Midgut proteases from larval Spodoptera littoralis (Lepidoptera: Noctuidae)
The presence and properties of proteases present in larval midgut extracts from Spodoptera littoralis was investigated. Trypsin and chymotrypsin activities were found mainly in the midgut lumen while leucine aminopeptidase and dipeptidyl aminopeptidase IV activities were found solely in the midgut tissue. Hydrolysis of carboxypeptidase substrates indicated carboxyesterase A activity only. The characteristics of trypsin, chymotrypsin and leucine aminopeptidase were determined with respect to a variety of factors including pH, temperature, substrate concentration, P(_1) amino acid specificity and molecular weight. Inhibition of the endopeptidases by a wide variety of protease inhibitors derived from chemical, microbial, plant and animal sources was also carried out. Endopeptidase activities were compared with proteases from Helicoverpa armigera and mammalian sources and the endopeptidase specificity discussed. In addition, a haemolymph phenoloxidase (PO) was characterised (pH, substrate concentration), purified and the effects of various zymogen activating and PO inhibitory substances determined. Finally, two parasites were studied. Firstly, the ultrastructure of stages in the life-cycle of a microsporidian parasite (Nosema sp.) from H. armigera and secondly, the morphological changes associated with a nuclear polyhedrosis virus (NPV) disease in S. littoralis, together with ultrastructural characterisation and comparison of restriction endonuclease patterns of the nucleic acids between NPVs from different sources.