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HOW ARE BAITS TRANSFERRED IN ANT COLONIES?

Understanding the feeding mechanisms and behaviours of ants gives insight into why baiting is such an effective control method.

The complex food cycle within an ant colony varies with the species of ant. Yet the way ants feed and digest remains similar across ant species. Understanding this is key to understanding how and why ant baits work.

The role of foraging ants is to bring food or water back to the colony and distribute it to the queen, other workers, and larvae by trophallaxis. The infrabuccal plate, present in adult ants, is a filtering mechanism that prevents solid food particles from entering their digestive tract. The solid prey/food which is most often seen being carried by workers is generally intended as food for the larvae, not for the adults themselves, which are typically considered as liquid feeders.

The role of larvae in food transfer

Larvae will commonly receive food when workers apply their mouth parts to those of the larvae and liquid food is regurgitated from the adult ant’s crop. This process, called stomodeal trophallaxis, has been observed in nearly all major ant families.

However, the larvae can also externally digest solid food brought back by adult ants. Food is placed on the external ‘stomach’ of the larvae, onto which they regurgitate digestive juices, turning the food into a liquid form which can be ingested by workers and subsequently spread through the colony by trophallaxis. This has led to the concept that ant larvae might serve as specialised digestive castes.

Ants displaying stomodeal trophallaxis

Theories of bait digestion

Recent studies to determine whether bait digestion by larvae is a key factor in the consumption and distribution of the toxicants from baits to worker ants, have shown interesting results. Understanding the mechanism that allows a bait toxicant to enter the colony is fundamental for control.

Previously the provision of the solid-phase or liquid-phase food to the larvae was seen as key to bait performance. However, what has been discovered is that the toxic component of the bait enters the body of worker ants through the exoskeleton or through the mouth parts, where food enters the cibarium, which then opens into a second chamber, the infrabuccal pocket, which is a collection site for solid particles of food.

Whereas liquid food is directly imbibed by ants, particles of solid food, obtained by licking with the tongue, or rasped off by the maxillae, are carried into the infrabuccal pocket where they are moulded into a nutritious pellet. Ants also use their tongues to cleanse one another and their brood, another means by which food particles may be carried more directly into the infrabuccal pocket. The solid portions, when no longer of any nutritive value, are cast out as a small pellet of refuse.

It appears that baits stored in the infrabuccal pocket come into contact with various glandular secretions, which release the toxicant, through trophallaxis, among workers. The toxicant then spreads rapidly through the colony, without the need for digestion by larvae. So, it now appears that the larvae are not critically important for the transmission of the toxicant in the colony.

Baiting with biology in mind

This feeding biology has been exploited in the range of fipronil baits from Ensystex including Magnathor Magnetic Insecticide, Attrathor Targeted Insecticide and Hymenopthor Ultra.

Ensystex’s regional director, Steve Broadbent, explained, “Fipronil is a tremendous active for use in baits for both ants and cockroaches. A key benefit that fipronil provides is that it is non-repellent, and can be transferred from one insect to the next. What many people do not realise though, is that impurities in the technical grade fipronil can negatively impact upon the non-repellent nature of the product. This why we only use Ensystex fipronil, which is protected by ten different process patents, to ensure we have a premium source of fipronil displaying ‘True viral transfer technology’.”

Traditionally the difficulty with baiting for ants has been the wide range of feeding preferences of the different species (see Table 1). This is further complicated by the fact that the colony’s feeding preferences can change during different seasons.

Relative Feeding Preference
Species Sugar Protein Oil
Pharaoh’s ant Moderate High Low
Argentine ant High Low Low
Coastal brown ant Moderate High
White-footed house ant High Moderate
Black house ant High Low Low
Meat ants Moderate High
Red imported fire ant High
Singapore ant Moderate High High
Green-headed ant Low High Moderate
Funnel ant Low Moderate
Odorous ant Moderate High Low

Table 1: Feeding preferences of common species of pest ants

Mr Broadbent added that Ensystex had overcome this challenge by exploiting different aspects of ant feeding biology to develop several unique ant bait options.

Magnathor Magnetic is a dry, flowable powder bait that uses a range of feeding attractants to draw the ants towards the target zone,” said Mr Broadbent. “The powers of paramagnetism then take over with the Magnathor being drawn to the polarity of the ant’s exoskeleton, so the ants don’t even need to eat the bait. Since Magnathor is a flowable powder, it can be ‘puffed’ into voids and harbourages that can’t be reached with other bait presentations. The Magnathor is then returned to the colony on the ant’s exoskeleton.

Magnathor Magnetic Insecticide with applicator

Attrathor, a liquid spray that is fast and easy to apply, provides an alternative for indoor and outdoor applications. Attrathor’s ‘Quick release insect attractant micro-capsules’ draw the ants in to the treated zone, where they either ingest, or pick up on their exoskeleton, the ‘Active Micro-capsules’ of Ensystex fipronil,” explained Mr Broadbent. “Again there is no requirement to consume the bait; the slow action of the fipronil ensures the toxicant-laden ants return to the colony to transfer the active to nestmates.

Hymenopthor Ultra Granular Bait

“In contrast, Hymenopthor Ultra employs a complex blend of sugars, animal proteins and oils with ‘Liquid Oil Phase Release Technology’ to ensures optimal palatability for all species of ants (and cockroaches). It works as both a liquid and a granular bait to exploit the ants’ social structure.”

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