Key to Costa Rica Azteca workers

This worker key is based on: [[Media:Longino J 2007.pdf|Longino, J.T. 2007. A taxonomic review of the genus Azteca in Costa Rica and a global revision of the aurita group. Zootaxa. 1491:1-63. PDF]]

The workers of Azteca nanogyna and Azteca quadraticeps are unknown.

Identifying Azteca species from the morphological traits of individual workers is difficult. Colonies show strong size variation among workers (Wheeler 1986), and the size of the largest workers increases as colonies mature. The larger a worker is, the more queen-like it is and the more differentiable from other species. The following key is most likely to work when a series from a mature colony is available, so that the largest workers can be selected for examination. When size ranges are given in the key, they refer to these larger workers.

Queens of Azteca generally exhibit more pronounced morphological differences and are often much more useful than workers for species identification. Details of the nests collections are made from, e.g., location, structure, etc. can also be useful. There is a Key to Costa Rica Azteca queens. Nesting details can be found on many of the species pages linked to from this key.

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Azteca

1

 * Middle and hind tibia lacking apical spur; anterior margin of clypeus strongly convex, median lobe protruding further than lateral lobes (HLB/HLA > 1.04), Fig. 3: pilosula and schimperi); palpal formula 4,3 (aurita group) . . . . . 2


 * Middle and hind tibia with distinct, pectinate apical spur; median lobe of clypeus not protruding, subparallel with lateral clypeal lobes (HLB/HLA < 1.01); palpal formula 5,3 or 6,4 . . . . . 3

2
return to couplet #1
 * Dorsal surface of mandible smooth, not striate; posterolateral margin of vertex evenly rounded (Fig. 3); sternal lobe of petiole with sharp, longitudinal carina . . . . . Azteca schimperi


 * Dorsal surface of mandible striate; posterolateral margin of vertex subangular (Fig. 3); sternal lobe of petiole longitudinally tectiform but not carinate . . . . . Azteca pilosula

3
return to couplet #1
 * Outer surface of hind tibia completely devoid of erect setae, rarely with 1 or 2 short setae on largest workers; palpal formula 5,3 . . . . . 4


 * Outer surface of hind tibia with 5 or more erect setae (these may be very short, less than a quarter of tibial width, and difficult to see); palpal formula 5,3 or 6,4 . . . . . 8

4
return to couplet #3
 * Promesonotum strongly produced, bulging, dropping steeply to flat dorsal face of propodeum (Fig. 7) . . . . . Azteca chartifex


 * Promesonotum less strongly produced, posterior mesonotum more shallowly sloping and meeting dorsal face of propodeum at more obtuse angle . . . . . 5

5
return to couplet #4
 * Dorsal surface of mandible largely smooth with small non-setose puncta, setigerous puncta restricted to masticatory margin (Fig. 1F) . . . . . 6


 * Dorsal surface of mandible evenly covered with large setigerous puncta (Fig. 1G) . . . . . 7

6
return to couplet #5
 * Dorsum of mesosoma with a relatively “clean” look, with relatively few erect setae, these of relatively uniform length (MNSC 2–17, median 8, Fig. 7) . . . . . Azteca alfari


 * Dorsum of mesosoma more "scruffy," with more setae, and these of irregular length (MNSC > 10, median about 20, Fig. 7) . . . . . Azteca ovaticeps

7
return to couplet #5
 * Dorsal face of propodeum with moderately abundant erect setae; SI > 50; HW of larger workers often > 1.1mm; basal half or more of mandible microalveolate, dull . . . . Azteca forelii


 * Dorsal face of propodeum devoid of erect setae; SI < 50; HW of larger workers usually < 1.0mm; entire mandible generally smooth and shiny on interspaces between puncta . . . . . Azteca brevis

8
return to couplet #3
 * Palpal formula 6,4; color yellow; dorsal face of propodeum and metanotal groove together form a single flat "shelf" that abruptly meets rising posterior mesonotum (Fig. 7); obligate Cecropia inhabitant . . . . . Azteca coeruleipennis


 * Palpal formula 5,3 or 6,4; color various; dorsal face of propodeum and mesonotum forming two convexities that meet at impressed metanotal groove (e.g., Fig. 7, sericeasur worker); nesting habits various . . . . . 9

9
return to couplet #8
 * Palpal formula 5,3; mostly species (with the exception of A. tonduzi) nesting in myrmecophytes (Cecropia, Cordia, Triplaris) or narrow-gauge live stems of various plant species, with foraging restricted to the hostplant stem interiors or surfaces . . . . . 10


 * Palpal formula 6,4; species nesting in large plant cavities or ant gardens, with conspicuous and generalized surface foragers . . . . . 17

10
return to couplet #9
 * Head relatively broad, CI > 86; obligate Cecropia inhabitants or nesting in dead stems . . . . . 11


 * Head relatively narrow, CI < 90; inhabitants of live stems but not obligate Cecropia specialists . . . . . 13

11
return to couplet #10
 * Setae on metatibia sparse and short, MTSC 10–20, length of setae one fourth to one third maximum width of tibia; HW of larger workers < 0.91mm; nests in dead stems often augmented with carton nests . . . . . Azteca tonduzi


 * Setae on metatibia abundant and longer, MTSC > 20, length of setae one half or more maximum width of tibia; HW of larger workers > 1.10mm; obligate inhabitants of Cecropia . . . . . 12

12
return to couplet #11
 * Petiole in profile with node more massive than sternal lobe, perpendicular distance from tergosternal suture to apex of node greater than or equal to distance to ventral margin of sternal lobe (Fig. 7); face with mottled coloration, light brown to orange with variable extent of medial infuscation (Fig. 3) . . . . . Azteca xanthochroa


 * Petiole in profile with node less massive than sternal lobe, perpendicular distance from tergosternal suture to apex of node less than distance to ventral margin of sternal lobe (Fig. 7); face uniformly brown (Fig. 3) . . . . . Azteca constructor

13
return to couplet #10
 * Most of dorsal surface of mandible covered with large piligerous puncta, mandibles appearing bristly (Fig. 1G); nesting in live stems of multiple plant species, not obligate inhabitant of Cordia or Triplaris . . . . . Azteca nigricans


 * Dorsal surface of mandible with large piligerous puncta, if present, restricted to masticatory margin and apex, mandibles not appearing bristly (Fig. 1F); nesting habits various, including obligate inhabitants of Cordia and Triplaris . . . . . 14

14
return to couplet #13
 * Setae on metatibia few and short, MTSC usually about 5, setae about as long as one quarter width of tibia; propodeum with cluster of about 4 setae where dorsal face rounds into posterior face, 0–4 setae anterior of this cluster on dorsal face, these setae short, 1–2 times width of propodeal spiracle; largest workers with HW > 1.0mm . . . . . 15


 * Setae on metatibia more abundant and longer, MTSC 8–17, setae about as long as half width of tibia; dorsal face of propodeum with 4 or more setae, these setae long, > 4 times width of propodeal spiracle; largest workers with HW < 1.0mm . . . . . 16

15
return to couplet #14
 * Face of largest workers yellow; dorsal surface of mandible with interspaces between puncta largely smooth and shining, at most basal third of mandible shagreened; posterior margin of sternal lobe of petiole with a layer of dense, short, pubescence-like pilosity and 2–4 longer setae; opportunistic inhabitant of multiple ant plants and live stems of non-myrmecophytes . . . . . Azteca beltii


 * Face of largest workers brown; dorsal surface of mandible with interspaces between puncta shagreened on basal half or more; posterior margin of sternal lobe of petiole with cluster of erect setae of even length; obligate inhabitant of Cordia alliodora . . . . . Azteca oecocordia

16
return to couplet #14
 * Head relatively broader (CI 78–91); obligate inhabitant of Cordia alliodora (or understory Lauraceae) . . . . . Azteca pittieri


 * Head relatively narrower (CI 73–81); obligate inhabitant of Triplaris melaenodendron . . . . . Azteca longiceps

17
return to couplet #9
 * Mandibles opaque, densely microalveolate/punctate, substriate; posteroventral margin of petiole with abundant long coarse setae, shorter pubescence layer much less conspicuous than long setae (Fig. 7); majors very large (HW up to 2.2mm); nests in hollow trunks of large, live trees, with nest entrance a fissure at the base of the tree . . . . . Azteca instabilis


 * Mandibles shiny to weakly sculptured; largest workers typically smaller, HW < 1.8mm; nesting habits various (the workers of the following species are highly variable and I have not been able to discover diagnostic characters that always differentiate them; the following key couplets reflect average differences among species, but I have examined many worker series in this complex that I could not place) . . . . . 18

18
return to couplet #17
 * Gastral dorsum bright yellow, sharply contrasting with dark brown petiole and mesosoma; measurements as in Figs. 6E, F (data plots in Longino 2007) . . . . . Azteca flavigaster


 * Gastral dorsum dark brown, or, if light yellow brown, petiole and mesosoma are lighter brown as well, gastral color not sharply contrasting with mesosoma color . . . . . 19

19
return to couplet #18
 * Head relatively broad (Fig. 3, 6E, CI 101–109); scape relatively short (SI 70–85); face usually uniformly dark brown (lighter orange brown in one series); setae on posterior margin of vertex usually long, subequal in length to eye length; forms ant gardens . . . . . Azteca gnava


 * Head relatively narrower; scape relatively longer; face color various but often a mixture of light and dark brown; setae on vertex margin usually shorter than eye length; nesting habits various . . . . . 20

20
return to couplet #19
 * Largest workers with HW usually > 1.2mm; general body coloration often light orange brown; head shape often strongly cordate (Fig. 3) . . . . . Azteca sericeasur


 * Largest workers with HW usually < 1.2mm; general coloration often dark brown with light orange brown restricted to anterior and lateral portions of head; head shape often less strongly cordate (Fig. 3: velox and nigra) . . . . . 21

21
return to couplet #20
 * Scape relatively short (SI 78–89); nests in plant cavities . . . . . Azteca velox


 * Scape relatively longer (SI 84–105); nests in ant gardens . . . . . Azteca nigra