Octostruma onorei

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Octostruma onorei
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Attini
Genus: Octostruma
Species: O. onorei
Binomial name
Octostruma onorei
(Baroni Urbani & De Andrade, 2007)

Nothing is known about the biology of Octostruma onorei.

Identification

Shares with Octostruma iheringi the structure of the propodeal spines, the longitudinal trough on the mesosomal dorsum, and the general habitus (based on the description and the figures in the original publication). It differs in having erect setae on the mesosoma and first gastral tergite, and the first gastral tergite is smooth and shining. (Longino 2013)

A Basiceros species belonging to the petiolatum-group as defined by Brown & Kempf (1960) (in Octostruma) and differing from all species of this group, inca, jheringi, stenoscapum, petiolatum and wheeleri (Brown & Kempf, 1960; Palacio, 1997), by the following combination of characters: occipital margin with a row of four clavate hairs, each upper scrobe margin with one clavate hair, pronotum and mesonotum with a pair of clavate hairs each, gaster with 4 rows of erect, clavate hairs (2,2,2,4), sides of the basal face of the propodeum strongly marginate, and propodeum, pleurae and gaster largely smooth, sub-opaque to shining. B. onorei differs from the 5 known species of the petiolatum-group of "Octostruma" as defined by Brown & Kempf (1960) by the combination of characters listed in the diagnosis. B. onorei shares with iheringi the head dorsum with irregular rugosities but differs from iheringi mainly by the presence of standing hairs on the mesosoma and gaster. B. onorei shares with petiolatum the mesosoma and gaster superficially smooth but differs from it mainly by having 6 standing hairs instead of 16 on the head dorsum and by the head weakly instead of broadly convex. (Baroni Urbani & De Andrade 2007)

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

Neotropical Region: Ecuador (type locality).

Distribution based on AntMaps

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Distribution based on AntWeb specimens

Check data from AntWeb

Biology

Longino (2013) - Brown and Kempf (1960) summarized the biology of basicerotines as follows: The basicerotines all come from tropical or subtropical areas, and predominantly from mesic habitats, particularly rain forest, where they live primarily in the upper layers of the soil and in the soil cover, including large and small pieces of rotten wood. They are fairly common in soil cover berlesates. Nests have been found in snail shells, and in the peaty masses gathered about epiphytic ferns above the ground level. So far as is known, colonies are small, consisting of one or more dealate—or rarely ergatoid—females, and a few workers. Judging from the structure of the workers and females, one would suppose that they were predaceous on small arthropods...

Besides this summary, the behavior of three basicerotine species has been studied. Wilson (1956) observed a small captive colony of Eurhopalothrix biroi, a New Guinea species. Workers moved slowly and captured a variety of small, soft-bodied prey, including spiders, symphylans, entomobryid Collembola, campodeids, and hemipteran nymphs. Wilson and Brown (1984) observed a captive colony of Eurhopalothrix heliscata, a species from Singapore. The colony contained over 400 workers, multiple alate and dealate queens, several adult males, and brood. Foraging workers acted "rather like miniature ferrets," readily wedging themselves into small crevices. They foraged solitarily, attacking a variety of prey but mostly termites. They used their sharply-toothed mandibles to abruptly snap onto appendages of prey, maintaining purchase and slowly reaching around with the gaster to sting the prey. The strongly sclerotized labrum was also employed to press against the clamped appendage. The behavioral repertoire was limited. There did not appear to be trophallaxis, as workers and larvae fed directly from prey in the brood chambers. Nor did there appear to be any form of alarm communication. While there was generally an increase in the number of foragers when clusters of prey were presented, there was no evidence of any pheromone-based recruitment. Workers were non-aggressive and responded to disturbance by tucking the appendages and becoming immobile, often for minutes at a time. Wilson and Hölldobler (1986) studied captive colonies of Basiceros manni from Costa Rica and observed behavior not substantially different from E. heliscata. Foraging workers of many basicerotines are often encrusted with a firmly bonded layer of soil, which is thought to function as camouflage, enhancing crypsis (Hölldobler & Wilson, 1986).

Knowledge of the basic natural history of these ants has hardly progressed since the observations of Wilson, Brown, and Hölldobler. More specimens are now available for examination due to quantitative litter sampling, enhancing knowledge of basicerotine diversity and distribution, but discovering nests remains exceedingly difficult. Quantitative samples of 1 m2 litter plots reveals that small basicerotines can be very frequent, occurring in over 50% of samples in some cases, but never in large numbers. Individual samples usually contain fewer than ten workers, and workers are often accompanied by dealate queens. These results suggest that colonies, at least among New World species, are usually small, with tens of workers.

Less than half of the species of Octostruma have their queens described. Ergatoid queens are known from some species. Males are known from collections for some species but none have been described. The mating biology of these ants and how common ergatoid queens are across the genus and within colonies is not known.

Castes

Nomenclature

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

  • onorei. Basiceros onorei Baroni Urbani & De Andrade, 2007: 133, fig. 47 (w.) ECUADOR. Combination in Octostruma (unpublished).

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

Longino (2013) - This species is known only from the holotype. From the description, it appears to be a version of Octostruma iheringi.

Description

Worker

Head dorsum weakly convex in full dorsal view. Posterolateral sides of the head with the two anterior thirds diverging posteriorly into a round angle and the posterior third gently converging into a weakly concave vertexal margin. Frontal lobes weakly expanded and convex. Antennal fossae ventrally with a marked carina visible in full-face view, straight, covering the lower margin of the scrobes and ending below the eye. Eyes small, with 4 ommatidia in the longest row, placed on the upper margin of the antennal scrobes. With head in profile the scrobe very distinct, with the upper margin behind the eye broad, lamellaceous, semitransparent and the lower one strongly carinate. Anterior clypeal border medially with a broad concavity. Scapes slightly compressed dorsoventrally, with strong subbasal bend. Antennae with eight joints. Apical funicular joint slightly longer than the rest of the funiculus. Mandibles triangular, with a series of 5 teeth and two irregular denticles before the subround apex.

Mesosoma anteriorly convex and posteriorly sloping in profile. Dorsum of the mesosoma medially with a broad, superficial, longitudinal sulcus spacing from the pronotum to the mesonotum. Propodeal suture superficially impressed. Posterior half of the basal face of the propodeum gently concave. Sides of the basal face of the propodeum strongly marginate. Propodeal teeth large, lamellaceous, transparent, apically pointed and with broad base. Upper bases of propodeal teeth strongly marginate, connected each other and forming a clear carina dividing the basal and declivous faces. Lower base of propodeal teeth ending on the middle of the declivous face. Posterior half of the declivous propodeal face weakly marginate. Propodeal spiracle large and below the lower base of the propodeal tooth.

Petiole with a long neck and with the node high anteriorly and sloping posteriorly. Ventral surface of the petiolar neck anteriorly with a small lamellaceous tooth pointed forwards. Postpetiole almost flat in side view; in dorsal view the anterior and posterior borders well marked by a thicker and anteriorly semitransparent carina.

Gaster oval. Base of the first gastral tergite clearly marginate. Base of the first gastral sternite superficially marginate.

Sculpture. Head reticulate-punctuate and with thin, irregular longitudinal rugosities. Pronotum and mesonotum irregularly reticulate and very superficially punctuate, the reticulation less marked on the posterior half of the mesonotum. Propodeum and pleurae smooth and shining, in addition the pleurae with a few minute punctures. Gaster smooth and shining, in addition the posterior border of the first gastral tergite, the anterior and posterior borders of the first gastral sternite and all remaining tergites and sternites with well impressed, large punctures.

Pilosity. Body with appressed, short, thin, decumbent hairs, very rare on the dorsum of the propodeum and pleurae. Posterior margin of the head dorsum with a row of four clavate erect hairs. Upper antennal scrobes with one clavate erect hair each. Pronotum, mesonotum and posterior half of the petiole and postpetiole with a pair of clavate, erect hairs each. First gastral tergite with four rows of clavate erect hairs, the first up to the third rows with two clavate hairs and the fourth row with four hairs close to the posterior border. Remaining gastral tergites with four clavate hairs, thinner than on the first tergite. First gastral sternite medially with erect, truncate or weakly clavate hairs; posterior half of the first gastral sternite and remaining gastral sternites with clavate hairs much thinner than on the tergites. Apex of the tibiae with a few clavate hairs.

Colour. Dark brown with slightly lighter antennae and legs.

Measurements (in mm) and indices: TL 2.84; HL 0.67; HW 0.74; SL 0.45; ML 0.22; EL 0.06; WL 0.76; CI 110.4.

Type Material

Holotype worker (unique) from Ecuador labelled: Banos de Agua Santa, Provo Tungurahua, 01 °24'S 78°25'W, 1860 m, sendero Bella Vista, leaf-litter, 26.VIII.2004, C. Baroni Urbani & M. L. de Andrade (Museo de Zoología, Escuela de Biología).

Etymology

This species is named after Prof. Dr Giovanni Onore who facilitated in multiple ways our Dacetini field work in Ecuador.

References

  • Longino, J.T. 2013. A revision of the ant genus Octostruma Forel 1912 (Hymenoptera, Formicidae). Zootaxa 3699, 1-61. doi:10.11646/zootaxa.3699.1.1