Linepithema gallardoi

A widespread South American species that is found across a wide elevational range (sea level to 3000m).

Identification
Wild (2007) – Worker Mesonotum relatively robust, mesonotal dorsum usually angular with distinct dorsal and posterior faces; pubescence moderate to sparse on anterior mesopleuron; propodeum relatively high and inclined anteriorly, posterior propodeal face in profile broken at level of propodeal spiracle; antennal scapes short, in repose exceeding posterior margin of head by a length less than or subequal to that of first funicular segment.

Workers of other species in the humile-group always have more densely pubescent mesopleura and often longer antennal scapes and legs. Workers of Linepithema neotropicum have a lower, more rounded propodeum and longer maxillary palps.

Although all populations share the characteristic robust mesosoma and the shiny, sparsely pubescent anteroventral mesopleura, Linepithema gallardoi shows significant variation among populations in size, color, and pubescence. The extent of mesopleural pubescence can vary from nearly absent over the entire sclerite to moderately dense across the posterior 2/3 and fading to sparse anteriorly. While local populations are often consistently homogenous in their mesopleural pubescence, there is little broad scale geographic structure to the variation. Worker specimens from central Argentina, including the type locality of gallardoi, often have sparse gastric pubescence, although the variation in pubescence is continuous and a few Paraguayan and Brazilian specimens are also sparsely pubescent. Santschi’s impotens type from Santa Catarina is very sparsely pubescent on both the mesosoma and metasoma. Some of the more northerly montane populations, including those from northern Colombia and some from around Cusco, Peru, are relatively large and medium reddish-brown in color.

Male Forewing with 1 submarginal cell; propodeum with strongly concave posterior face, overhanging petiole; mesosoma not greatly swollen (MML < 1.1); appendages not elongate (FI < 56); pubescence on head usually moderate to sparse in area posterior to compound eye.

Distribution
Venezuela and Colombia south to Argentina and southeastern Brazil.

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

Biology
Wild (2007) - Linepithema gallardoi is broadly distributed in South America from sea level to nearly 3000 meters in elevation and is most commonly recorded from open or low forest habitats. Nine records are from montane scrub grassland, three from grassland or pasture, two from urban lawns, one from pampas scrub, one from humid chaco, one from cleared cloud forest, one from subtropical forest edge, one from subtropical scrub forest, and one from a coffee plantation. This species has been collected in subterranean sausage traps and pitfall traps in Venezuela and at sardine baits in Brazil. Orr & Seike (1998) report this species (as “L. humile”, voucher specimens at UCDC examined) being attacked by Pseudacteon phorid flies near Monte Verde, Minas Gerais, Brazil.

Eight nest records of this species are from under stones, two from open soil, and one from leaf litter. I excavated several colonies near the type locality at La Falda, Córdoba, Argentina. Most were polydomous with a diffuse series of small brood chambers connected through subterranean tunnels near the soil surface or under stones. Single dealate queens were seen in two of eight excavations, with no queens seen in the remaining six excavations, indicating that L. gallardoi may be monogynous, although molecular genetic work will be needed for confirmation.

Alates have been recorded in nests of L. gallardoi nests during October and January in Argentina, in November in Brazil, and in April in Colombia. Queens of this species are flighted, and Queens and males have been collected flying to lights in Paraguay in November and December.

Escarraga & Guerrero (2016) - In Colombia, L. gallardoi occurs in high altitude localities. In the department of Caldas, the specimens were collected with pitfall traps near live fences. Workers from Boyacá were collected with Malaise trap, perhaps while foraging.

Nomenclature

 *  gallardoi. Dorymyrmex gallardoi Brèthes, 1914a: 95 (w.) ARGENTINA. Santschi, 1929d: 306 (q.). Wild, 2007a: 57 (m.). Combination in Iridomyrmex: Gallardo, 1916a: 105; in Linepithema: Shattuck, 1992a: 16. Subspecies of humile: Gallardo, 1916a: 105; Santschi, 1929d: 306. Raised to species and senior synonym of breviscapa, impotens: Wild, 2007a: 55.
 * impotens. Iridomyrmex impotens Santschi, 1923d: 67 (w.) BRAZIL. Combination in Linepithema: Shattuck, 1992a: 16. Junior synonym of gallardoi: Wild, 2007a: 55.
 * breviscapa. Iridomyrmex humilis st. breviscapa Santschi, 1929d: 306 (w.) ARGENTINA. [First available use of Iridomyrmex humilis r. platensis var. breviscapa Forel, 1914d: 286; unavailable name.] Santschi, 1916e: 390 (m.). Combination in Linepithema: Shattuck, 1992a: 16. Junior synonym of gallardoi: Wild, 2007a: 55.

Wild (2007):

The type specimen of L. gallardoi, ostensibly at MACN, was not seen during this study and could not be located. The name was originally combined in Dorymyrmex by Brèthes (1914), but after viewing specimens Gallardo (1916) transferred gallardoi to Iridomyrmex. Unfortunately, neither the original description nor the figures and redescription by Gallardo (1916) are sufficient to confirm even the generic association of gallardoi. Gallardo’s hastily prepared line drawing of the head seems to suggest that this ant may be as Brèthes suggested a Dorymyrmex, but the lateral view appears to show a Linepithema. The name gallardoi, at any rate, has been consistently applied in museum collections to the small, shiny, dark-colored Linepithema that is abundant at the type locality and in the Sierras del Córdoba of Argentina. Given that the brief description is not inconsistent with the common Linepithema from the region, I find it preferable to retain gallardoi in the current use. In the event that gallardoi proves inapplicable to the species described here, the name breviscapa Santschi 1929 remains available for this ant. I have designated lectotypes for breviscapa from Forel’s original series for the unfortunate reason that Santschi made the name available based on a misidentification of Linepithema micans.

Worker
(n = 20) HL 0.52–0.69, HW 0.43–0.65, MFC 0.13–0.17, SL 0.46–0.60, FL 0.39–0.54, LHT 0.40–0.56, ES 1.31–2.38, PW 0.29–0.44, CI 83–95, SI 89-107, CDI 24–29, OI 24–34.

Head in full face view somewhat longer than broad (CI 83–95), lateral margins convex, posterior margin concave. Head normally reaches widest point at or posterior to level of compound eyes. Compound eyes of moderate size (OI 24–34), comprised of 50–85 ommatidia. Antennal scapes relatively short (SI 89–107, usually less than 100), shorter than head length. In full face view, scapes in repose exceed posterior margin of head by a length less than or subequal to that of first funicular segment. Frontal carinae narrowly to moderately spaced (CDI 24–29). Maxillary palps relatively short, approximately ½ HL or less, ultimate segment (segment 6) subequal in length to segment 2.

Pronotum and anterior mesonotum forming a continuous curve. Mesonotum relatively bulky, mesonotal dorsum angular and usually lacking a mesal impression, declivitous face rising sharply to meet dorsal face. 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) normally lacking erect setae, very rarely with a single pair of subdecumbent setae near vertex. Pronotum with 1–3 erect setae (mean = 2.1). Mesonotum without erect setae. Gastric tergite 1 ( = abdominal tergite 3) bearing 2–8 erect to subdecumbent setae (mean = 4.4) including posterior row, tergite 2 bearing 2–8 erect setae (mean = 4.9), tergite 3 bearing 2–6 erect setae (mean = 3.5). Venter of metasoma with scattered erect setae.

Sculpture on head and mesosomal dorsum lightly shagreened and slightly to moderately shining. Pubescence dense on head, mesosomal dorsum, and gastric tergite 1. Pubescence variable from dense to sparse on gastric tergites 2–4, surface usually smooth and somewhat shining through pubescence. Mesopleuron with pubescence fading to moderate or sparse anteriorly, surface smooth and usually shining. Metapleuron with moderate pubescence.

Color variable, from light reddish brown to piceous, most commonly dark, mesosoma sometimes lighter than head and gaster.

Queen
(n = 5) HL 0.78–0.81, HW 0.75–0.78, SL 0.64–0.67, FL 0.65–0.69, LHT 0.69–0.74, EL 0.24–0.28, MML 1.45–1.62, WL 4.45–4.64, CI 94–97, SI 85–89, OI 31–35, WI 30–32, FI 42–47.

Relatively small species (MML < 1.7). Head slightly longer than broad in full face view (CI 94–97), posterior margin concave. Eyes of moderate size (OI 31–35). Ocelli of moderate size. Antennal scapes relatively short (SI 85–89), in full face view scapes in repose surpassing posterior margin by a length less than length of first funicular segment.

Forewings moderately short relative to mesosomal length (WI 30–32). Forewings with Rs+M subequal in length to M.f2. Legs of moderate length relative to mesosomal length (FI 42–47).

Dorsum of mesosoma and metasoma with numerous standing setae. Mesoscutum bearing 2–10 standing setae. Body color medium brown to piceous. Antennal scapes, legs, and mandibles concolorous with body, trochanters usually lighter.

Male
(n = 6) HL 0.50–0.53, HW 0.47–0.51, SL 0.11–0.14, FL 0.47–0.56, LHT 0.41–0.50, EL 0.19–0.20, MML 0.95–1.08, WL 2.21–2.72, PH 0.18–0.23, CI 93–98, SI 23–27, OI 45–49, WI 23–25, FI 49–52.

Head slightly longer than broad to about as long as broad in full face view (CI 93–98). Eyes of moderate size (OI 45–49), 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 23–27), about 2/3 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 8–13 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 23–25) 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 49–52).

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, lateral faces of pronotum, and often on the head posterior to the compound eyes.

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

Type Material
Type specimens not located, collection information given as Alta Gracia, Córdoba, Argentina, Gallardo.