Insecticidal Efficacy of Silica Nanoparticles Loaded with Several Insecticides in Controlling Khapra Beetle Larvae, Trogoderma granarium on Mosaic and Galvanized Steel Surfaces

The incidence of pests’ resistance to pesticides, adverse effects of pesticides on non-target species, and environmental hazards have increased the tendency of applying various pests control techniques. Nanopesticide formulations are thus considered as one of the recent techniques in controlling pests. Using this technology increases the effectiveness of pesticides under various environmental conditions, including light and hot situations. Indeed, it decreases the amount of pesticide use and ultimately decreases the chance of pests’ resistance to insecticides.

In the current study, the silica nanoparticles were prepared using the sol-gel method and loaded with deltamethrin, pyriproxyfen, and chlorpyrifos. The mosaic and galvanized steel surfaces were treated with either deltamethrin (0.0025 and 0.005 g(a.i.)/m2), pyriproxyfen (0.001, 0.01 and 0.1 g(a.i.)/m2) and chlorpyrifos (0.01 and 0.2 g(a.i.)/m2) alone or loaded in nanosilica. The experiments were carried out at 3 replicates, and 3 sub replicates. In each replicate, 10 small or large larvae of Trogoderma granarium Everts (Coleoptera: Dermestidae) were introduced, and 2 g wheat Chamran variety was utilized as food source. All experiments were conducted at 30±1 °C, 65±5 % RH, and darkness. The initial mortality of small and large larvae of T. granarium was counted 1, 3, and 7 days after exposure, and delayed mortality was assessed 7 days thereafter. For each larval group, the variance analysis of initial and delayed mortality was subjected to the factorial test (concentration and time as main effects). Means were separated by Tukey Kramer HSD test at p < /em> =0.05 using SPSS software version 16.

Results indicated that initial and delayed mortality increased by raising concentration levels and exposing time to each concentration in all experiments. In all cases, the small larvae of T. granarium were more sensitive than large larvae.  Deltamethrin, followed by chlorpyrifos, was the most toxic to the larvae of T. granarium. Due to our findings, the mortality was dramatically higher in galvanized steel than the mosaic one. It could be attributed to the steel's flat surface, reducing insecticide residues' absorbance within the surface. Moreover, the insecticidal efficacy of nanosilica loaded with insecticides was significantly greater than the application of insecticides without nanosilica. Utilizing nanoparticles, we found an increase in the ratio of surface area to volume of insecticides, resulting in more insect contact to insecticide particles and eventually improved the mortality rate of insecticide.

It is therefore concluded that the application of loaded insecticides in silica nanoparticles significantly increased T. granarium larvae's mortality rate. Furthermore, silica nanoparticles can be introduced as the carrier of insecticides to control T. granarium in the stored wheat efficiently. Besides, deltamethrin loaded SNPs is potentially recommended as one capable component that can be effectively conducted during pest management programs in terms of stored products pest control.