Inhibitory effects of barley and wheat seed protein on digestive α- Amylase and general protease activity of Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae)

Abstract

In the current study, the effects of barley and wheat seed proteins on Colorado potato beetle, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae) certain digestive enzymes and biological parameters were investigated. Ammonium sulfate precipitation proteinaceous fractions 0-30% and 30-50% of both seeds produced the greatest inhibition on L4 α-amylase but no significant inhibition on the protease activity. The inhibitory effects of fraction of 0-30% on the L1, L2, L3, L4 and adult's α-amylase activity of barley were 64, 53, 59, 49, and 56%, respectively, and of wheat were 70, 63, 63, 57, and 67%, respectively. While the inhibitory effects of the effective fraction of 30-50% on the L1, L2, L3, L4 and adult's α-amylase activity of barley were 45, 46, 52, 48, and 53%, respectively, and of wheat were 66, 59, 70, 56, and 68%, respectively. Type of inhibition in both cases was determined as partial mixed at the enzyme-inhibition kinetic tests. Zymograms confirmed the inhibition of insect α- Amylase activity. Bioassays were conducted using four cultivars of potato leaves treated with barley extract. Weight of L4 in Picasso and the percentage of L4 evolution in all cultivars were reduced and the developmental durations were significantly increased at Marx and Picasso, in comparison with control. However, there was no significant effect on gut amylase activity of survived individuals.