Dolichoderinae, Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
Queen, face view (original line drawing, reduced line drawing), mandible (small, large), petiole, lateral view (small, large), tibia (small, large).
Worker, mandible (small, large), petiole, lateral view (small, large), tibia (small, large).
Mexico to Costa Rica. Costa Rica: widespread in wet to moist habitats.
Measurements (n=10): HLA 2.42 (2.37-2.65), HW 1.97 (1.90-2.17), SL 1.32 (1.25-1.37), CI 82 (79-83), SI 54 (51-56).
Palpal formula 5,3; middle and hind tibia with prominent pectinate apical spur; dorsal surface of mandible smooth and shining or very faintly sculptured, with sparse small piligerous puncta, setae in puncta very short, appressed and little larger than width of puncta, larger puncta with long setae near masticatory margin; medial and lateral clypeal lobes at about same level (medial lobe not projecting anteriorly); head quadrate, sides subparallel to slightly diverging, strongly cordate posteriorly, with angulate posterolateral margins; petiolar node tall, triangular, acute; posteroventral petiolar lobe evenly convex, shallow, not strongly developed; scape with abundant erect setae, about as long as one half maximum width of scape; middle and hind tibia with abundant erect setae, longest of these one half to two thirds maximum width of tibia (MTSC 25-35); sides of head with 1-2 erect setae near mandibular insertions, absent elsewhere; posterior margin of head with abundant short erect setae; pronotum with abundant long setae on posterior third; mesoscutum with anterior one half to one third usually devoid of erect setae, posterior two thirds to one half with abundant setae, occasionally erect setae sparse to nearly absent throughout; scutellum with abundant long setae; propodeum with sparse erect setae, occasionally bare; petiolar node with 0-6 erect setae, 0-4 long setae and more abundant short, fine setae on posteroventral lobe; all gastral terga with abundant erect setae; color orange.
Measurements (n=4): HLA 1.59 (1.40-1.69), HW 1.41 (1.30-1.49), SL 1.05 (0.95-1.08), CI 89 (87-93), SI 67 (62-68).
Palpal formula 5,3; middle and hind tibia with prominent pectinate apical spur; dorsal surface of mandible smooth and shining, with sparse small piligerous puncta, setae in puncta very short, appressed and little larger than width of puncta, larger puncta with long setae near masticatory margin; medial and lateral clypeal lobes at about same level; head with convex sides, strongly cordate posterior margin; mesosoma in lateral profile with promesonotum forming a single broad convexity, or mesonotum forming a distinct, somewhat more strongly produced convexity; metanotal groove broad; petiole in profile with node larger than sternal lobe, perpendicular distance from tergosternal suture to apex of node greater than distance to ventral margin of sternal lobe (in contrast to A. constructor, on which the petiolar node is smaller relative to sternal lobe); scape with abundant erect setae, length of setae about one half maximum width of scape; mid and hind tibia with abundant erect setae, longest setae about one half maximum width of tibia; sides of head with erect setae short, sparse to absent; posterior margin of head with abundant short erect setae; pronotum with abundant long erect setae; mesonotum with setae absent on anterior half, grading to longer setae on posterior half; dorsal face of propodeum with very short setae, grading into pubescence; color brown to mottled orange brown.
The queens of A. xanthochroa are very distinctive and not easily confused with any other species. Workers of A. constructor and A. xanthochroa are very similar. Large workers of A. constructor retain a chocolate brown color, while large workers of A. xanthochroa become more mottled orange. The petiolar node of A. constructor workers is relatively low, while the posteroventral lobe is relatively deep and strongly convex. Workers of A. xanthochroa are the reverse, with relatively taller node and shallower ventral lobe.
The taxonomy and biology of A. xanthochroa is reviewed in Longino (1989b, 1991a, b). See also general treatment of the Cecropia-Azteca association in Costa Rica.
In Costa Rica, A. xanthochroa is one of the most common Cecropia ants in wet forested areas. In the Atlantic lowlands, colonies are most frequently found in C. obtusifolia, a common tree of disturbed areas. Cecropia insignis, a tree more often in primary forest, is dominated by A. ovaticeps. As one moves up-slope, both C. obtusifolia and A. ovaticeps drop out, and A. xanthochroa is then frequently found in C. insignis throughout the rest of its elevational range (up to 1100m in the Penas Blancas Valley east of Monteverde). Above this limit, C. insignis is replaced by the non-myrmecophytic C. angustifolia. Founding queens may be found in C. angustifolia saplings, well above the elevational limit of C. insignis, but never in mature trees. These queens are presumably doomed dispersants from lower elevations. On the Pacific slopes of northwestern Costa Rica, a narrow band of C. obtusifolia separates cloud forest C. angustifolia from the common C. peltata which is throughout the seasonally dry lowlands. Azteca xanthochroa is common in this narrow band, but does not occur at lower elevations where C. peltata dominates (Longino, 1989).
In C. obtusifolia, colonies maintain a longitudinal fissure near the base of the tree, from which very large workers emerge when the tree is disturbed. These large workers bite only infrequently, perhaps because they have difficulty maneuvering their large heads or obtaining a grip with their large mandibles (Perlman, pers. com.). Many smaller workers emerge from branch tips, however, and these are very aggressive and readily bite. All reproduction is concentrated in a single carton nest in the bole, and there are no entrance holes near this central nest. Internal communication is maintained with all branch tips, which contain only workers, coccoid homoptera, and cached muellerian bodies.
Nest structure appears quite different in C. insignis, perhaps due to the much thicker wood of the bole, or to the fact that it is inhabited mainly at higher elevations where it is much cooler and wetter. For example, in the Penas Blancas Valley (800-900m), colonies are smaller and less aggressive. They occur high in the tree, sometimes in only a portion of the crown, and they do not maintain a basal fissure.
John T. Longino, The Evergreen State College, Olympia WA 98505 USA. firstname.lastname@example.org
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