Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Identification
An obligate Cecropia ant (Longino 1991a,b).
Worker: scapes and tibiae with abundant but inconspicuous setae; color uniformly light yellow orange; head width of largest workers less than 1.05mm; in profile mesonotum drops to a shelf anterior to propodeal suture, metanotal area and propodeal dorsum in the same plane.
Queen: scapes and tibiae with abundant but inconspicuous setae; color shiny black; head much longer than broad (CI less than 0.85).
Workers of A. coeruleipennis are often misidentified as A. alfari because of the small size, weak polymorphism, and light color. Also, the tibial setae are very fine and easily overlooked. Wheeler (1942, and in MCZC collection) routinely misidentified A. coeruleipennis workers as A. alfari subspecies lucida. Workers of A. constructor have a similar mesosomal profile, but differ greatly from A. coeruleipennis in color and pilosity.
Range
Mexico to Pacific coast dry forest of Costa Rica.
Natural History
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).
Literature Cited
Longino, J. T. 1989. Geographic variation and community structure in an ant-plant mutualism: Azteca and Cecropia in Costa Rica. Biotropica 21:126-132.
Longino, J. T. 1991a. Azteca ants in Cecropia trees: taxonomy, colony structure, and behavior. Pages 271-288 in C. Huxley and D. Cutler, editors. Ant-plant interactions. Oxford University Press, Oxford, U.K.
Longino, J. T. 1991b. Taxonomy of the Cecropia-inhabiting Azteca ants. Journal of Natural History 25:1571-1602.
Skwarra, E. 1934. Okologie der Lebensgemeinschaften mexikanischer Ameisenpflanzen, Zeitschrift fur Morphologie und Okologie der Tiere 29:306-373.
Wheeler, W. M. 1942. Studies of neotropical ant-plants and their ants. Bulletin of the Museum of Comparative Zoology, Harvard 90:1-262.
Page author:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA. longinoj@evergreen.edu
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