SCREENING OF PLANT SEEDS FOR PROTEASE INHIBITOR AGAINST LARVAL GUT PROTEASES OF SPODOPTERA MAURITIA (BOISD.) (LEPIDOPTERA: NOCTUIDAE)

Plant protease inhibitors (PPIs) are widely distributed in plants and among other roles, it protects plants from insect attack. Plant protease inhibitors inhibit insect gut protease activity thereby hampering protein digestion. In this study, we screened plant seeds to identify PPIs against larval gut proteases of Spodoptera mauritia (Boisd.). Seeds were homogenized in bicarbonate buffer pH 9.0 (1ml/g tissue) and was centrifuged at 10,000 x g for 10 minutes at 4oC. The supernatant was used for protease inhibition assay using azocasein as substrate. Out of 30 different seeds screened, 10 showed greater than 40% inhibition and the highest percentage of inhibition was showed by Areca triandra (73.3±0.04%), followed by Abelmoschus manihot (72.57±1.3%), Mallotus tetracocus (53±1.7%), Mucuna pruriens, (47.30±3.46%). Crotalaria pallida (46.56±0.94%), Nephelium lappacum (45.66±1.28%), Persea Americana (44.38±0.09%), Ipomoea cairica (42.53±1.20%), Ricinus communis (41.77±3.28%) and Thunbergia alata (40.82±0.05%) respectively. This is the first report of presence of PPIs from Areca triandra, Abelmoschus manihot, Mallotus tetracocus, Ipomoea cairica and Thunbergia alata. Though there are reports of the presence of trypsin/ cysteine protease inhibitor from other plants reported here, in this study we showed for the first time that the seed extracts from these plants inhibited larval gut proteases of S. mauritia. Proteinase K treatment revealed that the inhibitor in Abelmoschus manihot is proteinacious in nature while the inhibitor in Areca triandra may be a non-proteinacious inhibitor. Identification and characterization of new PPIs against gut proteases of insects will be helpful in designing better insect control strategies