An investigation of Epiphyas postvittana (Walker), the light-brown apple moth, was begun in 1961 to test the relevance of Nicholson's (1954) concepts of population dynamics, while gaining information on the distribution, abundance, and injuriousness of the species. This objective was redefined in the mid-60s to comprise an empirical evaluation of the concept of life system (Clark et al. 1967) as a frame of reference wherein to describe the numerical determination of species populations.

It is concluded that: (1) in their elaboration as the life system concept, Nicholson's postulates provide an efficient schema for the study and explanation of numerical determination; (2) there are no limits to the possible extension and refinement of life system modelling as a means of explaining population events, although relatively crude, yet comprehensive, descriptions of functional processes would usually suffice for practical purposes; (3) information produced by life system studies is essential to the understanding and efficient management of pest situations; (4) because of the difficulty and cost of life system studies, ecologists should assemble increasingly refined and continuously up-dated sets of reference models, or type cases, for use by entomologists to identify pest situations and prescribe curative action. Procedural implications are considered.