Phytochemical, cytotoxic, and insecticidal effects of crude extracts of the alga Alsidium triquetrum (SGGmelin) Trevisan on Aedes aegypti

Aedes aegypti, the yellow fever mosquito, is the main vector of several arboviruses. It represents a public health problem and can develop resistance to chemical insecticides over time, requiring new formulations of ecologically friendly larvicides for its control. Seaweed is an abundant source of phytochemicals with diverse chemical compositions and is a prospective natural alternative to commercial insecticides. In this study, we aimed to investigate the larvicidal efficacy of the seaweed Alsidium triquetrum against Ae. aegypti by evaluating the toxic, morphological, and enzymatic effects of the ethanolic (AE) and hydroalcoholic (AH) extracts of the seaweed. The chemical composition of the extracts was evaluated using high-performance liquid chromatography and liquid chromatography coupled with high-resolution mass spectrometry, and the toxic effects were investigated by assessing the larvicidal activity, morphology of the larvae, and in vitro toxicity, along with enzymatic tests. The AH and AE extracts comprised primary and secondary metabolites, including amino and fatty acids and other compounds. The insecticidal bioassays showed larvicidal potential against Ae. aegypti at all concentrations tested, reaching 100% mortality in 24 h for both extracts. Morphological analysis of the larvae showed damage to the abdomen, changes in colour, disruption of the midgut, and loss of gill leaflets. The extracts stimulated similar activity for the enzymes amylase, trypsin, and acetylcholine esterase at concentrations above 0.5 μg mL⁻¹. The cytotoxicity of the algal extracts in vitro indicated non-toxicity at the concentrations tested. Therefore, both seaweed extracts are potential sources of new formulations for use as natural insecticides.