National Eradication of Argentine Ants Desirable

Forest and Bird, Issue 303, 1 February 2002, Page 8

National Eradication of Argentine Ants Desirable

SIAN ROBINSON

} orest and Bird is seeking a national eradication programme against the Argentine ant which arrived here 12 years ago and is considered the second mostserious ant pest in the world. (The worst ant pest, the fire ant, arrived also in New Zealand last year — see ‘Dangerous Insects..." opposite page.) Argentine ants are a serious pest of households, conservation, horticulture and forestry. The Ministry of Agriculture and Fisheries says the ants will ‘eat virtually anything’. By habit, the ants protect aphids and other insect pests so they can feed on the honeydew these creatures produce. This behaviour could have serious implications for the horticulture industry, and especially for organic farmers who rely on predatory insects to keep pests such as aphids under control. Argentine ants displace and wipe out other insect populations such as native ants. Although they do not fly, they will climb trees, swarm bird nests and devour fledglings. Preferring sweet foods, they also consume flower nectar that would otherwise be a food source for native birds, geckos and insects. They are light to dark honey-brown, two to three millimetres long and bite — but are not poisonous. In New Zealand the ants are still spreading, with new populations recently being found in Kaitaia and Hamilton. Since 1990, Argentine ants have been found in Christchurch, Dargaville, Hastings, Morrinsville, Mt Maunganui, Nelson, Warkworth, Wellington, Whangaparoa and Whangarei. The ants were also found on Tiritiri Matangi Island, a wildlife sanctuary in the Hauraki Gulf, where they probably arrived during construction of a

new wharf in 1998. Forest and Bird’s biosecurity officer, Karli Thomas, says the insects are considered one of the world’s worst pest ant species because they are aggressive and highly organised. Cooperation between separate colonies of the ants allows them to build up to phenomenal numbers — up to six nests per square metre have been found in Auckland. "The pressure from such a huge ant population — and its huge appetite — has impacts on households, primary industry and conservation, she says. "The ants are a huge headache for households, as they can get into

microwaves, fridges and even screw-top jars. There are currently no commercially available chemicals known to control the ants, but various baits are being trialled and MAF says it is still investigating the viability of completely eradicating Argentine ants. Early indications of the effectiveness of eradication trials on Tiritiri and in Nelson and Mt Maunganui are promising, but no clear results will be available until the end of this summer. Argentine ants were first found in New Zealand at the Mt Smart stadium in Auckland, site of the Commonwealth

Games in 1990. It is thought the ants arrived there via transported goods from an industrial area in nearby Onehunga. The then Ministry of Agriculture and Fisheries surveyed the area and found that the ants had already become well established in several Auckland suburbs. MAF says it was decided at that time that the ants would not be eradicated because there were no known control methods and the ants were not then considered a threat to agriculture. Since then Argentine ants have been spread from infested areas mainly through the collection of rubbish and movement of goods from car dealerships and plant nurseries. Most infestations have been in small areas, confined to less than two hectares, but Karli Thomas says action must be taken urgently to destroy the ‘satellite’ infestations outside Auckland and to prevent any further spread of the ant. With infestations in ports at Tauranga and Nelson there is a real risk of transporting the ants to other New Zealand ports, or even to trading partners overseas, Karli Thomas says.