Dolichoderinae, Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Additional images:
Queen, face view (original line drawing, reduced line drawing); mandible (small, large); petiole, lateral view (small, large); petiole, lateral view (second version) (small, large).
Worker, mandible (small, large); tibia (small, large).
Range
Mexico to Costa Rica. Costa Rica: northwestern lowlands.
Identification
Queen
Measurements (n=5): HLA 1.93 (1.74-1.98), HW 1.48 (1.35-1.53,8), SL 0.98 (0.90-1.03,8), CI 77 (75-78), SI 51 (50-53).
Palpal formula 6,4; middle and hind tibia with prominent pectinate apical spur; dorsal surface of mandible faintly microareolate, dull, with sparse small piligerous puncta, setae in puncta short, larger puncta with long setae near masticatory margin; medial and lateral clypeal lobes at about same level (medial lobe not projecting anteriorly); head quadrate, with sides slightly converging posteriorly; petiolar node low, bluntly rounded; posteroventral petiolar lobe evenly convex, shallow, not strongly developed; scape with abundant fine erect setae, about as long as one half maximum width of scape; middle and hind tibia with abundant erect setae, longest of these about as long as maximum width of tibia (MTSC 20-30); sides of head below level of eyes with 1-2 erect setae, sides of head posterior to eyes with 0-2 short erect setae; posterior margin of head with abundant long curved setae; pronotum with abundant long setae on posterior third; mesoscutum, scutellum, and propodeum with abundant setae, those on scutellum and propodeum longer than those on mesoscutum; petiolar node with variable number of long setae on apex, abundant long setae on posteroventral lobe; all gastral terga with abundant erect setae; color dark brown to black.
Worker
Measurements (n=3): HLA 1.00 (0.97-1.08), HW 0.93 (0.91-0.99), SL 0.71 (0.70-0.72), CI 94 (91-94), SI 72 (66-72).
Palpal formula 5,3; middle and hind tibia with prominent pectinate apical spur; dorsal surface of mandible largely smooth and shining, grading to dull, microareolate sculpture at base, with sparse small piligerous puncta, setae in puncta short, larger puncta with long setae near masticatory margin; medial and lateral clypeal lobes at about same level, medial lobe at most weakly projecting beyond lateral lobes; head with convex sides, strongly cordate posterior margin; mesosoma in lateral profile with promesonotum forming a continuous convexity or mesonotum somewhat elevated above pronotum; posterior mesonotum drops abruptly to metanotal groove, dorsal face of propodeum and broad metanotal groove form a flat, step-like junction with posterior mesonotum; scape and tibia with abundant erect setae, length of setae about one half maximum width of scape or tibia, respectively; sides of head with abundant erect setae from mandibular insertions to level of eye, extending variable distance posterior to eye, often leaving posterior portion devoid of setae; posterior margin of head with abundant erect setae; promesonotum with abundant long erect setae; dorsal face of propodeum with no erect setae or with sparse setae that are much shorter than those of promesonotum; color yellow orange.
Similar Species
Among the Cecropia ants, A. coeruleipennis is most easily confused with A. alfari and A. ovaticeps. The presence of tibial setae, the distinctive shape of the mesonotum, and the 6,4 palpal formula will separate A. coeruleipennis from A. alfari and A. ovaticeps.
Natural History
The taxonomy and biology of A. coeruleipennis is reviewed in Longino (1989b, 1991a, b). See also general treatment of the Cecropia-Azteca association in Costa Rica.
Azteca coeruleipennis is an obligate inhabitant of Cecropia trees (Skwarra 1934; Wheeler 1942; Longino 1989). Founding queens are found solely in Cecropia saplings, and large colonies occur in mature Cecropia trees. In Costa Rica, A. coeruleipennis is a common element of the Cecropia-inhabiting ant fauna in dry forest habitats, and exhibits abrupt declines at habitat boundaries (Longino, 1989). It occurs throughout the Guanacaste lowlands south to the central valley and adjacent Pacific coastal areas. Near Monteverde, it is common along the road from the PanAmerican highway and in the San Luis valley, abruptly dropping out at about 900m elevation. In many dry forest areas the only Cecropia species is C. peltata, hence this is the host tree species in which I have most often seen A. coeruleipennis. I have twice encountered colonies in mature C. obtusifolia trees, and I have twice encountered founding queens in C. insignis saplings less than 2m tall.
Pleometrotic founding is rare: I have 22 records of lone foundresses from sapling internodes, and 1 record of 4 foundresses together in an internode.
Mature colonies have a dispersed colony structure. There is no central carton nest. Brood and any alate sexuals are in branch tips. Older parts of the tree are gradually abandoned, and internal passages are not maintained among occupied branches. When a tree is molested bright yellow workers of rather uniform small size issue forth and descend the trunk, where they aggressively attack the intruder (Longino 1991a).
Azteca coeruleipennis may be a tropical dry forest specialist, with adaptations for tolerating prolonged drought. During the dry season, leafy branch tips are perforated by one or two active entrances, often 10 or more internodes back from the terminal sheathing stipule. In contrast, other Azteca species typically maintain five or more active entrances in the terminal 10 internodes (pers. obs.). Occupied branch sections which contain alate queens have active entrances which are only large enough for workers. Larger tunnels are excavated in the internode walls, but these end blindly within a millimeter of surface, as though the final perforation is suspended until wet season and/or the time of flight of new queens. Reduction of the number and size of entrances may be an adaptation for reducing water loss (Longino 1991a).
Comments
Prior to this report I had never investigated palpal formula in Azteca. It was surprising to discover that A. coeruleipennis had a palpal formula of 6,4, while all other Cecropia ants have 5,3. A palpal formula of 6,4 is probably plesiomorphic in the genus, which implies that A. coeruleipennis might be a very old Cecropia ant and sister to all the other Cecropia ants. Perhaps this species has survived the arrival of newer Cecropia ants by being a dry-forest specialist, a habitat that is marginal for Cecropia trees.
Page author:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA. longinoj@evergreen.edu
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