Effect of morphology on larvicidal activity of chemically synthesized zinc oxide nanoparticles against mosquito vectors.

We report the larvicidal effects of four different morphologies of zinc oxide nanoparticles (ZnO NPs) [star-shaped (S), needle-like (N), plate-like (P) and cubical (C)] on larvae of Aedes albopictus and Anopheles vagus ; the mosquitoes causing dengue fever and malaria, respectively. The nanoparticles were characterized by several analytical techniques, and their sizes and shapes were determined. Second instar larvae of the two types of mosquitoes were exposed to several concentrations of nanoparticles (25 mg L -1 , 50 mg L -1 , 75 mg L -1 , 100 mg L -1 ) at 25 ± 2 °C and 84 ± 5% R.H, separately, for each morphology. Larval mortality was reported at 24 h intervals up to 21 days. The resulting LC 50 for Aedes albopictus were, respectively, 38.90 mg L -1 , 47.53 mg L -1 , 68.38 mg L -1 , 50.24 mg L -1 for S-, N-, P- and C-shaped nanoparticles. The LC 50 of Anopheles vagus is lower (LC 50 4.78 mg L -1 , 6.51 mg L -1 , 13.64 mg L -1 , 10.47 mg L -1 ), respectively, for S-, N-, P- and C-shaped nanoparticles indicating that the nanoparticles are more toxic to Anopheles vagus larvae. The highest larvicidal effect was obtained from star-shaped nanoparticles [ Aedes albopictus (38.90 mg L -1 ) on Anopheles vagus (4.78 mg L -1 )], and the lowest was shown by the plate-like nanoparticles [ Aedes albopictus (68.38 mg L -1 ), Anopheles vagus (13.64 mg L -1 )]. The rate of development of surviving mosquito larvae was retarded when exposed to ZnO nanoparticles suggesting the possibility for these nanoparticles to kill and delay the growth of Aedes albopictus and Anopheles vagus larvae.