Successive extraction of the green alga, Scenedesmus acutus 276–3a with different solvents indicated that the petroleum ether extract was the most repellent to the hatched larvae of Spodoptera littoralis. The application of spray emulsified 1 % petroleum ether extract inhibited egg laying. At 0.25% concentration the moths laid only 52.4 of their egg masses on the treated oviposition sites in comparison to the untreated control. Concentration of 1% was protective against the immature stage by hindering the third instar larvae to feed on treated leaf discs. In addition, the water emulsion of petroleum ether extract was insecticidal. The percentage mortality was directly proportional to the concentration applied and to the duration of exposure.
