Predatory efficiency of the copepod Megacyclops formosanus and toxic effect of the red alga Gracilaria firma-synthesized silver nanoparticles against the dengue vector Aedes aegypti

Abstract

Vector control is a critical requirement in epidemic disease management, and improved mosquito control methods that are economic and effective are necessary. Cyclopoid copepods are common predators in numerous aquatic ecosystems and have been used as biological agents in programs to control mosquito larvae. In this study, we proposed a green synthesis of silver nanoparticles (AgNPs) using the seaweed, Gracilaria firma, and combined them with the copepod, Megacyclops formosanus, for controlling the dengue vector, Aedes aegypti. The green synthesis of AgNPs was characterized by UV–Vis spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. In mosquitocidal assays, the LC50 of G. firma extract against A. aegypti ranged from 0.091 (instar I) to 2.417 (pupae). LC50 of G. firma-synthesized AgNPs ranged from 25.895 (instar I) to 351.419 (pupae). Furthermore, we evaluated the predatory efficiency of copepod M. formosanus against the larvae of A. aegypti. The most characteristic effects were midgut columnar cell vacuolization, epithelium cell contents passing into the midgut lumen, and, finally, cell death. These results suggest that synthesized AgNPs in combination with copepods constitute ecofriendly and potential mosquito larvicidal agents.