Linepithema neotropicum

A widely ranging forest species that commonly nests in twigs within leaf litter (Fernandes et al., 2018).

Identification
Wild (2007) – Worker Maxillary palps relatively long ( > ½ HL; segment 6 longer than segment 2); propodeum low and rounded; metapleural bulla with at least some appressed pubescence.

This is a widespread and variable species that has been misidentified in various collections. Most worker specimens are dark brown in color, but in northeastern Brazil there are some color and pilosity intergrades with Linepithema cerradense, perhaps not surprising considering that L. neotropicum is possibly paraphyletic with respect to L. cerradense (Wild, molecular data). Some high elevation collections from Colombia and the records from Trinidad and Guyana are also lighter in color. Eye size varies somewhat. Some Costa Rican specimens and specimens from the Atlantic forest region of Brazil and Paraguay have the largest eyes (ES around 2.0, 60–70 ommatidia), while specimens from northwestern South America have the smallest eyes (ES around 1.5, 50–60 ommatidia). Costa Rican specimens are more variable in pilosity, sometimes bearing more than 2 erect setae on the pronotum. The extent of mesopleural pubescence varies over a north-south cline, with specimens from the northern part of the range having more extensive pubescence.

Workers of the closely-related Linepithema cerradense have a more flattened mesosomal profile, a narrower head, and shorter antennal scapes. Workers of Linepithema dispertitum, from Central America, normally have a more deeply impressed metanotal groove. Humile-group species have much shorter maxillary palps.

Male Forewing with 1 submarginal cell; petiolar node with dorsal scale taller than long in lateral view; posterior face of propodeum straight to slightly concave; sculpture of head not well developed and surface slightly shining through pubescence; mandibles with apical tooth unusually elongate; size moderate (MML 0.91–1.02).

Males of L. cerradense are similar in structure to L. neotropicum males but tend to be lighter in color and smaller in size (MML < 0.80).

Distribution
Costa Rica south to Paraguay and southeastern Brazil.

Distribution based on Regional Taxon Lists
Neotropical Region: Bolivia, Brazil, Colombia, Costa Rica, Ecuador, Paraguay, Venezuela.

Biology
Wild (2007) - This species inhabits a considerable range of forest habitats from sea level to over 2000 meters. Most records are from lowland tropical or subtropical humid forests, but several are from forest edge, 2nd growth, or logged primary forest. Specimens collected in the central Brazilian state of Tocantins are from cerrado or cerradão habitats. Five records are from park or garden habitats, and there are single collections of L. neotropicum from coffee, soy, cacao, banana, and pineapple fields. Six nest records are from soil, two from under stones, one in a rotting log, and one in soil under a rotting log. Soil nests often have several inconspicuous entrances not much larger than the width of a worker ant, with small piles of excavated earth around them (Wild, pers obs.).

Linepithema neotropicum, like most species, appears to be a trophic generalist. Ants have been observed recruiting to tuna, sardine, and honey baits in Colombia, Brazil, and Paraguay. One collection records root-feeding pseudococcids in a soil nest and another documents aphid-tending on vegetation above ground. Middens from a nest in Ecuador contained fragments of dead arthropods including nasute termites and Trachymyrmex ants.

The type series was collected by the author as an entire colony from the shaded north side of a laboratory building in Paraguay at the edge of a humid subtropical semideciduous forest. The colony had scaled the side of the building during the day as if to avoid a subterranean army ant predator (Gotwald 1995, pg 229), although no army ants were seen. The full colony consisted of 1022 worker ants, one dealate queen, 28 alate queens, 30 males, and 82 additional male pupae.

Alate males and females were observed flying to a fluorescent light in mid November at the Mbaracayú Reserve in Paraguay, between 21:00 and 23:00hr on a warm evening after two days of rain. Alate females have been taken in nests in November in Paraguay, alate males have been recorded from nests in Ecuador in December, and alate males and females have been collected in pan traps and in low vegetation in Rondônia, Brazil in November and December.

Escarraga & Guerrero (2016) - In Colombia, Linepithema neotropicum has been captured with different sampling methods (pitfall, entomological net, Malaise trap, Winkler trap, and beating tray) suggesting variable habits. Some specimen records were from paddocks. In other collections, this species was attracted to human excrement.

Nomenclature

 *  neotropicum. Linepithema neotropicum Wild, 2007a: 91, figs. 6, 29, 30, 65, 104 (w.q.m.) PARAGUAY.

Worker
Holotype: HL 0.66, HW 0.60, MFC 0.16, SL 0.60, FL 0.52, LHT 0.55, ES 1.97, PW 0.38, CI 91, SI 101, CDI 27, OI 29.

Worker: (n = 31) HL 0.54–0.70, HW 0.47–0.66, MFC 0.12–0.18, SL 0.50–0.64, FL 0.43–0.56, LHT 0.47–0.59, ES 1.24–2.37, PW 0.31–0.44, CI 87–96, SI 97-110, CDI 24–29, OI 23–34.

Head in full face view slightly longer than broad (CI 87–96), lateral margins convex, posterior margin concave. Compound eyes of moderate size (OI 23–34), comprised of 50–70 facets. Antennal scapes of moderate length (SI 97–110), shorter than head length. In full face view, scapes in repose surpass posterior margin of head by an amount subequal to the length of the first funicular segment. Frontal carinae narrowly to moderately spaced (CDI 24–29). Maxillary palps relatively long, greater than ½ HL, ultimate segment (segment six) longer than segment 2.

Mesosoma in lateral view with pronotum and mesonotum forming a single continuous convexity, mesonotal profile straight to very slightly impressed mesally. Metanotal groove slightly impressed to not at all impressed, propodeum low and rounded, dorsal and posterior faces rounding evenly into each other without a distinct angle.

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

Cephalic dorsum (excluding clypeus) lacking erect setae. Pronotum with one pair of erect setae. Mesonotum without erect setae. Gastric tergite 1 bearing 1–3 erect setae (mean = 1.7), tergite 2 with 1–4 erect setae, tergite 3 with 2–5 erect setae. Venter of metasoma with scattered erect setae.

Surface of head and mesosomal dorsum shagreened and moderately shining. Pubescence dense on head and mesosomal dorsum. Mesopleura with pubescence fading from moderate posterodorsally to sparse or absent anteroventrally. Metapleura with moderate to sparse pubescence thinner than on propodeal dorsum but never completely absent. Gastric tergites 1–4 with dense to moderate pubescence, surface moderately shining.

Body color light brown to dark brown, area on head surrounding mandibular insertions often lighter. Trochanters and tarsi pale whitish-brown.

Queen
(n = 5) HL 0.78–0.82, HW 0.70–0.73, SL 0.70–0.73, FL 0.69–0.73, LHT 0.75–0.80, EL 0.28, MML 1.59–1.72, WL 4.85–5.33, CI 89–91, SI 97–103, OI 34–36, WI 30–31, FI 43–45.

Moderately small species (MML < 1.8). Head narrow in full face view (CI 89–91), posterior margin straight. Eyes moderate to small (OI 34–36). Ocelli small. Antennal scapes moderate to long (SI 94–101), in full face view scapes in repose surpassing posterior margin by a length approximately that of first funicular segment.

Forewings moderately long relative to mesosomal length (WI 30–31). Forewings with Rs+M more than two times longer than M.f2. Legs of moderate length relative to mesosomal length (FI 43–45).

Dorsum of mesosoma and metasoma with scattered suberect standing setae. Mesoscutum bearing 0–6 standing setae. Body color medium brown. Trochanters and tarsi lighter.

Male
(n = 5) HL 0.46–0.51, HW 0.45–0.50, SL 0.12–0.13, FL 0.49–0.54, LHT 0.44–0.48, EL 0.20–0.23, MML 0.91–1.02, WL 2.32–2.54, PH 0.16–0.20, CI 95–101, SI 24–27, OI 40–47, WI 25–26, FI 52–56.

Head about as broad as long in full face view (CI 95–101). Eyes of moderate size (OI 40–47), occupying much of anterolateral surface of head and separated from posterolateral clypeal margin by a length less than width of antennal scape. Ocelli of moderate size and in full frontal view set above adjoining posterolateral margins. Antennal scape short (SI 24–27), about 2/3 length of 3rd antennal segment. Anterior clypeal margin convex medially. Mandibles moderately sized and somewhat elongate, masticatory margin broad, longer than inner margin, apical tooth enlarged as a sharp spine and followed by a series of 8–18 denticles. Inner margin and exterior lateral margin parallel to slightly diverging.

Mesosoma moderately developed and subequal in length to metasoma. Mesoscutum not greatly enlarged, projecting slightly forward over pronotum. Propodeum in lateral view not strongly overhanging petiole, posterior face slightly convex to slightly concave. Forewings of moderate length (WI 25–26) and bearing one submarginal cell.

Wings transparent, with pale brown wing veins and stigma. Legs of moderate length relative to mesosoma (FI 52–56).

Petiolar node bearing an erect scale, node height taller than node length. Venter of node bearing a convex downward-pointing process. Gaster ovoid in dorsal view, about 2 times as long as broad. Gonostylus produced as a pointed, triangular pilose lobe. Volsella with cuspis present, digitus short and downturned distally.

Dorsal surfaces of body with erect setae sparse, mesoscutum with 0–4 fine erect to suberect setae. Venter of gaster with scattered setae. Pubescence dense on body and appendages, becoming sparse only on medial propodeal dorsum. Sculpture on head and mesoscutum not well developed, surface shining through pubescence.

Head dark brown. Mesosoma and metasoma pale brown to medium brown. Mandibles, antennae, and legs pale whitish-yellow to light brown, much lighter than body.

Type Material
Holotype worker. Paraguay. Canindeyú: Reserva Natural del Bosque Mbaracayú, Jejuimi, 24º08’S 055º32’W, 12.xi.2002. A.L.Wild acc. no. AW1718. 1 worker,.

Paratypes. Same collection data as holotype, A. L. Wild acc. nos. AW1718, 1022 workers, 30 males, 29 queens,, , , , , , , , , , , , , , ,.

Etymology
The name refers to this ant’s wide distribution in the neotropics.

Determination Clarifications
This is a widespread and variable species that has been misidentified in various collections as Linepithema iniquum (MHNG), Linepithema humile (NHMB), Linepithema scotti (=Linepithema micans) (MZSP, NHMB), Linepithema leucomelas (NHMB), and Linepithema dispertitum (MCSN).