Bio-nanosilver synthesized by the entomopathogenic nematode-symbiotic bacterium as bio-insecticide for the red flour beetle (Tribolium castaneum)

Biological control can be another important way to manage post-harvest insect pests. Some organisms that showed biological control activity against some soil pests are insect-parasitic nematodes. There are two different species of nematodes, steinernematids and heterorhabditids, who carry within their bodies insect-pathogenic bacteria. Xenorhabdus spp are bacteria which infest steinernematids and Photorhabdus spp. bacteria infect heterorhabditids. The study aimed to develop pesticide alternatives by synthesizing silver bio-nanoparticles (AgNPs) using Xenorhabdus indica bacterial filtrate. The nanoparticles synthesized by the bacterial strains were purified and its cytotoxicity and bioactivity was examined against the larvae of the Tribolium castaneum. AgNPs were characterized by Scanning Electron Microscopy and X-Ray diffraction analysis, and the results revealed that the obtained nanoparticles are nanosilver with sizes ranging from 30 to 70 nm, with spherical shape and nonsmoothed surface. Insect larvae were initially exposed to descending concentrations (100, 50, 25, 10 and 5 μg/ml) of the biosynthesized nanosilver for 48 hours. Results of the bioassay showed that mortality of treated larvae was concentration-dependent with LC50 of 25 μg/ml. Higher mortality percentage (89%) was observed with the concentration 100 ug/ml and the lower one was obtained by the concentration 5 ug/ml (60%). Subsequently, data of the present study suggest these bio-AgNPs-bacterial filtrate complexes could be used as potentially effective eco-friend bio-control candidates. However, testing other types of bio-synthesized nanomaterials, and its vital effect as bio-insecticide for storage insect species are still under investigation.