Insect oviposition preference between Epichloë‐symbiotic and Epichloë‐free grasses does not necessarily reflect larval performance

Abstract

Variation in plant communities is likely to modulate the feeding and oviposition behavior of herbivorous insects, and plant‐associated microbes are largely ignored in this context. Here, we take into account that insects feeding on grasses commonly encounter systemic and vertically transmitted (via seeds) fungal Epichloë endophytes, which are regarded as defensive grass mutualists. Defensive mutualism is primarily attributable to alkaloids of fungal origin. To study the effects of Epichloë on insect behavior and performance, we selected wild tall fescue ( Festuca arundinacea ) and red fescue ( Festuca rubra ) as grass–endophyte models. The plants used either harbored the systemic endophyte (E+) or were endophyte‐free (E−). As a model herbivore, we selected the Coenonympha hero butterfly feeding on grasses as larvae. We examined both oviposition and feeding preferences of the herbivore as well as larval performance in relation to the presence of Epichloë endophytes in the plants. Our findings did not clearly support the female's oviposition preference to reflect the performance of her offspring. First, the preference responses depended greatly on the grass–endophyte symbiotum. In F. arundinacea , C. hero females preferred E+ individuals in oviposition‐choice tests, whereas in F. rubra , the endophytes may decrease exploitation, as both C. hero adults and larvae preferred E− grasses. Second, the endophytes had no effect on larval performance. Overall, F. arundinacea was an inferior host for C. hero larvae. However, the attraction of C. hero females to E+ may not be maladaptive if these plants constitute a favorable oviposition substrate for reasons other than the plants' nutritional quality. For example, rougher surface of E+ plant may physically facilitate the attachment of eggs, or the plants offer greater protection from natural enemies. Our results highlight the importance of considering the preference of herbivorous insects in studies involving the endophyte‐symbiotic grasses as host plants.

Root biomass and cumulative yield increase with mowing height in Festuca pratensis irrespective of Epichloë symbiosis

“…In E + plants the fungal hyphae grow between the plant’s embryotic cells (Supplementary Fig. 1 ) whereas in the E– plants the hyphae are not found (see 75 for the detailed method).…”

Epichloë Endophyte-Promoted Seed Pathogen Increases Host Grass Resistance Against Insect Herbivory

“…However, the ecological roles of microbes in plant–microbe interactions are often complex, diverse, and prone to change from mutualistic to antagonistic and vice versa, depending on the abiotic and biotic conditions (Hayward, 1974 ; Carroll, 1988 ; Ahlholm et al, 2002 ; Partida-Martinez and Heil, 2011 ; Marsberg et al, 2017 ; Marchetto and Power, 2018 ; Shaffer et al, 2018 ; Meier and Hunter, 2019 ; Afkhami et al, 2020 ; Franklin et al, 2020 ; Laihonen et al, 2020 ; Petipas et al, 2020 ; Saikkonen et al, 2020 ). This continuum of antagonistic to mutualistic interactions in space and time (Saikkonen et al, 1998 ; Hirsch, 2004 ; Drew et al, 2021 ) must be considered in studies on plant microbe interactions.…”