Digestive Amylase and Glucosidases in the Larval Stage of Elm Leaf Beetle, Xanthogaleruca Luteola (Col.: Chrysomelidae)

Elm leaf beetle, Xanthogaleruca luteola, is a serious pest (particularly at its larval stage) of elm trees in many areas. The existence of three important enzyms namely: α-amylase, α- glucosidase and β-glucosidase in the midgut of the insect at its larval stage was investigated. Optimum activity for α-, β-glucosidase and α-amylase was recorded at pHs 5.0, 6.0 and 6.0 against p-nitrophenyl-α-D-glucopyranoside, p-nitrophenyl-β-D-glucopyranoside and starch respectively. α and β-glucosidase exhibited more stability at pHs 4.0-6.0 than at either highly acidic or and alkaline pHs. These enzymes were respectively more stable at pH 5.0 and 6.0 with increased incubation time. α -amylase was stable at pHs 4.0-8.0. α and β-glucosidase and also α-amylase, when incubated at different temperatures were found to be maximally active at 45, 60 and 40°C, respectively. Alpha- glucosidase activity significantly decreased in the presence of Ca2+ and Mg2+. On the contrary, the ions K+ and Na+ did not significantly affect the enzyme’s activity. The ions K+, Mg2+ and Na+ did not significantly affect the enzyme activity. Zymogram analysis revealed the presence of one band each of amylase, α- and β-glucosidase activity in the insect’s larval midgut extract.