Linepithema humile (Mayr)

Wild, A. L., 2007, Taxonomic revision of the ant genus Linepithema (Hymenoptera: Formicidae)., University of California Publications in Entomology 126, pp. 1-159 : 61-65

Linepithema humile (Mayr)

(worker body Fig. 31; worker head Fig. 32; male head Fig. 74; male body Fig. 54; male wing Fig. 48; male volsella Fig. 50; distribution Figs. 101, 108).

Hypoclinea humilis Mayr 1868: 164 (W). Holotype worker, Buenos Aires, Argentina, Stroebel, 1866 [NHMW, examined].

Iridomyrmex humilis (Mayr) . Emery 1888: 386-388. First combination in Iridomyrmex .

Iridomyrmex humilis (Mayr) . Wheeler 1913a: 27-29 (M, Q, W). Male and queen description, worker redescription.

Iridomyrmex humilis (Mayr) . Newell and Barber 1913: 38-39 (egg), 40-41 (larva), 42-45 (W, M, Q pupae).

Iridomyrmex humilis var. arrogans Chopard 1921: 241-245 (W). Lectotype worker, by present designation [NHMB, examined], Cannes, Provence-Alpes-Cote d'Azur, France, Chopard [NHMB, examined]. Junior synonym of I. humilis by Bernard 1967: 251. Restored to subspecies of L. humile (Mayr) by Shattuck 1992a: 16. Returned to synonymy by Wild 2004: 1207.

Iridomyrmex riograndensis Borgmeier 1928: 64 (W). Lectotype worker, by present designation [MZSP, examined] and 7 worker paralectotypes, Rio Grande do Sul (s.loc.), Brazil, 19.i.1918 [MZSP, examined]. Junior synonym of L. humile (Mayr) by Wild 2004: 1207.

Iridomyrmex humilis (Mayr) . Wheeler and Wheeler 1951: 186-189. Summary of larval biology.

Iridomyrmex humilis (Mayr) . Crozier 1969: 250. Karyotype.

Linepithema humile (Mayr) . Shattuck 1992a: 16. First combination in Linepithema .

Linepithema humile arrogans (Chopard) . Shattuck 1992a: 16. First combination in Linepithema .

Linepithema riograndensis (Borgmeier) . Shattuck 1992a: 16. First combination in Linepithema .

Linepithema humile (Mayr) . Shattuck 1994: 123.

Linepithema humile arrogans (Chopard) . Shattuck 1994: 123.

Linepithema riograndensis (Borgmeier) . Shattuck 1994: 127.

Linepithema humile (Mayr) . Bolton 1995: 247.

Linepithema humile arrogans (Chopard) . Bolton 1995: 246.

Linepithema riograndensis (Borgmeier) . Bolton 1995: 247.

Linepithema humile (Mayr) . Wild 2004: 1204-1215 (M, Q, W). Distribution and taxonomic redescription.

Species group: Humile

Holotype worker measurements: HL 0.74, HW 0.66, MFC 0.16, SL 0.76, FL 0.65, LHT 0.68, PW 0.45, ES 2.93, SI 115, CI 89, CDI 24, OI 40.

Worker measurements: (n = 81) HL 0.62-0.78, HW 0.53-0.72, MFC 0.14-0.18, SL 0.62-0.80, FL 0.52-0.68, LHT 0.57-0.76, PW 0.35-0.47, ES 1.98-3.82, SI 108-126, CI 84-93, CDI 23-28, OI 32-49.

Worker diagnosis: Eyes large (OI> 30); antennal scapes long (SI> 105); pronotum and first two gastric tergites lacking erect setae; mesopleura and metapleura densely pubescent.

Worker description: Head in full face view longer than broad (CI 84-93), narrowed anteriorly and reaching its widest point just posterior to compound eyes. Lateral margins broadly convex, grading smoothly into posterior margin. Posterior margin straight in smaller workers to weakly concave in larger workers. Compound eyes large (OI 32-49), comprising 82-110 ommatidia (normally around 100). Antennal scapes long (SI 108-126), as long or slightly longer than HL and easily surpassing posterior margin of the head in full face view. Frontal carinae narrowly to moderately spaced (CDI 23-28). Maxillary palps relatively short, shorter than Vi HL, ultimate segment (segment six) noticeably shorter than segment 2.

Pronotum and mesonotum forming a continuous convexity in lateral view, mesonotal dorsum nearly straight, not angular or strongly impressed, although sometimes with a slight impression in anterior portion. Metanotal groove moderately impressed. Propodeum in lateral view inclined anteriad. In lateral view, dorsal propodeal face meeting declivity in a distinct though obtuse angle, from which the declivity descends in a straight line to the level of the propodeal spiracle.

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

Dorsum of head (excluding clypeus), mesosoma, petiole, and gastric tergites 1-2 (= abdominal tergites 3-4) devoid of erect setae (very rarely with a pair of small setae on gastric tergite 2). Gastric tergites 3-4 each bearing a pair of long, erect setae. Venter of metasoma with scattered erect setae.

Integument shagreened and lightly shining. Body and appendages including gula, entire mesopleura, metapleura, and abdominal tergites covered in dense pubescence.

Body and appendages concolorous, most commonly a medium reddish or yellowish brown but ranging in some populations from testaceous to dark brown, never yellow or piceous.

Queen measurements: (n = 13) HL 0.83-0.92, HW 0.83-0.93, SL 0.81-0.89, FL 0.78-0.90, LHT 0.88-0.97, EL 0.31-0.36, MML 1.67-2.09, WL 4.42-4.51, CI 93- 101, SI 96-102, OI 36-39, WI 24-27, FI 40-48.

Queen description: Moderately large species (MML 1.67-2.09). Head slightly longer than broad to as broad as long in full face view (CI 93-101), posterior margin slightly concave to slightly convex. Eyes of moderate size (OI 36-39). Ocelli small. Antennal scapes relatively long (SI 96-102), in full face view scapes in repose surpassing posterior margin by a length greater than length of first funicular segment.

Forewings short relative to mesosomal length (WI 24-27). Forewings with Rs+M at least three times longer than M.f2. Legs of moderate length relative to mesosomal length (FI 40-48).

Dorsum of mesosoma and metasoma with scattered standing setae. Mesoscutum bearing 2-11 standing setae. Body color medium reddish brown. Antennal scapes, legs, and mandibles concolorous with body.

Male measurements: (n = 12) HL 0.56-0.70, HW 0.56-0.74, SL 0.13-0.16, FL 0.60- 0.77, LHT 0.51-0.66, EL 0.31-0.34, MML 1.40-1.96, WL 2.55-3.26, PH 0.25-0.34, CI 99-106, SI 22-27, OI 51-55, WI 17-20, FI 37-45.

Male diagnosis: Forewing with single submarginal cell; mesosoma robust (MML> 1.3), mesoscutum greatly enlarged and overhanging pronotum; wings short relative to mesosomal length (WI <21).

Male description: Head about as broad as long in full face view (CI 99-106). Eyes large (OI 51-55), occupying much of anterolateral surface of head and separated from posterolateral clypeal margin by a length less than width of antennal scape. Ocelli large and in full frontal view set above adjoining posterolateral margins. Antennal scape of moderate length (SI 22-27), about 2/3 length of 3rd antennal segment. Anterior clypeal margin straight to broadly convex. Mandibles small, bearing a single apical tooth and 4-8 denticles along masticatory margin and rounding into inner margin. Masticatory margin relatively short, subequal in length to inner margin. Inner margin roughly parallel to, or converging distally with, exterior lateral margin.

Mesosoma unusually well developed, considerably wider than head width, and larger in bulk and in length than metasoma. Mesoscutum greatly enlarged, projecting forward in a convexity overhanging pronotum. Scutellum large, convex, nearly as tall as mesoscutum and projecting well above level of propodeum. Propodeum well developed and overhanging petiolar node, posterior propodeal face strongly concave. Forewings short relative to mesosomal length (WI 17-20) and bearing a single submarginal cell. Wing color whitish or yellowish with dark brown veins and stigma. Legs short relative to mesosoma length (FI 37-45).

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

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

Color as for worker.

Distribution: Native to the Parana river drainage of Brazil, Paraguay, Argentina, and Uruguay. Introduced worldwide.

Biology: This important pest species has a literature too extensive to be covered in depth here. An early general review of the biology of this ant is given by Newell and Barber (1913). The spread of Argentine ants around the world is documented by Roura-Pascual et al. (2004), Wild (2004), Giraud et al. (2002), and Suarez et al.

(2001). Ecological impacts of Argentine ant invasion have been detailed in numerous studies, including Suarez and Case (2003), Touyama et al. (2003), Christian (2001), and Human and Gordon (1997). Colony structure has also received considerable attention, and relevant papers include Holway and Suarez (2004), Tsutsui and Case (2001), Reuter et al. (2001), and Kreiger and Keller (2000). A series of studies by Cavill and colleagues (Cavill and Houghton 1973, Cavill and Houghton 1974, Cavill et al. 1980) describe some of the glandular and cuticular chemistry of L. humile . Chemical and biological control options are reviewed by Harris (2002).

Of the L. humile material examined, more than 90% of native range records are within 10 kilometers of a major river in the Parana drainage. Contrary to some reports (Buczkowski et al. 2004), L. humile can reach high densities in urban areas in Argentina and Paraguay (Wild 2004) as well as in less disturbed habitats (Heller 2004). Where nest information was recorded in the native range, 24 nests are from soil, five from under covering objects such as stones or garbage, one from an old termite mound, and one from under bark. This species is polygynous and polydomous, and many nests are recorded as having numerous dealate queens. In contrast to introduced populations, alate queens are not uncommon in nests in Argentina (Wild 2004). One observation in Victoria, Argentina, notes a live lycaenid larva in the brood nest (Wild, pers. obs.).

Similar species: Workers of the sister species L. oblongum , from the high Andes of Bolivia and northern Argentina, normally have at least some members of each series with dilute pubescence on gastric tergites 2-4. These ants also have, on average, smaller eyes (OI 28-38, Fig. 86) and longer antennal scapes (SI 120-139, Fig. 85) than L. humile . Workers of L. anathema, a rarely-collected Brazilian species, have a more produced propodeum (Fig. 33), a narrow head (CI <86), and usually bear short standing setae on gastric tergites 1-2. Workers of other Humile-group species have shorter antennal scapes and often bear erect setae on the pronotum and basal gastric tergites. Males of related species are much smaller than L. humile and lack the greatly swollen mesosoma.

Discussion: The taxonomy and distribution of L. humile was recently reviewed in depth by Wild (2004).

Material examined: ARGENTINA. Buenos Aires: Boca, 34°38'S 58°21'W [ALWC]; Buenos Aires, 34°36'S 58°28'W [BMNH, MHNG, NHMB, NHMW, UCDC]; Campana, 34°12'S 58°56'W [ALWC, BMNH, CASC, MZSP]; Reserva Costanera Sur, 34°07'S 58°21'W [AVSC]; Isla Martin Garcia [MACN, NHMB]; La Plata [NHMB]; Lima-Zarete [IFML]; Olivos [MACN]; Reserva Otamendi, 34°14'S 58°54'W [ALWC, AVSC, IFML]; Rosas- F.C.Sud [MACN]; Santa Coloma, 34°26'S 59°02'W [UCDC]. Chubut: Rawson, 43°18'S 65°06'W [PSWC]. Corrientes: Ayo. Cuay Grande, 28°47'S 56°17'W [UCDC]; Corrientes [MACN]; Ita Ibate, 27°25'S 57°10'W [AVSC]; Port Alvear, 29°07'S 56°33'W [AVSC]; Sto. Tome, 28°33'S 56°03'W [IFML]. Entre Rios: 10 km S Medanos, 33°29'S 58°52'W [ALWC, BMNH]; Colon, 32°15'S 58°07'W [AVSC]; Diamante, 32°01'S 60°39'W [ALWC]; Est. Sosa [MACN, MHNG, NHMB]; Parque Nacional El Palmar, 31°53'S 58°13'W [AVSC]; Parque Nacional Pre Delta, 32°7'S 60°38'W [AVSC]; Port Ibicuy, 33°48'S 59°10' [AVSC]; Victoria, 32°38'S 60°10'W [ALWC]; Villaguay [NHMB]. Formosa: Clorinda [IFML]; Formosa [MACN, NHMB]; Mojon de Fierro [IFML]. La Rioja: Aminga, 28°50'S 66°54'W [ALWC, IFML, UCDC]; Chuquis, 28°54'S 66°58'W [UCDC]. Misiones: Parque Nacional Iguazu, 25°42'S 54°26'W [IFML]; Posadas [MZSP]. Santa Fe: 10 km E Santa Fe, Ruta 168, 31°41'S 60°34'W [ALWC, MCZC, USNM]; Fives Lille [NHMB]; Port Ocampo, 28°30'S 59°16'W [AVSC]; Rosario [MACN]. Tucuman: Tichuco, 26°31'S 65°15'W [UCDC]. AUSTRALIA. New South Wales: Sydney [MZSP]. Victoria (s. loc.) [BMNH]. BELGIUM. Bruxelles Capitale: Brussels [BMNH, NHMB], Brussels Botanical Garden [MHNG]. BERMUDA. Bermuda (s. loc.) [BMNH]. BRAZIL. Amazonas: Manaus [MZSP]. Goias: Anapolis [MZSP]. Mato Grosso do Sul: Corumba, Faz. Sta. Blanca [MZSP]; Corumba, Pto. Esperanca [MZSP]; Passo do Lontra, 19°34'S 57°01'W [PSWC, UCDC]; Pto. Murtinho [MZSP]. Rio de Janeiro: Rio de Janeiro [MCSN, MCZC, MHNG]. Rio Grande do Sul: N. Wurtemberg [MZSP]; Pelotas [BMNH]. Brazil (s.loc.), Port-of-entry U.S. intercept [ALWC, UCDC, USNM]. CAMEROON. Centre-Sud: Nkoemvom [BMNH]. CHILE. Bio-Bio: 3 km W Florida [UCDC]; Los Angeles, 37°26'S 72°19'W [UCDC]. Coquimbo: Los Vilos [UCDC]. La Araucania: Temuco [MZSP]. Maule: 10 km E Curico [UCDC]. Region Metropolitana: Talagante [UCDC]. Santiago: Santiago, Metropolitan area, 33°27'S 70°40'W [AVSC]. Valparaiso: 10 km E Vina del Mar, 33°00'S 71°31'W [AVSC]; nr. El Melon, 1 km N of tunnel [UCDC]. COLOMBIA. Quindio: Armenia [WPMC]. ECUADOR. Pichincha: Carapungo, 00°05'S 78°30'W [ALWC, QCAZ]; Mitad del Mundo, 00°00'S 78°27'W [ALWC, BMNH, MCZC]; Quito, 00°11'S 78°30'W [QCAZ]. FRANCE. Provence-Alpes-Cote d'Azur: Cannes [MCZC, NHMB], Castellane [BMNH], Hyeres [BMNH], Ste. Maxime [NHMB]. Midi-Pyrenees: Toulouse [IFML]. GERMANY. Berlin: Botanical Garden [MHNG]. ITALY. Campania: nr. Naples [BMNH]. Liguria: San Remo [NHMB]. Sicilia: Palermo [BMNH]. Toscana: Monte Argentario Giannella [BMNH]; Orbetello [BMNH]; Varazze (Savona) [MZSP]. LESOTHO. Maseru: Maseru [BMNH]. MOROCCO. Tanger: Tangier [USNM]. MEXICO. Baja California: Ensenada, Cortera FR [AVSC]. Baja California Sur: Guerrero Negro [AVSC]. Distrito Federal: Mexico City [BMNH]; Distrito Federal (s.loc.) [WPMC]. Guanajuato: Guanajuato [ALWC]. Mexico: 18 km SW Toluca [UCDC]. NAMIBIA. Erongo: Swakopmund [BMNH]. PARAGUAY. Alto Paraguay: Pto. 14 de Mayo [MCSN]. Asuncion: Asuncion [IFML, MACN, NHMB, USNM]. Boqueron: P.N. Defensores del Chaco, Cerro Leon [ALWC]. Central: San Lorenzo, 25°20'S 57°31'W [ALWC]. Cordillera: San Bernadino [MHNG]. Neembucu: Pilar, 26°52'S 58°18'W [ALWC, MCZC]; 26°52'S 57°47'W [ALWC, LACM]. Pte. Hayes: Benjamin Aceval [USNM]; Rio Confuso, Ruta Trans-Chaco [ALWC, INBP]; Villa Hayes, 25°06'S 57°34 W [ALWC, INBP, MCZC]; 5 km SE Pozo Colorado, 23°33'S 58°46' [ALWC, BMNH, INBP, MCZC, USNM]; Rt. 5, 3 km SE Concepcion, 23°27'S 57°27'W [ALWC]. San Pedro: Pto. Rosario, 24°30'S 57°00'W [ALWC, MZSP]. PERU. Lima: Los Condores [MZSP]. POLAND. Dolnoslaskie: Breslau [NMHB]. PORTUGAL. Faro: Algarve, Luz nr. Lagos [BMNH]. Lisboa: Cascais [USNM]; Estoril [USNM]; Lisbona [MCZC, NHMB]; Mafra [USNM]; Praia das Macas [USNM]. Madeira: Funchal [MCZC, NHMB]; Porto Moniz [BMNH]; Ribeira Brava [BMNH]; Ilheu Chao [BMNH]; Porto Santo [BMNH]; Sao Vicente [BMNH]; Vale de Paraiso [BMNH]; Praia Formosa [BMNH]; Porto da Cruz [BMNH]; Feiteiras [BMNH]; Caramujo [BMNH]; Lower Levada [BMNH], Madeira Is. (s. loc.) [BMNH, MHNG, NHMB]. Porto: Leca [BMNH]; Oporto [BMNH]. SOUTH AFRICA. Eastern Cape: Queenstown [BMNH]; Somerset East [BMNH]. Mpumalanga: Nelspruit [BMNH]. Northern Cape: Colesberg [ALWC, MCZC]. Western Cape: Capetown [BMNH]; Table Mt. [BMNH]; nr. George [BMNH]. SPAIN. Andalucia: Malaga [USNM]. Canarias: Arenara [BMNH]; Cruz de Tejeda [BMNH]; Gran Canaria, Las Palmas, Telde [BMNH, MCZC, USNM]; Orotava [BMNH]; Santa Brigida [BMNH]; Tenerife, Agua Mansa [NHMB]; Tenerife, Ladera de Guimar [BMNH]; Tenerife, Volcan de Guimar [NHMB]; Tenerife (s. loc.) [BMNH]. Cataluna: Playa de Aro [NHMB]. Galicia: Mte. Ferro b. Bayona [BMNH]. Islas Baleares: Minorca, Cala Forcat [BMNH]. THAILAND. Port-of-entry U.S. intercept [USNM]. UNITED KINGDOM. Edinburgh: Edinburgh [BMNH]. Sussex: Lewes [BMNH]. Eastborne [BMNH]. Exeter [BMNH]. Windsor [BMNH]. Glasgow [BMNH]. W. Maidstone, Kent [BMNH]. Chillingham [BMNH]. Farnham House Lab, Imperial Bureau of Entomology [BMNH]. U.S.A. Alabama: Lowdnes Co., Ft. Deposit [USNM]. California: Alameda Co., Berkeley [UCDC, USNM]; Humboldt Co., Redway [ALWC, BMNH]; Los Angeles Co., Pasadena [MZSP, USNM]; Los Angeles Co.: Sta. Monica Mts, Big Rock Road, 34°02'N 118°37'W [UCDC]; Monterrey Co., Big Sur [ALWC]; Orange Co., Bolsa Chica Marsh [MZSP]; Riverside Co., Lake Skinner Camp [AVSC]; Sacramento Co., Sacramento [UCDC]; San Diego Co., UC Elliot Reserve [AVSC]; San Diego Co., San Diego [UCDC]; San Diego Co., E. San Diego [UCDC]; San Diego Co., Pacific Beach [UCDC]; San Diego Co., Mission Hills [UCDC]; San Diego Co., Kate Sessions Park [UCDC]; San Diego Co., Balboa Park [UCDC]; San Diego Co., Point Loma [UCDC]; San Joachin Co., Caswell State Park [PSWC]; San Luis Obispo Co., Oso Flaco Lake [LACM]; San Mateo Co., Colma [USNM]; San Mateo Co., San Bruno Mt. [PSWC]; Santa Clara Co., South Coyote [PSWC]; Sonoma Co., Russian R. 6 km E. Healdsburg [UCDC]; Yolo Co., 6 km W Capay [PSWC]; Yolo Co., Davis [PSWC, UCDC]; Yolo Co., Grasslands Regional Park, 8 km SW Davis [PSWC, UCDC]. Florida: Escambia Co., Gonzalez [MCZC]. Louisiana: Plaquemines Parish., Happy Jack [BMNH]; Orleans Parish, New Orleans [BMNH]; Louisiana (s. loc.) [BMNH]. Mississippi: Coahoma Co., Clarkesdale [USNM]; Copiah Co., Hazelhurst [MCZC]; Oktibbeha Co., Starkville [BMNH]. South Carolina: York Co., York [BMNH]. URUGUAY. Colonia: Carmelo [MACN, NHMB]; Colonia de Sacramento, 34°28'S 57°51'W [AVSC]. Montevideo: Montevideo [MACN, NHMB, NHMW].