Digestive amylase and pectinase activity in the larvae of alfalfa weevil Hypera postica (Coleoptera: Curculionidae)

Abstract

AbstractThe alfalfa weevil Hypera postica is a serious economic pest in most alfalfa grown in many countries worldwide. Digestive α‐amylase and pectinase activities of larvae were investigated using general substrates. Midgut extracts from larvae showed an optimum activity for α‐amylase against starch at acidic pH (pH 5.0). α‐Amylase from larval midgut was more stable at mildly acidic pH (pH 5–6) than highly acidic and alkaline pH. The enzyme showed its maximum activity at 35°C. α‐Amylase activity was significantly decreased in the presence of Ca2+, Mg2+ and sodium dodecylsulfate. On the contrary, K+ and Na+ did not significantly affect the enzyme activity. Zymogram analysis revealed the presence of one band of α‐amylase activity in in‐gel assays. Pectinase activity was assayed using agarose plate and colorimetric assays. Optimal pH for pectinase activity in the larval midgut was determined to be pH 5.0. Pectinase enzyme is more stable at pH 4.0–7.0 than highly acidic and alkaline pH. However, the enzyme was more stable at slightly acidic pH (pH 6.0) when incubation time increased. Maximum activity for the enzyme incubated at different temperatures was observed to be 40°C. Optimum pH activity for α‐amylase and pectinase is not completely consistent with the pH prevailing in the larval midgut. This is the first report of the presence of pectinase activity in H. postica.