The agricultural use of silica (SiO₂) nanoparticles (NPs) has the potential to control insect pests while the safety and tritrophic effects on plants and beneficial natural enemies remains unknown. Here, we evaluate the effects of silica NPs on insect pests with different feeding niches, natural enemies, and a plant. Silica NPs were applied at different concentrations (75–425 mg/L) on field-cultivated faba bean and soybean for two growing seasons. The faba bean pests, the cowpea aphidAphis craccivoraand the American serpentine leafminerLiriomyza trifolii, and the soybean pest, the cotton leafwormSpodoptera littoralis, were monitored along with their associated predators. Additional laboratory experiments were performed to test the effects of silica NPs on the growth of faba bean seedlings and to determine whether the rove beetlePaederus fuscipesis attracted to cotton leafworm-infested soybean treated with silica NPs. In the field experiments, silica NPs reduced the populations of all three insect pests and their associated predators, including rove beetles, as the concentration of silica NPs increased. In soybean fields, however, the total number of predators initially increased after applying the lowest concentration. An olfactometer-based choice test found that rove beetles were more likely to move towards an herbivore-infested plant treated with silica NPs than to a water-treated control, suggesting that silica NPs enhance the attraction of natural enemies via herbivore-induced plant volatiles. In the laboratory, while silica NPs inhibited the development of faba bean roots at 400 mg/L, they did not affect germination percentage, germination time, shoot length, or vigor index compared to the control.

Insects quickly develop their resistance to conventional synthetic chemical insecticides. Silica nanoparticles (SiO2NPs) is a new promising approach not only in decreasing insect pest numbers but also for its safety regarding agricultural organisms such as plants and beneficial natural enemies. Here, we investigate the safety of SiO2NPs on the faba bean Vicia faba (Fabaceae) as a model plant for toxicity studies and its control efficiency against the American serpentine leafminer Liriomyza trifolii (Diptera: Agromyzidae) as a major devastating insect pest against a wide range of crops. The concentrations of 50, 100, 200 and 400 mg/L of SiO2NPs (spherical shape, 15.3 nm) as well as distilled water as the control were used to investigate the effect of the nanoparticles. Early stages of development of V. faba were evaluated. The same concentrations of SiO2NPs were applied by spraying on two weeks old bean seedlings to evaluate their toxic effect on the feeding, survival and body mass of L. trifolii. A qRT-PCR analysis was conducted to assess oxidative stress on the gene expression level of the major antioxidative enzymes, catalase and superoxide dismutase, in L. trifolii. SiO2NPs inhibited root development only at a high concentration and did not affect the germination percentage, germination time, shoot length and vigor index compared to the control. The survival rate of larvae was lower than the control at the highest concentration and the larval feeding velocity and pupal weight decreased at high concentrations. Gene expression of both enzymes at the pupal stage were not affected by SiO2NPs at any concentrations. This study suggests that care must be taken to utilize SiO2NPs at a suitable concentration in controlling pests, avoiding negative effects on plant growth.