Mode of colony suppression of the leaf-cutting ant Atta sexdens (Hymenoptera: Formicidae) by an isocycloseram-based bait: caste mortality, behavior, and fungus garden collapse

Le résumé fourni par la source

Leaf-cutting ants are socially complex pests whose management requires colony-level suppression rather than individual mortality. Granular baits remain the main practical tactic, but the reliance on sulfluramid, an environmentally persistent perfluorooctane sulfonate precursor, has intensified the search for alternative active ingredients. Isocycloseram has shown high field efficacy against leaf-cutting ants, yet the mechanisms by which it disrupts colony function and leads to colony collapse remain poorly understood. Here, we evaluated an isocycloseram-based bait on Atta sexdens colonies under laboratory conditions, comparing its effects with those of a commercial sulfluramid bait and a nontoxic bait. We quantified leaf consumption, waste production, colony and queen survival, and worker mortality in colonies and assessed survival of forager and gardener castes on contaminated diets, as well as their behavioral interactions. Both isocycloseram and sulfluramid baits suppressed colonies, but the former caused a much faster decline in worker survival while maintaining rapid bait loading and low bait rejection. Isocycloseram exposure reduced leaf consumption and waste mass, and survival of foragers and gardeners on semi-solid diets did not differ, indicating relatively even dissemination among castes, whereas sulfluramid diets caused earlier mortality of gardeners. Behavioral assays showed that treated and untreated foragers under isocycloseram exhibited closer proximity and more frequent interactions than in control groups, suggesting enhanced social dissemination of the toxicant. Fungus gardens collapsed under both insecticidal baits, with subsequent Escovopsis sp. overgrowth and eventual queen death. Overall, isocycloseram-based bait rapidly compromised colony functions while remaining attractive and undetected during loading, highlighting its potential as an alternative active ingredient for managing leaf-cutting ants in a socially and environmentally constrained context.

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