Garry Webb, general manager of Sumitomo Chemical Australia, explains how understanding ant biology and behaviour leads to greater success with baiting. 

Ants are insects belonging to the order Hymenoptera (along with bees and wasps) and are one of the most successful insect groups on
the planet, having colonised every continent except Antarctica. Ants are considered ‘eusocial’ insects because of their complicated colony structure – these colonies rely on co-operation and well-defined roles.

Whereas bees and wasps can be solitary or live in small colonies, ant colonies are usually very large by comparison. An ant colony usually comprises a queen, or many queens, (and maybe a token king), larvae and workers. Usually once a year, the queen produces reproductive larvae that form the next wave of new colonies, the familiar flying ants observed in spring and summer. Not all ant species have a queen as such; in some species each individual has the potential to produce eggs.

Green-head ant (Rhytidoponera, pictured above)) is a good example of a ‘queenless’ ant, and bulldog ant (Myrmecia) workers maintain the ability to reproduce even if a queen is present.

Bulldog ant (Myrmecia nigriceps)

Ants differ in their biology, colony structure, food requirements and many other ways that complicate attempts to control or eradicate them. Foraging workers collect food from the environment and return it to the nest. 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 on to it, sometimes in a bizarre fashion.It has been recently discovered that late stage larvae of big-headed ant (Pheidole) actually lay on their backs with the solid food held in a depression in their abdomen, onto which they drool saliva. The worker ants collect the resulting ‘soup’ and distribute around the colony. This is the mechanism by which ants gain the proteinaceous food they require.

Although many ant baits focus on liquid or gel formats, due to their ease of processing within the colony, granular ant baits offer some real advantages, especially in outdoor, large area applications. Indeed for large area treatments, granular baits are the only bait to use due to their ease of application, and they also provide the best option for protein or oil feeders (as these food items are difficult to formulate into liquids and gels). Although granular ant bait technology has been used for a long time, pest managers sometimes report variable results. It’s worth pondering some of the biological reasons why failure may occur.

Bait matrix does not match food preference

We all know that many ants show strong preferences for different food types. But many species preferentially collect specific types of food at different times of the year. The application of ant bait of one food type in the wrong food window may result in rejection of the bait.

Bait may not be eaten immediately

Bait may be harvested by ants only to be cached in the nest for later consumption. As the bait action is delayed, the initial observation is that the bait has not worked.

Over-application of bait can disturb behaviour

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) sometimes display this behaviour, which results in removal and dumping of bait away from the nest. In this respect, sometimes less (and maybe more frequent) is better.

Delayed bait rejection

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) queens are much more sensitive to toxins than workers – so while the workers may collect the granule, the queen may reject the food source.

Of these four mechanisms of bait ‘failure’, only the last mechanism can truly be called a bait failure. The other causes of poor bait performance can be remedied by understanding the variations in ant biology and ensuring the correct bait and application techniques are used to deliver control. However, even with a good understanding of ant biology, we still need the tools to get control. For the pest management industry, the current range of granular ant baits are predominantly lipid-based (corn grit type baits) or protein based (extruded granules). Focusing on one food type rather restricts the range of species that can be controlled by a single bait, especially when it excludes the biggest group of ants – the sugar feeders.

Although we’ve all come to think of ants as being either sugar feeders or protein feeders, in reality all species must acquire the right balance of nutrients to maintain the health of the colony. Generally speaking, foragers of all species will take sugar to a greater or lesser extent; the foragers need energy more than protein or fat. However, the larvae and reproductives need protein for growth and reproduction. Many species show a big increase in protein preference when egg and brood production is on the rise. As a result, all ant colonies require a balance of carbohydrates (sugars), proteins and lipids and this can vary seasonally, expressed as an apparent preference for one food group or another. So a granular bait containing all these food components would have the potential to appeal to a wide range of species and remain attractive as their food preferences change through the year.

Sumitomo Chemical has been a key partner to government eradication programs of invasive ants such as red imported fire ant, electric ant and yellow crazy ant and continue to develop new types of baits to suit such programs as required.

Distance Plus evolved from these programs and is a single granule bait, containing multiple food attractants, to appeal to a broad spectrum of ants, with pyriproxyfen (IGR) as the active. Sumitomo Chemical has built on the performance of Distance Plus to create Synergy Pro ant bait, a truly unique granular bait.

Synergy Pro contains two separate food granules, each containing different combinations of carbohydrate, protein and lipids to ensure broad-spectrum appeal throughout the year. Performance is further enhanced with a dual active control system – a unique combination of pyriproxyfen (IGR) and hydramethylnon, to deliver the combined effects of queen sterilisation and worker mortality for more complete control. The combination of dual food granules and dual actives delivers a high performing, broad-spectrum bait that performs throughout the year – ‘Ant control made Simple’.

For successful ant control, ant identification is key and Sumitomo Chemical in conjunction with Bug Doctor Media has created the perfect tool for ant identification – The Pest Ant Handbook. The handbook also contains a wealth of information on ant biology which will help the pest management professional achieve successful control. Remember – it’s all about biology!

Garry Webb, General Manager, Environmental Health, Sumitomo Chemical Australia