The effects of feeding on different Poplar Clones on some biochemical properties of Gypsy moth larvaeAbstract : Gypsy moth (Lymantria dispar L.) is one of the most important pests in northern forests of Iran. For better understanding of the interaction between the pest and plant, the biochemical traits of larval body including glucose, cholesterol, protein, urea and also activity levels of alanin and aspartate amino transferase (ALT & AST) were measured in the 4th instar larvae fed by different clones of Populus deltoiedes, P. euramerican and P. caspica. Larval feeding on different clones of poplar caused considerable biochemical changes in their body. The results showed that glucose fluctuated in the body of these larvae from 35 to 93.3 mg/dl and its highest amount was observed in the larvae fed by P. e. triplo. Feeding on the leaves of P. deltoiedes caused cholesterol enhancement and in all the treatments ALT and AST activity levels followed the same pattern and AST was always higher than ALT. A considerable correlation was shown between these two enzymes while their activity levels were lower in the larvae fed on P. euramerican and P. caspica. Data outlined a negative correlation between glucose and other compounds in a way that if the metabolism was in the favor of carbohydrates, proteins and sterols decreased.