Azteca

All known species are arboreal, nesting in living or dead wood, or external carton nests. Some species exhibit obligate associations with myrmecophytes, especially of the genus Cecropia. Feeding habits are generalized with foraging occurring both arboreally and on the ground. The species level taxonomy of this genus is in need of revision, with the exception of a few modern treatments that have carefully delineated numerous species within species groups or from specific areas. Workers tend to have few distinguishing characters. Queens are more distinctive, so much so that species are now described and identified from the queens rather than workers. Unfortunately collecting a queen can be an onerous task..many species are very aggressive when their nests are disturbed. Dejean et al. (2018) found these territorially-dominant arboreal-ant species inhabited slightly more than half of the tree canopies they sampled in an Amazonian forest.

Identification
Queens are typically better for identifying Azteca species than the workers. See the caste and nomenclature sections below for more information about queen/worker morphology and species delineation problems within the genus. Longino (2007) - The taxonomic bounds of the genus have not changed since its inception (Forel 1878, Shattuck 1992). Members of the genus can be recognized by the combination of (1) a thin, somewhat flexible cuticle, (2) anterolateral margins of clypeus extending anterior to mediolateral regions (with the exception of the aurita group, as reported here), (3) mandible with 7–9 teeth, (4) at least larger workers with cordate head shape, with margin of vertex concave, (5) surface sculpture (other than on mandibles) smooth, micropunctate, microalveolate, or combinations of these, (6) the total absence of coarse surface elements such as spines, tubercles, carinae, rugae, striations, or large puncta, (7) a distinctive petiole which is strongly sloping anteriorly and has a rounded posteroventral lobe, and (8) worker caste polymorphism.

The Asian genus Philidris (former Iridomyrmex cordatus group) is highly convergent with Azteca. In contrast to Azteca, the anterolateral margins of the clypeus are posterior to the mediolateral portions, and the mandible has 10–12 teeth. Male characters (Shattuck 1992) and recent molecular evidence (P. S. Ward, pers. com.) ally Philidris with other Asian dolichoderines and confirm that the similarity is due to convergence.

Shattuck (1992) - Worker: Polymorphic, majors with ocelli; anterolateral clypeal margin with the corners expanded anterior of the mediolateral region; vertex concave; petiolar scale strongly inclined anteriorly, and with a distinct ventral node; dorsal face of propodeum longer than declivitous face; mandible with 7-9 teeth and no denticles, and with the apical tooth subequal in size to the subapical; metanotal groove forming a distinct angle between the mesonotum and propodeum. Central and South America. Queen: Propodeal angle indistinct; petiolar scale strongly inclined anteriorly and with the anterior face much shorter than the posterior face; venter of petiole with a well developed, rounded lobe; wing with one closed cubital cell. Male: Second funicular segment barrel-shaped; petiolar scale with a blunt angle or a single tooth or projection dorsally; pygostyles vestigial; mandible with 1 to 4 teeth and 0 to about 3 denticles; first gastral segment vertical (not concealing the petiole in dorsal view), and with a groove or indentation for the reception of the entire height of the petiole.

The worker caste can generally be recognized in the field by its cordate-shaped head, large foraging columns and habit of running with the gaster raised. Azteca workers are most similar to those of the Old World genus Anonychomyrma, but are separable based on the presence of ocelli in larger workers (ocelli are also present in one species of Anonychomyrma), a smaller subapical mandibular tooth, a strongly anteriorly inclined petiolar node, and a polymorphic worker caste. Additionally, the Azteca proventriculus is distinct in having the copula excised laterally, without phragma, and only slightly broader than the bulb; the bulb being exposed in lateral view; and the presence of an occlusory tract.

Species by Region
Number of species within biogeographic regions, along with the total number of species for each region.

Fossils
Fossils are known from:.

Biology
Longino (2007) - The dolichoderine genus Azteca is a strictly neotropical group of arboreal ants (Emery 1893, Forel 1928). They are abundant in lowland habitats from Mexico to Argentina, occurring as both generalized foragers and as specialized inhabitants of myrmecophytic plants. Azteca species exhibit a variety of nesting habits, including the construction of carton nests, the occupation of live and dead plant stems (Forel 1899, Ule 1901, Emery 1913, Davidson 1988, Ayala et al. 1996), and the formation of ant gardens. Ant gardens are arboreal ant nests which sprout epiphytes from carton nest material (Ule 1901, Wheeler 1921, Longino 1986, Davidson 1988, Corbara et al. 1999, Kaufmann & Maschwitz 2006). Striking cases of symbiosis occur between Azteca and highly specialized myrmecophytic plants, the most notable case being the relationship between Azteca and Cecropia (Müller 1876, 1880–1881, Bequaert 1922, Wheeler 1942, Benson 1985, Longino 1991a, b). Also, Azteca ants have developed complex trophic relationships with many species of coccoid Hemiptera (Wheeler 1942, Johnson et al. 2001, Davidson et al. 2003). Azteca workers are often found tending mealy bugs (Pseudococcidae) and soft scales (Coccidae). For Azteca species that nest in live stems, the interior walls of the nest are often encrusted with mealy bugs and scales. Species building carton nests and ant gardens maintain dense populations of mealybugs and scales under the carton of the main nest or under small carton “pavilions” scattered over the vegetation. Very little attention has been paid to the taxonomic diversity of Coccoidea associated with Azteca, and usually only cursory observations of their presence are made during field collections. Because of the richness of the ecological interactions among Azteca, plants, and hemipteran symbionts, Azteca species have been and will continue to be subjects in the study of adaptation and coevolution, and therefore taxonomic work on the genus is particularly important.

Correlated with sharp differences in queen morphology are distinctive nesting habits. Nesting habits show great interspecific variation and little intraspecific variation. For example, queens of Cecropia-inhabiting species colonize very young Cecropia saplings. These queens are often very abundant in the environment, colonizing saplings and apparently competing for domination of saplings (Longino 1989b). I have made extensive collections of neotropical arboreal ants by breaking live and dead branches, searching for carton nests and ant gardens, and dissecting other myrmecophytes such as Cordia, Acacia, Triplaris, Tococa, and Ocotea. The Azteca species which dominate Cecropia trees are found only in Cecropia trees. In spite of high queen density and competition for saplings, I have never encountered one of these Azteca species, either colonies or founding queens, in any plant cavity other than that of a Cecropia. Thus, when only workers are available, biological data on nest site can be of critical diagnostic importance.

A further dimension in the interaction between Azteca and Cecropia involves the cultivation of an Ascomycete (chaetothyriales) fungus by colony-founding queens (Mayer et al. 2018). Four Azteca species inhabiting three different Cecropia were investigated. Out of two possible scenarios of fungus recruitment (random infection through spores/hyphae from the environment, or transmission from mother to daughter colonies), dissection of the infrabuccal pocket in the heads showed that dispersing winged queens carry hyphal fragments from their mother colony. After entering the domatia of Cecropia, foundress queens scrape parenchyma from the inner wall, seal the entrance and produce small piles of it. This parenchyma is free of fungi, but after contact with the ant queens, the parenchyma piles contain fungal hyphae. Founding queens lay their eggs, and they do not feed on fungal material but feed it to the larvae. These findings suggest that fungiculture may be crucial for successful colony founding of arboreal ants in the tropics.

Castes
Longino (2007) - Wheeler and Bequaert (1929) stated “Apparently the females [i.e., queens] furnish more reliable characters for identification than the workers in the genus Azteca.” An analogy can be drawn between the taxonomy of Azteca and the taxonomy of many plants. Botanists typically shun sterile material because it is often more plastic within species and less differentiated between species than reproductive material. Such is the case in Azteca. Workers are polymorphic within colonies, and colonies exhibit prolonged ontogenetic changes in worker morphology (pers. obs.). In contrast, queens are much less variable morphologically and exhibit strong interspecific differences. Within a single locality, species with strongly differentiated queens may have workers that are barely distinguishable.

Worker Morphology
These characters are collated in the Worker Morphology table.

Nomenclature

 *  AZTECA [Dolichoderinae: Leptomyrmecini]
 * Azteca Forel, 1878: 384. Type-species: Liometopum xanthochroum, by monotypy.
 * [Type-species not Tapinoma instabilis, unjustified subsequent designation (based on inaccurate synonymy) by Wheeler, W.M. 1911f: 159. Type-species not Azteca muelleri, unjustified subsequent designation by Emery, 1913a: 31; repeated in Wheeler, W.M. 1913a: 78.]
 * [ Aztecum Bertkau, 1879: 13, incorrect subsequent spelling.]

Longino (2007) - The relative clarity of the generic status of Azteca is not mirrored in species-level taxonomy. Several factors contribute to taxonomic confusion in Azteca, some historical, some biological. The only revision of the genus Azteca is that of Emery (1893). Over 140 species-group names were subsequently published by Forel, Wheeler, and others, with no attempts at revision. Many species were described from workers only, with no biological data. Since it is often particularly difficult to separate Azteca species with workers only (Longino 1991a, b, 1996), many named Azteca species are difficult to circumscribe.

Because of the unreliability of worker morphology, many names in Azteca may remain in nomenclatural limbo indefinitely. Identities of species based solely on a type series of workers, with no data on queen morphology or nesting behavior, will only be resolved by a thorough understanding of the subtle differences between workers of all the species at the type locality

Description
Shattuck (1992):

Worker
HEAD. Vertex weakly to strongly concave. Compound eyes present, approximately round; relatively anterior on head. Ocelli present (in majors). Antennae 12 segmented. Scape short, at most surpassing the vertex by less than one- third its length. Anterolateral clypeal margin even with the mediolateral region and commonly with the corners expanded slightly anterior of the mediolateral region. Anteromedial clypeal margin entire, without a central notch or concavity of any type. Anterior clypeal setae 6-14; short, less than twice the maximum scape diameter; straight. Posterior clypeal margin between the anterior and posterior surfaces of the antennal socket cavities. Anterior tentorial pit nearer the antennal socket than the mandibular insertion. Frontal carina present. Anterolateral hypostoma reduced to a thin sclerite. Medial hypostoma entire. Psammophore absent. MOUTHPARTS. Palp formula 6:4,5:3,4:3 or 4:2 (rarely 5:3 partly fused into 4:3). Third maxillary palp segment subequal in length to segment 4. Fifth maxillary palp segment at the apical extreme of segment 4. Mandible with 7-9 teeth and no denticles. Apical tooth subequal in length to the subapical tooth. Basal angle distinct, with a well developed tooth or angle separating the masticatory and basal margins. Basal margin varying from smooth (without teeth or denticles) to denticulate along entire surface. MESOSOMA. Posteroventral pronotum lateral, rounded or angled. Mesopleural process absent. Anteromedial mesosternum even with the lateral regions. Declivitous face of propodeum convex; dorsal face flat or convex, longer than the declivitous face. Propodeal angle indistinct to moderately distinct. Mesosomal spines and tooth absent. Erect pronotal hairs 4-20 (rarely absent); when present elongate, much longer than the maximum scape width. Dorsal pro-mesonotal junction with the pronotum and mesonotum even, or with the mesonotum above the pronotum. Metanotal groove forming a distinct angle between the mesonotum and propodeum. Metanotal spiracle dorsal and lying on the dorsal surface when viewed in lateral profile. Propodeal spiracle lateral and ventral of the propodeal dorsum (sometimes appearing dorsal because of reduction of dorsal propodeum). Hind tibial spur with well developed barbules along entire inner surface (except extreme base). PETIOLE. Scale present; ridged and with a distinct angle dorsally; strongly inclined anteriorly and with the anterior face much shorter than the posterior face. Venter with a well developed lobe. GASTER.• First tergite vertical and not concealing the petiole in dorsal view and with a groove or indentation for the reception ofthe basal portion ofthe petiole. Anteriortergosternal suture ofthe first segment extending laterally from the helcium, without or with at most a very weak dorsal arch. Fifth tergite ventral, gaster with 4 apparent tergites. Gastral compression lateral, dorsoventral, or absent (gaster circular in cross section). Fourth sternite keel-shaped posteriorly. GENERAL CHARACTERS. Worker caste polymorphic. Chromosome number unknown. Integument thin and flexible, weakly sculptured. PROVENTRICULUS. Cupola slightly broader than bulb; excised; with short pile; smooth, without sculpture; and without phragma. Bulb exposed in lateral view. Longitudinal muscle No.1 present. Occlusory tract present.

Queen
HEAD. Vertex weakly convex to weakly concave. Compound eyes relatively anterior on head. Antennae 12 segmented. Scape short, surpassing the vertex by less than one-half scape length. Anterolateral clypeal margin even with the mediolateral region, or occasionally with the corners expanded slightly anterior of the mediolateral region. Anteromedial clypeal margin entire, without a central notch or concavity of any type. Anterior clypeal setae 8-10; short, less than twice the maximum scape diameter; straight. Posterior clypeal margin between the anterior and posterior surfaces of the antennal socket cavities. Anterior tentorial pit nearer the antennal socket than the mandibular insertion. Anterolateral hypostoma reduced to a thin sclerite. Medial hypostoma entire. Psammophore absent. MOUTHPARTS. Palp formula 6:4 or 4:3 (and possibly others, see worker description). Third maxillary palp segment (when present) subequal in length to segment 4. Fifth maxillary palp segment (when present) at the apical extreme of segment 4. Mandible with 7-8 teeth and 0-1 denticles. Apical tooth subequal in length to, to slightly longer than, the subapical tooth. Basal angle distinct, with a well developed tooth or angle separating the masticatory and basal margins. Basal margin varying from smooth (without teeth or denticles) to denticulate along entire surface. MESOSOMA. Posteroventral pronotum lateral, rounded or angled. Episternal suture complete. Mesopleural process absent. Anteromedial mesosternum even with the lateral regions. Axilla subparallel (very weakly constricted), constricted medially, or absent dorsally; when present, entire. Anterior axillar suture (when present) straight or angular medially. Declivitous face of propodeum convex; dorsal face convex, subequal in length to the declivitous face. Propodeal angle indistinct. Propodeal suture absent. Mesosomal spines and tooth absent. Erect mesoscutal hairs about 16-100; short, less than twice the maximum scape diameter to elongate, more than twice the maximum scape diameter. Propodeal spiracle lateral and ventral ofthe propodeal dorsum. Hind tibial spur with well developed barbules along entire inner surface (except extreme base). WINGS. Radial cell closed. Fore wing with 1 cubital and 1- 2 discoidal cells. Hind wing with 2 cells. PETIOLE. Scale present; ridged and with a distinct angle dorsally; strongly inclined anteriorly and with the anterior face much shorter than the posterior face. Venter with a well developed, rounded lobe. GASTER. First segment vertical and not concealing the petiole in dorsal view and with a groove or indentation for the reception of the entire height of the petiole. Fifth tergite vertical and with the distal terminus of the gaster not well defined. Gastral compression absent (gaster circular in cross section). Fourth sternite flat across entire posterior border.

Male
HEAD. I nner margin of eye entire, flat. Scape length shorter than the length of funicular segments 2+3. First funicular segment barrel-shaped. Second funicular segment barrel-shaped, straight. Funicular segments 2 and 3 at most twice as long as broad. Third and fourth funicular segments straight. Anteromedial clypeal margin entire, without a central notch or concavity of any type. Anterior clypeal setae 4-10; short, about as long as the maximum diameter of the scape; straight. Posterior clypeal margin even with or anterior to the anterior surfaces of the antennal socket cavities. Anterior tentorial pit nearer the antennal socket than the mandibular insertion. Anterolateral hypostoma reduced to a thin sclerite. Medial hypostoma entire. MOUTHPARTS. Palp formula 6:4 or 5:3 (and possibly others, see worker description). Third maxillary palp segment subequal in length to segment 4. Fifth maxillary palp at the apical extreme of segment 4. Mandible with 1-4 teeth and 0 - about 3 denticles. Apical tooth distinct. Basal angle indistinct, with a relatively uninterrupted curve between the two margins and without a distinct tooth or angle. Basal margin smooth and without teeth or denticles. MESOSOMA. Posteroventral pronotum lateral, rounded or angled. Episternal suture present, complete. Anteromedial mesosternum even with the lateral regions. Axilla parallel or constricted medially, and entire. Anterior axillar suture straight. Declivitous face of propodeum convex; dorsal face convex, subequal in length to the declivitous face. Propodeal angle distinct. WINGS. Radial cell closed. Fore wing with 1 cubital and 1-2 discoidal cells. Pterostigmal appendage absent. Hind wing with 2 cells. PETIOLE. Scale present; a blunt angle dorsally, or spined with a single tooth or projection dorsally; vertical and not inclined anteriorly. Venter with a well developed lobe. Attachment to gaster broad. GASTER. First segment vertical and not concealing the petiole in dorsal view and with a groove or indentation for the reception of the entire height of the petiole. GENITALIA. Pygostyles vestigial. Posterior margin of subgenital plate convex or even across entire width. Paramere entire. Digitus linear, without a down-turned tip; tip sometimes slightly swollen. Cusp is absent. Ventral lobe of volsella present as a swelling. Aedeagus with ventral teeth.

Larva
Shape crematogastroid. Protuberances present as 2 bosses located ventrolaterally on prothorax. Body hairs sparse and moderately abundant; simple and hooked; short and elongate. 10 spiracular pairs. Antennae large.