Abstract: The induced variation of some chemical substances in the body of the larch,Larix princippis-rupprechtii Mayr. injured by the larch case-bearer, Coleophora sinensis Yang, was studied. The tests were conducted in 1996～1998 in the forest areas of Wutai and Guandi Mountains located in Shanxi, China.The results showed that the North China larch could produce some secondary substances and change the compositions of some compounds in its body when it was injured by the larch case bearer. The first group of the secondary substances was tannin and free phenol. Tannin was raised so quickly with the case bearer feeding leaves in the moderate damaged forest that its content in leaves could exceed that in the other two areas. The second change was the variation of peroxidase activity in the leaves. The more damages the forest suffered, the more activities of the peroxidase the trees had. Another pest resistant factor of the forest was the dropping of its reducing sugar and Vc when the damage happened, so that the pest did not prefer to the nutrition of the leaves. These factors together took part in the chemical defense of the larch against the case-bearer attack.

Key words: Larix princippis－rupprechtii Mayr., Larch case-bearer, Coleophora sinensis Yang, Chemical defense, Induced pest-resistance