Evaluation of Brown and red seaweeds-extracts as a novel larvicidal agent against the deadly human diseases-vectors, Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus.

Infectious diseases such as malaria, dengue, and yellow fever are predominantly transmitted by insect vectors like Anopheles stephensi, Aedes aegypti, and Culex quinquefasciatus in tropical regions like India and Africa. In this study, we assessed the larvicidal activity of commonly found seaweeds, including Padina gymnospora, P. pavonica, Gracilaria crassa, Amphiroa fragilissima, and Spatoglossum marginatum, against these mosquito vectors. Our findings indicate that extracts from P. gymnospora Ethyl Acetate (PgEA), P. pavonica Hexane (PpH), and A. fragilissima Ethyl Acetate (AfEA) displayed the highest larval mortality rates for A. stephensi, with LC50 values of 10.51, 12.43, and 6.43 µg/mL, respectively. Additionally, the PgEA extract from P. gymnospora exhibited the highest mortality rate for A. aegypti, with an LC50 of 27.0 µg/mL, while the PgH extract from the same seaweed showed the highest mortality rate for C. quinquefasciatus, with an LC50 of 9.26 µg/mL. Phytochemical analysis of the seaweed extracts revealed the presence of 71 compounds in the solvent extracts. Fourier-transform infrared spectra of the selected seaweeds indicated the presence of functional groups such as alkanes, alcohols, and phenols. Gas chromatography-mass spectrometry analysis of the seaweeds identified major compounds, including hexadecanoic acid in PgEA, tetradecene (e)- in PpEA, octadecanoic acid in GcEA, and 7-hexadecene, (z)-, and trans-7-pentadecene in SmEA.