Azteca instabilis

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 : 35-37

Azteca instabilis (F. Smith 1862)

Figures 3,4A,5,7.

Tapinoma instabilis F. Smith 1862:31. Syntype workers: Panama [ BMNH] (examined).

Liometopum instabile (F. Smith) (part): Mayr 1878:870.

Azteca instabilis (F. Smith) : Emery 1893:135. Description of queen: Emery 1896a:2.

Azteca instabilis var. major Forel 1899:107. Syntype workers: Panama, Bugaba, Caldera (Champion) [ MHNG] (examined). NEW SYNONYMY

Queen characters. Measurements (n=5): HLA 2.49 (2.42-2.52), HW 2.47 (2.39-2.55), SL 1.50 (1.42-1.50), CI 100 (98-101), SI 60 (58-62).

Palpal formula 6,4; ocelli large (OCW> 0.20mm); middle and hind tibia with prominent pectinate apical spur; dorsal surface of mandible smooth, very faintly microareolate, with moderately abundant small piligerous puncta, setae in puncta short, suberect, 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 somewhat convex, cordate posteriorly; petiolar node tall, strongly compressed into thin scale at apex; posteroventral petiolar lobe evenly convex from front to back, broad and flat laterally, ending before posterior margin of sternite, leaving small rim formed by posteriormost portion of sternite; 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 about as long as one half maximum width of tibia (MTSC 30-35); sides of head without erect setae; posterior margin of head with abundant erect setae; pronotum with erect setae on anterior and posterior margins, absent from medial area; mesoscutum, scutellum, and propodeum with abundant erect setae; petiolar node with variable number of long setae on apex, abundant long setae on posteroventral lobe; all gastral terga with abundant erect setae; color red brown.

Worker characters. Measurements (n=4): HLA 1.88 (1.76-2.10), HW 1.85 (1.80-2.13), SL 1.39 (1.34- 1.41), CI 101 (95-102), SI 74 (67-76).

Palpal formula 6,4; middle and hind tibia with prominent pectinate apical spur; dorsal surface of mandible strongly microareolate, dull, with moderately abundant small piligerous puncta, setae in puncta short, erect, 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 sloping pronotum, mesonotum forming separate convexity, posterior mesonotum and dorsal face of propodeum together forming single shallow concavity, with no notch marking metanotal groove; 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 without erect setae; posterior margin of head with abundant erect setae; pronotum, mesonotum, and dorsal face of propodeum with abundant long erect setae; color dark brown to light orange brown, if somewhat bicolored gaster is darker then mesosoma.

Similar species. Azteca instabilis queens are readily identified by the large size and large ocelli. Azteca gnava and A. sericeasur are similarly large but have much smaller ocelli (OCW <0.15mm). Larger workers of A. instabilis are identified by the dull dorsal surface of the mandibles, large size, and densely setose tibiae.

Range. Kempf (1972) lists A. instabilis from scattered localities in Brazil, the Guianas, Peru, Colombia, Panama, Costa Rica, Honduras, Guatemala, Belize, and Mexico. I have examined material from Mexico, Honduras, Nicaragua, Costa Rica, Panama, and Bolivia.

Biology. Azteca instabilis is the largest species in the genus. It occurs in wet to dry forest habitats, usually below 500m elevation.

Azteca instabilis makes its nest in the hollow trunks of trees which have a large crevice or fissure at the base. When I encounter them, workers are issuing from the fissure in large numbers, usually ascending the tree and often blanketing the surrounding forest floor. In one case I was able to peer up into such a fissure, and I observed a very large carton nest filling the trunk cavity. Colonies can be long-lived. During extended field work at Sirena in Corcovado National Park, I frequently passed a large tree with a very active A. instabilis colony in the trunk, with workers flowing in and out of a large fissure at the base. I returned to the site 16 years later to find the same fissure with A. instabilis workers still active.

When examining Azteca queens in museum collections, A. instabilis is usually the most abundant species because the large queens frequently come to lights at night. This is in sharp contrast to most other Azteca , whose alate queens are usually encountered as diurnal strays, occasional specimens in Malaise traps, or parts of nest collections. This correlates with the fact that A. instabilis queen ocelli are absolutely and relatively far larger than ocelli on any other Azteca queen I have examined. The enlarged ocelli are not the result of an allometric relationship with head size, since A. sericea and A. sericeasur , with queens nearly as large, have tiny ocelli typical of smaller queens. Ocelli concentrate light and detect light of low intensity (Chapman 1982), suggesting a functional relationship between large ocelli and nocturnal habits.

Workers frequently forage on the surface, both day and night. They visit extrafloral nectaries, and may tend coccoid Hemiptera under small carton shelters.

Additional material examined. COSTA RICA: Alajuela: Upala, Colonia Libertad , 10°54'N, 85°02'W, 550m , 10 Nov 1987 (Lezama) - alate queen [ MUCR] ; Upala, Pilon de Bijagua , 10°54'N, 85°02'W, 750m , 18 Nov 1993 (Lezama) - alate queen [ MUCR] ; Upala, Colonia Libertad , 10°54'N, 85°02'W, 450m , 9 May 1988 (L. Gonzalez & J. Sot) - alate queen [ MUCR] ; Upala, Guatuso, Asent. La Garroba , 10°54'N, 85°02'W, 90m , 10 Nov 1987 (Lezama) - alate queen [ MUCR] ; Casa Eladio, Rio Penas Blancas , 10°19'N, 84°43'W, 800m , 22 May 1987 (J. Longino) - alate queen ; Guanacaste: Headquarters, Santa Rosa Nat. Park , 10°50'N, 85°37'W, 300m , 13 Jul 1985 (J. Longino) - worker ; Heredia: 10km SE La Virgen , 10°20'N, 84°05'W, 500m , 16 Feb 2003 (J. Longino) - alate queen ; La Selva Biological Station , 10°26'N, 84°01'W, 50m , numerous collections and dates (ALAS, G. Gentry, J. Longino, R. Vargas C.) - workers, alate queens [ INBC] ; 11km ESE La Virgen , 10°21'N, 84°03'W, 300m , numerous collections and dates (ALAS, D. Brenes) - workers [ INBC] ; 16km SSE La Virgen , 10°16'N, 84°05'W, 1100m , multiple dates and collections (ALAS, D. Brenes, R. Vargas. C) - workers [ INBC] ; Puntarenas: Curu Wildlife Refuge , 9°47'N, 84°55'W, 5m , 28- 29 Mar 1993 (J. Longino) - workers, alate queen ; Sirena, Corcovado National Park , 8°29'N, 83°36'W, 5m , multiple dates and collections(J. Longino) - workers, alate queens ; Llorona, Corcovado National Park , 8°35'N, 83°42'W, 5m , 22 Mar 1981 (J. Longino) - workers ; MEXICO: Chiapas: Ruinas Yaxchilan , 16°54'N, 90°50'W, 100m , 17 Dec 1991 (P. S. Ward) - workers ; Ruinas Bonampak , 16°42'N, 91°04'W, 300m , 18 Dec 1991 (P. S. Ward) - workers ; Veracruz: 10km N Cardenas , 10m , 28 May 1988 (W. P. Mackay) - workers ; PANAMA: Colon: Est. Biol. Galeta , 9°24'N, 79°52'W, 10m , multiple collections and dates (J. Dunn) - workers ; Darién: no specific locality (Festa) - alate queen, workers [ MCSN] .