Toxicity of Red Macroalga, Laurencia obtusa against Growth and Development of Spodoptera litura (Lepidoptera: Noctuidae)

Abstract

The present study evaluates the insecticidal efficacy of Red Macroalga, Laurencia obtusa against the lepidopteran pest, Spodoptera litura under laboratory conditions. The macroalga was harvested in Hare Island, Tuticorin and extracted with three solvents, hexane, dichloromethane and methanol. The extracts were used to treat castor leaf discs with different concentrations (0.7% to 10%) and second instar larvae of S. litura were exposed to the treated discs and the larval mortality and growth regulatory effects were determined. The findings showed that all three extracts had a dose-dependent toxic effect with methanol extract having the highest mortality (80.00% at 10% concentration) and the lowest LC50 value (3.32%), followed by dichloromethane and hexane. Moreover, methanol and dichloromethane extracts had a considerable inhibitory effect on larval development, pupation and adult emergence, and caused deformed adults, which is a strong indicator of Insect Growth Regulatory (IGR) activity. These results indicate that L. obtusa methanol extract contains strong bioactive compounds that can manage S. litura and interfere with its life cycle. The research identifies the possible use of L. obtusa as a source of marine algal biopesticides as an alternative to synthetic insecticides, which is safer to the environment.