Potential of using Clerodendrum inerme extracts, essential oil, and biosynthesized silver nanoparticles as ecofriendly natural pesticides for controlling the rust floor beetle, Tribolium castaneum infesting grain products in stores

Abstract

There is a renewed interest in seeking effective and ecofriendly green pesticides to mitigate the environmental dangers of synthetic ones. In that framework, Clerodendrum inerme essential oil (EO) was hydrodistiled and analyzed by using gas chromatography-flame ionisation detection (GC-FID) and GC/Mass spectrometry (MS). Isoeugenol (33.1 %) and dibutyl phthalate (29.3 %) were identified as the main oil components. Silver nanoparticles (Ci-based AgNPs) were produced using the methanol (MeOH) extract and characterized microscopically and spectroscopically. The phytochemicals showed considerable larvicidal, adulticidal, andtifeedant and acetycholinestearse inhibitory effects against the red flour beetle, T. castaneum. Upon a contact toxicity using treated filter paper, Ci-based AgNPs exhibited the strongest effect, followed by the EO, isoeugenol, dibutyl phthalate, MeOH, and aqueous extracts with larval LC₅₀ values after 48 h ranged between 14.8 and 53.7 μL/cm², and between 21.3 and 61.1 μL/cm² against adults. Using fumigation, EO was the strongest fumigant with LC_50's after 48 h of 13.4, and 19.6 μL/L air against larva and adult, respectively. At sub-lethal concentrations, the phytochemicals remarkably altered the nutritional parameters and feeding behavior of adult beetles. The phytochemicals significantly inhibited insect's AChE activity. They have been considered as safe for Eisenia fetida earthworm, at concentrations up to 150 mg/kg soil, and safe for albino rats at a maximum oral dosage of 3500 mg/kg b.w. They also did not induce phytotoxicity towards wheat grains at 150 μL/mL. The results revealed the potential of using C. inerme extracts, EO and Ag nanoparticles as environmentally benign green insecticides against T. castaneum.