Linepithema

The genus has recently been revised by Wild (2007) and species determinations are fairly straightforward using available keys. Linepithema ants are a common but often overlooked element of the Neotropical myrmecofauna. These small, monomorphic dolichoderine ants are native to a variety of forest, grassland, and montane habitats in Central and South America and the Caribbean. The genus is widely recognized for the pestiferous Argentine ant Linepithema humile, an insect that has received considerable attention for its invasive behavior in Mediterranean climates worldwide (Roura-Pascual et al. 2004), but Linepithema also contains nearly twenty additional species, some of them locally abundant, about which little is known. (Wild 2007)

Distribution
Ignoring the introduced range of Linepithema humile and Linepithema iniquum, Linepithema is found from the highlands of northern Mexico east into the Caribbean and south to northern Argentina. Common on Hispaniola and Puerto Rico. Relatively rare in the Amazon Basin, reaching their peak abundance and diversity instead between 20º and 30º degrees south latitude.

Species richness
Species richness by country based on regional taxon lists (countries with darker colours are more species-rich). View Data



Biology
From the modern revision of the genus by Alex Wild (2007):

In subtropical South America, Linepithema ants are found near sea level in rainforests, scrub forests, and floodplains. In the Central Andes they ascend to 4,000 meters elevation. In northern South America, Central America, and the Caribbean Linepithema species are more typically montane, sometimes occurring locally at high densities to the apparent exclusion of other ant species.

Two species, Linepithema humile and the Argentine ant Linepithema iniquum, have been carried around the world with human commerce, although L. iniquum seems to establish only in greenhouses (Wheeler 1929, Creighton 1950).

Although Linepithema ants are often observed in undisturbed primary habitat, most species may also readily be found in pastures, lawns, roadsides and other disturbed habitats, suggesting that populations weather deforestation and habitat modification reasonably well. Some species, including the notorious Argentine ant, likely thrive with disturbance. Nonetheless, a few of the uncommon species have been recorded only from primary habitats and one, Linepithema flavescens, is known only from Haiti and has not been collected since 1934.

Linepithema ants show a stereotypical nesting and feeding behavior. Mature colonies are populous, often with more than 1,000 individuals, and the worker caste is monomorphic. The trophic habits of these ants are not unusual for dolichoderines, as they are generalist scavengers and predators with strong proclivities for tending nectaries and honeydew-producing insects. Honeydew feeding is ubiquitous throughout the genus and occurs both inside and outside the nest. Linepithema ants readily form chemical recruitment trails and can recruit in large numbers to food sources. They are commonly seen running in files on the ground and on low vegetation and are active both day and night. Some species are attacked by hostspecific parasitoid Pseudacteon phorid flies (Orr et al. 2001, Wild, pers. obs.).

Most species are polydomous, many are also polygynous, and at least one species, the Argentine ant L. humile, has both multicolonial and unicolonial populations (Krieger and Keller 2003, Tsutsui and Case 2001). However, colony life history information outside of L. humile is sparse. Most Linepithema ants construct superficial nests in soil, leaf litter, rotting wood, or under stones, but at least two species, Linepithema iniquum and Linepithema leucomelas, are predominantly arboreal. The morphology of two poorly known species, L. flavescens and Linepithema cryptobioticum, indicates a primarily subterranean existence although this has yet to be confirmed by field observation.

Mating behavior is unknown for most species, but there are hints of extensive variation within this genus. Queens of L. humile are flightless and mate in the nest (Krieger and Keller 2000), but the few other species for which observational data are known have flighted queens (Wild, pers. obs.) Interestingly, male morphology is more variable within Linepithema than it is among many other ant genera, suggesting that mating behavior in Linepithema may show extraordinary diversity. Males vary in size from much greater than the workers to somewhat smaller, with variation in the number of closed cells in the fore wing, the relative elongation of the body and wings, the degree of development of the terminalia, the degree of development of the mesosoma, and the extent to which the head and petiolar morphology approaches the female condition (Shattuck 1992c, Wild, pers. obs). Mating flights, where they have been observed, take place around dusk (Wild, pers. obs).

Nomenclature

 *  LINEPITHEMA [Dolichoderinae: Leptomyrmecini]
 * Linepithema Mayr, 1866a: 496. Type-species: Linepithema fusca, by monotypy.