Abstract: The anti-herbivore effects of major secondary substances of wheat (Triticum aestivum L.), including tannic acid, total phenolic compound and coumarin, on the grain aphid, Sitobion avenae, were investigated by adding them to a chemically defined diet. The impact of these secondary chemicals on the activity of amylase, invertase, trehalase, esterase (CarE) and glutathione S-transferase (GST) in grain aphids was measured in vitro. The results show that tannic acid, total phenolic compound and coumarin significantly decreased nymphal survival, development and weight gain, with their resistant threshold concentrations being 0.06%, 0.08% and 0.065%, respectively. At these concentrations, tannic acid strongly inhibited the activity of invertase, trehalase, CarE and GST and gallic acid (total phenolic chemicals) greatly decreased the activity of invertase, CarE and GST. However, coumarin only strongly inhibited GST activity.

Key words: Sitobion avenae, sugar invert enzymes, detoxification enzymes, secondary substances, antiherbivore effect