(1) Graphical representations, non-parametric tests, and correspondence analysis are used to describe spatial and temporal structure in a population of a winter rape pest (Psylliodes chrysocephala L.) on three scales: between-plants, within-plots, and betweenplots. (2) The between-plants variability was related to the egg-laying of females and to the attractiveness of plants for young larvae. A density-dependent regulation mechanism occurs at this scale, either by differential mortality, or by dispersal of larvae. (3) The within-plot structures were analysed in terms of static spatial structures, of spatial and temporal interactions. and of variation during the life history of the pest. (4) The between-plots variability is described, and a qualitative model of plot invasion explains the between-plots variation in infestation. (5) Data are discussed from the point of view of methodology and population biology.