Population dynamics of codling moth, cydia pomonella (L) (Tortricidae), in the Australian Capital Territory.

Abstract

Under natural conditions in the Australian Capital Territory, the codling moth can multiply each year virtually to the limit of its supply of larval food, i.e. fruits. The circumstances which permit this are analysed and discussed. It was found that codling moth and its environment are best considered together as a life-system which tends to ensure a constant utilization of resources by minimizing changes in the numbers of the moth following variations in the availability of critical requisites. In the A.C.T., where climate and weather conditions approach the optimum for codling moth and the influence of natural enemies is negligible, the requisites which limit the abundance of the species are larval food and cocoon shelter. Intraspecific competition for those requisites is the mechanism which adjusts the number of codling moth to the supply of those requisites. Competition for cocoon shelter minimizes the effects of differences in crop size on codling moth abundance. Competition for fruit space minimizes the effects of differences between initial infestation levels in crops. Competition for the two requisites maintains the insect at the highest level of density which the intrinsic favourableness of the environment and the behavioural characteristics of the species will permit. The present findings are used to evaluate the conceptual models of population dynamics proposed by Nicholson and by Andrewartha and Birch.