Swift Fabrication of Silver Nanoparticles Using Bougainvillea glabra: Potential Against the Japanese Encephalitis Vector, Culex tritaeniorhynchus Giles (Diptera: Culicidae)

Mosquitoes are the most critical group of insects in the context of public health, since they transmit key parasites and pathogens, causing millions of deaths annually. Culex tritaeniorhynchus is an important vector of Japanese encephalitis (JE) across urban and semi-urban areas of Asia. In this study, we bio-fabricated silver nanoparticles (Ag NP) using the leaf extract of Bougainvillea glabra as reducing and stabilizing agent. The synthesis 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 determined by energy dispersive X-ray (EDX) spectroscopy. Fourier transform infrared (FTIR) spectroscopy analysis investigated the identity of secondary metabolites, which may act as Ag NP capping agents. The acute toxicity of B. glabra extract, synthesized Ag NP and a combined treatment testing blends of both mosquitocidals was evaluated against larvae and pupae of Cx. tritaeniorhynchus. B. glabra showed LC 50 of 198.93 (larva I), 234.50 (II), 309.18 (III), 371.69 (IV) and 466.09 (pupa) µg/ml, Ag NP LC 50 ranged from 7.77 (I) to 19.44 µg/ml (pupa). Combined treatments with B. glabra leaf extract plus 5.12.5 µg/ml of Ag NP lowered the botanical LC 50 to 66.09 (I), 76.48 (II), 99.02 (III), 133.43 (IV) and 179.74 µg/ml (IV), respectively. The effectiveness of green-fabricated Ag NP against the JE vector was confirmed in adulticidal tests, as well as evaluating the impact of Ag NP on fecundity and longevity of adult mosquitoes. Lastly, the larvicidal effectiveness of Ag NP was confirmed in the field, treating sewage water bodies. Overall, this study suggests that the green-synthesized Ag NP fabricated using B. glabra can be considered a potential mosquito control device against the JE vector, C. tritaeniorhynchus in Asian regions.