Acquired Chemical Defences in Grasses: The Role of Fungal Endophytes

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Abstract
Microbial symbionts of plants can affect the interaction between their hosts and herbivores. Systemic fungal endophytes (Clavicipitaceae, Ascomycetes) infect grasses and produce alkaloids in host tissues. The objectives of this study were to determine the effects of these fungi infecting a variety of grasses on leaf and seed-feeding insects. Survival, growth, and development of fall armyworm (Spodoptera frugiperda) reared on infected or noninfected plants were compared. Larvae reared on infected plants tended to exhibit reduced survival and growth and retarded development compared with larvae reared on noninfected plants. There was considerable variation in these variables among host grasses and between different trials using the same grass grown in different environments. Population growth of flour beetles (Tribolium castaneum) on ground seeds from infected or noninfected perennial ryegrass (Lolium perenne) and tall fescue (Festuca arundinacea) were also compared. Mean beetle population growth rates were significantly lower on infected seeds and especially on tall fescue. We conclude that insect resistance is a general property of endophyte-infected grasses and that infection may be beneficial to host plants in nature.