Synthesis and toxicological evaluation of silica nanoparticles as chlorpyrifos carrier against the beetle pests Rhyzopertha dominica and Tribolium confusum

In this study, silica nanoparticles (SNPs) were prepared by sol-gel technique. Chlorpyrifos (40.8% EC) was loaded on the SNPs by immersion loading method. The Specific surface area (SBET) of nanosilica was characterized by BET and recorded 102.24 m2/g. Loading efficiency of chlorpyrifos-loaded in silica nanoparticles (Ch-SNPs) was measured 86.79% using UV-VIS spectrophotometer. According to FT-IR results, chlorpyrifos properties remained intact after loading on nanosilica because of physical adsorption process of the insecticide in the pores. The residual toxicity of Ch-SNPs was assessed against two stored product insect species, Rhyzopertha dominica F. and Tribolium confusum Jacquelin du Val. on Petri dish, galvanized steel, mosaic and concrete surfaces. Residual toxicity was evaluated 7, 15, 30, 45 and 60-day post treatment. For each post treatment, the mortality was counted after 6, 24, 48 and 72 h of exposure. The mortality increased with increasing concentration of insecticide and time exposed to each concentration. According to the results, the Ch-SNP was effective against the both pest species, but the toxicity varied depending on the surface material. Ch-SNPs provided long-term protection on petri dishes against the pests, whilst concrete followed by mosaic surfaces with less protection. For instance, R. dominica mortality percentage after 24 h exposure to Petri dish, galvanized steel, mosaic and concrete treated with 0.2 mg cm-2 Ch-SNPwas 100, 82.8, 40 and 1.4%, whereas the mortality was 100, 97.1, 20 and 18.5 % for T. confusum at 60-day post-treatment, respectively.