Tree Physiology and Forest Pests

Abstract

Abstract Some aspects of host biology which influence host-pest relations are discussed. Insects and diseases affect tree growth in a complex manner by interfering with rates and balances of physiological processes. A sequential and very complicated series of metabolic disturbances of trees follows attacks by insects or fungi. Inhibition of cambial growth by defoliation does not appear to be due primarily to lack of food, but rather to a lack of regulatory compounds which influence utilization of food. Effects of insect attack or fungus disease on tree growth may or may not be drastic, depending on which physiological processes are checked and on the physiological condition of the host at the time of attack. The time of year when forest pests attack trees, together with inherent growth characteristics of trees, also influence the nature and extent of injury. The importance of water economy of trees in relation to attacks by insects and fungus pathogens is discussed. Incidence of insect attack and disease is correlated with physiological aging of trees. The specific nature of predisposition to invasion by fungi and insects varies with host species and often is related to physiological changes in the host.