Interactions of Root Disease and Bark Beetles

Associations between root diseases and bark beetles (Scolytidae) constitute some of the most serious pest complexes affecting forests in North America and elsewhere. The interactive functioning of these pests derives from the following relationships: 1) root diseases predispose trees to bark beetle infestation by lowering resistance, and perhaps increasing attractiveness, of trees to the attacking beetles; 2) bark beetles may be vectors of root disease fungi or may create infection courts for them. Symbioses between bark beetles and fungi are common in nature, and previous reviewers (e.g., Graham 1967) have identified several types of these symbiotic relationships, some of which appear to be beneficial to both (mutualism), and others which apparently benefit only one (competition, predation, parasitism). These relationships will be discussed in relation to interactions between root diseases and bark beetles. Others, which benefit neither (i.e., commensalism or cohabitation), are not considered to be true interactions as defined here, and will not be further mentioned.