Biochemical properties of digestive proteases of melon ladybird, Epilachna chrysomelina (Fabricius) (Col.: Coccinellidae)

Melon ladybird, Epilachna chrysomelina (Fabricius) (Col.: Coccinellidae)is a major pest of cucurbitaceous plants by feeding on leaves at larval and adult stages. In this study, biochemical properties of digestive proteases of the melon ladybird were studied in its alimentary canal. Enzyme activity in the digestive systems of 2nd, 3rd and 4th larval instars and adults showed that the highest specific enzyme activities occurred in 3rd instar larvae while no significant differences observed in adults. The optimal pH and temperature for protease activity in alimentary canal were found 5 and 30°C, respectively. The inhibitory effect of EDTA, TLCK, TPCK, PMSF and Iodoacetate were determined 44.32, 26.05, 22.27, 19.04 and 18.93% in the gut of E. chrysomelina, respectively. With respect to the highest inhibition rate in proteolytic activity caused by Iodoacetate, cysteine proteinases are considered as the main proteases in the midgut of the melon ladybird. Zymogram pattern in the native gel indicated that the protease enzyme had one isoform in the alimentary canal of the pest.