The Dynamics of the Viburnum Whitefly (Aleurotrachelus jelinekii): A Case Study of Population Regulation

Abstract

(1) The study of Southwood and Reader (1976) on the population dynamics of the viburnum whitefly (Aleurotrachelus jelinekii (Frauenf.)) on three viburnum bushes (A, B and C) is extended for the population on a single bush (B). (2) Key factor analysis on the sixteen generations of data now available confirms Southwood and Reader''s earlier conclusion that this method fails to detect any significant density-dependent processes that might be regulating the population. This does not preclude, however, the possibility that such processes are operating but are not detected by the key factor analysis. (3) In nine of the sixteen generations (1968-69 to 1976-77), a more detailed analysis was done of numbers from egg stage to adult on thirty labelled leaves. Density dependence is now identifiable on a leaf-to-leaf basis in eight of the nine generations. (4) A model is developed of the whitefly population per bush in which the total eggs are distributed from leaf to leaf according to a negative binomial distribution and survivorship per leaf is density-dependent. The model predicts well the observed pattern of population increase on bush B, with the exception of the abrupt decrease in the observed egg population in 1974-75 and in the following 2 years while the population increased once more towards the predicted pattern of growth. (5) The model is sensitive to the values of several of its parameters; for example, the degree of spatial aggregation of immature whiteflies, the net reproductive rate of the adults and the assumed pattern of bush growth measured by the total number of leaves each year.(6) The failure to detect the important density dependence acting upon this population using key factor analysis is discussed. It arises primarily because of the spatial scale upon which the density dependence operates, in conjunction with the inevitable stochastic elements that are present.