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Willow leaf beetle, Plagiodera versicolora is an important pest of willow trees that feeds on the leaves both as larvae and as adults. -Amylases (EC 3.2.1.1) are the major insect digestive enzymes that catalyze the endohydrolysis of long -1,4-glucan chains such as starch and glycogen. In the current study, -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 -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 Na²⁺, K⁺ and Zn²⁺. 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.    

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Nutritional indices of the willow leaf beetle, Plagiodera versicolora Laicharting, third instar larvae and adults were studied on four host plants including Salix alba L., Salix aegyptica L., Populus caspica Bornm.and Populus alba L.at 22 ± 2 ºC, 70 ± 10% R.H., and a photoperiod of 16:8 h (L: D). The results showed that the highest consumed food by the larvae and adults (148.5 ± 18.0 and 175.21 ± 4.51 mg dry weight, respectively) was on P. caspica. The larvae fed on S. alba and S. aegyptica had the highest efficiency of conversion of ingested food (ECI) (2.3 ± 0.33 and 2.23 ± 0.67%, respectively) and efficiency of conversion of digested food (ECD) (2.5 ± 0.35 and 2.41 ± 0.72%, respectively). Approximate digestibility (AD) of larvae was the highest on P. caspica and P. alba (98.51 ± 0.25 and 98.14 ± 0.1%, respectively). The lowest relative consumption rate (RCR) of the larvae and adults was on S. alba (0.14 ± 0.001 and 0.13 ± 0.006 mg/mg/day, respectively). ECI and ECD values of the adults fed on various host plants were not significantly different. Adults fed on P. caspica had the highest values of RCR (0.59 ± 0.01 mg/mg/day), relative growth rate (RGR) (0.02 ± 0.008 mg/mg/day) and AD (98.72 ± 0.24%). These results demonstrated the higher feeding performance of the willow leaf beetle on P. caspica and its poorer performance on P. alba.