Backyard blitz: feral fire ants are costing the country millions in control programs. Why? Because we've seen the impact of these ferocious pests on the outdoor lifestyle in America.
But the bull ant has nothing on the red imported fire ant. A tiny, aggressive feral that attacks en masse, swarming over its victim and stinging repeatedly. Identified in February last year in Brisbane, Australia has been battling this angry little menace ever since as it has the potential to ruin our cherished outdoor lifestyle and seriously threaten native wildlife and agriculture.
Red imported fire ants (Solenopsis invicta--"invicta" being the Latin for undefeated or unconquered) appeared in two locations almost simultaneously. This was concerning enough for authorities, but the two colonies also appeared to be of slightly different strains. Scientist concluded that one colony had come from North America and the other from South America.
Investigation began into how the ants had arrived in Australia, how long ago and, more importantly, how far they had spread. Authorities hastily declared them an exotic pest and set in place procedures to attempt containment and eradication.
It is thought that fire ants were probably here for three to five years prior to discovery, and that while they have appeared in Victoria they have largely been confined to Brisbane's south-western suburbs and a smaller area near the mouth of the Brisbane River.
While authorities are little further down the path of discovering how they got here, except to say that it was probably by boat, what is of more concern is that they broke through quarantine twice, and weren't discovered until years later.
So why the panic? What damage can ants just two to six millimetres long do? Fire ants pose a threat on a number of fronts.
Fire ants are highly aggressive and when disturbed they attack in large numbers. Their bite is painful, produces pussy blisters and causes severe itching that can last for a week. Although rare, if a victim is allergic to the bite, the result can be fatal.
The fire ant's ability to reproduce and spread rapidly means that large areas could become virtually unusable for outdoor recreation. Schoolyards, parks and backyards are all vulnerable, along with the lifestyle that most of us take for granted.
The second threat posed is their effect on the surrounding environment and the fauna and flora. Due to their aggressive nature, fire ants tend to displace native ants, disturbing the natural ecosystem. Moreover they are capable of killing a large number of small creatures, such as frogs and lizards, even newborn calves.
It is anticipated that the presence of fire ants could result in the elimination of a number of species vital to the health and wellbeing of localised ecosystems, dramatically affecting biodiversity levels in Australia. Researchers have observed that in areas of infestation the local skink lizard populations have been wiped out, despite prospering in nearby areas, and bush cockroach numbers have been reduced by up to 90 per cent.
Fire ants also pose a critical threat to agriculture. Among other sources of food, they feed on seeds and interfere with root growth. The direct result is lower yields for crops and poorer returns for farmers. In North America, attacked crops have ranged from citrus trees to corn and soybeans.
In addition, fire ants are known to infest fruiting trees and plants. While they may not diminish the quality of the crop, their presence will dramatically impede harvesting.
Finally, and curiously, fire ants are a serious threat to electrical infrastructure. They are attracted to devices such as electrical motors, circuit boxes and relays and when in contact with these devices, they often cause short circuits that result in fires.
Fire ants originate from South America and managed to travel to North America in the 1930s. The ants are now a major pest in Texas, California and other parts of the south. Texas spent approximately $US580 million last year tackling the problem and estimates of damage run to $US2 billion per year. America is now beyond the point of eradication but is making advances in techniques for reducing the population.
In South America the ants are naturally controlled by parasitic flies (phorid flies) and other ant-eating creatures. The tiny flies, hardly visible to humans, hover above the ants until selecting a target. They then strike rapidly by injecting an egg into the ant's abdomen. This temporarily paralyses the ant.
Over the next 10 days the egg develops into a larva and expands into the ant's head, slowly killing it. Once the ant is dead the larva emerges through the head and develops into an adult fly.
Texas also has a native fire ant (not the red imported fire ant) that is kept in check by a very similar fly and so has never become a pest. Research is being conducted in Texas to see if the introduction of the South American phorid flies will assist in controlling the population. But as Queenslanders well know, thanks to the cane toad, biological controls can have a devastating impact in new ecosystems. Phorid flies also appear to have quite a complex set of requirements for their hosts so no single phorid species will target all fire ants. As a result many species and combinations of species have to be bred and tested.
Australian governments have set aside $123 million for a national fire ant eradication program to run over five years. Close to 500 staff have been employed and quarterly treatment has begun of 68,000 properties suspected of infestation.
Treatment involves baiting properties for 3 years. The bait is a combination of two active ingredients (S-methoprene and pyriproxyfen) plus a food source, normally vegetable oil. The ants carry the bait back to the nest. Once there, it is combined with the rest of the food supply and quickly makes its way to the queen and her young.
The active ingredients are "insect growth inhibitors" and work by preventing the ant larvae from developing into adult ants.
Unfortunately, the bait is also attractive to other insects.
Initial indications point to baiting being an effective control but no country has ever achieved eradication of the fire ant before.
Ants may be controlled but there will always be the risk of re-emergence. And who's to say they won't arrive "fresh off the boat" through imported products again?
Knowledge and reporting are two essential ingredients of successful control programs. It's important that we learn to recognise fire ants through their appearance, the character of their nests and behaviour.
Red fire ants are small (2-6 mm long), reddish-brown with a black abdomen, agitated and aggressive when disturbed, have nests up to 25cm high, normally with no opening (native ants nest usually do have a visible opening) and a nasty sting that produces blisters.
Check imported materials such as pot plants for their presence, be vigilant if travelling interstate, and report any sightings immediately to the Department of Primary Industries in your state.
Despite the fact that we seem to have responded to the threat of fire ants, only time will tell if it is enough. Yet in truth even if it is enough, it is unlikely to be the last time these measures will be brought into place. All up, we are in a position where we must remain vigilant and continually improve our watch. We must be prepared with disaster plans in place ready to go.
In the meantime, I intend to go on a picnic and console myself with icecream.
Lucy Spence is ACF's website officer.
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|Date:||Feb 1, 2002|
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