Complex Interactions among Sheep, Insects, Grass, and Fungi in a Simple New Zealand Grazing System

Epichloë fungi (Ascomycota) live within aboveground tissues of grasses and can have important implications for natural and managed ecosystems through production of alkaloids. Nonetheless, vertebrate herbivores may possess traits, like oral secretions, that mitigate effects of alkaloids. We tested if sheep saliva mitigates effects of Epichloë alkaloids on a beetle pest of perennial ryegrass (Lolium perenne L.) in a New Zealand pasture setting. Plants with one of several fungal isolates were clipped with scissors, grazed by sheep, or clipped with sheep saliva applied to cut ends of stems. We then assessed feeding damage by Argentine stem weevils on blade segments collected from experimental plants. We found that clipping plants induced synthesis of an alkaloid that reduces feeding by beetles and that sheep saliva mitigates this effect. Unexpectedly, the alkaloid (perloline) that explains variation in beetle feeding is one produced not by the endophyte, but rather by the plant. Yet, these effects depended upon fungal isolate. Such indirect, complex interactions may be much more common in both managed and natural grassland systems than typically thought and could have implications for managing grazing systems.