Azteca xanthochroa (Roger

Longino, J. T., 2007, A taxonomic review of the genus Azteca (Hymenoptera: Formicidae) in Costa Rica and a global revision of the aurita group., Zootaxa 1491, pp. 1-63 : 52-54

Azteca xanthochroa (Roger 1863)

Figures 2,3,4A,5,6D,7.

Liometopum (?) xanthochroum Roger 1863:167. Holotype queen: Mexico .

Iridomyrmex xanthochrous (Roger); Mayr 1866:497 (part) [Mexican workers described; later found to be a different species].

Liometopum instabile ; Mayr (not Smith) 1877:870 (part) [incorrectly synonymized under instabile ].

Azteca instabilis var. xanthochroa (Roger) ; Emery 1893:137 (part) [reinstated].

Azteca xanthochroa (Roger) ; Emery 1896b:2 [description of Costa Rican workers; exclusion of Mexican workers described in Mayr 1866]; Wheeler 1942:248 [description of workers from Guatemala].

Azteca xanthochroa var. costaricensis Wheeler 1942:248 [n.nov. for Costa Rican workers described by Emery 1896b:2 as xanthochroa ]. Lectotype worker: Costa Rica, Limón province, Jimenez (Alfaro) [label: "Jimenez, C.R. v.95 "] [ NHMW] (examined). Synonymy by Longino 1991b:1594.

Queen characters. 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.

Worker characters. 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.

Similar species. 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.

Range. Mexico to Costa Rica.

Biology. The taxonomy and biology of A. xanthochroa is reviewed in Longino (1989b, 1991a, b). The species is an obligate Cecropia ant. It is one of the most common Cecropia ants in Costa Rica, occurring in wet to moist forest habitats and extending to relatively high elevations (up to 1400m). Mature colonies occupy a single carton nest in the bole of the tree. All larvae and alate sexuals are concentrated in this single nest. Branch tips, which all communicate internally with the carton nest, contain only workers and Hemiptera. Workers of this species are very aggressive, and respond to any disturbance by pouring out of branch tips. A distinctive feature of this species is that workers maintain a vertical fissure near the base of the tree, far below the carton nest. Workers can move freely inside the trunk from the nest to this fissure. Thus, when the tree is disturbed at the base, workers suddenly appear on the trunk at ground level (Longino 1991a).

Material examined. See Longino (1991b).