Toxicity of herbal extracts used in ethno-veterinary medicine and green-encapsulated ZnO nanoparticles against Aedes aegypti and microbial pathogens.

Abstract

Dengue and chikungunya are arboviral diseases mainly vectored by the mosquito Aedes aegypti. Presently, there is no treatment for these viral diseases and their prevention is still based on vector control measures. Nanopesticides fabricated using herbal extracts as reducing and capping agents currentlyrepresent an excellent platform for pest control. In this scenario, the present study assessed the acute toxicity of seven plants employed in ethno-veterinary medicine of southern India, as well as the green synthesis of zinc oxide nanoparticles, on third-instar larvae of A. aegypti. Larvae were exposed to extracts of the seven plants obtained with solvents of different polarity (acetone, ethanol, petroleum ether, and water) for 24h. Maximum efficacy was observed for Lobelia leschenaultiana leaf extracts prepared using all the four solvent extracts (LC50=22.83, 28.12, 32.61, and 36.85mg/L, respectively). Therefore, this plantspecies was used for the synthesis and stabilization of ZnO nanoparticles based on its maximum efficacy against third-instar larvae of A. aegypti. L. leschenaultiana-encapsulated ZnO nanoparticles showed 100% mortality when tested at 10mg/L, the LC50 wasextremely low, 1.57mg/L. Zinc acetate achieved only 65.33% when tested at 60mg/L, with a LC50 of 51.62mg/L. Additionally, ZnO nanoparticles inhibited growth of Pseudomonas aeruginosa, Proteus vulgaris, Shigella sonnei, and Vibrio parahaemolyticus and also inhibited biofilm formationon selected microbila pathogens, showingimpact onEPS production and hydrophobicity. Overall, our results suggest that L. leschenaultiana-fabricated ZnO nanoparticles have a significant potential to control A. aegypti mosquitoes and Gram-negative bacterial pathogens.