Dataset and README file for paper from Denarie et al.

1. Many plants take up silicon (Si) from the soil and deposit in their tissues to resist insect herbivory via physical and chemical mechanisms. Si-supplemented wheat, for example, negatively impacts insects such as the cotton bollworm (<i>Helicoverpa armigera</i>).2. Si-based defences are rapidly deployed, but it is unclear whether levels of Si defence affect herbivore performance linearly (i.e. increasing levels of Si continue to decrease performance), or whether resistance is only achieved above certain threshold levels.3. We examined how a gradient of Si-defence in wheat affected relative growth rates (RGR) and mandible wear of <i>H. armigera</i>. Plants were either not provided with Si or supplemented with one of four levels of Si (0.25mM, 0.5mM, 2mM and 4Mm) in hydroponic solutions and fed to second instar <i>H. armigera</i> larvae. RGR declined most with higher levels of Si compared to the lowest levels of Si supplementation and there was significant negative correlation between plant Si and RGR. Significant decreases in RGR, however, were generally achieved midway through the Si gradient (2mM). Si supplementation increased plant biomass overall and ameliorated biomass losses due to herbivory. The wearing of insect mandibles was lower on larvae that had fed on silicified plants.4. Our study also revealed that wheat can take up Si at concentrations beyond its polymerization threshold of 2mM. We demonstrate that although wheat can acquire Si at relatively high concentrations, accumulation beyond a certain level does not continue to confer further benefits in terms of herbivore defence.