Enzymatic activity of α-amylase in alimentary tract Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae): Characterization and Compartmentalization

The Egyptian cotton leafworm, Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) damages a wide variety of crops in Middle East. Their hosts include cotton, alfalfa, eggplant, tomato, lettuce, bean and some ornamental crops. The intensive use of broad-spectrum insecticides against S. littoralis has led to the development of resistance to many registered pesticides use for its control. The purpose of the present study is biochemical characterization of digestive enzymes of this pest to gain a better understanding of the digestive physiology. The physiology and biochemistry of the insect digestive enzyme had an important role in the study of novel insecticidal strategies. The Egyptian cotton leafworm alimentary canal consists of a short foregut, a long midgut and a short hindgut. Application of pH indicators showed that alimentary canal was alkaline. Our results showed that activities of gut α-amylase were different in three parts of the insect gut. Also shown the greatest activity of α-amylase observed in the midgut followed by hindgut and foregut, respectively. However, there were not significant differences in activity of the enzyme in the midgut and hindgut. The optimal pH α-amylase in foregut, midgut and hindgut were 10.0. Zymogram analysis of different part of gut showed four bands in midgut, hind gut and two bands in foregut. Therefore, in midgut of S. littoralis, four isoenzymes were present. These results explain why more amylase activity was seen in these regions in the spectrophotometric assay