Bruchid pests are of considerable economic importance, infesting legume seeds and pods in fields and stores, predominately in the semi-arid tropics. One of the foremost bruchid pests"Callosobruchus maculatus is a niche generalist in that it can infest seeds whilst within pods or when loose. It exhibits a much greater degree of polyphagy than its wild relatives, perhaps partly due to behavioural plasticity. As their larvae are restricted to a single seed, resources available for growth are directly related to egg distribution by the ovipositing female. Host selection is a complex process and involves host finding, recognition (which may occur before or after contact with the plant), and host acceptance which is manifested as contact inspection behaviour and culminates in oviposition. Numerous factors influence these processes including the nature of host chemistry and the presence of conspecific epideictic pheromones. The purpose of this study was to investigate the factors which modulate the tendency to oviposit and oviposition behaviour itself. 2 The oviposition behaviour of newly emerged beetles was recorded on several seeds that vary in their attractiveness as hosts. The behavioural repertoire and the stereotypical sequences that characterise the acceptance or rejection of a host were recorded on pristine and egg laden seeds. These sequences were used to construct flow charts of transitions between the most common behaviours. Several indicators of a host's acceptahility were identified and quantified, including the duration of selected key behaviours. The combination of behaviours exhibited, their position in the transitional matrix and their respective durations, indicated the relative acceptability of the host seeds studied, and provided information on how the different sense organs have complementary roles in the process of host acceptance. This demonstrated that the perception of primary host and conspecific stimuli which influence host acceptance is undertaken by the palps and., to a lesser extent, by the antennae. The study of oviposition behaviour in conjunction with studies on the course of oviposition over extended periods on real and artificial hosts provided the tools by which the chemical bases of host acceptance could be investigated. Host seed extracts were screened for their ability to influence behaviour, and some of the active components were identified as a number of commonly occurring fatty acids. These same fatty acids have been shown to stimulate egg laying, and in different proportions and concentrations, to deter oviposition both as components of a conspecific oviposition deterrent pheromone, and as components of vegetable oils added to stored seeds as a protectant