Comparative Toxicological Effects of Silica and Nanosilica against Trogoderma granarium under Variable Temperature Conditions

According the importance of the stored grains and other products, it is an essential to keep them from khapra beetle, Trogoderma granarium infestation. This study determined the mortality percentage of 5th instar larvae of T. granarium fed on wheat seeds (25gm) treated with different weights of silica as well as silica nanoparticles (20, 40, 60 and 80 mg) at different temperature (9 °C, 25 °C, and 35 °C). Study showed that using silica nanoparticles in cold temperature (9 °C) was the most efficient treatment with the lowest LC50 (lethal concentration required to kill 50% of the population) value and caused the highest toxicity index. In contrast, the least efficient treatment (25 °C) with the highest LC50 value and showed lowest toxicity index was using silica in normal temperature, when using silica nanoparticles, the cold temperature was the best condition followed by hot temperature (35 °C) and finally the normal temperature. On the other hand, using silica in hot temperature was most effective followed by silica with cold temperature and finally silica with normal temperature. The biochemical assays revealed that the change in the experimental temperature had a nonsignificant effect on the total protein content of the larvae. The total lipids and total carbohydrates exhibited a significant increase due to hot treating. 5th instar larvae of T. granarium treated with LC50 of silica at high temperature led to a nonsignificant (p ≤ 0.05) decrease in Acetylcholinesterase (AchE) activity compared to treatment at normal temperature. In contrast, Glutathione S-transferase (GST) and Peroxidase activities were significantly (p ≤ 0.05) raised due to the treatment conducted at high temperature. Additionally, treating larvae with LC50 of silica nanoparticles at low temperature caused a significant increase in both GST and peroxidase activities, while the increase in AChE was nonsignificantly (p ≤ 0.05) compared to treatment at normal temperature. Using silica at low temperature could be used as an alternative to chemical insecticides to control T. granarium larvae.