ABSTRACT
Fungal endophytes are ubiquitous in the plant kingdom. Some are pathogenic but many form a symbiotic relationship with their host which spans the continuum between parasitism and mutualism. Many of those interactions between plant and fungus will alter the chemical composition of the plant which, positively or negatively, has an impact on insect herbivores. If the primary function of a mutualistic relationship is to provide protection to both the partners, then the mutualism can be described as defensive. The Pooid grasses and their associations with fungal endosymbionts are a very well-documented and fascinating example of a mutualism considered to be defensive in its role. Despite the widespread occurrence of other fungal endophytes, however, further examples of defensive mutualisms are rare.
