Clearly a very diverse range of herbivorous insects is associated with tall fescue. Much of this information is derived from studies of tall fescue in turf, where insect damage is highly visible. In pasture situations, however, definitive information on insect pests and the impact of their herbivory is lacking. Research comparing the performance of E+ and E- tall fescues in Australia (Wheatley et al., 2003) and New Zealand (Cooper et al., 2002) has shown that endophyte improves tall fescue productivity and persistence at least partly as a result of protection from insect pests. In the United States, however, the poor yields and lack of persistence of E- tall fescue have been attributed mainly to the ability of the endophyte to protect the plant from abiotic stresses (see Chapter 2) such as drought. Certainly, tall fescue is more tolerant of insect herbivory than other forage species, but the cumulative effect of damage by several insect pests is easy to underestimate.
Fungal endophyte infection in tall fescue has some effect on many of the insects that are able to use this plant as a food source. Effects may be severe, as occur for some aphid species that cannot survive on E+ tall fescue or for the African black beetle, which avoids feeding on tall fescue plants. For other insects, such as fall armyworm and root feeding scarab larvae, the effects of endophyte are equivocal and may be of little importance in protecting the plant in the field.