Toxicity of gracilaria verrucosa methonal extract against selected medically important vector mosquitoes (diptera: culicidae) of Puducherry, India

Objective: To evaluate the larvicidal, ovicidal and repellent activities of methanol extract of Sargassum ilicifolium (Phaeophyta), Caulerpa sertularoides (Chlorophyta) and Gracilaria verrucosa (Rhodophyta) against Aedes aegypti, Anopheles stephensi and Culex quinquefasciatus. Methods: The selected seaweed extracts were dissolved in DMSO to prepare graded concentrations. Larvicidal efficacy of selected seaweed were tested at various concentrations against the early third instar larvae of Ae.aegypti, An.stephensi and Cx.quinquefasciatus. Bioassay test was carried out as per the guidelines of WHO (2005). The 24h LC50 values of the selected seaweed extracts were determined by probit analysis. For ovicidal activity modified method of Su and Mulla was used. Ovicidal activity was determined against selected mosquitoes at various concentrations ranging from 25-200 ppm under laboratory conditions. The hatch rates were assessed 48h post treatment. The Gracilaria verrucosa repellent efficiency was determined against selected mosquitoes at three concentrations such as 1.0, 2.0 and 3.0 mg/cm2 under laboratory conditions. Results: The LC50 and LC90 values of methanol seaweed extract of Gracilaria verrucosa against early third instar larvae of Ae. aegypti, An. stephensi and Cx. quinquefasciatus were 0.125, 0.131, 0.135; ppm, respectively. The crude extract of seaweed exerted 100% egg mortality (zero hatchability) at 240, 300 and 360 ppm for Ae. aegypti, An. stephensi and Cx. quinquefasciatus. Similarly, a higher concentration of 8 mg/cm2 provide 100% protection up to 210, 180 and 150 min against Ae. aegypti, An. stephensi and Cx. quinquefasciatus. Conclusions: The present results suggest that the Gracilaria verrucosa methanol seaweed extract provides an excellent potential for controlling selected medically important vector mosquitoes.