RESPONSES OF ABIES GRANDIS TO ATTACK BY SCOLYTUS VENTRALIS (COLEOPTERA: SCOLYTIDAE)

Abstract

The reactions of resistant and susceptible Abies grandisto attacks by Scolytus ventralisare described. Resistant reactions were characterized by the production of secondary resin in the cells of the phloem parenchyma and the formation of callus tissue and traumatic resin cavities at the cambium–sapwood interface. S. ventralisexhibited varying degrees of gallery establishment on resistant hosts. Some individuals were repelled by phloem resinosis before reaching the vascular cambium while others were able to construct galleries of varying length before they were repelled by resin flow from the phloem and traumatic cavities. The degree of gallery establishment appeared to be inversely associated with the rapidity of the host’s response. Necrotic resinous lesions developed around the attack and extended vertically to various distances from the attack. Callus tissue, produced at the margins of this lesion, eventually grew over and healed the wound. Vulnerable grand firs were characterized by the lack of resinosis in the phloem parenchyma, and the absence of extensive callus production and traumatic cavity formation.