Influence of Filamentous Fungi on Nectar Chemistry and Cascading Effects for the Longevity of the Insect Parasitoids Trissolcus basalis and Ooencyrtus telenomicida

Flowering plants serve as a valuable source of nectar, which supports the survival and reproductive success of flower-associated insects, including adult parasitoids. Fermentation by nectar-inhabiting microbes can alter nectar chemistry, which in turn, could affect the performance of nectar-feeding parasitoids. Although there is growing evidence on how yeasts and bacteria influence flower-visiting insects, the potential role of other microbial taxa that can colonize nectar has been largely neglected. In this study, we tested the hypothesis that filamentous fungi isolated from the nectar of buckwheat, Fagopyrum esculentum, affect nectar chemistry with cascading effects for the longevity of insect parasitoids. As model organisms, we used Trissolcus basalis and Ooencyrtus telenomicida, two co-occurring egg parasitoids of the southern green stink bug, Nezara viridula. Laboratory bioassays showed that the longevity of T. basalis was reduced when wasps were fed on synthetic nectar fermented by Cladosporium sp. SAAF 22.2.12 and Cladosporium sp. SAAF 22.3.29, compared with wasps that fed on non-fermented synthetic nectar. On the contrary, no effects of fermentation by nectar-inhabiting fungi were reported in terms of longevity for O. telenomicida. Chemical analyses revealed that nectar fermentation by filamentous fungi substantially increased the chemical diversity of the nectar medium, with a total of 12 sugars and sugar alcohols detected in the fermented products of the different fungal strains, although in varying proportions. Altogether, these findings highlight the potential of neglected microbial taxa to affect nectar chemistry and longevity of adult parasitoids, broadening our understanding of plant-microbe-insect interactions.