Aggressive li’l invader now insect enemy number one

Aggressive li’l invader now insect enemy number one

27 January 2008

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Australia — In 1939, the year that much of Victoria was burnt to a crisp by the Black Friday bushfires, another natural disaster came to the state: the Argentine ant. The bushfires went. The ant, unfortunately, stayed and thrived.

Nearly 70 years later, the aggressive little invader is likely to become only the second insect, after the bumblebee, to be formally declared a potential threat under the state Flora and Fauna Guarantee Act. Given that the bumblebee is not yet in Victoria, this makes the three-millimetre black ant our nastiest alien insect.

The ants were first noticed in Balwyn, of all places, in the late 1930s. Now they are in almost every state, killing swarms of native ants in their path. The loss of native ants has flow-on effects: some plants rely on them to spread their seeds and animals such as the threatened pink-tailed worm lizard feed on them.

The State Government scientific advisory committee that recommended listing the Argentine ant described it as “one of the most widespread and invasive ant species in the world (with an) aggressive nature and an ability to recruit high numbers compared to indigenous ants”.

The convener of the committee, La Trobe University invertebrate ecologist Timothy New, said there was nothing significant about the location of the ant’s discovery. “I suspect it wasn’t introduced in Balwyn, it was just noticed there. My suggestion would be that it probably came in imported goods, but there’s no obvious direct proof of that.”

He said the committee was accepting public comment until the end of February, after which it would make its final decision. As to what difference it would make to eradication measures to have it officially listed, Professor New admitted that “in practice it may not make much of a difference” but at least the ant would be officially “flagged as a threat for serious consideration”.

“One of the things about flagging threatening processes is that they then gain support for (eradication) action and so on.”

The Argentine ant joins a long list of pest invaders. Rabbits, introduced from England in 1859, and cane toads, introduced in 1935, are probably the worst. Other introduced species such as the fox, deer, trout, carp, ostrich, camel, buffalo, blackbird, rat, mouse, European wasp and cattle tick, have had more subtle effects.

Unfortunately, Argentine ants are probably here to stay. Experts say that introduced social insects such as ants, wasps and bees are hard to control because their biology is geared to a social existence which allows them to overcome measures taken against them.

The ants have a sophisticated social structure. A Monash University study in 2004 found that colonies of the ants in Argentina, their homeland, were aggressive towards each other. But in Melbourne, said Monash researcher Elissa Suhr, “the ants are genetically uniform, no longer fight and have formed a giant supercolony that extends at least 100 kilometres across the city”.

The problem isn’t only in Australia. Thanks to global shipping, countries with Mediterranean climates have an Argentine ant problem. In California, supercolonies span 3000 kilometres.

Commercial traps are available to tackle ant colonies. Homemade remedies such as a mix of boric acid, water and sugar, placed in a shallow dish, can also be effective, and talcum powder may repel them.

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