Linepithema aztecoides

The type series was collected by the author in humid subtropical low forest along the edge of a small cerrado in eastern Paraguay. The other localities suggest that this rarely-encountered ant inhabits low, open forests such as cerrados and riparian gallery forests. Linepithema aztecoides recruit to baits; the type series was collected at a honey bait, and the Chapada do Guimarães collection was at a sardine bait. Male and queen castes are not known, and there are no records of nests. In the field these ants run about with their gasters held above their heads, giving them the appearance of a small monomorphic Azteca. (Wild 2007)

Identification
Wild (2007) – Worker Head, mesosoma, and petiole dorso-ventrally flattened; posterolateral corners of propodeum formed by propodeal spiracles; color reddish brown to dark brown.

Given the distinct flattened habitus of L. aztecoides, this species is unlikely to be confused with any other Linepithema.

L. aztecoides varies considerably in body proportions across its range. Specimens from Mato Grosso, Brazil consistently have longer appendages (FL > 0.53; LHT > 0.58; SL > 0.63; SI > 110) than specimens from Goiás, São Paulo and Paraguay (FL < 0.53; LHT < 0.59; SL < 0.64; SI < 113), although there is some overlap. The Mato Grosso specimens are also less setose and redder in color. Given the allopatry of these variations and the scarcity of L. aztecoides specimens in collections, it is preferable to treat the different forms as a single species.

Distribution
Central and southeastern Brazil from Mato Grosso to São Paulo and west into Paraguay.

Distribution based on Regional Taxon Lists
Neotropical Region: Argentina, Brazil, Paraguay.

Nomenclature

 *  aztecoides. Linepithema aztecoides Wild, 2007a: 34, figs. 43, 44, 105, 110 (w.) PARAGUAY.

Worker
Holotype: HL 0.66, HW 0.57, MFC 0.17, SL 0.60, FL 0.49, LHT 0.55, PW 0.37, ES 1.57, SI 105, CI 86, CDI 30, OI 24.

Worker: (n = 16) HL 0.61–0.69, HW 0.52–0.60, MFC 0.14–0.18, SL 0.57–0.70, FL 0.46–0.61, LHT 0.52–0.64, PW 0.32–0.40, ES 1.35–1.93, SI 99–117, CI 85–91, CDI 25–31, OI 21–28.

Head in full face view chordate, widest at or posterior to compound eyes, and narrowed anteriorly. Posterior margin concave. Clypeus relatively larger than in other Linepithema species, projecting forward such that overall clypeal length, measured from level of posterior margin between antennal insertions to level of anterior projection, is about half total clypeal width. Anterior clypeal margin with a relatively narrow but concave medial excision. Compound eyes of moderate size (OI 21–28) and comprised of 65–80 ommatidia (mean = 70). Antennal scapes long (SL 0.57–0.70; SI 99–117), slightly shorter than head length (Paraguay and southeastern Brazil) to slightly longer than head length (Mato Grosso) and projecting well beyond posterior margin with head in full face view. Frontal carinae moderately to widely separated (CDI 25–31) and terminate near midpoint level of compound eye. In lateral view, head noticeably dorso-ventrally flattened, dorsal and ventral faces straight and parallel to each other. Maxillary palps relatively long, greater than ½ HL, ultimate segment (segment six) longer than segment 2.

Mesosoma dorso-ventrally compressed. Pronotum and mesonotum with dorsal surfaces nearly flat. In lateral view, mesonotal profile nearly straight, without mesal impression. Propodeum in lateral view short, dorsal face nearly straight, much longer than posterior face, and declining posteriorly. Posterolateral corners of propodeum formed by propodeal spiracles. Posterodorsal face of propodeum between spiracles broadly concave.

Petiole with a broad, low, anteriorly-inclined dorsal scale. Base of scale in lateral view longer than scale height. Anterior face of scale rounded in lateral view, posterior face straight. Ventral process of petiole evenly convex.

Gaster dorso-ventrally compressed and triangular on posterior view. In lateral view, gastric tergite 1 ( = abdominal tergite 3) somewhat depressed, anterior face considerably shorter than dorsal face, such that less of gastric volume appears contained under 1st gastric tergite than in most other Linepithema species.

Cephalic dorsum often with a single pair of short, suberect setae near vertex, rarely with a single pair of short erect setae just posterior of antennal insertions. Pronotum bearing a pair of long erect setae. Gastric tergite 1 ( = abdominal segment 3) with 2–6 setae along the posterior margin, tergite 2 with 6–10 setae along the posterior margin and 1–2 setae elsewhere, tergite 3 with a posterior row of setae and 1–4 setae elsewhere, tergite 4 with a pair of long setae. Venter of metasoma with scattered erect setae.

Pubescence dense on most of body and on all gastric tergites. Pubescence sparse on posterolateral face of pronotum, on mesopleuron, on metapleuron, and on posterior propodeal face. Surface of body shagreened and lightly shining.

Color medium reddish brown to dark brown over body, legs, and antennae. Mandibles reddish brown. Trochanters and tarsi lighter, to nearly white.

Type Material
Holotype worker. Paraguay. Canindeyú: Reserva Natural del Bosque Mbaracayú, Lagunita, 24º08’S 55º26’W, 220m, 13.xi.2002. A.L.Wild acc. no. AW1683. 1 worker,.

Paratypes. Same collection data as holotype, A. L. Wild acc. nos. AW1683, AW1686; 31 workers,, , , IFML, , , , , , , , , ,.

Etymology
In the field this species appears similar to ants in the genus Azteca.

References based on Global Ant Biodiversity Informatics

 * Schmidt F. A., and R. R. C. Solar. Is it important to collect hypogaeic ants? How to collect them? Biológico, São Paulo 69(2): 267-270.
 * Schmidt, F.A. and R.R.C Solar. 2010. Hypogaeic pitfall traps: methodological advances and remarks to improve the sampling of a hidden ant fauna. Insectes Sociaux 57:261-266.
 * Wild A. L. 2007. Taxonomic revision of the ant genus Linepithema (Hymenoptera: Formicidae). University of California Publications in Entomology 126: 1-151
 * Wild, A. L.. "A catalogue of the ants of Paraguay (Hymenoptera: Formicidae)." Zootaxa 1622 (2007): 1-55.