Charles McClintock of Sumitomo Chemical shares his tips on how to ensure ants take the bait during the winter months.

Termite professionals are very aware that bait performance drops off in winter. Termites may continue to take bait back to the nest, but colony control does not appear to kick in until the weather warms up in spring. The result is that termite baiting over winter can take many months to provide control. The question is, does this occur when using baits on ants?

To address this question, it is important to understand how baits work, how baits are processed in the colony, food preference in winter and the reproductive status of the colony in winter. Ant baits work very differently to termite baits.

Termite baits contain an insect growth regulator and kill workers when they moult. In most species the rate of moulting decreases or stops during winter so termite baits appear not to work – the workers do not die, even though they will have ingested a lethal dose. The bait will also have impacted egg laying and brood development, but this will not have resulted in a noticeable drop in the level of foraging. Termites may continue to take bait back to the nest and cache it for later use.

Ant baits generally use only insecticides (although some may also use insect growth regulators), and as long as an ant ingests the bait, it will die.

With ant baiting in winter, the first challenge is to get the bait back to the nest. To do this, the ants need to be out actively foraging. For example, the main picture above shows big-headed ants excavating dirt from under pavers – very much active, despite the cooler weather. For many outdoor nesting species, activity will drop off dramatically in cooler temperatures, often only being active during the warmer periods in the middle of the day. Species nesting indoors may remain more active due to indoor heating.

However, although ants may be out foraging, often their food preferences will differ during winter. This is because the nutrient requirements of the colony are often very different in colder weather. During winter the amount of egg laying and brood in the colony can drop off dramatically. With the requirement for protein diminished, it is not uncommon to see a shift to more of a sugar-based diet in winter – the workers are foraging for food to sustain themselves rather than looking for protein for the growing brood. Argentine ants are a classic example of this shift in food preference.

This lack of brood in the colony can also impact the preferred bait format. Whereas liquid or gel baits are readily imbibed by workers, solid food needs to be transferred back to the colony to be processed by the later stage larval instars. If there is a lack of brood in the colony, then it is likely that solid foods may be ignored or taken back to the nest and cached for processing in spring when the brood numbers increase.

Synergy Pro from Sumitomo Chemical has been designed to overcome the differences in ant foraging behaviour experienced between species and counter the changes in food preferences as they occur through the year. Containing two different food granules, one protein (with a bit of sugar) and one oil, Synergy appeals to a broad range of ant species. Being a granular product, it may appear to be less optimal for colonies without brood to process the solid granules, however it can still deliver control as the granules, although appearing dry, contain small amounts of oil which the workers ingest directly.

So if you’ve got actively foraging ants in winter, baiting is still a viable alternative, but it becomes even more important to do a ‘taste test’ to see which food types/bait formats the ants will actively forage. It is also important to monitor performance to ensure that the bait has indeed been processed back at the nest. If the bait hasn’t controlled the nest within 1-2 weeks, you may need to consider an additional treatment, possibly with a different bait.

Charles McClintock, Professional Products Business Manager, Sumitomo Chemical Australia

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