Fatemeh Ahmadi - Department of Plant Protection, Faculty of Agriculture, University of Zabol, Zabol, Iran.
Abbas Khani - Department of Plant Protection, Faculty of Agriculture, University of Zabol, Zabol, Iran. Tel. and Fax: +۹۸-۵۴۲-۲۲۴۲۵۰۱; E-mail address: abbkhani@yahoo.com
Mohammad Ghadamyari - Department of Plant Protection, Faculty of Agricultural Science, University of Guilan, Rasht, Iran.

Biochemical characteristics of α-amylase in the digestive system and head glands of Cryptolaemus montrouzieri, a key predator of citrus mealybug, Planococcus citri (Pseudococcidae), were studied. The major isoform of α-amylase with the same molecular weight was detected in both gut and head glands loaded on polyacrylamide-starch gel electrophoresis. Moreover, a minor band with much lower intensity was observed in zymogram analysis of gut. Results showed that the specific activity of α-amylase from head glands (۰.۸۹ ± ۰.۰۲ μmol/min/mg protein) was significantly more than that of digestive system (۰.۷۶ ± ۰.۰۱ μmol/min/mg protein) in common condition (temperature equal to ۲۵ ± ۱ oC). The optimal pH and temperature for α-amylases activity were determined to be nearly ۴ and ۵۰°C in digestive system and ۶ and ۶۰ °C in head glands, respectively. EDTA (Ethylenediamine tetra acetic acid), Mg۲+, Na+, Co۲+, Fe۲+ and Ca۲+ inhibited the enzyme activity but Ba۲+, Zn۲+, Hg+ and K+ enhanced enzyme activity in digestive system. EDTA and all tested metal ions except Ba۲+ inhibited the enzyme activity of head glands. Detectable levels of α-amylase activity in the insect reflect adaptation of the coccinellid for using starch granules or sugars (honeydew; sugary excreta of homopterans; and nectar) as a source of food in addition to predatory habits.

α-amylase, digestive enzyme, Cryptolaemus montrouzieri