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INVASIVE ANTS IN AUSTRALIA – A BIGGER PROBLEM THAN WE REALISE

Garry Webb, general manager of Sumitomo Chemical Australia, outlines the very real risk Australia faces from invasive ants.

Australia is an ideal environment for the introduction and establishment of invasive ants. There is an endless stream of container ships arriving at Australian ports from all over the world, and the geography of Australia provides a wide range of environments for even the most biologically specialised foreign ant species to find a home.

There are five ant species on the world’s most invasive species list and Australia has all five of them – Argentine ant, African big-headed ant (pictured above) yellow crazy ant, little fire ant and red imported fire ant. Along with these we have tropical fire ant and the very recent introductions of Lepisiota frauenfeldi at Perth Airport and red imported fire ant at the Botany port terminal in Sydney. There are also a range of ant species of cosmopolitan but uncertain origin including pavement ants (Tetramorium), white- footed house ant (Technomyrmex), ghost ant (Tapinoma), black crazy ant (Paratrechina) and various species of Monomorium, that very likely are also invasive species.

Invasive ant species have certain characteristics that allow them to rapidly exploit new environments:

  • Omnivorous – able to eat a wide range of food types
  • Multi-queen, multi-nest colony structures – allows for rapid expansion to dominate a given area with the potential for the formation of super-colonies
  • Strongly territorial – not only out-competing other ants species for food sources but tend to actively defend their territories.

When invasive ants gain a foothold in an area, they can rapidly expand their territory and become very difficult to control.

Red imported fire ant (RIFA) was discovered in Brisbane in 2001 and since then the joint federal and state task force has spent in excess of $280M attempting to eradicate them. To a large extent they have been successful in this endeavour. They have eliminated them from the core areas of infestation but less so in limiting their outward expansion and re-infestation of past-infested areas due to operational difficulties in limiting the movement of soil, plants, building material and earthmoving equipment. Nevertheless, the Brisbane program has been the most successful eradication program worldwide, with the exception of the elimination of a small infestation in New Zealand.

RIFA remains a very significant cost to the economy of southern USA where it has now spread from Florida to California. The very recent discovery of a RIFA nest in Sydney has served as a reminder that complacency is dangerous and RIFA has the potential to wreak havoc on the economy and the environment.

However, RIFA is just the tip of the iceberg. We recognise the human and environmental cost of this one species – it has a painful sting that can cause anaphylaxis, it can cause crop and livestock losses, and rapidly dominates natural environments. But rarely do we consider the impact of other invasive species.

Yellow crazy ant has a very significant environmental impact worldwide and incursions on Christmas Island, in Arnhem Land and in Cairns are the subject of current eradication programs. Many people would be familiar with the story of the demise of red crabs on Christmas Island. Similarly, the infestation of Cairns and surrounding areas by little fire ant is the focus of a separate eradication program.

Little fire ant (Wasmannia auropunctata)

Tropical fire ant is a recognised ecological risk in northern Australia, particularly on outlying islands. Argentine ant in southern Australia and African bigheaded ant in coastal eastern Australia, northern Australia and around Perth are now accepted incursions with little or no effort to eradicate or control them. African big-headed ant (or coastal brown ants as most of us call them) is probably the oldest incursion first recognised in the 1930’s but very likely present here for in excess of 100 years.

Where these species take hold they change the ecosystem. By dominating the ant and insect fauna they upset the food chain. Impacting other invertebrates has a knock on effect to small reptiles and birds that continues up the food chain. The end result is that the balance of the ecosystems can quickly change, causing the disappearance of many species.

Argentine ant (Linepithema humile)

Such rapid changes in ecosystems are likely to have other unintended consequences that we cannot predict. However, as these species do not present an immediate health risk or their financial impact cannot be quantified, in many cases we’ve given up the challenge of eradication and come to accept them even though the environmental cost is significant.

But if we want to attempt control or at least check the advance of these species, what control methods should we use? Common to all ant eradication programs is the utilisation of a combination of control measures, but primarily a reliance of ant bait technology using a range of slow acting active ingredients such as the IGRs pyriproxyfen and s-methoprene, as well as hydramethylnon and fipronil.

Identifiable colonies can be treated by direct nest treatment with a liquid toxicant while granular bait technology offers the advantage of broadcast application by hand, ATV or helicopter for residual and preventative treatments where colonies are not readily identifiable. As with all ant control programs, development of a food matrix to match the food preferences of the target species is key, as is understanding their biology so that the timing and frequency of bait application provides the best chance of control.

Complacency and reduced political will (and funding) are the risk we face in the future. Increased diligence in border interceptions and incursion response are key to keeping Australia relatively free of species that threaten both the economy and environment. Professional pest managers can play an important role in maintaining vigilance against incursions by reporting all unusual ant sightings to state authorities.

Garry Webb, General Manager, Environmental Health & Professional Products, Sumitomo Chemical Australia