Characterization of digestive α-amylase in the midgut of willow leaf beetle Plagiodera versicolora (Coleoptera: Chrysomelidae)

Willow leaf beetle, Plagiodera versicolora is an important pest of willow trees that feeds on the leaves both as larvae and as adults. α-Amylases (EC 3.2.1.1) are the major insect digestive enzymes that catalyze the endohydrolysis of long α- 1,4-glucan chains such as starch and glycogen. In the current study, α-amylase activity was studied in the midgut of larvae and adults of P. versicolora. Amylase activity in the midgut of larvae and adults was 0.6807 and 0.1162 μmol/min/mg protein, respectively. The optimal pH for α-amylase activity of larvae and adults was 4 and 8, respectively and the optimal temperature for both was 35 °C. The enzyme activity of larvae was inhibited by the addition of Na^2+, K^+ and Zn^2+. K^+ (at 5 mmol) had the most positive effect on α-amylase activity in adults. EGTA had significant influence on decreasing the enzyme activity in larvae. EDTA had the most effect on increasing the activity of the enzyme in adults. Plant amylase inhibitors play important role against insect pests. Therefore, the characterization of digestive enzymes and the examination of inhibitors on the enzyme activity could be useful in tackling insect pests.