Oxidative effects of foliar-applied silica, titania, and silver nanoparticles on the leafminer, with additional studies of silica nanoparticle impacts on survival and development time

As the potential applications of nanoparticles (NPs) in insect pest management continue to be explored, the focus has primarily been on external feeders, leaving a notable knowledge gap regarding internal leaf feeders. In this study, we investigated the effects of silica (SiO₂), titania (TiO₂), and silver (Ag) NPs on the American serpentine leafminer, Liriomyza trifolii (Diptera: Agromyzidae), a devastating pest of a diverse array of crops. NPs were sprayed on the leaves of seedlings of the common bean, Phaseolus vulgaris (Fabaceae), at concentrations of 50, 100, 200, and 400 mg/L to evaluate their effects on the survival, development, feeding rate, and body mass/size of the leafminer. qRT-PCR was used to assess oxidative stress in pupae based on the expression of genes for two major antioxidant enzymes, catalase (CAT) and superoxide dismutase 2 (SOD2). Total protein content was also quantified. Compared to the control (distilled water), neither SiO₂, TiO₂, nor Ag NPs affected larval feeding rate. SiO₂NPs decreased puparia weight, while TiO₂ and Ag NPs increased both the weight and length of puparium as well as wing length in adults. The lowest tested concentration of TiO₂NPs (50 mg/L) and the highest of AgNPs (400 mg/L) led to upregulation of SOD2, whereas SiO₂NPs had no significant effects on the expression of either CAT or SOD2. Total protein content was not affected by any NP treatment. Further assessment of the effects of SiO₂NPs revealed fewer observed mines, reduced larval survival, leading to a reduction in the number of emerging adults at 400 mg/L, delay in mine appearance, pupariation, and adult emergence at varying concentrations, and visible wing deformities; the LC₅₀ of SiO₂NPs was estimated to be 550 mg/L. Ultimately, because the preapplication of TiO₂ and Ag NPs on P. vulgaris increased the body size (wing length) of emerging adult leafminers, compared to the largely negative effects of SiO₂NPs, plant-mediated chronic exposure to TiO₂ and Ag NPs at sublethal concentrations may increase rather than decrease the performance of phytophagous insects. Our results have important implications for the use of NPs in the management of internal feeders and other insect pests.