Linepithema micans

Identification
Wild (2007) - Worker Pubescence dense throughout mesopleuron, metapleuron, and gastric tergites; antennal scapes moderately long (SI 97–110), in repose usually exceeding posterior margin of head by a length greater than or equal to that of first funicular segment; first and second gastric tergites bearing numerous standing setae.

Workers of Linepithema gallardoi have mesopleural pubescence fading to sparse anteroventrally and often have slightly shorter legs and antennal scapes. Linepithema humile workers lack standing setae on gastric tergites 1–2 and usually have larger eyes. Linepithema oblongum and Linepithema anathema workers are more gracile with longer antennal scapes (SI > 115, Figs. 83–85). Linepithema neotropicum workers have much longer maxillary palps, a less pubescent mesopleura, and a lower, more rounded propodeum.

Male Forewing with 1 submarginal cell; propodeum with strongly concave posterior face, overhanging petiole; mesosoma not greatly swollen (MML < 1.3); appendages not elongate (FI < 56); pubescence on head moderate to dense in region posterior to compound eye.

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

Biology
Wild (2007) - Linepithema micans has been recorded from sea level to 2300 meters elevation. Where habitat information has been noted, five records are from pasture or grassland, two from high elevation semideciduous forest, two from wet montane forest, and two from second growth riparian forest. Seven nests were collected from under stones, two from rotting wood, and three from sandy soil. Linepithema micans has also been taken at baits, in pitfall traps, and in sifted litter. Alates have been recorded in the nests in Argentina from August to January, and in Brazil year round. Orr and Seike (1998) report that this species (as. “L. humile”, voucher specimens at UCDC examined) is attacked by Pseudacteon pusillum phorid flies at several locations in Brazil, and that these attacks alter the outcome of competitive interactions with other ant species at baits.

Leuderwaldt (1926: 286) reported the following observations on this species (as “Iridomyrmex dispertitus For. subsp. micans For.”, and translated from Portuguese):

Alates in the nest: April. Colonies in natural habitats under rocks; small colonies, containing around 50 workers. A nest was found on the trunk of a Cyathea schanschin Mart. between the leaf stalks, close to a nest of Linepithema leucomelas. In nest #10362 many staphylinids Aleochara leuderwaldti Bernh. were found; in another #11,942, Atheta tuberculicauda Bernh. with 5 from nest #2,650 under a rock, in Campo do Itatiaya (Rio).” Given the polydomy of other Linepithema species, I suspect Leuderwaldt’s small colony size estimate refers not to colony size but perhaps to nest size within a larger colony.

Rosumek (2017) - Linepithema micans is common in south Brazilian vineyards, strongly associated with sap-sucking insects (Morandi Filho et al., 2015). This species certainly suffers from a misdiagnosed past, and Nondillo et al. (2013) suggest that many previous records of L. humile in infested vineyards should be L. micans instead. Rosumek assessed trophic resource use and period of activity within the ant community in a southern Brazil Atlantic forest. He found a number of Linepithema, reporting "None of these species showed statistically significant preferences, due to low number of records and use of several resources. Linepithema micans and Linepithema pulex seem to use resources more broadly than Linepithema iniquum, which might descend to the ground mostly to scavenge animal resources.

Nomenclature

 *  micans. Iridomyrmex dispertitus subsp. micans Forel, 1908c: 394 (w.m.) BRAZIL. Forel, 1911c: 306 (q.). Combination in Linepithema: Shattuck, 1992a: 16. Raised to species, senior synonym of platensis, scotti and material of the unavailable names pertaesta, transiens referred here: Wild, 2007a: 85.
 * platensis. Iridomyrmex humilis r. platensis Forel, 1912h: 46 (w.q.m.) ARGENTINA. Combination in Linepithema: Shattuck, 1992a: 16. Junior synonym of micans: Wild, 2007a: 86.
 * scotti. Iridomyrmex humilis st. scotti Santschi, 1919f: 52 (w.) ARGENTINA. Combination in Linepithema: Shattuck, 1992a: 16. Junior synonym of micans: Wild, 2007a: 86.

Wild (2007):

Linepithema micans is morphologically a rather generalized species that appears to form the paraphyletic core of the humile complex from which the more distinctive Linepithema humile, Linepithema oblongum, and Linepithema gallardoi arose (Wild, molecular data). The boundaries of L. micans remain problematic, and there are possibly several cryptic species within the current conception of this taxon. This possibility is supported by broad elevational and habitat differences among populations of this species.

Forel’s type workers of L. micans from São Paulo are large and medium reddish brown in color, with a slight medial mesonotal impression and relatively short pubescence. Specimens closely similar to the micans type, including many of the ants observed in Orr and Seike’s (1998) ant-phorid study, are among the most commonly encountered Linepithema in São Paulo state. Judging from specimens at MZSP, Borgmeier was apparently misled by the local abundance of L. micans in southern Brazil and mistook L. micans for L. humile, consequently failing to recognize true L. humile and unnecessarily naming a new species, Linepithema riograndense, for a population of Argentine ants from Rio Grande do Sul (synonymized by Wild [2004]).

Populations outside the Atlantic forest region are more divergent, and some of them may later merit elevation to specific status. Towards the south into Paraguay and Argentina workers of most populations become dark brown in color, often showing a slightly more robust build and lacking a mesonotal impression, as in Santschi’s Linepithema scotti types from Córdoba and Forel’s Linepithema platense types from La Plata. Workers from montane populations near Tucumán, Argentina and some from Minas Gerais are lighter in color with large eyes and unusually broad heads.

Worker
Lectotype: HL 0.77, HW 0.68, MFC 0.19, SL 0.70, FL 0.64, LHT 0.69, ES 2.91, PW 0.48, CI 89, SI 102, CDI 27, OI 38.

Worker: (n = 40) HL 0.50–0.84, HW 0.42–0.80, MFC 0.12–0.20, SL 0.46–0.79, FL 0.39–0.71, LHT 0.42–0.77, ES 1.03–3.38, PW 0.30–0.49, CI 84–95, SI 97-110, CDI 21–29, OI 20–40.

Head in full face view somewhat longer than broad (CI 84–95), lateral margins convex, posterior margin straight to concave. Head normally reaches widest point at or posterior to level of compound eyes. Compound eyes moderate to large in size (OI 20–40), comprised of 60–105 ommatidia. Antennal scapes moderately long (SI 97–110), as long as or slightly shorter than head length. In full face view, scapes in repose usually exceed posterior margin of head by a length greater than or equal to that of first funicular segment. Frontal carinae narrowly to moderately spaced (CDI 21–29). Maxillary palps relatively short, approximately ½ HL or less, ultimate segment (segment 6) subequal in length or shorter than segment 2.

Pronotum and anterior mesonotum either forming a continuous curve, or curve interrupted by a slight medial mesonotal impression. Metanotal groove slightly to moderately impressed. Propodeum relatively high and inclined anteriorly, posterior propodeal face in profile broken at level of propodeal spiracle.

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

Cephalic dorsum (excluding clypeus) bearing 0–5 erect to suberect setae (mean = 1.3). Pronotum with 0–3 erect setae (mean = 1.1). Mesonotum without erect setae. Gastric tergite 1 ( = abdominal tergite 3) bearing 2–10 erect to subdecumbent setae (mean = 5.1) including posterior row, tergite 2 bearing 2–16 erect setae (mean = 8.1), tergite 3 bearing 4–10 erect setae (mean = 5.9). Venter of metasoma with scattered erect setae.

Sculpture on head and mesosomal dorsum shagreened and slightly shining to moderately opaque. Pubescence dense on head, mesosoma and metasoma. Mesopleuron and metapleuron with dense pubescence.

Color variable, from testaceous to piceous, mesosoma sometimes lighter than head and gaster.

Queen
(n = 8) HL 0.79–0.98, HW 0.75–0.95, SL 0.71–0.87, FL 0.70–0.91, LHT 0.79–1.00, EL 0.28–0.36, MML 1.55–2.38, WL 4.68–5.35, CI 95–100, SI 86–94, OI 33–37, WI 28–31, FI 38–48.

Moderate to large species (MML > 1.5). Head slightly longer than broad to about as long as broad in full face view (CI 95–100), posterior margin concave. Eyes of moderate size (OI 33–37). Ocelli small to moderate in size. Antennal scapes of moderate length (SI 86–94), in full face view scapes in repose surpassing posterior margin by a length less than to slightly greater than length of first funicular segment.

Forewings moderately short relative to mesosomal length (WI 28–31). Forewings with Rs+M subequal to about twice length of M.f2. Legs of moderate length relative to mesosomal length (FI 38–48).

Dorsum of mesosoma and metasoma with numerous standing setae. Mesoscutum bearing 5–15 standing setae. Body color light brown to piceous. Antennal scapes, legs, and mandibles concolorous with or somewhat lighter than body.

Male
(n = 6) HL 0.51–0.59, HW 0.49–0.58, SL 0.14–0.16, FL 0.52–0.65, LHT 0.45–0.54, EL 0.22–0.28, MML 0.98–1.24, WL 2.27–2.71, PH 0.19–0.27, CI 95–102, SI 26–30, OI 40–49, WI 21–24, FI 49–56.

Head robust, about as long as broad in full face view (CI 95–102). Eyes moderate to large in size (OI 40–49), occupying much of anterolateral surface of head anterior of midline and separated from posterolateral clypeal margin by a length less than width of antennal scape. Ocelli small and in full frontal view set above adjoining posterolateral margins. Antennal scape moderately long (SI 26–30), about 3/4 length of 3rd antennal segment. Anterior margin of median clypeal lobe broadly convex. Mandibles variable, small to moderate in size, usually bearing a single apical tooth and 7–13 denticles along masticatory margin. Masticatory margin relatively narrow to relatively broad, longer than or subequal in length to inner margin. Inner margin and exterior lateral margin converging, parallel, or diverging.

Mesosoma moderately developed, slightly larger or subequal in bulk to metasoma. Mesoscutum enlarged, projecting forward in a convexity overhanging pronotum. Scutellum large, convex, nearly as tall as mesoscutum and projecting above level of propodeum. Propodeum well developed and overhanging petiolar node, posterior propodeal face strongly concave. Forewings of moderate length relative to mesosomal length (WI 21–24) and bearing a single submarginal cell. Wing color clear to slightly smoky with light to dark brown veins and stigma. Legs moderately short relative to mesosoma length (FI 49–56).

Petiolar scale sharp and taller than node length. Ventral process well developed and pointing posteriorly. Gaster oval in dorsal view, nearly twice as long as broad. Gonostylus produced as bluntly rounded pilose lobes. Volsella with cuspis present, digitus short and downturned distally.

Dorsal surfaces of body largely devoid of erect setae, mesoscutum lacking standing setae, posterior abdominal tergites with a few fine, short setae. Venter of gaster with scattered setae. Pubescence dense on body and appendages, becoming sparse only on medial propodeal dorsum and lateral faces of pronotum.

Head, mesosoma and metasoma light to dark brown. Legs, mandibles, and antennae often lighter in color.

Type Material
Lectotype worker, by present designation, examined, 2 worker and 1 male paralectotypes, São Paulo, Brazil, Ihering MHNG, , examined.