Insecticidal Activity of Phytosynthesized Silver Nanoparticles (AgNPs) against Spodoptera frugiperda and Plutella xylostella

The application of nanotechnology in crop protection holds a significant promise and metal based nanoparticle reported to exhibit insecticidal property. Present study, aims to photosynthesize Silver Nanoparticles (AgNPs) using Catharanthus roseus aqueous leaf extract, characterize them and evaluate for their insecticidal efficacy against 2^nd and 3^rd instar larvae of Spodoptera frugiperda and Plutella xylostella. Phytosynthesized silver nanoparticles (AgNPs) were initially identified by the change in color from colorless to dark brown. These silver nanoparticles were characterized using UV-Visible spectroscopy that revealed an absorbance peak at 448 nm. Spherical shape with an average nanoparticle size of 48 nm and the presence of elemental silver was confirmed using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) spectrum respectively, Atomic Force Microscopy (AFM) analysis showed the surface of the nanoparticles was rough and undulated and the Fourier Transform Infrared Spectroscopy (FTIR) spectrum revealed functional groups of biomolecules in the plant extract responsible for the reduction of silver nitrate to silver nanoparticles. Further, insecticidal bio efficacy data revealed that the highest concentration of AgNPs (8000 ppm) induced 100% and 53.33% mortality at 120 h in 2^nd and 3^rd instar larvae of Spodoptera frugiperda respectively. Whereas, 4000 ppm (Highest concentration) phytosynthesized AgNPs induced 82.75% and 66.66% mortality at 120 h in 2^nd and 3^rd instar larvae of Plutella xylostella respectively. Collectively, this study suggests the potential use of phytosynthesized AgNPs for management of agricultural insect pests.