An induced defense reaction in white spruce to attack by the white pine weevil, Pissodesstrobi

An induced defense reaction in the leaders of white spruce, Piceaglauca (Moench) Voss, occurs in response to attack by the white pine weevil, Pissodesstrobi Peck. The response was initiated shortly after feeding 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 developing xylem. In sectioned leaders, these traumatic resin canals could be seen emptying their contents into feeding and oviposition cavities dug by the adults, and into the larval galleries. This defense reaction killed eggs and larvae. When the leader survived the attack, the cambium reverted to producing normal xylem tissue, leaving one or more rings of traumatic resin canals embedded in the xylem annual ring.