Silica Nanoparticles Modulate Potato Defense and Tritrophic Interactions in a Growth-Stage-Dependent Manner: Effects on <i>Myzus persicae</i> Performance and Natural Enemy Behavior

Silica nanoparticles (SiNPs) enhance plant defenses; however, their stage-specific effects in tritrophic systems remain underexplored. This study evaluated potato plants treated with SiNPs (0.25-1 mM) at four developmental stages, assessing impacts on the peach potato aphid (<i>Myzus persicae</i>) and its natural enemies, the parasitoid <i>Aphidius gifuensis</i> and predator <i>Harmonia axyridis</i>. SiNPs reduced aphid survival, fecundity, and population growth with stronger effects in early stages. Parasitism by <i>A. gifuensis</i> increased on 1 mM-treated plants at stages 1, 3, and 4. While olfactometer assays revealed no insect preference for treated plants, SiNPs reduced leaf hydrogen peroxide and enhanced the emission of defensive volatiles (caryophyllene, longifolene, and phenol), providing a mechanistic basis for the observed aphid suppression and increased parasitoid activity. These findings demonstrate that SiNPs modulate plant defenses in a growth stage-dependent manner, highlighting their potential as a targeted tool in integrated pest management (IPM).