“…On the other hand, there is evidence that Si increases production of defence metabolites (Fauteux et al, 2005;Fawe, Abou-Zaid, Menzies, & Bélanger, 1998;Ghanmi, Mcnally, Benhamou, Menzies, & Bélanger, 2004;Han et al, 2016;Kim et al, 2014;Reynolds et al, 2009;Rodrigues et al, 2004;Ye et al, 2013), including collard plants (Teixeira et al, 2017) Variation in N content of plants is vitally important and strongly affects many life-history traits of herbivores (Leather, 1990;Mattson, 1980). Cell wall fibre can be highly unfavourable to herbivorous insects in terms of palatability, digestibility and nutritional value of volume ingested (Hanley, Lamont, Fairbanks, & Raverty, 2007;Hochuli, 1996;Hochuli & Roberts, 1996) but improved leaf N, GLS and water status. In both studies, the improvements in leaf water status and soluble N did not benefit P. xylostella and B. brassicae.…”