Abstract: For evaluating the insect resistance property of a wild rice Oryza punctata, five extracts of the wild rice plants with petroleum ether, chloroform, ethyl acetate, n-butanol and water were tested for their antifeedant activity against Spodoptera litura larvae. The results showed that chloroform extract was the most effective one among the five extracts. In 24 h and 48 h of treatment, the antifeedant rate of the chloroform extract against 3rd instar larvae of S. litura at 2.5 mg/mL was 55.62% and 52.66%, respectively. The chloroform extract was further separated through silica gel column and the fractions were  monitored with analytical thin layer chromatography (TLC). Fourteen fractions were obtained and also tested for their antifeedant activity against S. litura larvae. The bioassay results showed that fraction 4 and 10 at 1 mg/mL had higher antifeedant activity to 3rd instar larvae of S. litura than other fractions. The antifeedant rate of fraction 4 was 56.01% in 24 h of treatment and 38.06% in 48 h of treatment, while that of fraction 10 was 51.56% in 24 h of treatment and 64.30% in 48 h of treatment. The inhibiting activity of the two fractions against two digestive enzymes lipase and α-amylase from the midgut of S. litura was tested. The results showed that the activity of both enzymes was inhibited effectively by the two fractions. The inhibiting rates of fraction 4 and 10 at 1 mg/mL against α-amylase activity of 3rd instar larvae of S. litura were 25.06％ and 27.40％ in 72 h of treatment, respectively. Fraction 10 could inhibit the activity of lipase of 3rd instar larvae of S. litura significantly, with the inhibiting rate 19.82％ in 48 h of treatment and 34.60％ in 72 h of treatment, respectively. The results of assay suggested that the digestive enzymes of the midgut of S. litura might be the action targets of the active ingredients fromO. punctata.

Key words: Oryza punctata, Spodoptera litura, antifeeding component, lipase, α-amylas