Insecticidal effects of Sargassum vulgare and Caulerpa racemosa extracts on Aedes aegypti.

Abstract

Dengue is a viral disease present in many regions of the world. Aedes aegypti transmits it, and the most effective way to eliminate the mosquito is during the larval stage. Seaweeds possess metabolites with insecticidal properties, making them potential sources of new larvicides and viable alternatives to synthetic products used to control insect vectors of diseases. Thus, this study aimed to investigate the chemical composition, in vitro toxicity, and larvicidal activities of the ethanolic extract of the seaweed Sargassum vulgare (SE) and hydroalcoholic extract of the seaweed Caulerpa racemosa (CH) against Ae. aegypti. The chemical composition of the crude extracts was evaluated by high-performance liquid chromatography coupled with mass spectrometry (LC-MS), and toxic effects were assessed through in vitro cytotoxicity. The larvicidal activity was evaluated by determining mortality and lethal concentrations (LC₅₀ and LC₉₀), morphological analyses of larvae, and evaluation of the enzymatic action mechanism. The results showed that the extracts contained primary and secondary metabolites, mainly, alkaloids, terpenoids, carbohydrates, fatty acids, and chlorophyll derivatives, all of which were biocompatible at all tested concentrations (3 to 100 μg/mL). The SE and CH extracts showed larvicidal potential at all tested concentrations, achieving 95 % and 50 % mortality after 48 h. Observed changes in the external morphology of the larvae included color change, loss of bristles, and gill filaments. At the same time, the enzymatic action mechanism occurred through stimulation of amylase, trypsin, and acetylcholinesterase activities. Therefore, both seaweed extracts offering alternatives to synthetic chemical insecticides.