Lethal Effects of Red Macroalgal Extracts against Tobacco Cutworm, Spodoptera litura Fabricius

Abstract

Aims: The purpose of the present paper was to study the toxicity of aqueous and methanol Red macro algal extracts against the cosmopolitan pest, Tobacco cutworm: Spodoptera litura Fabricius.
 Place and Duration of Study: Department of Agricultural Entomology, Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu.
 Methodology: The bioassay was carried by treating aqueous and methanol extracts of three different Red macroalgae at 0.7, 1.00, 3.00, 5.00, 7.00 and 10.00 per cent concentration with three replications of ten larvae per treatment and the mortality data was recorded every 24 hours up to adult emergence.
 Results: The aqueous and methanol extracts of three different Red macroalgae viz., Acanthophora spicifera, Gracilaria corticata and Jania rubens were used to find out their lethal effects against tobacco cutworm, Spodoptera litura under laboratory condition. The larval mortalities were observed for both extracts. Percentages of mortalities, after 96 hours of exposure, increased at the highest concentration of 10 per cent of A. spicifera, G. corticata and J. rubens, extracts. Respectively, 60.00, 46.66 and 26.66 per cent of larvae mortalities were observed in aqueous extracts and 40.00, 26.66 and 23.33 per cent of lethality were recorded in methanol extracts. The pre-pupal and pupal mortalities were recorded in all the concentrations showing malformations during the growth. The pupation and the adult emergence were also affected with the highest inhibition by the extracts of A. spicifera.
 Conclusion: The Red macroalgae possess an insecticidal and growth inhibitory potential which can be exploited for eco-friendly management of Spodoptera litura. Further studies should be carried out to purify the active biomolecules of the tested extracts and to evaluate the effect of Red macroalgae on other lepidopteran larvae.