<p>The increasing use of engineered nanoparticles in agriculture has raised concerns regarding their potential impacts on non-target beneficial insects. In this study, we evaluated the concentration-dependent effects of chitosan (ChNPs), silver (AgNPs), and zinc oxide (ZnONPs) nanoparticles on the growth, survival, and midgut ultrastructure of the Eri silkworm, <i>Samia cynthia ricini</i>. Larvae were fed nanoparticle-treated host plant leaves at concentrations ranging from 25 to 500 ppm, and larval growth parameters, mortality, developmental abnormalities, and midgut histopathology were assessed. All three nanoparticles induced significant, dose-dependent reductions in larval length and girth, accompanied by increased mortality and developmental defects, particularly at higher concentrations. Chitosan nanoparticles produced the most pronounced adverse effects, followed by AgNPs and ZnO NPs. Dose–response analysis revealed a typical sigmoidal mortality pattern, indicating threshold-dependent toxicity. Histological and ultrastructural examinations of the midgut identified severe epithelial disruption, loss of microvilli, vacuolization, mitochondrial degeneration, and muscle layer damage in larvae exposed to 500 ppm nanoparticles. These alterations suggest impaired digestive function and nutrient assimilation as central mechanisms underlying growth inhibition and reduced survivorship. This study highlights the vulnerability of non-mulberry silkworms to nanoparticle exposure and underscores the need for careful ecological risk assessment of nanoparticle applications in agro-ecosystems. </p>