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The Argentine ant (''Linepithema humile''), formerly ''Iridomyrmex humilis'', is an
ant Ants are eusocial insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from vespoid wasp ancestors in the Cretaceous period. More than 13,800 of an estimated total of 22,0 ...
native to northern
Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
, Uruguay, Paraguay,
Bolivia , image_flag = Bandera de Bolivia (Estado).svg , flag_alt = Horizontal tricolor (red, yellow, and green from top to bottom) with the coat of arms of Bolivia in the center , flag_alt2 = 7 × 7 square p ...
and southern Brazil. It is an invasive species that has been established in many Mediterranean climate areas, inadvertently introduced by humans to many places, including South Africa, New Zealand, Japan,
Easter Island Easter Island ( rap, Rapa Nui; es, Isla de Pascua) is an island and special territory of Chile in the southeastern Pacific Ocean, at the southeasternmost point of the Polynesian Triangle in Oceania. The island is most famous for its nearly ...
, Australia, Europe, Hawaii, and the continental United States.


Description

The worker ants are long and can easily squeeze through cracks and holes as small as in size. Queens are long, much smaller than other species of ants. These ants will set up quarters in the ground, in cracks in concrete walls, in spaces between boards and timbers, even among belongings in human dwellings. In natural areas, they generally nest shallowly in loose
leaf litter Plant litter (also leaf litter, tree litter, soil litter, litterfall or duff) is dead plant material (such as leaves, bark, needles, twigs, and cladodes) that have fallen to the ground. This detritus or dead organic material and its constituent ...
or beneath small stones, due to their poor ability to dig deeper nests. However, if a deeper nesting ant species abandons their nest, Argentine ant colonies will readily take over the space. Austrian entomologist Gustav L. Mayr identified the first specimens of ''Hypoclinea humilis'' in the vicinity of
Buenos Aires Buenos Aires ( or ; ), officially the Autonomous City of Buenos Aires ( es, link=no, Ciudad Autónoma de Buenos Aires), is the capital and primate city of Argentina. The city is located on the western shore of the Río de la Plata, on South Am ...
, Argentina in 1866. This species was shortly transferred to the genus ''
Iridomyrmex ''Iridomyrmex'' is a genus of ants called rainbow ants (referring to their blue-green iridescent sheen) first described by Austrian entomologist Gustav Mayr in 1862. He placed the genus in the subfamily Dolichoderinae of the family Formici ...
'', and finally to ''Linepithema'' in the early 1990s.


Distribution

The native range of Argentine ants is limited to around major waterways in the lowland areas of the Paraná River drainage. They have recently spread into parts of Argentina, Brazil,
Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...
, Colombia, Ecuador, and Peru. The species has become established in at least 15 countries throughout the world, on six continents, as well as many
oceanic islands Oceanic may refer to: *Of or relating to the ocean *Of or relating to Oceania **Oceanic climate **Oceanic languages **Oceanic person or people, also called "Pacific Islander(s)" Places * Oceanic, British Columbia, a settlement on Smith Island, ...
.


Global "mega-colony"

The absence of aggression within Argentine ant
colonies In modern parlance, a colony is a territory subject to a form of foreign rule. Though dominated by the foreign colonizers, colonies remain separate from the administration of the original country of the colonizers, the '' metropolitan state'' ...
was first reported in 1913 by Newell & Barber, who noted "…there is no apparent antagonism between separate colonies of its own kind". Later studies showed that these " supercolonies" extend across hundreds or thousands of kilometers in different parts of the introduced range, first reported in California in 2000, then in Europe in 2002, Japan in 2009, and Australia in 2010. Several subsequent studies used genetic, behavioral, and chemical analyses to show that introduced supercolonies on separate continents actually represent a single global supercolony. The researchers stated that the "enormous extent of this population is paralleled only by human society", and had probably been spread and maintained by human travel.


Behavior

They have been extraordinarily successful, in part, because different nests of the introduced Argentine ants seldom attack or compete with each other, unlike most other species of ant. In their introduced range, their genetic makeup is so uniform that individuals from one nest can mingle in a neighboring nest without being attacked. Thus, in most of their introduced range, they form 'super-colonies'. "Some ants have an extraordinary social organization, called unicoloniality, whereby individuals mix freely among physically separated nests. This type of social organization is not only a key attribute responsible for the ecological domination of these ants, but also an evolutionary
paradox A paradox is a logically self-contradictory statement or a statement that runs contrary to one's expectation. It is a statement that, despite apparently valid reasoning from true premises, leads to a seemingly self-contradictory or a logically u ...
and a potential problem for kin selection theory because relatedness between nest mates is effectively zero." The 'Very Large Colony', which covers territory from San Diego to beyond San Francisco, may have a population of nearly one trillion individuals. Conflict does occur between members of different supercolonies. In 1997, UC San Diego researchers observed fighting between different Argentine ants kept in lab, and in 2004 scientists began to map out the boundaries of the different supercolonies that clashed in San Diego. On the border of the 'Very Large Colony' and the '
Lake Hodges Lake Hodges is a lake and reservoir located within the city limits of San Diego, California. It is about north of Downtown San Diego, just north of the Rancho Bernardo community, and just south of the city's border with Escondido. When full, th ...
Colony' thirty million ants die each year, on a battlefront that covers many miles. While the battles of other ant species generally constitute colony raids lasting a few hours, or skirmishes that occur periodically for a few weeks, Argentine ants clash ceaselessly; the borders of their territory are a site of constant violence and battles can be fought on top of hundreds of dead ants. Fights may be halted by adverse weather such as rain. In contrast, native populations are genetically more diverse and form colonies that are much smaller than the supercolonies that dominate the introduced range. Colonies living in close proximity are territorial and aggressive toward one another. Argentine ants in their native South America also co-exist with many other species of ants, and do not attain the high population densities that characterize introduced populations.''Success of Introduced Argentine Ants Tied to Reduced Genetic Variation.''
Kim McDonald, University of California, May 2000
In a series of experiments, ants of the same colony were isolated and fed different diets. The hydrocarbons from the diet were eventually incorporated into the cuticle of the subjects. Those that had the same diet appeared to recognize one another as kin. Those who had at least some overlap in dietary composition also appeared to react non-aggressively to one another. These interactions contrasts drastically with the groups that fed on completely different sources, such as those who lived off
flies Flies are insects of the order Diptera, the name being derived from the Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advanced ...
and those that fed on grasshoppers. The groups appeared to have incorporated hydrocarbons that were not similar to the others and created an unfamiliar identity cue. These groups reacted violently towards each other. This suggests that dietary factors affect the recognition cues for colony members.


Reproduction and seasonal colony trends

Like workers in many other ant species, Argentine ant workers are unable to lay reproductive eggs but can direct the development of eggs into reproductive females; the production of males appears to be controlled by the amount of food available to the larvae. Argentine ant colonies almost invariably have many reproductive queens, as many as eight for every 1,000 workers. The seasonal low occurs in mid-winter, when 90% of a representative colony consists of workers and the remainder of queens, and no reproductive activity and minimal birthing. Eggs are produced in late-winter, nearly all of which hatch into sexual forms by May. Mating occurs after the females emerge. Worker production increases steadily from mid-March to October, after which their numbers are not replenished; thus, their numbers drop steadily over the winter months. Colonies in the Argentine ant's native habitat are kept within a range of ten to one hundred meters by colonies of interspecific and intraspecific rivals. As the colonies expand, they appear to form fluctuating territory borders, which contract and expand on a seasonal and conditional basis. There is an expansive push outward in the summer months, with a retreating motion in the winter. This has to do with soil moisture and temperature conditions. At the edges of these borders are either rival ''L. humile'' colonies or other obstacles that prevent further expansion, such as an inhospitable environment for nests.


Impact

The ants are ranked among the world's 100 worst invasive animal species. In its introduced range, the Argentine ant often displaces most or all native ants and can threaten native invertebrates and even small vertebrates that are not accustomed to defending against the aggressive ants. This can, in turn, imperil other species in the ecosystem, such as native plants that depend on native ants for seed dispersal, or
lizard Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia althou ...
s that depend on native ants or invertebrates for food. For example, the recent severe decline in coastal
horned lizard Horned lizards (''Phrynosoma''), also known as horny toads or horntoads, are a genus of North American lizards and the type genus of the family Phrynosomatidae. The common names refer directly to their horns or to their flattened, rounded bodies ...
s in southern California is closely tied to Argentine ants displacing native ant species on which the lizards feed. Argentine ants sometimes tend
aphid Aphids are small sap-sucking insects and members of the superfamily Aphidoidea. Common names include greenfly and blackfly, although individuals within a species can vary widely in color. The group includes the fluffy white woolly aphids. A t ...
,
mealybug Mealybugs are insects in the family Pseudococcidae, unarmored scale insects found in moist, warm habitats. Many species are considered pests as they feed on plant juices of greenhouse plants, house plants and subtropical trees and also act as a ...
, and
scale insect Scale insects are small insects of the order Hemiptera, suborder Sternorrhyncha. Of dramatically variable appearance and extreme sexual dimorphism, they comprise the infraorder Coccomorpha which is considered a more convenient grouping than the ...
colonies, sometimes relocating the parasites to unaffected plants, and their protection of these plant pests from predators and parasitoids can cause problems in agricultural areas. In return for this protection, the ants benefit by feeding off an excretion known as "honeydew". Thus, when Argentine ants invade an agricultural area, the population densities of these plant parasites can increase followed by an increase in damage to crops. There is also evidence that the presence of Argentine ant may decrease the number of pollinators that visit natural flowering plants via predation on the larvae of the pollinators.


Pest control

Argentine ants are a common household pest, often entering structures in search of food or water (particularly during dry or hot weather), or to escape flooded nests during periods of heavy rainfall. When they invade a kitchen, it is not uncommon to see two or three queens foraging along with the workers. Due to the large number of queens, eliminating a single queen does not stop the colony's ability to breed.
Diatomaceous earth Diatomaceous earth (), diatomite (), or kieselgur/kieselguhr is a naturally occurring, soft, siliceous sedimentary rock that can be crumbled into a fine white to off-white powder. It has a particle size ranging from more than 3  μm to le ...
has been used to dust trails, feeding sites and nest entrances.
Borate A borate is any of several boron oxyanions, negative ions consisting of boron and oxygen, such as orthoborate , metaborate , or tetraborate ; or any salt with such anions, such as sodium metaborate, and disodium tetraborate . The name also ...
-sucrose water baits are toxic to Argentine ants, when the bait is 25% water, with 0.5–1.0%
boric acid Boric acid, more specifically orthoboric acid, is a compound of boron, oxygen, and hydrogen with formula . It may also be called hydrogen borate or boracic acid. It is usually encountered as colorless crystals or a white powder, that dissolves ...
or borate salts. In spring, during a colony's growth phase, protein based baits may be more effective due to much higher demand from the egg-laying queens. Due to their nesting behavior and presence of numerous queens in each colony, it is generally impractical to spray Argentine ants with pesticides or to use
boiling water Boiling is the rapid vaporization of a liquid, which occurs when a liquid is heated to its boiling point, the temperature at which the vapour pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding atmosphere. Ther ...
as with mound building ants. Spraying with pesticides has occasionally stimulated increased egg-laying by the queens, compounding the problem.
Pest control Pest control is the regulation or management of a species defined as a pest; any animal, plant or fungus that impacts adversely on human activities or environment. The human response depends on the importance of the damage done and will range ...
usually requires exploiting their omnivorous dietary habits, through use of slow-acting poison bait (e.g.
fipronil Fipronil is a broad-spectrum insecticide that belongs to the phenylpyrazole chemical family. Fipronil disrupts the insect central nervous system by blocking the ligand-gated ion channel of the GABAA receptor and glutamate-gated chloride (GluC ...
,
hydramethylnon Hydramethylnon is an organofluorine compound. It is also known as AC 217,300. It is in a chemical class called trifluoromethyl aminohydrazone, which is a metabolic inhibitor. It is classified as a pesticide designed to control insects that are ...
, sulfluramid), which will be carried back to the nest by the workers, eventually killing all the individuals, including the queens. It may take four to five days to eradicate a colony in this manner. Researchers from the
University of California, Irvine The University of California, Irvine (UCI or UC Irvine) is a public land-grant research university in Irvine, California. One of the ten campuses of the University of California system, UCI offers 87 undergraduate degrees and 129 graduate and p ...
, have developed a way to use the scent of Argentine ants against them. The exoskeletons of the ants are covered with a hydrocarbon-laced secretion. They made a compound that is different, but similar, to the one that coats the ants. If the chemical is applied to an ant, the other members of the colony will kill it. The chemical method may be effective in combination with other methods. Another approach for a large scale control of the Argentine ant has been proposed by researchers from Japan, who showed that it is possible to disrupt its trails with synthetic pheromones. This has been confirmed in various later trials by a New Zealand-led team in Hawaii and by researchers from Victoria University of Wellington who showed that this approach is beneficial for other local ant species.


See also

* Linepithema humile virus 1, a virus carried by Argentine ants


References


External links

* with information on habits, habitat and prevention * * * {{DEFAULTSORT:Argentine Ant Dolichoderinae Agricultural pest insects Household pest insects Insects described in 1868 Hymenoptera of New Zealand Ants of New Zealand