AN INDUCED DEFENSE REACTION IN WHITE SPRUCE TO ATTACK BY THE WHITE-PINE WEEVIL, PISSODES STROBI

An induced defense reaction in the leaders of white spruce, Picea glau ca (Moench) Voss, occurs in response to attack by the white pine weevi l, Pissodes strobi Peck. The response was initiated shortly after feed ing and oviposition in the attacked shoot and consisted of the cambium switching from producing normal tracheids and parenchyma ray cells to producing traumatic resin canals, arranged in a ring fashion in the d eveloping xylem. In sectioned leaders, these traumatic resin canals co uld be seen emptying their contents into feeding and oviposition cavit ies dug by the adults, and into the larval galleries. This defense rea ction killed eggs and larvae. When the leader survived the attack, the cambium reverted to producing normal xylem tissue, leaving one or mor e rings of traumatic resin canals embedded in the xylem annual ring.