The study of tri-trophic interactions is a vast field of basic ecological studies which are also of paramount importance for the development of environment-friendly methods of pest management. Within the Diptera, the Tephritidae family represents an interesting model for such studies because of the variable host-specificity of species in this group, and the important role that some natural enemies may play in the regulation of their populations. Furthermore, the great economic importance of many species in this family offers a large array of applications to research results. La Réunion, a French island situated in the south-west of the Indian Ocean, is a favourable area for studying such interactions, because of the number of tephritid species present in the island, and the great variability of its climatic conditions. On fruit crops, a complex of three polyphagous species of tephritids cause considerable damage: the Mediterranean fruit fly, Ceratitis capitata, the Natal fruit fly, Ceratitis rosa, and the Peach fruit fly, Bactrocera zonata. In addition, another complex of Dacini is harmful to cucurbit crops: the Melon fly, Bactrocera cucurbitae, the Ethiopian cucurbit fly, Dacus ciliatus, and the Indian Ocean cucurbit fly, Dacus demmerezi. Conversely, on Solanaceous crops such as tomato, the Tomato fruit fly Neoceratitis cyanescens, is the only species of economic importance. Over the last twenty years, many field studies allowed us to specify the host-range and relative importance of the different species on cultivated crops. Of particular interest are some host preferences observed in the field in some otherwise very polyphagous species, such as C. capitata. Detailed studies (lab, wind tunnel and field cages) were also devoted to the host location behaviour of stenophagous species, taking as a model the tomato fruit fly, N. cyanescens. Other behavioural studies also highlighted the preferences of the different species for particular host-plants during foraging or