Insect-fungus symbiosis: diversity and potential ecological roles of the hypocrealean fungus Trichoderma in colonies of termites (Blattodea: Termitidae)

• Ano de defesa: 2018
• Autor(a) principal: Pereira, Thairine Mendes
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Fungos antagônicos; Relação hospedeiro-parasito; Sociedades de insetos; Fungos - Filogenia; Entomologia Agrícola
• Link de acesso: https://locus.ufv.br//handle/123456789/27258

Insects and microbes have mutualistic and antagonistic symbioses that can drive important processes of hosts and symbionts. We found a symbiosis between termites (Blattodea: Termitidae) and Trichoderma (Ascomycota: Hypocreales). This fungus produces cellulolitic and fungistatic compounds, but its ecological role in termites is unclear. We estimated the prevalence and investigated the diversity of Trichoderma in three species of termites: Cornitermes cumulans, Diversitermes sp. and Termes sp. Considering Trichoderma strategies of habitat exploration, we hypothesized that the fungus would contribute to termite nutrient acquisition and increase their survival. We obtained 136 isolates of Trichoderma from workers, soldiers and nest wall, belonging to 12 different phylogenetic species from 3 clades: section Trichoderma, clade Harzianum and clade Virens. We found a low prevalence of Trichoderma inside termite bodies, indicating that this termite-fungus interaction is not an obligatory symbiosis. No fungi were isolated from immatures, suggesting that Trichoderma may be acquired in later stages of the insect life. To assess termite acquisition of nutrients, we compared residual fat content of workers of C. cumulans with or without the fungus. Fat content of workers varied from 0 to 0.5 mg and the presence of Trichoderma was not related to residual fat content so it is likely that the fungus is not determinant for termite nutritional status. To evaluate termite survival, we created 24 arenas using macerated fragments of nest walls from 8 nests of C. cumulans as substrates (collected from Viçosa/MG). For each nest, three groups of 20 workers and 4 soldiers were exposed to T. harzianum or Lichtheimia brasiliensis, inoculated on to sterilized sugar cane, or no fungi. Survival was assessed every 8h for 25 days. After 25 days, survival of termites exposed to T. harzianum was lower than termites exposed to control or L. brasiliensis. Trichoderma harzianum is widely applied in agriculture as antagonist of plant and soil pathogens. Our results showed an unexpected negative effect on termite survival, one that may be neglected in other systems. Our research therefore indicates that Trichoderma likely has no specific ecological role that benefits termites and might be a potential parasite to termite colonies.