Evaluating the Effects of Epichloë Fungal Endophytes of Perennial Ryegrass on the Feeding Behaviour and Life History of Rhopalosiphum padi

The bird cherry-oat aphid, <i>Rhopalosiphum padi</i> (L.), is an economically significant pest of pasture grasses, the latter being capable of hosting several fungal endophyte-perennial ryegrass symbiota rich in alkaloids and toxic to vertebrates and invertebrates. Measuring aphid feeding behaviour can provide insights into the effectiveness and mode of action of different fungal endophytes. This study investigated the effects of different <i>Epichloë</i>-perennial ryegrass symbiota on the feeding behaviour of <i>R. padi</i> using the electrical penetration graph technique while also assessing the aphid life history. In most cases, endophytes had significant feeding deterrence and paired fecundity and mortality effects. But, in some instances, endophytes with the highest aphid mortality did not significantly deter feeding, suggesting a more complicated scenario of interactions between the relative concentration of metabolites, e.g., host plant defence response metabolites and alkaloids, and/or physical changes to leaf morphology. Overall, this study sheds light on the mode of action of <i>Epichloë</i> endophytes against aphids and highlights the importance of <i>Epichloë</i>-perennial ryegrass symbiota in the management of insect pests such as aphids in pasture-based grazing systems.