Linepithema humile

The Argentine ant is one of the most well known invasive ants and has been introduced in many parts of the world.

Distribution
This introduced species occurs sporadically throughout Florida, in places forming massive populations. It occurs in both moist and dry open habitats, usually in heavily disturbed sites. Pest status: can become a nuisance by sheer numbers, trailing long distances to outdoor eating areas and into buildings. First published Florida record: Wheeler 1932; earlier specimens: 1914. (Deyrup, Davis & Cover, 2000.)

Linepithema humile was previously reported in Colombia (Sanabria & Chacón de Ulloa 2009; Wild 2004, 2007). However, we found that the specimens identified as L. humile in Sanabria & Chacón de Ulloa (2009), and many other “Linepithema humile” specimens in Colombian entomological collections, were misidentified. In most cases these specimens were Linepithema piliferum or Linepithema neotropicum, and in no cases were L. humile. In order to confirm the occurrence of L. humile in Colombia (Wild 2007), we studied the L. humile specimens reported in Wild (2007) and deposited in WPMC. We confirm that the specimens are L. humile, and this remains the only known collection of the species in Colombia. These ants were collected in the Colombian coffee zone (Armenia, Quindio) in 1973, but despite subsequent intensive sampling done in that area by the program Paisajes Rurales (Instituto Alexander von Humboldt), there are no more L. humile records from Armenia or elsewhere. Thus it is possible that this was an introduction that did not persist and the species no longer occurs in Colombia. (Escarraga & Guerrero, 2016)

Distribution based on Regional Taxon Lists
Afrotropical Region: Lesotho, Mozambique, Namibia, Saint Helena, United Arab Emirates. Australasian Region: Australia, New Zealand, Norfolk Island. Indo-Australian Region: Hawaii, Vanuatu. Nearctic Region: United States. Neotropical Region: Argentina, Bermuda, Brazil, Ecuador, French Guiana, Mexico, Paraguay, Uruguay. Palaearctic Region: Balearic Islands, Belgium, Bulgaria, Canary Islands, Channel Islands, Democratic Peoples Republic of Korea, France, Germany, Gibraltar, Greece, Iberian Peninsula, Iran, Japan, Malta, Monaco, Montenegro, Morocco, Poland, Portugal, Spain, United Kingdom of Great Britain and Northern Ireland.



Biology
This ant forms what has been called supercolonies: a large number of nests spread over large areas where the individuals from one nest can be brought to any other nest and accepted as nestmates. Linepithema humile do not have nuptial flights (Passera and Keller 1990). Queens mate with related males in their natal nests (Markin 1970).

Inou et al. (2015) suggested the results of a genetic study of four supercolonies in Kobe Japan showed that these colonies replaced their queens during the reproductive season. Genetic differentiation among workers varied significantly in comparing May samples to September samples. They feel this provides evidence for queen execution, which has been reported in two introduced populations (USA, Markin 1970 and France Keller et al. 1989).

Bertelsmeier et al. (2015a, b) examined elements of interspecific aggression, and food resource discovery and dominance, between this species and several other highly invasive ants. In laboratory assays Linepithema humile was highly aggressive when confronted with workers of other invasive ants. Of the group of four species that were found to be aggressive, L. humile was found to be fairly adept at finding and recruiting to food in a laboratory arena experiment.

Regional Notes
DaRocha et al. (2015, Brazil) studied the diversity of ants found in bromeliads of a single large tree of Erythrina, a common cocoa shade tree, at an agricultural research center in Ilhéus, Brazil. Forty-seven species of ants were found in 36 of 52 the bromeliads examined. Bromeliads with suspended soil and those that were larger had higher ant diversity. Linepithema humile was found in a single bromeliad and was associated with the suspended soil and litter of the plant.

Espadaler (2007) - Canary Islands: The Argentine ant is known from all the Canary Islands (Espadaler & Bernal, 2003). At El Hierro it occupies habitats from next to sea level to one thousand meters, in pine forests. Confronted with the two populations known to exist in North Mediterranean Europe (Giraud et al., 2002), the Argentine ants from El Hierro showed aggressiveness towards the “Catalan” population and reacted peacefully towards the “Main” population from mainland Europe. Aggression tests (one to one worker; five replicates) were run with two samples from El Hierro (La Frontera; Mirador de las Playas). I conclude that both samples from El Hierro belong to the genotypic profile of the “Main” population, the more abundant in Western Mediterranean Europe.

Collingwood (1979) - Europe: This species was introduced into Europe from South America and has become an established and notorious pest in the Mediterranean area, developing very populous multi-queened colonies along the coast. It is sometimes brought into North Europe with plant materials and occasionally colonises heated premises. It does not appear to be able to establish outside in northern latitudes but is present and said to be increasing in the Channel Islands.

Other Insects
This ant has been observed tending larvae of Lampides boeticus (Obregon et al. 2015).

Genetics
Linepithema humile has had their entire genome sequenced.

Palomeque et al. (2015) found class II mariner elements, a form of transposable elements, in the genome of this ant.

Castes
Queens differ in their Cuticular Hydrocarbons according to ovarian activity. Whereas the cuticular profile of non-laying queens is similar to that of sterile workers, it gradually changes both qualitatively and quantitatively once queens start to lay eggs. These changes are independent of mating status, since virgin egg-laying queens show a CH profile similar to that of mated egg-laying queens (de Biseau et al. 2004).

Nomenclature

 *  humile. Hypoclinea humilis Mayr, 1868b: 164 (w.) ARGENTINA. Forel, 1908c: 395 (m.); Newell, 1908: 28 (q.); Wheeler, G.C. & Wheeler, J. 1951: 186 (l.); Crozier, 1969: 250 (k.). Combination in H. (Iridomyrmex): Mayr, 1870b: 959; in Iridomyrmex: Emery, 1888d: 386; in Linepithema: Shattuck, 1992a: 16. Senior synonym of arrogans, riograndensis: Wild, 2004: 1207. See also: Gallardo, 1916a: 97; Bernard, 1967: 251; Collingwood, 1979: 33; Smith, D.R. 1979: 1418; Ward, 1987: 1; Wheeler, G.C. & Wheeler, J. 1990a: 465; Shattuck, 1994: 123; Wild, 2007a: 61; Solis, Fox, Rossi & Bueno, 2010: 19.
 * arrogans. Iridomyrmex humilis var. arrogans Chopard, 1921: 237 (footnote),:241, figs. 1-31 (w.q.m.l.) FRANCE. [Also described as new by Santschi, 1929d: 306 (in key).] Combination in Linepithema: Shattuck, 1992a: 16. Junior synonym of humile: Bernard, 1967: 251. Revived from synonymy as subspecies of humile: Shattuck, 1992a: 16. Junior synonym of humile: Wild, 2004: 1207.
 * riograndensis. Iridomyrmex riograndensis Borgmeier, 1928b: 64 (w.) BRAZIL. Combination in Linepithema: Shattuck, 1992a: 16. Junior synonym of humile: Wild, 2004: 1207.