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OUTDOOR ANT CONTROL: NOT ALWAYS A SIMPLE SOLUTION

Successful ant control comes down to skill, pest knowledge and using the right products for the job.

 

There is nothing simple about ant control. Simply carrying out a spray treatment and killing just a few worker ants on their foraging trails will not resolve the problem. There are many species of ant that can infest the home and yard and they all require slightly different approaches to achieve effective control. Inside the premises, the best options are likely to be a combination of gels and sprays; but outside requires a more sophisticated approach that incorporates greater knowledge of the biology of each species.

Ants differ in their biology, colony structure, food requirements and many other ways, which complicates attempts to control or eradicate them. The key role of the worker ants is to feed the colony. Worker ants can forage a long way away from the nest, which may not be located where the problem appears to be. In an open outdoor environment, ants may seek food from multiple sources.

Liquid food, such as honeydew from plants and sap- sucking insects, is ingested and then transferred to the larvae and queen by trophallaxis (regurgitation of the liquid). Solid food such as insects, seeds and granular bait is returned to the nest where the larvae are able to digest it by secreting enzymes onto it. Control efforts must be targeted at the key elements of the colony – the queen and her larvae – because worker ants usually have a short lifespan. They ‘wear out’ and are rapidly replaced by the next generation of workers.

Ant bait technology provides the mechanism for delivering toxins directly to the colony, irrespective of where it is located, by utilising the ants’ natural foraging behaviour. Granular ant bait technology has been used for a long time with variable success and it is worth pondering some of the biological reasons why inconsistent results may occur. Understanding the variations in ant biology is key to determining why ant baits may not give the desired effect.

Some species such as the green-head ant and big-headed ant (coastal brown) readily take most forms of bait and therefore are relatively easy to control. Other species may preferentially collect specific types of food at certain times of the year and the application of ant bait in the wrong ‘food window’ may result in rejection of the bait. This has been observed in the Argentine ant and yellow crazy ant.

Bait may also be harvested by ants only to be cached in the nest for later consumption and hence a delayed reaction occurs. Even the mode of application can interfere with bait acceptance. For instance, placing a large amount of bait directly on the nest may lead to rejection because the ants consider it a threat or a disturbance to their normal mound activity. Meat ants (Iridomyrmex spp.) sometimes display this behaviour, resulting in the removal and dumping of bait away from the nest. In this respect sometimes less (and maybe more frequently applied) is better.

Bait harvesting by ants does not necessarily guarantee consumption. While granules may be taken into the nest, they may soon reappear and be dumped because the colony has detected some threat from the bait, usually detection of the toxin. Argentine ant (Linepithema spp.) queens (main picture, above) are much more sensitive to toxins than workers – so while the workers may collect the granule, the queen may reject the food source.

The latest threats on the horizon for pest managers to consider (at least in Queensland and northern Australia) are those invasive ants from tropical regions of the world. These include red imported fire ant, tropical fire ant, Singapore ant, pharaoh ant and browsing ant. Luckily most of these are susceptible to a range of different ant baits, but browsing ant infestations in Brisbane, Darwin and Perth have proved problematic for the same reasons that yellow crazy ant and Argentine have been – an inconsistent uptake of bait.

Sumitomo Chemical has been a key partner to government eradication programs of invasive ants and some of the baits developed for these programs are available to professional pest managers for general ant control.

Distance Plus, containing the IGR pyriproxyfen, was developed originally for the control of red imported fire ants, but through careful enhancement with food-grade ingredients that are attractive to other species of ant, it is now suitable for use against a wide range of ants found commonly in urban environments. It was developed in response to the need for a more all-purpose bait suitable for those finicky feeders such as yellow crazy ants and Argentine ants. Based on an insect growth regulator, with a favourable safety profile, it is ideal for ant control programs in sensitive accounts and even cropping areas and national parks. There is, however, a speed of action trade-off, with the insect growth regulator taking several weeks to gain control.

For faster control of outdoor ants, Synergy Pro is the preferred option. Synergy Pro contains two different food granules, which can help overcome bait avoidance. It also contains two active ingredients (the IGR pyriproxyfen and the ATP inhibitor hydramethylnon), which means it combines the effects of queen sterilisation with worker mortality. As ant colonies may require different food types at different times of the year, or may have an overriding preference for one food type, Synergy Pro offers an effective solution for such problematic species.