Plants and herbivorous insects have been locked in an evolutionary arms race for over 300 million years. As a result, plants have evolved a plethora of defences against herbivory, many of which are triggered by herbivore-associated stimuli, including mechanical stimulation (e.g., vibrations from herbivore movement), tissue damage (wounding), chemical elicitation, and transmission of microbes (including pathogens). Understanding how these stimuli affect plant defences is confounded by the fact that herbivores introduce uncontrolled bias stemming from variation in feeding patterns, intensity of damage, and the introduction of biotic and abiotic signals in a non-standardised way. Simulated herbivory is often incorporated into studies to uncouple the relative impacts of herbivore-associated stimuli, glean mechanistic details regarding plant defences, and for standardisation purposes. Some plants, namely grasses, have evolved the ability to uptake Si from the soil and accumulate it throughout their aboveground tissues. The role of Si in plant ecology is complex, as it has proven beneficial for plants in the context of growth, reproduction, and mitigation of diverse environmental stressors. But perhaps one of the most apparent advantages of Si accumulation is its strong anti-herbivory quality. In grasses specifically, it has been suggested that Si plays a critical role in their ability to combat herbivore attack. Although Si is well known to mitigate the negative impacts of herbivory, there are many knowledge gaps regarding the temporal scales of induced Si-based resistance and the mechanisms behind Si accumulation and deposition. Using both simulated and authentic herbivory techniques, this work identifies the extent that Si is integrated into wider plant defence machinery, how rapidly Si defences can be effectively deployed, and how quickly plants develop resistance to herbivores once Si is supplied. Collectively, this PhD research highlights the importance of herbivore-specific signals in shaping plant defence responses and integrates simulated and true herbivory to yield a robust mechanistic understanding of the temporal scale at which Si-based defences, which are critical for resistance to herbivory, are deployed in a model grass. These findings could have implications for the way Si is utilised in agricultural systems and provide novel insights regarding potential evolutionary strategies evolved in grasses to utilise Si as an inducible defence in an analogous way to inducible specialised metabolites. Collectively these works provide novel evidence for the specified role of Si as an anti-herbivore defence in grasses and systematically identify the role of simulated herbivory in ecological research
