Daceton armigerum

Daceton armigerum has been studied extensively by Wheeler & Wheeler (1954, description of larvae), Wilson (1962, ecology and behavior), Blum & Portocarrero (1966, trail pheromone and venom), Hölldobler et al. (1990, chemical communication), Moffet & Tobin (1991, physical castes), Groenenberg (1996, mandibular mode of action), and Bolton (1999, 2000, classification).

Identification
Key to the two Daceton species.

Pronotal humeral spines bifurcate, the anterior tip larger than the posterior one. First gastral tergite without standing hairs (sometimes with very short, appressed hairs). Mesonotum and metanotum divided by a strongly impressed metanotal groove. Inner (masticatory) margin of mandibles with a row of short think setae. . . . . Daceton armigerum

Pronotal humeral spines long and simple. First gastral tergite with suberect to subdecumbent hairs. Mesonotum and metanotum divided by a weakly impressed metanotal groove. Inner (masticatory) margin of mandibles lacking a row of short thick setae. . . . . Daceton boltoni

Distribution
Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Peru, Suriname, Trinidad and Venezuela.

This taxon was described from Brazil.

Habitat
Terra Firma and flooded forests.

Biology
Azorsa & Sosa (2008) - Typically nests in cavities in the branches and trunks of trees previously bored by beetles and other insects. Blum and Portocarrero (1966) and Moffet and Tobin (1991) state that colonies of D. armigerum contain up to 2500 individuals, whereas Wilson (1962) and Hölldobler & Wilson (1990) estimate that colonies contain between 5000 to 10000 workers. Daceton armigerum has a complex continuously polymorphic caste system, in which smaller workers nurse the brood and larger workers hunt, dismember prey items, and defend the nest (Wilson 1962; Oster & Wilson 1978; Hölldobler & Wilson 1990). Wilson (1962) reports that workers of this highly predaceous myrmicine ant hunt individually for a variety of live insects, including flies, grasshoppers, larvae and adults of moths and beetles, and fulgorids. In addition, some workers have been observed tending coccids (Bodkin in Crawley 1916; Brown & Wilson 1960; Wilson 1962). (Refer to Wilson [1962] for further information on the behavior of D. armigerum.) Recently, Yanoviak et al. (2005) found that individuals of D. armigerum show controlled aerial descent behavior. The genus has been considered primitive with respect to other members of the Dacetini (Brown and Wilson 1959; Bolton 1998, 1999, 2000), but a phylogenetic analysis of the tribe is necessary to fully understand the relationships of its constituent species and genera. Current molecular phylogenetic evidence suggests that Dacetini may not be monophyletic (Brady et al. 2006).

Nomenclature

 *  armigerum. Formica armigera Latreille, 1802c: 244, pl. 9, fig. 58 (w.) BRAZIL. Smith, F. 1853: 226 (q.m.); Wheeler, G.C. & Wheeler, J. 1955a: 122 (l.). Combination in Daceton: Perty, 1833: 136. Senior synonym of cordata: Roger, 1862c: 290. See also: Wilson, 1962b: 401; Bolton, 2000: 18; Azorsa & Sosa-Calvo, 2008: 30.
 * cordata. Myrmecia cordata Fabricius, 1804: 425 (w.) CENTRAL AMERICA. Junior synonym of armigerum: Roger, 1862c: 290.

Worker
Azorsa & Sosa (2008) - Measurements (mm): EL 0.44–0.87, GL 1.89–4.50, HL 1.44–4.06, HW 1.58–4.17, ML 0.79–3.32, PL 0.78–1.93, PPL 0.26-0.51, PSL 0.32-1.59, PW 1.38-4.60, SL 0.94-2.77, TL 6.91-17.8, WL 1.70–4.24.

Indexes: CI 102–113, MI 55–88, PI 41–52, PSI 18–39, SI 59–73 (17 measured).

Polymorphic. Head wider than long, heart-shaped. Mandibles linear and elongate, each with an apical fork of two teeth that overlap at full closure, of which the ventral tooth is the largest. Inner (masticatory) margin of mandibles lacking any dentition but with a series of short, thick setae that differ from any other pilosity present on mandibles. Outer margin of mandibles lacking hairs completely or with very short, appressed hairs. Mandibles, in full-face view, somewhat long and narrow [(MW/ML')*100= 25–40]. Palp formula 5,3. Depressions, adjacent to and ventral to the mandibular insertion, deep. Clypeus without standing hairs. Pronotal humeri with acute tubercles. Lateral pronotal spines bifurcate, the anterior tips larger than the posterior ones. Metanotal groove deeply impressed. Mesosoma glabrous. Petiolar node with an anterior-lateral pair of long spines and a pair of small but sharp tubercles, located underneath the anterior-lateral spines. First gastral tergite finely reticulate and devoid of any erect or semi-erect pilosity, sometimes with very short, appressed hairs. Color of head, mesosoma, and metasoma, usually red-brown to red-yellowish, sometimes dark red-brown or rarely bicolored; petiole, postpetiole, and gaster darker than rest of body.

Most of the within-species morphological variation in D. armigerum workers is manifested in the form of the promesonotum and, to a lesser degree, in the forms of the petiole, postpetiole, and gaster. This variation includes: (i) Lateral spines bifurcate, the posterior spine projecting upwards and curving at the tip in major workers, whereas in small or median workers this spine not curving at the tip. In small workers the posterior spine is very short, almost vestigial when viewed in profile, but conspicuous in dorsal view. (ii) Short, simple, and appressed hairs present on the first gastral tergite in some individuals from Brazil and Peru. On other workers, hairs on the first gastral segment are absent. (iii) Humeral spines, in smaller workers, vestigial or present as very low carinae. Median and larger-sized workers with humeral tubercles that are spinose or acute. (iv) The posterior pair of petiolar tubercles reduced, rounded and low in smaller workers, whereas tubercles acute in larger workers. (v) Large workers with posterior promesonotal tubercles truncate and flattened in profile. (vi) Anterior spines of petiole long and diverging with intervening space concave or with intervening space discontinuous. Anterior spines of petiole in smaller workers shorter than in other castes.

Type Material
Azorsa & Sosa (2008): Syntype(?) worker, Brazil (not seen).

Myrmecia cordata. Syntypes, 2 workers, America Meridionali [South America]. (seen)

Myrmecia cordata Fabricius, Syntypes, 2 workers, labeled: “Essequibo [possibly Guyana], Smidt. Mus. de Sehestedt. Armigerum, Latr. [Latreille] Myrmecia cordata, worker, Fabr. [Fabricius].” Deposited in.