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Social interactions between fungus garden and external workers of Atta sexdens (Linnaeus) (Hymenoptera: Formicidae)

Lacerda, F. G., Della Lucia, T. M. C., Desouza, O., Pereira, O. L., Kasuya, M. C. M., De Souza, L. M., Couceiro, J. C., De Souza, D. J.
The Italian journal of zoology 2014 v.81 no.2 pp. 298-303
Atta sexdens, Trichoderma, aggression, antagonists, avoidance behavior, fungi, fungus gardens, gardens, grooming (animal behavior), leaf-cutting ants, mortality, pathogens, risk, social insects, spores, wastes, weeds
Social insects can live in densely populated colonies where mortality risks are increased by inter-individual transmission of pathogens. Thus, diverse strategies are employed against such infection risks, including the display of sophisticated behavioural traits. Considering that the waste of the leaf-cutting ant contains pathogens, worker ants that tend the fungus garden – here called fungus garden workers – should exhibit avoidance behaviour toward midden workers to minimize contamination of the fungus garden. We studied the behaviour of garden workers when confronted with midden and forager workers in colonies of Atta sexdens (Linnaeus, 1758). Eight colonies were used: in four colonies, the midden was inoculated with spores of the weed fungus Escovopsis weberi (Muchovej and Della Lucia, 1990), and in the other four colonies there was no artificial contamination. Grooming, self-grooming, inspection, immobilization and aggression behaviours were quantified. Additionally, we checked for fungal contaminants on the body surfaces of midden and garden workers from non-inoculated colonies. Garden workers displayed more intense behaviours (grooming, inspection and immobilization) toward midden workers than toward foragers; these behaviours did not differ between Escovopsis -inoculated and non-inoculated colonies. No antagonist behaviour was displayed by garden workers toward midden or forager workers independently of the inoculation treatment. Eight fungus species were isolated from the midden and garden workers, including Trichoderma sp., a probable antagonist of the fungus garden. Garden workers of A. sexdens discriminate against midden workers; however, a previous hypothesis that pathogens from the midden induce the aggressiveness of internal workers is not supported by our study.