Biosynthesis and characterization of silver nanoparticles from symbiotic bacteria Xenorhabdus nematophila and testing its insecticidal efficacy on Spodoptera litura larvae.

Spodoptera litura, one of the polyphagous pests, causes huge economical lose and use of chemical pesticide causes impact to the environmental. The present study deals with the use of cell- free supernatant of bacteria Xenorhabdus nematophila NP-1 strain for synthesizing silver nanoparticles and analyzing its larvicidal ability against Spodoptera litura. Color change from yellow to dark brown specifies the synthesis of AgNPs. UV-Vis spec indicates the presences of AgNPs at 440 nm λmax and functional groups; alcohols, carboxylic acids, aromatics, alkylhalides, ethers and phenols were confirmed by FTIR. SEM revealed the synthesized AgNPs is in spherical shape, EDaX confirms the elemental composition and the crystalline nature were observed using XRD. GC-MS analysis showed presence of Benzencepropanoic acid, 1, 3, 5 Trichloropent-2-ene, 1,1-Dichloro-2,3- dicmethycycloprone and 1,2-benzenedicarboxylic acid bioactive compounds some of which may be responsible for insecticidal and antibacterial activity. The antibacterial activity against S. aureus, B. subtilis and K. pneumoniae showed maximum zone of inhibition at 100 µL/mL. Larvicidal activity of S. litura shows highest mortality at 48 h. In potted plant experiment, AgNPs treated plants showed less damage, with less leaf consumption by S. litura larvae. Further, the synthesis of AgNPs were targeted to zebrafish embryos (non- target organism) and it didn't exhibit any toxic effect even at higher concentration. Our experiment concludes that, AgNPs synthesized using NP-1 strain has highest antimicrobial and insecticidal activity, which can be used in biomedical and biopesticides.