Larvicidal Efficacy of a Tropical Seaweed (Dictyota ciliolata) Extracts on Vectorial Mosquito Species and Non-Target Effect on Guppy Fish (Poecilia reticulata)

Abstract

Extracts of seaweeds are promising candidates for eco-friendly, safe, and biodegradable larvicides and as alternatives to chemical larvicides used in mosquito control strategies. This study evaluated the larvicidal effects of Dictyota ciliolata on the mosquito larvae of Aedes aegypti, Anopheles gambiae, and Culex quinquefasciatus. The seaweed was extracted using ethanol and methanol. The larvicidal assays were conducted per WHO standards by exposing twenty 4th instar larvae to 100, 200, 300, 400, 500, and 600 mg/L of the derived extracts. The LC₅₀ and LC₉₅ values were obtained by calculating the probit values of the observed mortalities. LC₅₀ of the ethanolic and methanolic extracts of Dictyota ciliolata against Anopheles gambiae larvae were 238.45 mg/L and 497.28 mg/L respectively; 179.02 mg/L and 224.96 mg/L respectively against Aedes aegypti, and 167.49 mg/L and 226.69 mg/L respectively for Culex quinquefasciatus. The results established that ethanolic and methanolic seaweed extracts were most influential on Culex quinquefasciatus followed by Aedes aegypti and Anopheles gambiae. Although mortalities were recorded for Poecilia reticulata, such may not be enough to de-emphasize the observed larvicidal potentials of Dictyota ciliolata as some other factors could have been responsible for the said mortalities in the non-target species.