Amoimyrmex silvestrii

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Amoimyrmex silvestrii
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Attini
Genus: Amoimyrmex
Species: A. silvestrii
Binomial name
Amoimyrmex silvestrii
(Emery, 1905)

Acromyrmex silvestrii casent0217815 p 1 high.jpg

Acromyrmex silvestrii casent0217815 d 1 high.jpg

Specimen Labels

Found in open and dry habitats of the Chaco and Pampas. The nest entrance is a simple hole in the soil surface, never with a mound or crater, with all vegetation removed from around the perimeter.

Identification

Cristiano, Cardoso and Sandoval (2020) - Workers can be distinguished from congeners by combination of the following features: body reddish‐brown to dark brown with dark brown gaster; pronotum without median pronotal projections, best seen in frontal view; shiny integument covered by rough irregular striae and sparse yellowish non‐decumbent setae, varying in length.

Am. silvestrii can easily be distinguished from the sympatric Amoimyrmex bruchi by its larger size, which is more evident in major workers, absence of median pronotal spines (always present and well developed in Ac. bruchi), head with rounded posterior cephalic corners (laterally sub‐rectangular in bruchi and striatus), less non‐decumbent pilosity, mainly on the metasoma, compared to Am. bruchi, and irregular striae restricted to the antero‐central portion of the first gastral tergite (more broadly distributed in Am. bruchi).

Keys including this Species

Distribution

Latitudinal Distribution Pattern

Latitudinal Range: -16° to -37.12°.

     
North
Temperate
North
Subtropical
Tropical South
Subtropical
South
Temperate

Distribution based on Regional Taxon Lists

Neotropical Region: Argentina (type locality), Uruguay.

Distribution based on AntMaps

AntMapLegend.png

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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Biology

Explore-icon.png Explore Fungus Growing 
For additional details see Fungus growing ants.

A handful of ant species (approx. 275 out of the known 15,000 species) have developed the ability to cultivate fungus within their nests. In most species the fungus is used as the sole food source for the larvae and is an important resource for the adults as well. Additionally, in a limited number of cases, the fungus is used to construct part of the nest structure but is not as a food source.

These fungus-feeding species are limited to North and South America, extending from the pine barrens of New Jersey, United States, in the north (Trachymyrmex septentrionalis) to the cold deserts in Argentina in the south (several species of Acromyrmex). Species that use fungi in nest construction are known from Europe and Africa (a few species in the genera Crematogaster, Lasius).


The details of fungal cultivation are rich and complex. First, a wide variety of materials are used as substrate for fungus cultivating. The so-called lower genera include species that prefer dead vegetation, seeds, flowers, fruits, insect corpses, and feces, which are collected in the vicinity of their nests. The higher genera include non leaf-cutting species that collect mostly fallen leaflets, fruit, and flowers, as well as the leafcutters that collect fresh leaves from shrubs and trees. Second, while the majority of fungi that are farmed by fungus-feeding ants belong to the family Lepiotaceae, mostly the genera Leucoagaricus and Leucocoprinus, other fungi are also involved. Some species utilise fungi in the family Tricholomataceae while a few others cultivate yeast. The fungi used by the higher genera no longer produce spores. Their fungi produce nutritious and swollen hyphal tips (gongylidia) that grow in bundles called staphylae, to specifically feed the ants. Finally, colony size varies tremendously among these ants. Lower taxa mostly live in inconspicuous nests with 100–1000 individuals and relatively small fungus gardens. Higher taxa, in contrast, live in colonies made of 5–10 million ants that live and work within hundreds of interconnected fungus-bearing chambers in huge subterranean nests. Some colonies are so large, they can be seen from satellite photos, measuring up to 600 m3.

Based on these habits, and taking phylogenetic information into consideration, these ants can be divided into six biologically distinct agricultural systems (with a list of genera involved in each category):

Nest Construction

A limited number of species that use fungi in the construction of their nests.

Lower Agriculture

Practiced by species in the majority of fungus-feeding genera, including those thought to retain more primitive features, which cultivate a wide range of fungal species in the tribe Leucocoprineae.

Coral Fungus Agriculture

Practiced by species in the Apterostigma pilosum species-group, which cultivate fungi within the Pterulaceae.

Yeast Agriculture

Practiced by species within the Cyphomyrmex rimosus species-group, which cultivate a distinct clade of leucocoprineaceous fungi derived from the lower attine fungi.

Generalized Higher Agriculture

Practiced by species in several genera of non-leaf-cutting "higher attine" ants, which cultivate a distinct clade of leucocoprineaceous fungi separately derived from the lower attine fungi.

Leaf-Cutter Agriculture

A subdivision of higher attine agriculture practiced by species within several ecologically dominant genera, which cultivate a single highly derived species of higher attine fungus.

Note that the farming habits of Mycetagroicus (4 species) are unknown. Also, while species of Pseudoatta (2 species) are closely related to the fungus-feeding genus Acromyrmex, they are social parasites, living in the nests of their hosts and are not actively involved in fungus growing. ‎

Cristiano, Cardoso and Sandoval (2020) - Occurs in sympatry with Am. bruchi (Brandão 1991; Delabie et al. 2011; Simões‐Gomes et al. 2017), in the Chaco and Pampas and always nests in open and dry habitats. External appearance of nests similar to those of its congeners, never with mounds or craters. The entrances are simple holes in the soil surface with all vegetation removed from around their perimeters. Nest architecture was previously described by Weber as several subterranean chambers connected by tunnels. The fungus gardens are restricted to the deeper chambers, where the fungus is suspended from the ceilings. None of the superficial chambers contain fungus, only workers and brood. Armani and Quirán (2007) suggested that Am. silvestrii (as Ac. striatus) is a generalist species, cutting small quantities of available monocots.

Barrera et al. (2015) studied the diversity of leaf cutting ants along a forest-edge-agriculture habitat gradient. Their study site, in Chaco Serrano of Central Argentina, had forest remnants of various sizes within an agriculture area with wheat, soy and maize. A few colonies of A. silvestrii and Acromyrmex heyeri were found along the forest edge. Acromyrmex crassispinus had the highest occurance (42% of 162 colonies) and was most abundant in the forest interior. Acromyrmex lundii and A. striatus were also present, with the former also found in the forest interior. The latter and Amoimyrmex striatus were the most abundant in the forest edge habitat with A. crassispinus present at a slightly lower density.

Castes

Worker

Cristiano, Cardoso and Sandoval 2020, Figure 14.
Cristiano, Cardoso and Sandoval 2020, Figure 15.

Reproductive Castes

Queen. Cristiano, Cardoso and Sandoval 2020, Figure 16.
Male. Cristiano, Cardoso and Sandoval 2020, Male, Figure 17.

Nomenclature

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

  • silvestrii. Atta (Moellerius) silvestrii Emery, 1905c: 42 (w.) ARGENTINA (Córdoba).
    • Type-material: lectotype worker (by designation of Cristiano, et al. 2020: 662).
    • [Note: original description implies more than one syntype present.]
    • Type-locality: Argentina: Córdoba, La Carlota (F. Silvestri).
    • Type-depository: MSNG (lectotype).
    • [Also noted as new by Emery, 1906c: 166.]
    • [Misspelled as sylvestrii by Cherrett & Cherrett, 1989: 52.]
    • Forel, 1911c: 292 (q.m.); Santschi 1912e: 530 (q.m.).
    • Combination in Acromyrmex (Moellerius): Forel, 1913l: 236;
    • combination in Amoimyrmex: Cristiano, et al. 2020: 662.
    • Subspecies of striatus: Gallardo, 1916d: 338; Santschi, 1920d: 380.
    • Status as species: Forel, 1911c: 292; Forel, 1912e: 180; Santschi, 1912e: 530; Forel, 1913l: 236; Bruch, 1914: 217; Bruch, 1915: 529; Bruch, 1916: 326; Santschi, 1916e: 389; Bruch, 1923: 198; Emery, 1924d: 351; Santschi, 1925a: 389 (in key); Kempf, 1972a: 16; Zolessi, et al. 1988: 5; Fowler, 1988: 290; Cherrett & Cherrett, 1989: 52; Brandão, 1991: 323; Bolton, 1995b: 57; Cristiano, et al. 2020: 662 (redescription).
    • Distribution: Argentina, Paraguay.

Type Material

Cristiano, Cardoso and Sandoval (2020) - We designate the following syntype (worker) as the lectotype 1☿(Museo Civico di Storia Naturale, Genoa) ‘La Carlota, silvestrii/Atta silvestrii Emery/ANTWEB CASENT0905007’ [image examined]. Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.

Description

Worker

Cristiano, Cardoso and Sandoval (2020) - Range (specimen used for redescription): TL 4.02–8.71 (8.06), HL 0.82–2.00 (1.76), HW 0.92–2.29 (2.09), ML 0.35–0.85 (0.68), SL 0.82–1.82 (1.68), EL 0.16– 0.35 (0.29), WL 1.20–2.85 (2.47), PL 0.26–0.74 (0.68), PW 0.25–0.62 (0.50), PPL 0.22–0.63 (0.56), PPW 0.45–1.00 (0.91), GL 0.98–2.21 (1.91), CI 100.00–133.33 (118.33), MI 31.67–46.77 (38.33), OI 12.66–19.61 (14.08), SI 88.00– 117.65 (95.00) [N = 82].

Head. In full‐face view, posterior cephalic margin medially emarginate. Posterior cephalic corner rounded, with a small and sharp spine directed upwards, rising on the top of head in lateral view, and a small tubercle laterad. Integument covered by rough irregular striae and sparse yellowish non‐decumbent setae, varying in length. Frontal carina, that may be confused with striae, extending to vertex and almost reaching posterior cephalic corner. Mandible with 8–11 teeth (some can be considered denticles, varying in size and position), dorsally glossy, striated and covered by light‐coloured hairs, with larger ones at the masticatory margin. Eye convex, 16–24 ommatidia across largest diameter. Frontal lobe partially covering antennal insertions, with a hook shape. Antennal scrobe absent. Antennal scape slightly surpassing the posterior cephalic margin, less than 1/3 of its length (SI = 88.00–117.65). Colour reddish‐brown. Mesosoma. Pronotum armed with two large lateral pronotal spines and without median pronotal projections, best seen in frontal view. Mesonotum with two lateral mesonotal spines and two posterior mesonotal spines, with similar size and less than half of size of lateral pronotal spines. Propodeum bearing two large sharp spines, moderately larger than lateral pronotal spines. Integument covered by rough irregular striae and sparse non‐decumbent pilosity, reaching up the spines. Legs with conspicuous reticulation, in some cases with coxa and femur darker than the rest of body. Metasoma. Petiolar node with four spine‐like projections directed up and backwards and two lateral longitudinal carinae. Postpetiole node with two small teeth on lateral margins, located in medial portion, projected to the sides and slightly backwards, best seen in dorsal view, and two lateral longitudinal carinae. Dorso‐posterior region of node with up to four small tuberculiform projections. Integument of petiole and postpetiole covered by irregular striae and non‐decumbent pilosity. Gaster darker than rest of body with smooth and shiny integument and dense yellowish non‐decumbent setae of two sizes, the longest ones twice the length of short ones. Antero‐central portion of first gastral tergite with irregular striae, discernible in medium magnification (~50×), bearing sometimes a pair of reddish to yellowish spots laterad.

Queen

Cristiano, Cardoso and Sandoval (2020) - TL 9.50–10.70, HL 1.75–1.95, HW 2.25–2.30, ML 0.80–1.00, SL 1.50–1.65, EL 0.35–0.40, WL 2.65–3.25, PL 0.73–0.85, PW 0.65–0.75, PPL 0.65–0.78, PPW 1.05–1.30, GL 2.70–3.10, CI 115.38–131.43, MI 43.24– 54.05, OI 15.56–17.78, SI 81.08–84.61 [N = 10].

Head. In full‐face view, posterior cephalic margin medially emarginate but less accentuated than in worker. Posterior cephalic corner rounded, with a small spine directed upwards and an inconspicuous tubercle directed laterad. Integument covered by rough irregular striae, as in worker. Frontal carina present but shorter than in worker. Eye larger than in worker. Number of ommatidia across largest eye diameter 24– 28. Mandibles with 10 teeth (two can be considered denticles) and very large and sharp apical tooth, four times more prominent than in worker but less striate. Mesosoma. Integument with well‐defined longitudinal irregularstriae, denser and more parallel than in worker, and sparse non‐decumbent pilosity. Scutum in dorsal view with reduced notauli forming a shallow impression. Median mesoscutal line with only anterior portion visible as a slightmark on the integument. Scutellum strongly convex in lateral view, narrowing posteriorly with a trapezoidal outline in dorsal view, bearing two tubercles in the posterior margin. Propodeum with a pair of protruding long spines, directed upwards, in lateral view. Metasoma. Petiole with a well‐developed subpetiolar process armed with a truncated spine. Integument of postpetiole covered by transversestriae. First gastral tergite with two yellowish spots located anterolaterally in dorsal view. Presence of semicircular striae on the first gastral tergite, mainly at the base. Dense yellowish non‐decumbentsetae of two sizesin all gastral tergites, being denser in the apical ones.

Male

Cristiano, Cardoso and Sandoval (2020) - TL 7.80–7.99, HL 1.13–1.16, HW 1.33–1.43, ML 0.50–0.52, SL 1.28–1.31, EL 0.38–0.40, WL 2.50–2.53, PL 0.60–0.62, PW 0.73–0.77, PPL 0.33–0.42, PPW 1.13–1.17, GL 2.70–2.74, CI 122.22–123.27, MI 44.44–44.82, OI 27.27–27.97, SI 112.93–113.33 [N = 8].

Head. In full‐face view subquadrate, posterior cephalic margin straight, without emargination. Posterior cephalic corner rounded with a small spine directed upwards. Integument opaque, reticulated and covered by irregularstriae, denser than in worker and queen. Eye bigger and more convex than worker and queen. Number of ommatidia across largest eye diameter 34–35. Mandibles elongate with two well‐developed teeth at apex and some sparse denticles along the internal margin. Mesosoma. Scutellum convex, less so than in queen in lateral view, narrowing posteriorly with a trapezoidal outline in dorsal view, bearing two tuberculiform denticles on posterior margin. Propodeum with a pair of protruding long spines, directed backwards, in lateral view. Integument with well‐defined longitudinal and parallel striae, non‐decumbent pilosity in scutum. Fine decumbent pilosity scarce on pronotum and denser at the base of propodeal spines. Metasoma. Petiole with short peduncle, subpetiolar process smaller than in queen and not forming a spine. Postpetiolar process well developed, larger than in queen. Integument of petiole and postpetiole with scarce irregular striae. Gaster with smooth and shiny integument, without tubercles and striae. Non‐decumbent pilosity less dense and shorter than in queen.

Karyotype

  • 2n = 22, karyotype = 20M+2SM (Argentina) (Micolino et al., 2021).

References

References based on Global Ant Biodiversity Informatics

  • Bruch C. 1914. Catálogo sistemático de los formícidos argentinos. Revista del Museo de La Plata 19: 211-234.
  • Bruch C. 1915. Suplemento al catálogo de los formícidos argentinos. I. (Addenda et corrigenda). Revista del Museo de La Plata 19: 527-537.
  • Bruch C. 1916. Contribución al estudio de las hormigas de la provincia de San Luis. Revista del Museo de La Plata 23: 291-357.
  • Cuezzo, F. 1998. Formicidae. Chapter 42 in Morrone J.J., and S. Coscaron (dirs) Biodiversidad de artropodos argentinos: una perspectiva biotaxonomica Ediciones Sur, La Plata. Pages 452-462.
  • Culebra Mason S., C. Sgarbi, J. Chila Covachina, J. M. Pena, N. Dubrovsky Berensztein, C. Margaria, and M. Ricci. 2017. Acromyrmex Mayr (Hymenoptera: Formicidae: Myrmicinae): species distribution patterns in the province of Buenos Aires, Argentina. Rev. Mus. Argentino Cienc. Nat. 19(2) 185-199.
  • Fernández, F. and S. Sendoya. 2004. Lista de las hormigas neotropicales. Biota Colombiana Volume 5, Number 1.
  • Forel A. 1912. Formicides néotropiques. Part II. 3me sous-famille Myrmicinae Lep. (Attini, Dacetii, Cryptocerini). Mémoires de la Société Entomologique de Belgique. 19: 179-209.
  • Forel A. 1913. Fourmis d'Argentine, du Brésil, du Guatémala & de Cuba reçues de M. M. Bruch, Prof. v. Ihering, Mlle Baez, M. Peper et M. Rovereto. Bulletin de la Société Vaudoise des Sciences Naturelles. 49: 203-250.
  • Gallardo A. 1916. Notes systématiques et éthologiques sur les fourmis attines de la République Argentine. Anales del Museo Nacional de Historia Natural de Buenos Aires 28: 317-344.
  • Kempf, W.W. 1972. Catalago abreviado das formigas da regiao Neotropical (Hym. Formicidae) Studia Entomologica 15(1-4).
  • Marcus H. 1945. La diferencia en la fauna de las hormigas de Cochabamba y Liriuni. Revista de Agricultura 3: 28-29.
  • Santschi F. 1912. Quelques fourmis de l'Amérique australe. Revue Suisse de Zoologie 20: 519-534.
  • Santschi F. 1925. Revision du genre Acromyrmex Mayr. Revue Suisse de Zoologie 31: 355-398.
  • Vittar, F. 2008. Hormigas (Hymenoptera: Formicidae) de la Mesopotamia Argentina. INSUGEO Miscelania 17(2):447-466
  • Vittar, F., and F. Cuezzo. "Hormigas (Hymenoptera: Formicidae) de la provincia de Santa Fe, Argentina." Revista de la Sociedad Entomológica Argentina (versión On-line ISSN 1851-7471) 67, no. 1-2 (2008).
  • Zolessi L. C. de, Y. P. Abenante, and M. E. de Philippi. 1988. Lista sistematica de las especies de Formicidos del Uruguay. Comun. Zool. Mus. Hist. Nat. Montev. 11: 1-9.
  • Zolessi L. C. de; Y. P. de Abenante, and M. E. Philippi. 1989. Catálogo sistemático de las especies de Formícidos del Uruguay (Hymenoptera: Formicidae). Montevideo: ORCYT Unesco, 40 + ix pp.
  • de Zolessi, L.C., Y.P. de Abenante and M.E. Philippi. 1987. Lista sistemática de las especies de formícidos del Uruguay. Comunicaciones Zoologicas del Museo de Historia Natural de Montevideo 11(165):1-9