DEFENSE REACTIONS OF NORWAY SPRUCE (PICEA-ABIES KARST) TO CONTROLLED ATTACKS OF IPS-TYPOGRAPHUS (L) (COL, SCOLYTIDAE) IN RELATION TO TREE PARAMETERS

The defence reactions of 105 Norway spruce trees in response to contro lled attacks of Ips typographus were analysed and five groups with dif ferent defence reactions were recognized. Growth- and vigour-indices s howed no significant correlation with the induced reactions, but param eters of bark anatomy were most important. Due to secondary radial gro wth, the formation of periderm was intensified. Thereby, the density a nd thickness of radial resin ducts in the phloem increased, the number of boring attempts decreased and the number of boring attempts, defen ded by primary resin exudation, increased. Seasonal changes in the def ence reaction could partly be traced back to changes in starch reserve s in the phloem. Temporary changes in carbohydrate and water balance m ay affect the defences, but structural and anatomical properties of th e bark govern the basic conditions for the responses to invading bark beetles.