Octostruma amrishi

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Octostruma amrishi
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Attini
Genus: Octostruma
Species: O. amrishi
Binomial name
Octostruma amrishi
(Makhan, 2007)

Octostruma amrishi P casent0423555.jpg

Octostruma amrishi D casent0423555.jpg

Specimen Label

Octostruma amrishi is a lowland to lower montane species. It occurs mostly in mature wet forest, less often in second growth forest. In the northern part of the range in Central America, where Octostruma gymnogon does not occur, it extends into cloud forest to 1500 m. In southern Central America, where O. gymnogon occurs, it exhibits an elevationally parapatric distribution with O. gymnogon and is restricted to elevations below 600 m. Almost all collections are from Berlese and Winkler samples of sifted litter and rotten wood from the forest floor. Dealate queens and intercaste workers occasionally occur together with workers in litter samples. One collection was of foragers on clay soil in a rainforest. See additional comments under Octostruma balzani.

Identification

Keys including this Species

Distribution

Honduras to southern Peru and Amazonian Brazil.

Distribution based on Regional Taxon Lists

Neotropical Region: Belize, Brazil, Colombia, Costa Rica, Ecuador, El Salvador, French Guiana, Guatemala, Guyana, Honduras, Nicaragua, Panama, Peru, Suriname (type locality), Venezuela.


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

Worker

Fig 11. Octostruma amrishi, worker (INBIOCRI001259486, Costa Rica), face and lateral views. Scale bar = 0.25 mm face view, 0.5 mm lateral view.

Nomenclature

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

  • amrishi. Pyramica amrishi Makhan, 2007a: 1, figs. 1, 2 (w.) SURINAM. Combination in Octostruma: Bolton, Sosa-Calvo, et al. 2008: 62. Junior synonym of balzani: Bolton, Sosa-Calvo, et al. 2008: 62. Revived from synonymy: Longino, 2013: 15.

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

Longino (2013) - Sampling of Octostruma is less thorough in South America than in Central America, but specimens that match the morphology of O. amrishi occur in lowland to midmontane rainforest in northern South America and throughout the Amazonian lowlands. Specimens from the southern portion of the range, including Amazonian Brazil and the eastern and western foothills of the Ecuadorian Andes, show reduced punctation on the first gastral tergite, becoming smooth and shining on a variable extent of the posterior portion of the tergite. See additional comments under Octostruma balzani. Although the type of O. amrishi was not examined, if it exists, the characteristic setal pattern can be seen on the figures in the original publication.

Description

Worker

Longino (2013) - HW 0.54–0.64, HL 0.50–0.60, WL 0.54–0.70, CI 106–110 (n=8). Matching in most respects the description for Octostruma balzani; mandible with 8 teeth, tooth 1 a broad blunt lamella, strongly differentiated from tooth 2, teeth 2–5 acute, similar in shape, with denticles between them; teeth 5–8 forming an apical fork, with 5 and 8 large, 6 and 7 small partially confluent denticles (O. balzani complex); face setation lacking erect setae on posterolateral margins of head (present in O. balzani, Octostruma megabalzani, and Octostruma trithrix), a medial pair present on vertex margin (lacking in Octostruma gymnogon); mesosomal dorsum usually lacking a pair of erect setae (present in O. balzani, O. megabalzani, and O. trithrix); metanotal groove usually not impressed in profile view (impressed in O. balzani, O. megabalzani). When sympatric with O. balzani, O. amrishi is often a lighter red brown.

Queen

Longino (2013) - HW 0.60, HL 0.56, WL 0.73, CI 106 (n=1). Similar in all respects to O. balzani.

Type Material

Longino (2013) - Holotype worker: Suriname, Kasikasima, 27 Mar 1996 (D. Makhan) [repository unknown; see discussion in Bolton et al., 2008] (not examined).

References