Linepithema tsachila

Linepithema tsachila is locally abundant along the western slopes of the Andes in Ecuador and Colombia with collection records running from near sea level to 2,000 meters. This species occurs in a broad range of habitats and can reach high numbers in some human disturbed areas. Eight collection records are from rainforest, seven from tree plantations or orchards, five from forest edge habitats, four from pastures, and three from second growth forest. Six nesting records are from under stones, along with one record each from rotting wood, soil, and leaf litter. I observed several colonies in Ecuador in 2002. Surface nest entrances are inconspicuous and nests are often diffuse, spreading out as networks of tunnels under several rocks and in the soil and litter. One colony was observed making use of old termite carton tubes. L. tsachila has been recorded tending honeydew-producing insects, once with coccids and once with pseudococcids on a Cecropia tree, and in Ecuador I observed these ants scavenging pieces of dead insects, recruiting to an earthworm, and recruiting to the body of a recently-killed rodent. Males have been taken at light traps in August and alates collected in nests in May and December. (Wild 2007)

Identification
Wild (2007) – Worker Posterior margin of head in full face view concave; head broad, reaching widest point near level of compound eyes; cephalic dorsum with a pair of standing setae near posterior margin; mesonotum without strong medial impression; mesopleura and metapleura lacking pubescence and moderately shining; integument often with a faint blue sheen.

Linepithema tsachila shows habitat and nesting associations much like those of the morphologically similar sister species, L. piliferum. The two species are locally sympatric in some localities in Ecuador with no signs of hybridization, an observation that supports the present treatment of L. tsachila as a valid species. Most populations of this species are uniform in appearance. At Unión Toachí, at 1000 meters on the western Andean slopes, some collections are smaller and darker in color with relatively longer scapes. These might represent workers from young colonies, as molecular evidence indicates little or no DNA sequence divergence in several loci from large, light colored forms collected at the same location (Wild, unpublished data).

Workers of the sister species Linepithema piliferum, whose range broadly overlaps with that of L. tsachila, have longer antennal scapes (SI > 99), a narrower head, and lack the faint opaque bluish sheen to the integument. Workers of Linepithema angulatum (in South America) and Linepithema fuscum lack standing setae on the vertex and usually also have fewer pronotal setae. Additionally, L. fuscum workers are normally somewhat smaller (HW < 0.52). Males of other Fuscum-group species have smaller ocelli and a much less concave dorsal margin of the volsella.

Male Forewing with 2 submarginal cells; volsella with distal arm shorter than 1/3 length of proximal arm; dorsal profile of volsella and proximal arm strongly concave; eyes large (EL > 0.38, OI > 54).

Distribution based on Regional Taxon Lists
Neotropical Region: Colombia, Ecuador.

Biology
Escarraga and Guerrero (2016) - Linepithema tsachila ranges from 286–1800 m in Colombia and has been collected in very humid tropical forest and very humid premontane forest.

Nomenclature

 *  tsachila. Linepithema tsachila Wild, 2007a: 109, figs. 19, 20, 47, 51, 63, 64, 103 (w.q.m.) ECUADOR.

Worker
Holotype: HL 0.66, HW 0.63, MFC 0.17, SL 0.57, FL 0.52, LHT 0.54, ES 1.50, PW 0.40, CI 94, SI 91, CDI 27, OI 23.

Worker: (n = 13) HL 0.53–0.72, HW 0.49–0.72, MFC 0.14–0.19, SL 0.53–0.65, FL 0.45–0.62, LHT 0.46–0.62, ES 1.08–2.14, PW 0.31–0.45, CI 86–99, SI 87–97, CDI 25–29, OI 19–29.

Head in full face view relatively broad (CI 86–99, usually > 94), lateral margins convex, running subparallel or converging posterior of compound eyes. Posterior margin slightly to deeply concave. Head in most workers reaches widest point near level of compound eyes. Compound eyes of moderate size (OI 19–29), comprised of 45–60 ommatidia. Antennal scapes relatively short (SI 87–97), shorter than head length. In full face view, scapes in repose exceed posterior margin of head by a length less than length of first funicular segment. Frontal carinae moderately spaced (CDI 25–29). Maxillary palps of moderate length, approximately ½ HL or less, ultimate segment (segment 6) shorter than or subequal in length to segment 2.

Pronotum and anterior mesonotum in lateral view forming a single convexity. Mesonotal dorsum relatively straight, sometimes with a slight mesal impression. Metanotal groove not impressed or only slightly impressed. Propodeum in lateral view relatively high, dorsal propodeal face straight to convex, posterior propodeal face convex.

Petiolar scale relatively sharp and inclined anteriorly, in dorsal view relatively narrow, in lateral view falling short of propodeal spiracle.

Cephalic dorsum (excluding clypeus) with a pair of suberect to subdecumbent setae near vertex and sometimes with 1–3 additional standing hairs closer to antennal insertions. Pronotum with 2–8 erect to suberect setae (mean = 4.9), some setae longer than maximum diameter of compound eye. Mesonotum without erect setae. Gastric tergite 1 ( = abdominal tergite 3) bearing 1–4 erect setae (mean = 1.9) mesally, exclusive of a row of 6–15 subdecumbent setae along posterior margin of tergite, tergite 2 bearing 2–6 erect setae (mean = 4.1) exclusive of posterior row, tergite 3 bearing 5–7 erect setae (mean = 6.0) exclusive of posterior row. Venter of metasoma with scattered erect setae.

Sculpture on head and mesosomal dorsum shagreened and relatively opaque. Pubescence dense on head, mesosomal dorsum, and gastric tergites 1–4. Mesopleura and metapleura without pubescence and shining.

Color testaceous to medium brown, head often somewhat darker than mesosoma. Surface of body sometimes with a faint opaque bluish sheen.

Queen
(n = 4) HL 0.92–1.02, HW 0.92–0.97, SL 0.78–0.85, FL 0.90–1.00, LHT 1.00–1.14, EL 0.36–0.47, MML 1.97–2.28, WL 6.85–7.04, CI 93–100, SI 85–89, OI 39–46, WI 31–32, FI 42–46.

Moderately large species (MML 1.97–2.28). Head slightly longer than broad to about as long as broad in full face view (CI 93–100), posterior margin concave. Eyes unusually large (OI 39–46). Ocelli large. Antennal scapes relatively short (SI 85–89), in full face view scapes in repose surpassing posterior margin by a length less than that of first funicular segment.

Forewings moderately long relative to mesosomal length (WI 31–32). Forewings with Rs+M somewhat greater in length than M.f2. Legs moderately short relative to mesosomal length (FI 42–46).

Dorsum of mesosoma and metasoma with scattered erect to subdecumbent setae, mesoscutum with more than 10 suberect to subdecumbent setae. Body and appendages concolorous medium to brown.

Male
(n = 4) HL 0.71–0.74, HW 0.69–0.71, SL 0.21–0.24, FL 1.10–1.15, LHT 1.09–1.13, EL 0.39–0.43, MML 1.53–1.62, WL 4.35–4.51, PH 0.29–0.33, CI 93–97, SI 30–32, OI 55–58, WI 27–28, FI 70–71.

Head slightly longer than broad in full face view (CI 93–97). Eyes large (OI 55–58), occupying much of anterolateral surface of head and separated from posterolateral clypeal margin by a length less than width of antennal scape. Ocelli very large, median ocellus as wide as separation between antennal insertions. Antennal scape moderately long (SI 30–32), 75–90% length of 3rd antennal segment. Anterior clypeal margin broadly convex medially. Mandibles large and worker-like, masticatory margin broad, much longer than inner margin, bearing 1–2 apical teeth followed by alternating series of teeth and denticles, similar to worker dentition. Inner margin and exterior lateral margin strongly diverging.

Mesosoma moderately developed, shorter in length than metasoma. Mesoscutum slightly enlarged, not projecting strongly forward or overhanging pronotum. Scutellum large, convex, nearly as tall as mesoscutum and projecting well above level of propodeum. Propodeum in lateral view not overhanging petiole, dorsal face rounding evenly into posterior face, posterior face straight to convex. Forewings long relative to mesosomal length (WI 27–28) and bearing two submarginal cells. Wing color clear to slightly smoky with darker brown veins and stigma. Legs long relative to mesosoma length (FI 70–71).

Petiolar node bearing a blunt, broadly-rounded scale, node height slightly shorter than node length. Ventral profile of node straight to slightly convex. Gaster elongate in dorsal view, 3–3.5 times as long as broad. Gonostylus produced as a slender filament. Volsella with ventrodistal process present as a spine or sharp tooth. Digitus elongate, distal arm short and hook-like, shorter than 1/3 length of proximal arm. Proximal arm broad at base, greater than ½ height of adjoining volsella, and tapering distally. Dorsal profile of volsella and proximal arm strongly concave, digitus arching upwards. Cuspis absent.

Dorsal surfaces of body with scattered erect setae, mesoscutum with more than 4 erect setae. Venter of gaster with scattered setae. Pubescence dense on body and appendages, becoming sparse only on medial propodeal dorsum.

Head and body medium brown in color. Mandibles, antennae, and legs lighter.

Type Material
Holotype worker. Ecuador. Pichincha: Endesa forest, 00º06’N 79º02’W, 700m, 5.xii.2003, Next to station buildings in mixed tree plantation, Trail up tree trunk in old termite tubes. A. L. Wild acc. no. AW2212, 1 worker,.

Paratypes. Same data as holotype, 26 workers and 8 males,, , , , , , ,.

Etymology
This name refers to the Tsa’chila people of western Ecuador, and is given as a noun in apposition.