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Keywords:

  • biotic stressors;
  • herbivore performance;
  • induced defence;
  • mechanical barrier;
  • plant resistance

Summary

  • 1
    Silicon (Si) has received increased attention as a nutrient capable of providing some measure of defence for plants against fungal pathogens, and insect and mammalian herbivores.
  • 2
    On the basis of a study including two generalist insect folivores and a phloem feeder, Massey, Ennos & Hartley (2006; Journal of Animal Ecology, 75, 595–603) have drawn attention to a putative distinction between the effects of plant Si in defending against folivorous and phloem-feeding insects. On the basis of their results they imply that phloem feeders are less likely to be adversely affected by increased plant Si than folivores.
  • 3
    However, in making this suggestion, Massey et al. have ignored many previous studies demonstrating a clear effect of plant Si on a range of phloem-feeding and some xylem-feeding insects, and that this effect stems not only from leaf mechanical properties based on opaline silica, but also from induced chemical defences seemingly mediated by soluble Si.
  • 4
    Furthermore, Massey et al. cannot claim that their study was the first demonstration of a direct effect of Si on insect herbivore preference and performance; there have been numerous earlier studies demonstrating this from folivores, stem borers, and phloem and xylem feeders.
  • 5
    We contend that current evidence indicates that Si is likely to be involved to a similar extent in enhancing resistance to all four insect feeding guilds and that any conclusion to the contrary is, at this stage, premature.