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TRAMP ANT INVASION IN AUSTRALIA – THE RISKS AND CONSEQUENCES

Garry Webb of Sumitomo Chemical summarises the risk posed by tramp ants. 

Australia is a geographically isolated environment, with unique flora and fauna. It is the only country that occupies an entire continent. With a landmass of 7.6 million square kilometres and a massive 36,000 km of coastline, such dynamics pose all sorts of difficulties in minimising the incursion of any invasive organism, including tramp ants.

Our porous borders have minimal quarantine surveillance, despite the best efforts of federal and state Biosecurity agencies. Some of our worst invasions have been man- induced – witness the rise of the cane toad, the rabbit, the fox and many others – but most are the unintended consequence of trade and people movement.

Australia has a diverse and highly endemic ant fauna that is highly susceptible to habitat invasion by tramp ants from elsewhere. The International Union for Conservation of nature (IUCN) lists five ant species among the 100 most invasive alien species, all of which have already established in Australia. These include the yellow crazy ant (sixth on the list), Argentine ant (48), African big-headed ant (68), red imported fire ant (86) and little fire ant (100) and there are many other alien ant species already here that do not even make the list.

The threat is so acute that the Australian Government has prepared a ‘Threat Abatement Plan’, which establishes a national framework to guide and coordinate Australia’s response to tramp ants. The plan lists six key threatening species, the five listed above, plus the tropical fire ant. These are all considered to have significant impacts on society and the environment including human health, urban amenity, tourism, agriculture, forestry, biodiversity and ecological communities.

Australia’s response to tramp ants focuses on these high impact species, but there is recognition that Australia is under threat from a wide range of other tramp species, many of which are already well established here. A number of some species commonly encountered by pest management professionals are in fact invasive species.

These include white-footed house ant, ghost ant, black crazy ant, Singapore ant, pharaoh ant and many others.

Tramp ants have several key characteristics in common which make them superb invaders – broad food and habitat requirements, polygyny (multiple queens), ability to form super-colonies (multiple co-operating nests), high levels of aggression towards native ants and well developed mutualism with honeydew producing insects. These characteristics pose serious challenges for the detection of invasions, the long-term management or eradication of these invasive species and minimising the impact on native ant species.

Most pest management professionals would now be aware of the significant incursions of the red imported fire ant (RIFA) in Brisbane and then later in Gladstone and more recently in Sydney. Complete eradication of RIFA from Australia is the goal of the current programs
in both Queensland and NSW. Such is the threat that the funding under the national cost-sharing scheme has already reached in excess of $280 million for the eradication effort since the first detection in Brisbane in 2001.

In the southern USA where RIFA has been established since the 1930s and eradication is no longer an option, it is estimated that the economic and social cost is in the order of US$6 billion per year with $1 billion per year in Texas alone.

While RIFA has a much higher profile and significantly more media attention than the other five species largely because of its potent sting and potential human impacts like anaphylactic shock and sensitisation, the threat profile of the other species is no less important from other perspectives. Little fire ant also has a potent sting and is of concern to human health. The more localised infestation in Cairns is still under active management with the ultimate goal of eradication in the next few years.

Yellow crazy ant is listed at number six on the IUCN list largely because of its ecological impacts. Many would have seen the various documentaries and news items on the impact of yellow crazy ant on the Christmas Island red crab. There have many other, albeit, lower profile incursions of yellow crazy ant in the Northern Territory (Arnhem Land, Darwin), in Queensland (Cairns and the Wet Tropics, Brisbane, Gladstone) in NSW (Yamba) and on Cocos Island. Some infestations have been eradicated, but the battlefront remains in Arnhem Land and in the Wet Tropics.

The fight to eradicate tropical fire ant, Argentine ant (pictured above) and African big-headed ant is over and all three have become widely established within their preferred climatic ranges. There are still sporadic attempts to eradicate isolated infestations when they occur, such as the tropical fire ant on the Tiwi Islands and in northern WA, and African big-headed ant in some conservation areas in the Northern Territory.

In fact African big-headed ant has become so widespread since its likely introduction over 100 years ago, Australia has adopted it as its own – the coastal brown ant!

The most recent incursions of tramp ants both involved the browsing ant (Lepisiota frauenfeldti) at Perth airport and in Darwin, with local agencies pursuing eradication strategies.

Where these invasive species take hold they change the ecosystem – by dominating the ant and insect fauna they upset the food chain. The impact on other invertebrates has a knock on effect to small reptiles and birds, a knock on effect that continues up the food chain. They can have direct impacts on breeding populations of seabirds, turtles and crustaceans. The end result is that the balance of the ecosystems can quickly change, causing the disappearance of many species.

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.

Complacency and reduced political will (which effects funding) are the risks 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 of Australia. Professional pest managers can play an important role in maintaining vigilance against incursions by reporting all unusual ant sightings to state authorities.

Other ant species.

Garry Webb, General Manager Professional Products, Sumitomo Chemical

References:

Lowe S.J., Brown M. and Boudjelas S. (2001). 100 of the world’s worst invasive alien species. Aliens: The Invasive Species Bulletin 12: 1-14.

Commonwealth of Australia (2006). Background document for the threat abatement plan to reduce the impacts of tramp ants on biodiversity in Australia and its territories. Dept of the Environment and Heritage, Canberra.