Some properties of α-amylase in the digestive system and head glands of Cryptolaemus montrouzieri (Coleloptera: Coccinellidae)

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 (0.89 ± 0.02 μmol/min/mg protein) was significantly more than that of digestive system (0.76 ± 0.01 μmol/min/mg protein) in common condition (temperature equal to 25 ± 1 oC). The optimal pH and temperature for α-amylases activity were determined to be nearly 4 and 50°C in digestive system and 6 and 60 °C in head glands, respectively. EDTA (Ethylenediamine tetra acetic acid), Mg2+, Na+, Co2+, Fe2+ and Ca2+ inhibited the enzyme activity but Ba2+, Zn2+, Hg+ and K+ enhanced enzyme activity in digestive system. EDTA and all tested metal ions except Ba2+ 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.