Ants Evade Harmful Foods Through Active Abandonment

Effective control of invasive ants is a major conservation goal. Yet, recent discoveries reveal that ants actively abandon toxic baits, thereby reducing the entry of harmful food into the colony. This behavioral response may represent a threat to the success of invasive ant control measures.
Ants Evade Harmful Foods Through Active Abandonment
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Invasive ants, such as the Argentine ant, pose a serious economic and ecological threat. Despite advances in baiting techniques, effectively managing established ant populations remains a daunting challenge that often ends in failure. While much research effort has been devoted to developing attractive and effective baits, there is a paucity of studies examining the potential behavioral responses of ants toward the toxic baits in real control situations. This could be a key point to explain why toxic baits have not been more effective in controlling ant populations.

 Through my own experiences controlling ants indoors, primarily in hospital and research facilities, I have consistently observed a pattern in ant behavior that defied our traditional understanding of bait-based control. Liquid baits initially attract a massive number of ants in a short period of time. However, after a few hours, the surrounding area shows little to no ant activity. How could toxic baits, which are slow-acting in laboratory, work so quickly in real-world conditions? We also frequently observed that when baits are strategically placed inside, the ants indoors quickly disappear, but their trails on the other side of the wall remain unchanged. Even when using a very viscous bait, which results in minimal consumption, they generate a similar effect. The question that arises is: How could such a small amount of bait wipe out such a vast population?

 These observations stimulated my interest in understanding how baits work and the possible strategies of responses ants exhibit toward such harmful food. While some pest control professionals frequently refer to "bait shyness" or "bait abandonment," there has been no scientific exploration of this phenomenon. In an effort to delve deeper, together with Dr. Czaczkes and Ph.D. candidate Zanola, we conducted the research. Our recent field study aimed to explore the behavioral response of ants to toxic bait in real situations.

In these experiments, we provided two sucrose feeders, each generating a new foraging path from the same main trail. Then, one of the sucrose feeders switched to offering toxic food. For 2 or 3 hours, ant activity remained unchanged at all sites. Thereafter, ants dramatically reduced their presence on the foraging trails toward the toxic bait, while activity on the other foraging trail and the main trail remained similar. Afterwards, the abandoned area progressively expands, from only the closest section of the main trail and gradually spreading to the surrounding area. We demonstrate that the decrease in ant presence could not be explained by mortality, lack of motivation to forage, or fidelity to alternative food sources.

Our results also showed that palatability assays should only assess immediate responses to baits or quantify consumption within the first two hours. Past this point, palatability may be masked by abandonment behavior.

This abandonment behavior is an active response strategy that minimizes the entry of dangerous foods into the nest, acting as a protective social mechanism. Our findings offer a new perspective on ant baiting strategy paradigms and a complementary interpretation of their results, shedding new light on the intriguing and complex behavioral responses of these social insects.

Figure 1: Activity dynamics in response to toxic bait. Two wooden bridges connected to a main trail initially offered sucrose, establishing foraging trails. One bridge switched to toxic bait, resulting in sustained initial activity for 2-3 hours. Subsequently, activity significantly declined in the toxic bait bridge, followed by a gradual decrease in activity along the trunk trail close to the toxic bait bridge. This area abandonment effect persisted throughout the experiment; as observed in indoor control settings, this abandonment may endure for weeks or even months.

Figure 1: Activity dynamics in response to toxic bait. Two wooden bridges connected to a main trail initially offering sucrose, establishing foraging trails. One bridge switched to toxic bait, resulting in sustained initial activity for 2-3 hours. Subsequently, activity significantly declined in the toxic bait bridge, followed by a gradual decrease in activity along the trunk trail close to the toxic bait bridge. This area abandonment effect persisted throughout the days of the experiment; as observed in indoor control settings, this abandonment may endure for weeks or even months.

Poster image: AntWeb. Version 8.103.2. California Academy of Science, online at https://www.antweb.org. Accessed 10 January 2024. By Philip Herbst.

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