distribution of this species seems large but discontinuous, and O. inquilinus is apparently locally rare (Delsinne et al. 2011).

Biology

Kempf (1974) - 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).

Delsinne et al. (2011): Oxyepoecus inquilinus was sampled in two localities of the Paraguayan dry Chaco. In the literature, O. inquilinus was reported from two savanna localities of the Brazilian Cerrado, one Brazilian pasture, one anthropogenic area (i.e., the “Jardin del Instituto Miguel Lillo”) from the Argentinean Tucum´an province, and one locality in the Bolivian Beni Department. In addition, one worker closely related to O. inquilinus was collected in a savanna morichal habitat from Colombia, but its specific status awaits further investigation. Finally, O. inquilinus was recently sampled in a Valdivian forest of Chile [5]. If the identity of the Colombian specimen is confirmed, O. inquilinus is the most broadly distributed species of the genus. In fact, its Colombian and Chilean localities represent both the northernmost and southernmost limits of distribution for the entire genus. Although data are insufficient to determine the exact requirements of this species, O. inquilinus seems to be present both in open and closed habitats, in degraded and pristine ecosystems, and in dry and wet areas. The distribution of this species seems large but discontinuous, and O. inquilinus is apparently locally rare, justifying its vulnerable status. O. inquilinus is suspected to be inquiline in Pheidole radozskowskii nests. At T. Enciso N.P., the same Winkler sample collected two workers of O. inquilinus and 11 workers of Ph. radozskowskii. However, at Nueva Asuncion the latter was not recorded in our 60 Winkler and 60 pitfall samples, suggesting that O. inquilinus is not restricted to this host species.

Explore-icon.png 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).

Association with Other Organisms

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Castes

Only known from the worker.

Nomenclature

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

  • inquilinus. Martia inquilina Kusnezov, 1952h: 720 (diagnosis in key) (w.) ARGENTINA. Combination in Oxyepoecus: Ettershank, 1966: 146. Senior synonym of turgidus: Kempf, 1974b: 489.
  • turgidus. Oxyepoecus turgidus Kempf, 1969: 278, figs. 1-3 (w.) BRAZIL. Junior synonym of inquilinus: Kempf, 1974b: 489.


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

Kempf 1974 oxyepoecus fig. 1-10.jpg

Kempf (1974) - When originally proposed (Kusnezov, 1952: 720), inquilinus was not given any formal description, but only a few, in part worthless differential characters were pointed out both in the text and in the key to the Argentine species of the genus. A direct comparison between the holotypes of inquilinus and turgidus (nov. syn.) proved that both are conspecific, the latter being a straight synonym of the former.

This heavy-set species is striking by its elongate, sublinear mandibles which it shares with Oxyepoecus vivax and to some extent also with Oxyepoecus vezenyii, in which they are already a bit shorter and somewhat variable. Inquilinus differs from vezenyii in the slightly broader head, the more expanded frontal carinae which cover at least one third of the head width, the much larger eyes with over 50 ommatidia, the lack of margination in front and on sides of pronotum, the lack of a humeral angle, the stronger propodeal spines, the dentate, not lobate subpetiolar process.

The worker of vivax is unknown, but to judge from the queen, the shape of the petiole and the postpetiole readily separates both species.

All the Argentine material was found within the nests of Pheidole radoszkowskii Mayr, as already pointed out in the introduction of this paper. For the remaining specimens from Brazil and Bolivia, we have no such evidence.

Note. Three stray males, taken on December 15, 18 and 19, 1957 at Tucumán, Argentina (IML) definitely belong to Oxyepoecus and probably represent the male sex of the present species, inquilinus. They differ from the male of rastratus in the following details:

Slightly larger in size, thorax heavier; frons with a smooth, impressed, longitudinal stripe between clypeus and anterior ocellus; scutum entirely smooth and shining; scutellum mostly smooth, lightly sculptured on sides; mesopleura mostly costate-rugose; basal face of propodeum with heavy, coarse transverse rugae; petiolar node more distinctly set off from the peduncle, its peak narrowly rounded in side-view.

Description

Worker

Kempf (1974) - (holotype). Total length 2.7 (2.5-2.9) mm; head length 0.60 (0.53-0.64) mm; head width 0.51 (0.46-0.53) mm ; scape length 0.41 (0.35-0.44) mm; maximum diameter of eyes 0.16 (0.12-0.16) mm; Weber's length of thorax 0.80 (0.68- 0.80) mm; maximum width of pronotum 0.44 (0.38-0.44) mm; hind femur length 0.48 (0.43-0.51) mm; petiole width 0.27 (0.22-0.28) mm; postpetiole width 0.33 (0.27-0.36) mm;

Kempf 1974 Oxyepoecus fig 11-22.jpg

cephalic index 83-91. Chestnut brown; gaster fuscous brown to black; mandibles, scapes and legs yellowish brown; occiput somewhat infuscated. Integument smooth and shining; piligerous punctures on cephalic dorsum conspicuous. Hairs abundant, erect on body, oblique on mandibles, antennae and legs; on head, most hairs are oblique, curved mesad dorsally on disc, the remaining ones curved forward; fine pubescence present only on antennal club, coxae and tarsomeres.

Head. Mandibles sublinear, strikingly elongate, basal border much longer than chewing border, the small basal tooth separated from the stronger subbasal tooth by a broad and shallow diastema. Median apron of clypeus very strongly and sharply carinate on both sides, the anterior teeth and accessory denticles well developed. Frontal area impressed, indistinctly delimited. Frontal carinae short, moderately expanded laterad, terminating at level of anterior orbit of eyes, bearing dorsally a few fine longitudinal costulae which curve obliquely laterad above eyes without reaching them and do not extend caudad beyond level of posterior orbit of eyes; maximum distance between outer edges of frontal carinae at least one third of maximum head width. Cheeks longitudinally striate in front and above eyes. The latter comparatively very large, moderately convex, with about 10 facets in a row across the greatest diameter, the total number of ommatidia being about 50 in all. Antennal scape relatively long but not quite reaching the occipital corner when laid back over the head. Funicular segment I longer than VIII and IX taken individually, as long as II-V combined; segments II-VII visibly broader than long; segments VIII and IX subequal in length, about as long as broad.

Thorax stout and heavy-set. Promesonotum continuously vaulted in both directions, immarginate in front and on sides; shoulders completely rounded, not angular nor subdentate. Metanotal groove scarcely to not at all impressed; no metanotal suture present. Basal face of propodeum transversely costulate, the 10 or more fine costae fading out on sides of propodeum; the last costa between the comparatively prominent and acute propodeal spines separating the basal from the declivous face; the latter smooth and shining, laterally sharply marginate. Metasternal lobes rounded. Sides of thorax on postero-inferior corner with a few strong costulae, curved around the bulla of the metasternal gland; mesopleura also with a narrow band of short, faint, horizontal costulae along the posterior border.

Petiole strongly pedunculate, node high and rounded above, antero-posteriorly compressed, scalelike, nearly as broad as postpetiole; subpetiolar process in the form of a sharp sagittal crest terminating in front in a very prominent tooth. Postpetiole very broad, scalelike, not as high as petiole, its posterior surface with a few faint, transverse costulae. Gaster smooth and shining throughout.

Type Material

Kempf (1974):

Argentina, Tucuman, Jardin del Instituto Miguel Lillo, 2-V-1948, N. Kusnezov leg. 2 workers (IML n. 1832, holotype and paratype) ; same locality and collector, 6-1-1948, 7 workers (IML n. 111, paratypes).

Brazil, Sao Paulo State : Agudos, Fazenda Santo Antonio, 23-1X-1954, W. W. Kempf leg. 1 worker (WWK s/n, holotype of turgidus) , same locality and collector, 25-1-1953, 1 worker (WWK n. 740, paratype of turgidus).

Albuquerque and Brandao (2004) - Brasil: Goiás: Anápolis; 18.iii.1964, Kempf # 3852, W. Kempf [col.] [16°19’S 48°57’W] (2 ", paratypes of Oxyepoecus turgidus Kempf, 1969); same locality, 2.i.1966, Kempf # 4300, W. Kempf [col.] (1 " paratype of Oxyepoecus turgidus Kempf, 1969). São Paulo: Agudos; 23.ix.1954, W. Kempf [col.] [22°27’S 49°00’] ("holotype of Oxyepoecus turgidus Kempf, 1969); same locality, 25.i.1953, Kempf # 740, same collector (1 " paratype of Oxyepoecus turgidus Kempf, 1969). In Kempf ’s collection accession book we found the information that the paratypes of O. turgidus were found in the “Cerrado do Seminário”, that is in a savanna close to the convent where Father Kempf was living at the time.

References

References based on Global Ant Biodiversity Informatics

  • Albuquerque N. L. and Brandão, C. R. F. 2004. A revision of the Neotropical Solenopsidini ant genus Oxyepoecus Santschi, 1926 (Hymenoptera: Formicidae: Myrmicinae). 1. The Vezenyii species-group. Papeis Avulsos de Zoologia (São Paulo) 44: 55-80.
  • Albuquerque, N.L. and C.R.F. Brandao. 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(23): 289-309.
  • Brandao, C.R.F. 1991. Adendos ao catalogo abreviado das formigas da regiao neotropical (Hymenoptera: Formicidae). Rev. Bras. Entomol. 35: 319-412.
  • Kempf W. W. 1969. Miscellaneous studies on Neotropical ants. V. (Hymenoptera, Formicidae). Studia Entomologica 12: 273-296.
  • Kempf W. W. 1974. A review of the Neotropical ant genus Oxyepoecus Santschi (Hymenoptera: Formicidae). Studia Entomologica 17: 471-512.
  • Kempf W. W. 1978. A preliminary zoogeographical analysis of a regional ant fauna in Latin America. 114. Studia Entomologica 20: 43-62.
  • Kempf, W.W. 1972. Catalago abreviado das formigas da regiao Neotropical (Hym. Formicidae) Studia Entomologica 15(1-4).
  • Pacheco R., and H. L. Vasconcelos. 2012. Subterranean Pitfall Traps: Is ItWorth Including Them in Your Ant Sampling Protocol? Psyche doi:10.1155/2012/870794
  • Ulyssea M. A., C. R. F. Brandao. 2013. Catalogue of Dacetini and Solenopsidini ant type specimens (Hymenoptera, Formicidae, Myrmicinae) deposited in the Museu de Zoologia da Universidade de Sao Paulo, Brazil. Papies Avulsos de Zoologia 53(14): 187-209.
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