Comparative entomotoxic effects of nanosilica and microsilica on Crocidolomia pavonana larvae

Nanosilica represents a promising material for insect pest management. This study compared the physicochemical properties and entomotoxic effects of nanosilica and microsilica powders against Crocidolomia pavonana larvae. The X-Ray-Fluorescence and X-Ray-Diffraction analysis confirmed higher purity in nanosilica (99.9%) than in microsilica (86.2%), with both showing amorphous structures. Particle size distribution and morphological analysis showed that nanosilica had an average particle diameter of 206.7 ± 127.7 nm, while microsilica measured 1144 ± 290.6 nm and formed a semi-spherical aggregate. Brunauer-Emmett-Teller revealed that nanosilica had a larger pore surface area (317 m²/g), total pore volume (1.539 cm³/g), and an average pore diameter (13.123 nm) compared to microsilica. Dust spray method confirmed that nanosilica had higher entomotoxicity than microsilica against C. pavonana 2^nd instar larvae. This was observed from the 100% mortality achieved by nanosilica at all concentrations (N1-N4) at 72 hours (P < 0.05), whereas a similar trend was only observed at the highest microsilica concentration (M4). The median lethal concentration analysis showed that microsilica was more toxic at 24 hours (LC₅₀ = 0.395 mg/cm²), whereas nanosilica exhibited higher toxicity at 48 and 72 hours with a lower LC₅₀ value of 0.137 mg/cm² and 0.106 mg/cm². The shortest median lethal time was recorded for N₄ (LT₅₀ = 26.85 hours) treatment, indicating a faster lethal effect than M₄ (LT₅₀ = 30.91 hours) treatment. The morphological alterations in larvae included desiccation, cuticle damage, and nanosilica entrapped in the spiracle trichome, which potentially led to an obstruction. The results showed the strong insecticidal potential of nanosilica as an alternative for managing cabbage pests.