The biological activities of acetone crude extracts from the leaves of Solanum melongena L., Lycopersicum esculentum Mill., Capsicum annuum L. and fruit extract of S. melongena plants, were evaluated against two major pests, cluster caterpillar, Spodoptera litura Fab. and castor semilooper, Achaea janata L. The crude extracts were purified in a column and its purified fractions were assessed for its antifeedant and growth inhibitory activities by oral feeding method. The leaf extract of C. annuum and fruit extract of S. melongena showed strong antifeedant activity against S. litura and A. janata in leaf disc bioassays with a range of EC50 31.4- 34.7 mg/10cm² as compared to other extracts tested. The fruit extract of S. melongena and leaf extract of L. esculentum caused significant larval growth inhibition after seven days of feeding to both the larvae by oral feeding assay. The fruit extract of S. melongena and leaf extracts of L. esculentum and C. annuum interfered with the molting process and produced morphological abnormalities by oral ingestion. Methanol eluted purified fraction from S. melongena fruit extract produced more potent antifeedant and larval growth inhibitory activity against test larvae than the other eluted test fractions. The effect of these plant extracts on proteolytic activity of the midguts of the two lepidopteran larvae were analyzed using azocasein/BApNA/SAAPFpNA as substrates. The serine protease activity was inhibited in all midguts fed with S. melongena fruit extract, when compared to the other treated and controlled midguts. Fruit extract from S. melongena showed more potent activity against both lepidopteran larvae.