Argentine ant
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| Linepithema humile Mayr, 1868 |
Native to northern Argentina, Uruguay, Paraguay, and southern Brazil, the Argentine ant (Linepithema humile, formerly Iridomyrmex humilis) has been inadvertently introduced by humans to many other areas of the world, such as South Africa, New Zealand, Japan, Easter Island, Australia, Hawaii, Europe, and many parts of United States, including the southeastern U.S. and California. In its introduced range, the Argentine ant often displaces most or all native ants. This can, in turn, imperil other species in the ecosystem, such as native plants that depend on native ants for seed dispersal, or lizards that depend on native ants for food. Argentine ants also cause problems in agricultural areas by protecting plant pests, such as aphids and scale insects, from predators and parasitoids. In return for this protection, the ants receive a sweet excretion, known as "honeydew". Thus, when Argentine ants invade an agricultural area, the population densities of these plant parasites increase, and so too does the damage they cause to crops. Finally, 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. Argentine ant colonies almost invariably have many reproductive queens, as many as eight for every 1,000 workers, so eliminating a single queen does not stop the colony's ability to breed. When they invade a kitchen, it is not uncommon to see two or three queens foraging along with the workers.
German entomologist Dr. Gustav L. Mayr identified the first specimens of Hypoclinea humilis in the vicinity of Buenos Aires, Argentina in 1866. This species was shortly transferred to the genus Iridomyrmex, and finally to Linepithema in the early 1990s.
They have been extraordinarily successful, in part, because different nests of the Argentine ants do not attack or compete with each other, unlike most other species of ants. 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 "supercolonies". In contrast, native populations are more genetically diverse, genetically differentiated (among colonies and across space), and form colonies that are much smaller than the supercolonies that dominate the introduced range. Argentine ants in their native South America also co-exist with many other species of ants (including, in some places, another damaging invasive ant, the red imported fire ant), and do not attain the high population densities that characterize introduced populations.
These tiny 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. The worker ants are only about 1.6 mm (1/16th inch) long. They can easily squeeze through cracks and holes no more than 1 mm (0.040 inch) in size. Queens are two to four times the length of workers.
They are attracted by electrical currents and are known to have caused damage to air conditioners, heat pumps, telephone junction boxes, traffic lights, gasoline pumps, and so on. When they become lodged or electrocuted between the contacts of relays, it damages the contacts and causes the equipment controlled by the relay to malfunction.
[edit] Pest control
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 as with mound building ants. Indeed, spraying with pesticides will stimulate increased egg-laying by the queens, compounding the problem. The most effective control is through use of slow-acting poison bait, 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. An effective homemade recipe1 consists of a solution of granulated white table sugar and boric acid, placed in a shallow dish in the area being invaded:
- 1/4 teaspoon boric acid powder
- 3 tablespoons water
- 1 tablespoon sugar
The boric acid will dissolve only if the water is hot, or one can mix the ingredients cold, then place the container in a microwave oven to bring the water to boiling temperature. When mixed in small quantities, the solution can be stored in a dropper bottle and dispensed as needed to replenish the bait dish. Although the solution isn't particularly hazardous when used in small quantities as described here, the bait dish should be placed out of reach of pets and children.
This formula works by desiccation and laceration. The solution begins to draw water from the ant's body, causing slow dehydration. Also, as the ants or their larvae transpire water, the solution becomes more concentrated, causing the boric acid to crystallize and lacerate the digestive tract.
In areas where the use of liquids or poisons are not desirable, Argentine ants may be repelled by ordinary talcum powder (baby powder) which contains talc. The powder does not appear to kill the ants, but they will try to avoid it after contact.
Scientists have developed a way to use the scent of Argentine ants against them. The exoskeleton 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 success of the chemical for controlling Argentine ants will depend on the cost, the ease of application, toxicity to non-target organisms and the frequency of reapplication. The chemical may work best in combination with other methods. [1]
[edit] Notes
Note 1: The recipe is scaled down from an article by Keith Muruoka in the Morgan Hill Times, Friday, December 27, 2002. The original formula called for 4 teaspoons boric acid powder, 3 cups of water and 1 cup of granulated sugar.
