Silicon fertilisation affects morphological and immune defences of an insect pest and enhances plant compensatory growth

Abstract Herbivorous insects have evolved various anti-predator defences, including morphological, behavioural, and immune which can make biocontrol of herbivorous pests challenging. Silicon (Si) accumulation in plants is a potent physical defence against mandibulate insects. However, it remains uncertain how Si affects the defences insect herbivores plant following herbivory. We grew model grass, Brachypodium distachyon , hydroponically with (+Si) or without (–Si) investigated plant-mediated effects on cotton bollworm, Helicoverpa armigera integrating morphological (i.e. integument resistance thickness), defences. also examined compensatory growth leaf trichome production. Larval growth, consumption, were lower when feeding +Si compared to –Si plants. thickness, defensive behaviours, haemocyte density, lysozyme-like activity haemolymph unaffected by Si. Larvae fed had higher phenoloxidase (PO) total-PO activities than larvae plants, although this did not enhance melanisation response larvae. Furthermore, supplies increased compensation for herbivory constitutive production, whereas induced production only provide first evidence an herbivore. suggest that Si-supplemented could contribute their vulnerability natural enemies high PO may impose fitness costs (e.g. delayed development).