α-amylase activity of stored products insects and its inhibition by medicinal plant extracts

the experiment was conducted to determine α-amylase activity and the effect of seven plant species extracts including punica granatum l. (punicaceae), rheum officinale b. (polygonaceae), rhus coriaria l. (anacardiaceae), artemisia sieberi b. ( compositae), peganum harmala l. (nitrariaceae) , datura stramonium l. (solanaceae) and thymus vulgaris l. (lamiaceae) on α-amylase activity of four stored insect pests including callosobruchus maculatus f. (coleoptera: bruchidae), rhyzopertha dominica f. (coleoptera: bostrichidae), sitophilus granarius l. (coleoptera: curculionidae), and trogoderma granarium e. (coleoptera : dermestidae). also, gut ph and optimum temperature for α-amylase activity of these insects were determined. it was found that α -amylases midgut ph of all four insect species was acidic and optimum temperature was between 30 and 40 °c. beyond these temperatures, the α-amylases activities sharply decreased. plant extracts caused inhibitory activity on insect α-amylases varying from nearly 4% to 95% inhibition. d. stramonium and r. officinali extracts had the highest amylase inhibitory activity among the tested extracts, while methanolic extracts of p. harmala, and t. vulgaris (except for s. granaries α-amylase) showed the lowest inhibitory activity. gel assays revealed that more than one isoform of α -amylase detected in midgut crude extracts of the four insect pests examined could be inhibited by the plant extracts.