Insecticidal Potential of Garlic Nanoparticles Versus Raw Extract against Callosobruchus maculatus (F.) and Their Non-target Effects on the Parasitoid Anisopteromalus calandrae (Howard)
Abstract
Background: Stored grains are still being protected and preserved with synthetic chemical pesticides, which has major environmental and health concerns and needs to be met with more sustainable and biocompatible means. In this study, we examined the insecticidal activity of biosynthesized silver nanoparticles (Ag NPs) derived from Iraqi garlic extract and their synergistic effects against the larvae of southern cowpea beetle Callosobruchus maculatus (F.), which is a major stored-products pest of this plant. Methods: The garlic aqueous extract (Allium sativum L.) was used to synthesize green silver nanoparticles (Ag NPs) which were characterized by XRD, FESEM, FTIR and EDS techniques. To calculate adult mortality of Callosobruchus maculatus, three concentrations (20, 30 and 50 ppm) of both the Nano and crude extracts of garlic were tested and compared for seven days. Mortality of third- and fourth-instar larvae of C. maculatus within the seeds was also calculated using the same concentrations of the Nano and crude extracts. Additionally, larval mortality due to the ectoparasitoid Anisopteromalus calandrae was calculated. Finally, larval mortality due to the synergistic effect between the Nano and crude extracts at the same concentrations mentioned above and the ectoparasitoid A. calandrae, was studied and the number of resulting ectoparasitoid offspring was calculated after 25 days. Result: Biosynthetic silver nanoparticles (Ag NPs) exhibited the best toxicity against the adults C. maculatus with a high mortality of 73% at 50 ppm (p less than 0.01). A noteworthy synergistic effect was also observed for killing C. maculatus larvae. Ag NPs had 75% mortality at 50 ppm, while Ag NPs combined with A. calandrae had 100% mortality at 30 ppm of C. maculatus larvae. The bioavailable silver nanoparticles and the parasitoid synergized extremely well, which was confirmed through statistical analysis. Also, a high rate of parasitoid emergence was obtained, indicating that there was excellent selection and biocompatibility between the bioavailable nanoparticles and natural enemy.