Virulence of the fungi Escovopsis and Escovopsioides to the leafcutter ant-fungus symbiosis

• Ano de defesa: 2018
• Autor(a) principal: Mendonça, Débora Mello Furtado de
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Atta; Acromyrmex; Parasitismo; Simbiose; Entomologia Agrícola
• Link de acesso: https://locus.ufv.br//handle/123456789/27318

Eusocial insects interact with a diversity of parasites that can threaten their survival and reproduction. The amount of harm these parasites cause to their hosts (i.e. their virulence) can be influenced by numerous factors, such as the ecological context in which the parasite and its host are inserted. Leafcutter ants (genera Atta and Acromyrmex, Attini: Formicidae) are an example of a eusocial insect whose colonies are constantly threatened by parasites. These ants cultivate and use the fungus Leucocoprinus gongylophorus (Basidiomycota: Agaricales) as the colony main food source. Leafcutter ants also interact with the fungi Escovopsis and Escovopsioides (Ascomycota: Hypocreales), which are considered a highly virulent parasite and an antagonist to their fungal cultivar, respectively. Since both fungi are common inhabitants of healthy colonies, which remain growing and foraging, we hypothesized that they are of low virulence. However, this virulence could vary depending on the ecological context that the colonies are inserted. We therefore tested two hypotheses: (i) Escovopsis and Escovopsioides are of low virulence to colonies; (ii) virulence increases with decreasing of colony complexity. For this, we used three levels of complexity: queenright colonies (fungus garden with queen and workers), queenless colonies (fungus garden and workers, without queen) and fungus gardens (without any ants). Each level was exposed to conidial suspensions of Escovopsis moelleri, Escovopsioides nivea, Trichoderma longibrachiatum or to a control (water with Tween 80 ® + saline solution). Trichoderma longibrachiatum was used for comparison with E. moelleri and E. nivea since it is also a fungus commonly found in the colonies of leafcutter ants. The parameters evaluated were weight, midden production, amount of leaves cut by ants and survival of each colony complexity level. We also evaluated the in vitro interactions between these fungi with L. gongylophorus through a paired culture bioassay. Our results showed that, in general, these fungi were of low virulence to queenright colonies, while the queenless colonies and fungus gardens were suppressed. Moreover, E. nivea and T. longibrachiatum seems to be less aggressive than E. moelleri, this was observed in both, in vivo and in vitro experiments. The results highlight the importance of each element (queen, workers and fungus garden) in the leafcutter ants-fungus symbiosis. Furthermore, we showed that Escovopsis and Escovopsioides may be not virulent to healthy colonies yet, depending on colony condition, the virulence level of Escovopsis can increase.