Characterization of α-amylase in the midgut and the salivary glands of rice striped stem borer, Chilo suppressalis Walker (Lepidoptera: Pyralidae)

The rice striped stem borer, Chilo supprressalis, is a destructive pest of rice that was introduced to Iran in 1973 and has since become widely distributed. Amylases are hydrolytic enzymes that catalyze the hydrolysis of the α-d-(1,4)-glucan linkage in glycogen and other related carbohydrates. Laboratory-reared 4th stadium larvae were randomly selected; the midgut and the salivary glands were removed by dissection under a dissecting microscope and α-amylase activity was assayed using the dinitrosalicylic acid procedure. The activity of α-amylase in the midgut and salivary gland were 0.06 and 0.036 μmol/min/mg protein, respectively. The optimal pH and temperature for α-amylase were 9 and 35-40 °C, which is consistent with reports of other lepidopteran insects. The enzyme activity was inhibited by addition of NaCl, KCl, MgCl2, Urea, EDTA, and SDS. CaCl2 enhanced enzyme activity. Ca2+ ions also had inhibitory effects on glucosidase activity. Plant amylase inhibitors play important role against insect pests. Hence, the characterization of digestive enzymes and the examination of inhibitors on enzyme activity could be useful in tackling of insect pests.