Urban garden. Image – Colin Muerk
Unlike many other ant species, Argentine ants have a relatively slow rate of natural spread because their queens do not disperse by flight, but rather by a process of 'budding', in which a fertile queen and workers split off from an existing nest to form a new colony close by. This limits the natural expansion of Argentine ants to about 150 m per year. Therefore, containment should be achievable where effective and coordinated management can restrict Argentine ant infestations to relatively small areas, and even lead to the possibility of localised eradication. However, this would depend on having the very best suite of control tools available, a well-resourced management team, and a total commitment to the cause.
As yet, total eradication of an Argentine ant infestation in New Zealand has not been verified. Several baiting campaigns have come close, with the most well known being the near-total removal of Argentine ants from Tiritiri Matangi Island by the Department of Conservation. Ten years after beginning the campaign on Tiritiri Matangi, a few small colonies of Argentines are still being detected, but it is unclear whether these are true survivors of the original infestation or represent subsequent new incursions to the island (Chris Green, pers. comm.) However, what is clear is that the ongoing control undertaken on Tiritiri Matangi has been successful in completely minimising the spread and impacts of Argentine ants on the island .
In New Zealand, Argentine ants are still primarily associated with urban and suburban areas, and these habitats have their own challenges when it comes to managing ant populations. Concrete kerbing, footpaths, and sealed surfaces provide ant highways, allowing them to move more rapidly and over longer distances than if they had to move through grass or leaf-litter. Concrete surfaces are also alkaline in nature and rapidly break down many existing insecticidal surface treatments. Land ownership and management is often divided into small blocks, especially in residential areas, leading to major difficulties in coordinating control activities over an entire infestation. In these situations, there is no one-size-fits-all approach to ant control, and a variety of effective control tools and techniques are required.