One-pot biogenic fabrication of silver nanocrystals using Quisqualis indica: Effectiveness on malaria and Zika virus mosquito vectors, and impact on non-target aquatic organisms

Currently, mosquito vector control is facing a number of key challenges, including the rapid development of resistance to synthetic pesticides and the recent spread of aggressive arbovirus outbreaks. The biosynthesis of silver nanoparticles (AgNPs) is currently considered an environmental friendly alternative to the employ of pyrethroids, carbamates and microbial agents (e.g. Bacillus thuringiensis var. israelensis), since AgNPs are easy to produce, effective and stable in the aquatic environment. However, their biophysical features showed wide variations according to the botanical agent using for the green synthesis, outlining the importance of screening local floral resources used as reducing and stabilizing agents. In this study, we focused on the biophysical properties and the mosquitocidal action of Quisqualis indica-fabricated AgNPs. AgNPs were characterized using spectroscopic (UV, FTIR, XRD) and microscopic (AFM, SEM, TEM and EDX) techniques. AFM, SEM and TEM confirmed the synthesis of poly-dispersed AgNPs with spherical shape and size ranging from 1 to 30 nm. XRD shed light on the crystalline structure of these AgNPs. The acute toxicity of Quisqualis indica extract and AgNPs was evaluated against malaria, arbovirus, and filariasis vectors, Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus, as well as on three important non-target aquatic organisms. The Q. indica leaf extract showed moderate larvicidal effectiveness on Cx. quinquefasciatus (LC50 = 220.42), Ae. aegypti (LC50 = 203.63) and An. stephensi (LC50 = 185.98). Q. indica-fabricated AgNPs showed high toxicity against Cx. quinquefasciatus (LC50 = 14.63), Ae. aegypti (LC50 = 13.55) and An. stephensi (LC50 = 12.52), respectively. Notably, Q. indica-synthesized AgNPs were moderately toxic to non-target aquatic mosquito predators Anisops bouvieri (LC50 = 653.05 μg/mL), Diplonychus indicus (LC50 = 860.94 μg/mL) and Gambusia affinis (LC50 = 2183.16 μg/mL), if compared to the targeted mosquitoes. Overall, the proposed one-pot biogenic fabrication of AgNPs using Q. indica is a low-cost and eco-friendly tool in the fight against Zika virus, malaria and filariasis vectors, with little impact against non-target aquatic mosquito predators.