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

Silicon Application Enhances Sugarcane Growth by Impairing the Development of Larval Sugarcane Borer

“…These results are in agreement with [66], who also found similar results when studying a soil dwelling herbivore interacting with sugarcane and Si. However, [25] observed increased values of phenol oxidase activity in the hemolymph of H. armigera larvae fed on the Si-fertilized model grass Brachypodium distachyon. Despite Si did not result in changes of phenol oxidase activity in the hemolymph of larval D. saccharalis, the activity of this enzyme was greater in larvae fed with IAC91-1099 plants than in those fed with SP80-3280 plants.…”

“…Another way to assess the negative effects of Si over herbivore insects would analyzing their immune system [25]. The insect immune system consists of structural barriers and active responses against foreign elements that enter the haemocoel.…”

“…The exposure of the insect to foreign elements can induce various immune responses that stimulate the production of hemocytes, which are responsible for cell encapsulation and constitute the nal barrier of the insect defense system [26-28]. Silicon has already been reported in the literature to interfere with the immune system of Helicoverpa armigera (Hübner, [1808]) (Lepidoptera: Noctuidae), in which caterpillars fed on siliconfertilized grasses showed higher activities phenol oxidase and total phenol oxidase [25].…”

Influence of silicon and growth regulator on leaf, whorl and cob damage of maize fall armyworm in vivo

“…Ganapathy et al [11] con rmed that highest per cent reduction of pod borer of green gram in potassium silicate @ 0.5% + gibberellic acid @ 50 ppm (54.87%) followed by potassium silicate @ 1% + gibberellic acid @ 100 ppm (51.79%) and silicic acid @ 0.2% + gibberellic acid @ 100 ppm (49.35%). Similarly, NuamboteYobila et al [12] revealed that Si treated plants disturbed the larval growth of FAW larvae only from the corn strain but not from the rice strain. Tarikul Islam et al [13] reported that the lower integument resistance of larvae when fed on Si supplemented plants could contribute to their vulnerability to natural enemies and high polyphenol oxidase activity in the haemolymph led to delayed development.…”

Silicon and Epichloë‐endophyte defences in a model temperate grass diminish feeding efficiency and immunity of an insect folivore

“…The impacts of plant antiherbivore defence on insect immunity have been much neglected (Islam et al, 2022). To our knowledge, there are no reports of the effects of Epichloë defences on herbivore immunity traits, and the effects of Si defences on herbivore immunity are poorly understood, with just two studies to date reporting that Si alone has no clear effects on chewing herbivore immunity (Frew et al, 2017; Islam et al, 2022). Frew et al (2017) reported that Si defences did not affect the immunity of a root‐feeding insect whereas Islam et al (2022) found that immunity of H. armigera was not affected by Si alone.…”