Facile biosynthesis of silver nanoparticles using Barleria cristata: mosquitocidal potential and biotoxicity on three non-target aquatic organisms.

Mosquitoes (Diptera: Culicidae) act as vectors of important pathogens and parasites, such as malaria, dengue, chikungunya, Japanese encephalitis and lymphatic filariasis. The use of synthetic mosquitocides often leads to high operational costs and adverse non-target effects. Recently, plant-borne compounds have been proposed for rapid extracellular biosynthesis of mosquitocidal nanoparticles. However, the impact of these nanomosquitocides against biological control agents of mosquito larval populations has been poorly studied. In this research, we biosynthesized silver nanoparticles (Ag NP) using the Barleria cristata leaf extract as a reducing and stabilizing agent. The biosynthesis of Ag NP was confirmed analyzing the excitation of surface plasmon resonance using ultraviolet-visible (UV-vis) spectrophotometry. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed the clustered and irregular shapes of Ag NP. The presence of silver was confirmed by energy-dispersive X-ray (EDX) spectroscopy. Fourier transform infrared (FTIR) spectroscopy investigated the identity of secondary metabolites, which may also act as Ag NP capping agents. The acute toxicity of B. cristata leaf extract and biosynthesized Ag NP was evaluated against larvae of Anopheles subpictus, Aedes albopictus, and Culex tritaeniorhynchus. Compared to the leaf aqueous extract, biosynthesized Ag NP showed higher toxicity against An. subpictus, Ae. albopictus, and Cx. tritaeniorhynchus with lethal concentration (LC)50 values of 12.46, 13.49, and 15.01 μg/mL, respectively. Notably, biosynthesized Ag NP were found safer to non-target organisms Diplonychus indicus, Anisops bouvieri, and Gambusia affinis, with respective LC50 values ranging from 633.26 to 866.92 μg/mL. Overall, our results highlight that B. cristata-fabricated Ag NP are a promising and eco-friendly tool against young instar populations of mosquito vectors of medical and veterinary importance.