Effect of nano silica on some biological and histological aspects cotton leaf worm Larvae spodoptera littoralis (bosid) (lepidoptera: noctuidae)

Abstract

The study aims to prepare silica nanoparticles and their effect against larvae of cotton leafworm Spodoptera littoralis. The silica nanoparticles were prepared by sol–gel method in two forms, Silica nanoparticles hydrophilic (TSiNP HPHI), silica nanoparticles hydrophobic (TSiNP HPHO) from Tetraethyl orthosilicate (TEOS) and nano silica hydrophilic from sodium silicate (SSiNP HPHI) in addition traditional silica (TSi) from sand by grinding the sand in Ball mill device. The obtained silica powders were characterized by using spectroscopy with high resolution Transmission Electron Microscope (TEM). The crystalline shape of the particles was determined using X-ray diffraction (XRD). Chemical bonds were identified By Fourier Transform-Infrared Spectroscopy (FTIR). The results showed that, all particles were in nano size and amorphs form. Nano silica consist of silica and oxygen only in TSiNP HPHI and SSiNP HPHI while TSiNP HPHO nano silica was consist of silica, oxygen and carbon. The effect of silica nanoparticles and traditional silica on the second and fourth larvae of S.littoralis were studied to determine the mortality ratio and estimate LC50 values using four concentrations, 10, 20, 40, 60 g / L. Results showed that all tested concentrations of compounds caused mortality of second and fourth larvae of S. littoralis. The concentrations of 60 and 40g/L for all three nano silica caused100% mortality of second larvae. The mortality rate in the fourth larvae was100% at 60g/L in all treatments. While the traditional silica treatment did not exceed 70% in the second larvae and 68% for the fourth larvae at the highest concentration of (60g/L). The LC50 values were calculated through these results. Values of The LC50 were 10.48, 10.76, 14.01and 42.99 g/L of TSiNP HPHO, TSiNP HPHI and TSi, respectively. According to LC50 values, the most effective compounds were TSiNP HPHO and SSiNP HPHI. The 4th instar were more tolerant than 2nd instar larvae.

When studying the effect of silica nanotubes and traditional silica on some biological aspects, the results showed that larval, pupal duration and adult longevity of S.littoralis were decreased compared to control. While weight of pupal was significantly lower in weight compared to control in all treatments. hatching rate was 89% for control, while the lowest for hatching was 85% in TSiNP HPHO.

The determination of both the total protein and the activity of chitinase, amylase, protease and phenol oxides enzymes, results showed that the three nanoparticles in addition to the traditional silica caused a significant decrease in total protein as compared to control. The coefficients of silica nanoparticles only resulted in a significant decrease in the activity of protease and amylase enzymes, while significantly increasing the activity of chitinase and phenol-oxidase compared to control. The results showed that the effect of traditional silica was insignificant in the activity of the former enzymes compared to control. When studying the effect of silica nanoparticles on the histologic side of the midgut of fourth instar larvae S.littoralis. The results showed that TSiNP HPHO caused disruptive of midgut followed by SSiNP HPHIM then TSiNP HPHI and It was noted that traditional silica had the least impact compared with control where, midgut was without any damage.