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DOI: 10.1101/2023.05.16.540952

Can nestmate corpses cause bait neglect in invasive ants?

T.Wagner T. J. Czaczkes
Invasive ants like Linepithema humile (the Argentine ant) pose a significant threat to ecosystems and economies worldwide, making it imperative to understand their behaviour and find effective management strategies. However, traditional eradication methods such as baiting have had limited success due to low bait consumption rates over time, driven in part by the abandonment of toxic baits. We propose that ants learn to avoid the odour of toxic baits because they are associated with the corpses of ants which fed on them. We investigated the effect of corpsescent association on the odour and flavour preferences of ants by using scented corpses and corpses killed by feeding on scented toxicant-laden baits. Ants were tested in a Y-maze or a dual-choice feeder after exposure to scented corpses or dummies. When focal ants encountered scented freeze-killed ants, 69% (n = 64) avoided a branch of a Y-maze bearing the same scent. At a collective level, when colonies were given access to two differently scented food sources via a path laden with scented ant corpses, the matching food source was neglected compared to an alternative food source. However, ants exposed to scented corpses did not feed for less time on food scented to match the corpse compared to a control food in a dual-choice feeder. Moreover, when ants encountered ants killed by ingesting scented poison, as opposed to artificially-scented corpses, no avoidance was found. This study demonstrated that nestmate corpses act as a negative stimulus for Linepithema humile ants, leading to avoidance of odours associated with the corpses and potential avoidance of toxic bait at both individual and collective levels, but not a reduction in feeding once the food source is encountered. Why the more realistic trial with poisoned ants elicited no avoidance is unclear: it may be due to weaker odour cues from ingested food, a counterbalancing of the negative corpse stimulus by the positive presence of food remains on the corpse, or some other reason. Nonetheless, this study demonstrates that conspecific corpses act as a negative stimulus for ants, and this should be kept in mind when planning control efforts.