Insecticidal efficacy of synthesized ZnO nanoparticles using brown algae Cystoseira baccata extract against Callosobruchus Maculatus (F.) (Col.: Chrysomelidae)

Abstract The environmental and human health risks of chemical insecticides have prompted extensive searches for alternative methods to protect stored products. Recently, nanoparticles have been considered as promising alternatives to synthetic chemical products. In this study, ZnO nanoparticles (NPs) were synthesized using Cystoseira baccata algae extract, and characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR), and Field emission scanning electron microscopy (FE-SEM). Three different types of ZnO NPs, ZnO-A, ZnO-B, and ZnO-C, were synthesized using algae extract by two different methods. Their insecticidal activity was evaluated and compared with the chemically synthesized ZnO-D NPs against the cowpea weevil, Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae) on stored cowpea. Biosynthesized ZnO-A, ZnO-B, and ZnO-C NPs exhibited higher activity against C. maculatus when compared with ZnO-D NPs. Porous ZnO-A NPs with the smallest particle size (24.3 nm) were determined to be the most toxic nanoparticles, causing the highest mortality rate of C. maculatus adults after five days of exposure. While ZnO-D NPs were the least effective for C. maculatus control. A significant oviposition inhibition (35.1 to 44.9%) and progeny reduction (35.7 to 45.6%) was also observed for insects exposed to ZnO-A NPs-treated cowpeas at 500 to 2000 mg kg-1. The average weight loss of cowpea seeds treated with ZnO-A, ZnO-B, and ZnO-C NPs at 2000 mg kg-1 was 23.8, 28.1, and 33.5%, respectively. The potential of using biosynthesized ZnO NPs as a viable alternative for controlling C. maculatus in stored cowpeas is discussed.