Developmental stage determines the efficacy of silica nanoparticles in shaping maize defence, aphid performance and tritrophic interactions

BACKGROUND Silica nanoparticles (SiNPs) are emerging as promising elicitors of plant defence, yet how plant developmental stage influences their effectiveness remains poorly understood. We investigated whether maize vegetative stage modulates SiNP‐mediated defence responses, and their consequences for herbivores and natural enemies. We hypothesized that SiNPs induce stage‐ and concentration‐dependent defence, with stronger effects at earlier vegetative stages. RESULTS Maize plants at four vegetative stages (V3–V6; corresponding to stages 1–4) were treated with different SiNP concentrations, and responses were assessed across multiple biological levels. SiNP application did not significantly affect plant height, leaf length, root length or dry root weight across stages. However, leaf surface hydrophobicity and hydrogen peroxide (H 2 O 2 ) accumulation increased, whereas malondialdehyde (MDA) levels decreased, indicating enhanced oxidative defences and reduced lipid peroxidation. SiNP treatment significantly altered volatile organic compound (VOC) profiles, notably increasing levels of key compounds, such as sesquiterpenes. Aphid ( Rhopalosiphum maidis ) survival, fecundity and population growth were reduced on treated plants, accompanied by reduced settlement in choice assays, whereas olfactory preference in Y‐tube tests remained unchanged. Foraging duration of the parasitoid Aphidius gifuensis increased on SiNP‐treated plants at early stages, while predator ( Harmonia axyridis ) behaviour was unaffected. CONCLUSION Maize developmental stage critically determines the efficacy of SiNP‐induced defence and its cascading effects across trophic levels. These findings provide mechanistic insights for optimizing the timing of SiNP application in sustainable integrated pest management strategies, enhancing plant resistance while supporting beneficial natural enemies.