Larvicidal and pupicidal activity of synthesized silver nanoparticles using Leucas aspera leaf extract against mosquito vectors, Aedes aegypti and Anopheles stephensi

Abstract

Mosquitoes are one of the most medically significant groups of vectors, having an ability to transmit parasites and pathogens that can have devastating impacts on humans. The development of reliable and ecofriendly processes for the synthesis of metallic nanoparticles is an important step in the field of application of nanotechnology. In this study, we address the biosynthesis of silver nanoparticles (AgNPs) using <em>Leucas</em> <em>aspera</em> leaf extract, and evaluate its lethal concentration (LC<sub>50</sub> and LC<sub>90</sub>) values against first to fourth instar larvae and pupae of the mosquito vectors, <em>Aedes</em> <em>aegypti</em> and <em>Anopheles</em> <em>stephensi</em>. The nanoparticles were characterized by UV-Vis spectrum, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier-transformed infrared spectroscopy analysis. Larvae and pupae were exposed to varying concentrations of aqueous extracts of synthesized AgNPs for 24 h. The maximum mortality was observed from synthesized AgNPs, with LC<sub>50</sub> values for I-IV instars and pupae ranging from 13.06 to 25.54, and LC<sub>90</sub> values ranging from 24.11 to 47.34 for <em>A. aegypti</em>; for <em>A. stephensi</em>, the corresponding LC<sub>50</sub> values ranged from 12.45 to 22.26, and the LC<sub>90</sub> values ranged from 23.50 to 42.95. With methanol leaf extract of <em>L. aspera</em> against <em>A. aegypti</em>, the LC<sub>50</sub> values ranged from 174.89 to 462.96 and the LC<sub>90</sub> values ranged from 488.16 to 963.74; for <em>A. stephensi</em>, the corresponding LC<sub>50</sub> values ranged from 148.93 to 417.07 and the LC<sub>90</sub> values ranged from 449.72 to 912.94. The study suggests that nanoparticles could be a preferred alternative to the most hazardous existing chemical pesticides, contributing to a more healthy environment by providing an ideal ecological and user-friendly vector control strategy for managing malaria and dengue, and contributing to their eventual elimination in the near future.