Insect-fungus symbiosis: prevalence of the fungus \textit{Trichoderma} within termites

Symbiosis between insects and microorganisms may benefit important process of the host such as nutrition and defences. In social insects, several fungi are observed inside nests, such as species of the genus \textit{Trichoderma} (Hypocreales), that are known for production of cellulosic and fungistatic substances. Because of these substances are produced by many species among this genus, we hypothesized that termites may potentially benefit from the presence of \textit{Trichoderma} in the nest. However, before testing this hypothesis, we aimed to assess the fungal diversity and prevalence inside nests, as well as whether \textit{Trichoderma}'s prevalence differs within the insects and nests. To verify the prevalence, we collected 30 nymphs, 30 soldiers, 30 workers and 30 fragments of internal nest wall from 4 nests of \textit{Cornitermes cumulans} and 4 nests of \textit{Diversitermes} sp. (N=960). We identified 62 strains of \textit{Trichoderma}, belonging to 5 different species. \textit{Trichoderma}'s average prevalence in \textit{C. cumulans} was similar between soldiers (2.5±1.32) (mean±SE) and workers (2.5±0.29; Chi<0.001, d.f.=1, P=1). In \textit{Diversitermes}, we only found \textit{Trichoderma} in workers (1.25±0.63). The low prevalence of \textit{Trichoderma} strains inside termites' body indicates that this termite-fungus interaction is not an obligatory symbiosis for the insects. Surprisingly, we found a high prevalence in nest walls (\textit{C. cumulans}=17.25±1.89, \textit{Diversitermes}=4.25±1.49), and we will further investigate if termites may benefit from presence of \textit{Trichoderma} spp. at the nest wall. For both \textit{Cornitermes} and \textit{Diversitermes}, no fungi was isolated from nymphs, which suggest \textit{Trichoderma} may be acquire in the later stages of the insect life.