Two distinct species of fire ants (genus Solenopsis ) from South America have been introduced into the United States this century. The South American black fire ant (S. richteri ) was first introduced into the United States in 1918. Its close relative, the red fire ant (S. wagneri ), was introduced in 1940, probably escaping from a South American freighter docked in Mobile, Alabama. Both species became established in the southeastern United States, spreading into nine states from Texas across to Florida and up into the Carolinas. It is estimated that they have infested over 320 million acres (130 million ha) covering 13 states as well as Puerto Rico.
Successful introduced species are often more aggressive than their native counterparts, and this is definitely true of fire ants. They are very small, averaging 0.2 in (5 mm) in length, but their aggressive, swarming behavior makes them a threat to livestock and pets as well as humans. These industrious, social insects build their nests in the ground—the location is easily detected by the elevated earthen mounds created from their excavations. The mounds are 18–36 in (46–91 cm) in diameter and may be up to 36 in (91 cm) high, although mounds are generally 6–10 in (15–25 cm) high. Each nest contains as many as 25,000 workers, and there may be over 100 nests on an acre of land.
If the nest is disturbed, fire ants swarm out of the mound by the thousands and attack with swift ferocity. As with other aspects of ant behavior, a chemical alarm pheromone is released that triggers the sudden onslaught. Each ant in the swarm uses its powerful jaws to bite and latch onto whatever disturbed the nest, while using the stinger on the tip of its abdomen to sting the victim repeatedly. The intruder may receive thousands of stings within a few seconds.
The toxin produced by the fire ant is extremely potent, and it immediately causes an intense burning pain that may continue for several minutes. After the pain subsides, the site of each sting develops a small bump which expands and becomes a tiny, fluid-filled blister. Each blister flattens out several hours later and fills with pus. These swollen pustules may persist for several days before they are absorbed and replaced by scar tissue. Fire ants obviously pose a problem for humans. Some people may become sensitized to fire ant venom, have a generalized systematic reaction, and go into anaphylactic shock. Fire-ant induced deaths have been reported. Because these species prefer open, grassy yards or fields, pets and livestock may fall prey to fire ant attacks as well.
Attempts to eradicate this pest involved the use of several different generalized pesticides, as well as the widespread use of gasoline either to burn the nest and its inhabitants or to kill the ants with strong toxic vapors. Another approach involved the use of specialized crystalline pesticides which were spread on or around the nest mound. The workers collected them and took them deep into the nest, where they were fed to the queen and other members of the colony, killing the inhabitants from within. A more recent method involves the release of a natural predator of the fire ant, the "phorid" fly. The fly releases an egg into the fire ant. The larva then eats the ant's brain while releasing an enzyme . The enzyme systematically destroys the joints causing the ant's head to fall off. The flies were released in 11 states as of 2001 and seem to be slowly inhibiting the growth of the fire ant population. As effective as some of these methods are, fire ants are probably too numerous and well established to be completely eradicated in North America.
[Eugene C. Beckham ]
Holldobler, B. The Ants. Cambridge: Harvard University Press, 1990. Taber, Stephen Welton. Fire Ants. Texas A&M University Press, 2000.
Vergano, Dan. "Decapitator Flies will Fight Fire Ants." USA Today, November 20, 2000.
"Imported Fire Ant." NAPIS Page for BioControl Host. April 2001 [cited May 2002]. <http://www.ceris.purdue.edu/napis/pests/ifa/ifabc.html>.
"Invasive Species and Pest Management: Imported Fire Ant." Animal and Plant Health Inspection Service. May 2002 [cited May 2002]. <http://www.aphis.usda.gov>.
Aina mbili tofauti za chungu wa moto (genus Solenopsis) kutoka Amerika Kusini zimeingizwa nchini Marekani karne hii. Nyigu wa moto mweusi (S. richteri) alianzishwa mwaka 1918 na kuenea katika nchi za Amerika Kusini. Nyigu wa moto (S. wagneri) alianzishwa mwaka 1940 na kuhamishwa kutoka kwa meli ya kubebea mizigo ya Amerika Kusini iliyokuwa imesimama katika bandari ya Mobile, Alabama. Spishi zote mbili zilianza kuenea katika sehemu ya kusini-mashariki mwa Marekani, na kuenea katika majimbo tisa kuanzia Texas hadi Florida na hadi Carolina. Inakadiriwa kuwa imeathiri zaidi ya ekari milioni 320 (130,000,000) katika majimbo 13 na Puerto Riko. Mara nyingi aina za chungu zinazopatikana kwa mafanikio huwa na jeuri zaidi kuliko zile za asili, na hilo ni kweli kabisa kuhusu chungu wa moto. Wao ni wadogo sana, wastani wa urefu wa 0.2 in (5 mm), lakini tabia yao ya uhasama, ya kuvuja, huwafanya kuwa tishio kwa mifugo na wanyama wa kufugwa na wanadamu. Wadudu hao wenye bidii na wenye kushirikiana na wengine hujenga viota vyao ardhini - mahali pao panapoonekana kwa urahisi ni kwenye vilima vya udongo vilivyoinuliwa kutokana na uchimbaji wao. Milima hiyo ina kipenyo cha sentimita 46 na inaweza kuwa na urefu wa sentimita 36 na sentimita 91 ingawa kwa ujumla milima hiyo huwa na urefu wa sentimita 15 na sentimita 25. Kila kiota kina wafanyakazi 25,000, na huenda kukawa na kiota zaidi ya 100 kwenye ekari moja ya ardhi. Kiota hicho kinapovurugwa, maelfu ya chungu wa moto hutoka ndani ya kilima hicho na kushambulia kwa ukali. Kama ilivyo na mambo mengine ya tabia ya chungu, pheromone ya kemikali ya kuonya hutolewa ambayo husababisha shambulio la ghafula. Kila chungu katika kundi hilo hutumia taya zake zenye nguvu kuuma na kushikamana na chochote kinachovuruga kiota, huku akitumia kisu kilicho kwenye ncha ya tumbo lake kuuma mhasiriwa mara kwa mara. Mvamizi anaweza kuumwa maelfu ya mara kwa sekunde chache tu. Sumu inayotokezwa na chungu huyo ni yenye nguvu sana, na mara moja husababisha maumivu makali ya kuchoma ambayo yaweza kuendelea kwa dakika kadhaa. Baada ya maumivu kupungua, mahali pa kila kuumwa hutokea mlipuko mdogo ambao huongezeka na kuwa mlipuko mdogo uliojaa umajimaji. Kila mlipuko hufifia baada ya saa kadhaa na kujazwa na umajimaji. Pustuli hizo zilizovimba zaweza kudumu kwa siku kadhaa kabla ya kufyonzwa na kubadilishwa na tishu ya kidonda. Ni wazi kwamba chungu wa moto ni tatizo kwa wanadamu. Watu fulani wanaweza kuwa na hisi ya sumu ya chungu, kuwa na athari ya kawaida, na kupata mshtuko wa anaphylactic. Mauaji yanayosababishwa na chungu wa moto yameripotiwa. Kwa sababu spishi hizo hupendelea mashamba au viwanja vilivyo wazi, wanyama-vipenzi na mifugo yaweza pia kushambuliwa na chungu wa moto. Jitihada za kuangamiza wadudu hao zilitia ndani kutumia dawa kadhaa za kuua wadudu, na pia kutumia petroli ili kuchoma kiota na viumbe wake au kuua chungu kwa kutumia mvuke wenye sumu. Njia nyingine ilihusisha matumizi ya dawa za kuua wadudu za kipekee zilizosambazwa juu au karibu na kilima cha kiota. Wafanyakazi hao waliwakusanya na kuwapeleka ndani ya kiota, ambapo walilishwa na malkia na washiriki wengine wa koloni, wakiwaua wakazi kutoka ndani. Mbinu ya hivi karibuni zaidi inahusisha kuachilia huru mwindaji wa asili wa chungu wa moto, nzi anayeitwa "phorid". Nzi hutoa yai ndani ya chungu cha moto. Kisha chungu huyo hula ubongo wa chungu huyo huku akitoa enzyme. Enzyme hiyo huharibu viungo kwa utaratibu na kusababisha kichwa cha chungu kianguke. Ndege hao waliachiliwa katika majimbo 11 kuanzia mwaka 2001 na wanaonekana kuwa wanazuia ukuaji wa idadi ya chungu wa moto. Ingawa mbinu hizo zina matokeo mazuri, huenda ikawa kwamba chungu wa moto ni wengi sana hivi kwamba hawawezi kuangamizwa kabisa huko Amerika Kaskazini. [Eugene C. Beckham] Holldobler, B. Chungu. Cambridge, Harvard University Press, 1990) ni moja ya maktaba ya chuo kikuu cha Uingereza. Taber, Stephen Welton. Chungu wa Moto. Texas A&M University Press, 2000) ni moja ya maktaba ya Marekani. Vergano, Dan. "Nzige Watoa-Kichwa Watapigana na Chungu wa Moto". USA Today, Novemba 20, 2000 "Mnyama wa Moto Aliyeingizwa". NAPIS ukurasa kwa ajili ya BioControl Host. Aprili 2001 [kutajwa Mei 2002]. "Hii ni kwa sababu ya ""Cerise"" (Cerise) na ""Purpose"" (Purpose) na ""Purpose"" (Purpose) na ""Purpose"" (Purpose) na ""Purpose"" (Purpose) na ""Purpose"" (Purpose) na ""Purpose"" (Purpose) na ""Purpose"" (Purpose) na ""Purpose"" (Purpose) na ""Purpose"" (Purpose) na ""Purpose"" (Purpose)." "Aina za Wanyama Wanaovamia na Udhibiti wa Wadudu: Chungu wa Moto Aliyeingizwa". Huduma ya Ukaguzi wa Afya ya Wanyama na Mimea. Mei 2002 [kutajwa Mei 2002]. "Hii ni kwa sababu ya ""http: www.phys.usda.gov."