Atta sexdens

Distribution based on Regional Taxon Lists
Neotropical Region: Argentina, Bolivia, Brazil, Colombia, Costa Rica, Ecuador, French Guiana, Guyana, Panama, Paraguay, Peru, Suriname, Uruguay, Venezuela.

Biology
Travaglin et al. 2015 (Abstract): Foraging behavior of leaf cutting ants: How do workers search for their food? Forager ants search for adequate food sources in nature and, after their discovery, they decide whether the source is suitable or not for the colony. However, we asked “How do workers seek out the substrate for cultivation of the symbiontic fungus on which they feed? To answer this question, we evaluated the distance traveled by individual workers in the search of food and the distance traveled to return to the nest, as well as the time and velocity necessary for these activities. The results showed that the distance traveled by the leaf cutting ant, Atta sexdens rubropilosa, in the search of food was greater than the distance traveled to return with the substrate to the colony. On the other hand, the mean time and velocity were similar for food search and return to the colony. These results support the hypothesis of information transfer, according to which the worker needs to return to the nest at the beginning of foraging to transfer information to other workers and thus to establish the process of worker ant foraging. It can be concluded that workers travel large distances in a random manner until finding their substrate, but the return to the nest is efficient considering the shorter distance traveled.

Viera et al. (2015) - Queens of leaf-cutting ants found their nests singly, each consisting of a vertical tunnel and a final horizontal chamber. Because of the claustral mode of nest founding, the queen and/or her initial fungus garden are exposed to threats imposed by several soil pathogens, and the antibiotic secretions produced by their metapleural glands are considered a main adaptation to deal with them. Nests of two Atta leafcutting ant species, Atta vollenweideri and Atta sexdens rubropilosa, occur in different soil types, alfisols and oxisols. Their queens are known to excavate the initial nest in different soil horizons, clayish and organic, respectively, which differ in their fertility and associated microbiota. The results revealed that metapleural glands of A. sexdens rubropilosa have a larger number of secretory cells, and consequently a higher production of antibiotic secretions, which may have been selected to allow nest founding at the superficial horizon of oxisols rich in organic matter and microorganisms. Glands of A. vollenweideri, on the contrary, presented fewer secretory cells, suggesting less production of antibiotic secretions. We argue that the excavation of deep founding nests in A. vollenweideri was primarily selected for during evolution to avoid the risk posed by flooding, and further hypothesize that a reduced number of cells in their metapleural glands occurred because of a weak pathogen-driven selective pressure at the preferred soil depth.

Dambros et al. (2018) - Atta sexdens was collected via arboreal fogging in an inundated northern Pantanal (Mato Grasso, Brazil) cambarazal forest. The seasonally flooded forest was dominated by Vochysia divergens Pohl. (Vochysiaceae). This presumably soil/ground dwelling A. sexdens was putatively driven into the trees by the seasonally high water.

Dijkstra and Boomsma (2006) investigated the viability of worker produced eggs in Atta cephalotes, Atta sexdens and Atta colombica. Most Atta workers have rudimentary, non-functional ovaries in a queenright colony but a few, typically tending the queen, can produce trophic eggs (Dijkstra et al., 2005). These eggs are feed to the queen. It was not known if any worker eggs can produce males. No Atta sexdens eggs developed into males. They found Atta workers are not completely infertile, as a few males were found in experimentally orphaned A. colombica colonies, but worker fertility is very low. They hypothesize that worker reproduction in orphaned Atta field colonies is almost never successful because the last workers die before their sons can be raised to adulthood, but the importance of worker-laid trophic eggs for queen feeding has precluded the evolutionary loss of worker ovaries.

Association with Other Organisms

 * Eidmann (1937) - The springtail species Seira edmanni (Stach) (Seiridae) is known from nests of this ant.

Nomenclature

 *  sexdens. Formica sexdens Linnaeus, 1758: 581 (w) "America meridionali". Mayr, 1865: 82 (q.m.); Wheeler, G.C. 1949: 681 (l.). Combination in Atta: Fabricius, 1804: 422; in Atta (Neoatta): Gonçalves, 1942: 349. Senior synonym of sexdentata: Latreille, 1802a: 228; of abdominalis, coptophylla: Mayr, 1865: 80; of flavicornis: Forel, 1905b: 161; of autuorii, fuscata, piriventris (and its junior synonym lugens), and rubropilosa: Borgmeier, 1959b: 359.
 * flavicornis. Formica flavicornis Fabricius, 1789: 280 (q.) SURINAM. Junior synonym of sexdens: Forel, 1905b: 161.
 * sexdentata. Formica sexdentata Latreille, 1802a: 228, pl. 9, figs. 59, 60 (w.) FRENCH GUIANA. Junior synonym of sexdens: Latreille, 1802a: 228.
 * coptophylla. Atta coptophylla Guérin-Méneville, 1844a: 422 (w.) BRAZIL. Junior synonym of sexdens: Mayr, 1865: 80.
 * abdominalis. Oecodoma abdominalis Smith, F. 1858b: 184, pl. 10, fig. 22 (q.) no locality given ("various parts of South America"). Combination in Atta: Roger, 1863b: 35. Junior synonym of sexdens: Mayr, 1865: 80.
 * rubropilosa. Atta sexdens var. rubropilosa Forel, 1908c: 348 (w.q.m.) BRAZIL. Subspecies of sexdens: Santschi, 1929f: 93; Borgmeier, 1939: 422; Gonçalves, 1947a: 187. Junior synonym of sexdens: Borgmeier, 1959b: 359.
 * piriventris. Atta vollenweideri var. piriventris Santschi, 1919f: 50 (w.) ARGENTINA. Subspecies of sexdens and senior synonym of lugens: Gonçalves, 1942: 351. Junior synonym of sexdens: Borgmeier, 1959b: 359.
 * fuscata. Atta sexdens var. fuscata Santschi, 1922b: 362 (w.) BOLIVIA. Subspecies of sexdens: Gonçalves, 1942: 350. Junior synonym of sexdens: Borgmeier, 1959b: 359.
 * lugens. Atta vollenweideri var. lugens Borgmeier, 1939: 424, fig. 19 (w.) BRAZIL. Junior synonym of piriventris: Gonçalves, 1942: 351.
 * autuorii. Atta (Neoatta) sexdens subsp. autuorii Borgmeier, 1950d: 253, figs. 32-34 (w.q.m.) BRAZIL. Junior synonym of sexdens: Borgmeier, 1959b: 359.

Taxonomic Notes
Gusmao et al. (2001) treat Atta sexdens rubropilosa as a subspecies of A. sexdans rather than as a synonym, but provide no justification for this change and their proposal is not followed here.