α-Amylase Activities in Larval Midgut Extracts from Four Species of Lepidoptera (Tortricidae and Gelechiidae): Response to pH and to Inhibitors from Wheat, Barley, Kidney Bean, and Streptomyces

Abstract

Levels of α-amylase activity between 0.6 and 5.0 µmoles maltose minute-1 gram insect-1 occurred in larval midgut extracts from 4 species of lepidopterous pests-light brown apple moth, Epiphyas postvittana (Walker), Planotortrix octo (Dugdale), and Ctenopseustis Obliquana (Walker) are pests of apple leaves and fruit, and potato tuber moth, Phthorimaea Operculella (Zeller), is a pest of potato tubers and foliage. Activity response curves described the optima for activity at a highly alkaline pH range (pH 10.5 in leafrollers and pH 9.5 in potato tuber moth). This result is consistent with the known high midgut pH in other species of Lepidoptera and with the pH optima of their digestive proteases. The 3 wheat derived α-amylase inhibitors inhibited enzyme activities of all 4 species of Lepidoptera, but the other 3 (barley tetramer, Streptomyces, and kidney bean inhibitors) had no effect. Wheat dimeric inhibitor (30 µM) completely inhibited α-amylase activity in potato tuber moth midgut extracts.