Octostruma inca

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Octostruma inca
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Attini
Genus: Octostruma
Species: O. inca
Binomial name
Octostruma inca
Brown & Kempf, 1960

Octostruma inca P mcz-ent00030879.jpg

Octostruma inca D mcz-ent00030879.jpg

Specimen Label

Nothing is known about the biology of Octostruma inca.

Identification

The combination in the worker of large compound eyes with many ommatidia, antennal scrobe a shallow impression without carinate rim, base of scape lacking flattened anterior lobe, and HW > 0.68 uniquely identify this species. (Longino 2013)

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

Neotropical Region: Bolivia, Colombia, Peru (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.

  • inca. Octostruma inca Brown & Kempf, 1960: 185, figs. 16, 29 (w.q.) PERU. Wheeler, G.C. & Wheeler, J. 1977: 600 (l.). See also: Kempf, 1968b: 400.

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

Longino (2013) - The measurements reported in Brown and Kempf (1960) for the holotype of O. inca are considerably larger than the six workers measured for this report. HW of six measured workers, including three paratypes, is 0.69–0.87; HW of the holotype is reported as 0.91. The larva described by Wheeler and Wheeler (1977) was a specimen from Colombia sent by W. L. Brown. MCZ material examined for this report includes what appear to be two nest series collected by W. L. Brown in Dept. Valle, Colombia.

Description

Worker

Holotype. TL 4.2, HL 0.92, HW 0.91 (CI 99), WL 1.12 mm. Form of head and alitrunk shown in the figures. Disc of clypeus somewhat convex, posterior border of median lobe distinct. Front and vertex with occiput gently convex in both directions. Antennal scrobe very shallow, set off above and below by rather feeble margins. Eyes large for an Octostruma, with 8-9 facets across the greatest diameter. The gentle emargination of the occipital excision is partly filled in by a narrow lamina or carina that is visible in full-face view. Scape strongly bent at base, but not greatly broadened and without a marked lobate expansion at the bend. Funicular segment I distinctly longer than broad, II-IV about as broad as long, VII (apical) slightly shorter than I-VI combined. Palpi 2: 2 (d. Characters of the Tribe).

Mandibular blades sharply and densely reticulate-punctate at base, shining and nearly smooth at apex; when closed, basal borders engage anterior c1ypeal border their full lengths; masticatory border with 8 larger subtriangular teeth, smaller and more acute toward the apex, larger and more blunt basad; after the second, third and fourth teeth from the base, there is a shorter acute denticle.

Promesonotal suture obsolescent; metanotal groove distinct but narrow. Dorsal face of propodeum with a rather strong median longitudinal ruga that forks posteriad to join the propodeal teeth, which in this species are low and not distinguishable from the body of the infradental lamellae guarding each side of the propodeal declivity.

Petiole with peduncle about as long as its node; anteroventral process of peduncle oblique, blunt. Dorsal face of node transverse, submarginate at the sides, sloping posteriad, rather flat. Postpetiole about 1 ½ times as broad as petiolar node; seen in profile rather flat above over the anterior 2/3, the posterior limb curved downward. Gaster broader than head.

Head, alitrunk, petiole and postpetiole densely and finely reticulate-punctate, the head (especially toward the sides and occipital corners) with a superimposed open network of fine rugae; sparse rugae superimposed on promesonotum, where they form a reticulum, and along posterior pleura and dorsal face of propodeum, where they are more or less longitudinal. The discs of both nodes, as well as the coxae are indistinctly rugose over their punctulation. Legs otherwise, and scapes, finely and densely punctulate. Gastric dorsum covered with fine, separated punctulae, the interspaces more or less shining, so that the surface is subopaque.

Ground pilosity consisting of minute, slightly broadened, recumbent, yellowish hairs, mostly inconspicuous on body, more evident on pedicellar nodes and gaster, quite distinct on. Legs and scapes. Specialized erect hairs long, narrowly clavate, distributed on head and alitrunk; a pair on posterior petiolar node; 6 on postpetiolar node (4 on posterior border); about 24 on first gastric tergite, in rough rows, and a transverse row on each apical tergite, plus several on gastric sternites. Shorter clavate hairs on tibial apices, mostly recumbent. Anterior scape border with 7-8 clavate hairs, decreasing in size from basal lobe to apex. Ferruginous; disc of postpetiole slightly darker.

Paratype workers: TL 3.6-4.2, HL 0.Sl-0.92, HW 0.78-0.91 (el 96-99), WL 0.96-1.12 mm. The paratypes agree with the holotype in all essential respects apart from absolute measurements; some are a little more brownish in color.

Queen

TL 5.9, HL 1.03, HW 1.11 (CI l08), greatest diameter of compound eye 0.27, WL 1.82 mm.

This female is even larger and more robust than the female of O. petiolata, but the head shape, mandibular dentition, sculpture and shape of nodes all correspond so well to what these parts of a female accompanying the O. inca syntypes should be like that the association seems to us quite firm despite the different proveniences of the two castes.

Alitrunk very high and swollen, strongly convex in profile; pronotum mostly vertical anteriorly; bulbous scutellum overhanging metanotum and propodeum, the latter with an almost vertical dorsal face. Petiole and postpetiole compressed anteroposteriorly as compared to worker, the postpetiole forming a mere convex cap fitted to the anterior end of the voluminous gaster.

Rugulation a little more distinct than in worker, transverse on pronotum, longitudinal on scutal disc, irregular-transverse on scutellum and petiolar node, reticulate on postpetiole. Gaster very finely and contiguously punctulate and opaque on anterior half of first tergite, subcontiguously punctulate and feebly shining on posterior half.

Pilosity finer and more abundant than in the workers; alitrunk and gaster with abundant tapered and truncate erect hairs (unfortunately most of these were lost when the specimen was soaked in solvent to remove the crust of old glue it carried). Color ferruginous, the gaster very bright ferruginous yellow; ocellar triangle blackened and mesonotum somewhat infuscate, especially behind.

Described from an old specimen from the Wheeler Collection miscellany [MCZ 1 labelled simply "Bolivien", apparently from Staudinger and Bang-Haas lots; the pin bears a small green square of paper. When first found, this specimen lacked the funiculi of both antennae, and had only the damaged right forewing remaining among the wings. The forewing was figured by Brown and Nutting, 1950:; probably the vein labeled as r-m is really a section of Rs.

Paratype Specimen Labels

Type Material

Holotype worker with 14 paratype workers from an unknown locality in Peru, probably on the Amazon drainage (W. Weyrauch leg., No. 732). Holotype in WWK, paratypes WWK, MeZ, IML, WW.

Longino (2013) - Holotype worker: Peru, "unknown locality... probably on the Amazon drainage" (W. Weyrauch, No. 732) Museu de Zoologia da Universidade de Sao Paulo; paratype workers: same data as holotype Museu de Zoologia da Universidade de Sao Paulo, Museum of Comparative Zoology; non-type queen: Bolivia MCZC (MCZ paratype workers and non-type queen examined).

References

  • Brown, W. L., Jr.; Kempf, W. W. 1960. A world revision of the ant tribe Basicerotini. Stud. Entomol. (n.s.) 3: 161-250 (page 185, figs. 16, 29 worker, queen described)
  • Kempf, W. W. 1968b. Miscellaneous studies on Neotropical ants. IV. (Hymenoptera, Formicidae). Stud. Entomol. 11: 369-415 (page 400, see also)
  • 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
  • Wheeler, G. C.; Wheeler, J. 1977a. Supplementary studies on ant larvae: Myrmicinae. Trans. Am. Entomol. Soc. 103: 581-602 (page 600, larva described)