Biological activity of Dolichos biflorus L. trypsin inhibitor against lepidopteran insect pests.

Protease inhibitors confer resistance in plants against insect pests by inhibiting larval gut proteases. Cultivars of Dolichos biflorus were screened for their inhibitory activity against midgut proteases of Pieris brassicae larvae. Seed extracts of developing and germinating seeds of HPK4 cultivar inhibited larval gut proteases of Spodoptera littoralis efficiently. Neonate larvae of P. brassicae fed on cabbage leaf discs coated with 0.025-2.50 mg protein (seed extract) resulted in 10-80% larval mortality and significantly reduced leaf area eaten and faecal matter as compared to control. The treated larvae had 40% less soluble proteins per mg faecal matter and there was similar decline in midgut proteases of treated larvae (@ 2.5 mg protein) compared to untreated ones after 5 days. The LC50 and LT50 value was calculated to be 1.05 mg/leaf disc and 4.8 days (2.5 mg protein), respectively for neonate larvae of P. brassicae. Significant reduction in egg hatching (75%) was observed in egg mass treated with 5.3 mg of crude inhibitor protein of mature seeds. This could be due to the inhibition of proteases involved in the hydrolysis of egg chorion proteins. The studies demonstrated the insecticidal activity of D. biflorus seed extracts.

Hyptis brevipes (Lamiaceae) Extracts Strongly Inhibit the Growth and Development of Spodoptera littoralis (Boisd.) Larvae (Lepidoptera: Noctuidae).

Hyptis brevipes (Lamiaceae) extracts are shown to exhibit strong insecticidal activity against the 3rd instar larva of the cotton leaf worm Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae), inducing complete larval mortality due to the arrest and/or disruption of metamorphosis. This disruption induced a wide range of abnormalities. The LC50 value of the dichloromethane extract of H. brevipes was 3.0% (95% F.L. = 2.2% - 4.4%; slope = 3.185± 0.952) after three days of treatment. Two active compounds were isolated from the extract following bioassay-guided fractionation and were identified as 5-hydroxy-7,4'-dimethoxy-flavon-3-ol and 5- hydroxy-7-methoxy-2-(4`-methoxy-phenyl)-chromen-4-one based on spectroscopic data. This is the first report of these secondary metabolites in H. brevipes.