From wheat to wheat: synergistic effect of silica nanoparticles synthesized from wheat straw assisted by gamma irradiation against khapra beetle, Trogoderma granarium everts on wheat grain

Abstract Background Trogoderma granarium Everts (Coleoptera: Dermestidae) is one of the most deleterious post-harvest pests of wheat grain in the first place and many other stored commodities. Sustainable, environmentally safe alternatives to chemical control methods are urgently needed, especially for food materials. Therefore, this study proposes a novel approach that utilizes wheat straw, an agricultural waste, to synthesize amorphous silica nanoparticles (SiO 2 NPs) and enhance their efficacy by exposing them to different doses of gamma irradiation. Methods Silica nanoparticles (SiO 2 NPs) were synthesized and exposed to different gamma irradiation doses (25, 50, 100 and 200 kGy). Characteristics of the as-synthesized SiO 2 NPs were evaluated using different characterization techniques such as Fourier transform infrared (FTIR), Transmission electron microscope (TEM), X-ray diffraction (XRD), energy-dispersive X-ray analysis spectrometer (EDX), electron spin resonance (ESR), thermal gravimetric analysis (TGA) and Brunauer–Emmer–Teller analysis (BET). Bioassay experiments were conducted at four concentrations (0.5, 1, 2 and 4 mg per treatment) to evaluate the insecticidal activity of the as-synthesized SiO 2 NPs using the median lethal concentration (LC 50 ) for both unirradiated and gamma-irradiated insects and wheat group at a sublethal dose of 100 Gy. Results The 50-kGy-irradiated SiO 2 NPs (50kGy_SiO 2 NPs) showed the most prominent characteristics, such as the uniform dispersion, a small particle size (5.4 ± 0.04 nm) and the highest surface area (148.70 m 2 /g). The combination of 50 kGy SiO 2 NPs with 100-Gy-irradiated insects showed the most potent insecticidal activity with the lowest LC 50 . A powerful synergistic effect was observed when (4 mg/5 g) of 50kGy_SiO 2 NPs was combined with the 100-Gy-irradiated insects, resulting in 95% and 100% larval mortality at 7 and 14 days post-treatment, respectively, accompanied by 100% antifeedant percentage, pupal inhibition and complete suppression of adult emergence. Conclusion Combining gamma-optimized SiO 2 NPs with sublethal irradiation of insects can provide a potent, reliable and eco-friendly approach for the integrated pest management of stored grain pests. Such a combination aims to reduce the applied amount of SiO 2 NPs and lower the irradiation dose required for controlling T. granarium in their separate usage. To our knowledge, this study is the first to report the synergistic insecticidal effect of gamma-irradiated SiO 2 NPs derived from wheat straw for T. granarium control. Graphical abstract