Conservation biological control provides pollen, nectar, shelter and/or alternative prey/hosts for natural enemies of insect pests. This can improve their fitness and enhance their efficacy as biological control agents. For parasitoids, recent results show that when flowers are added to an agro-ecosystem, parasitism rate of cereal aphids can reach 35%. In their absence, this rate declines to zero. A key question concerns the dispersal behaviour of the natural enemies after they have used resource subsidies. Recent publications have reviewed the methods available for marking and tracking beneficial arthropods. One very useful approach is the use of rubidium chloride (RbCl) as an internal marker. Atomic absorption spectroscopy can analyse rubidium in an insect which has fed on the nectar of treated plants and compare these with background concentrations in soil and plants. Recent New Zealand work has used rubidium to mark parasitoids in vines and brassicas. Clear dispersal patterns have been revealed and these raise a series of questions concerning the ways in which this marking technique can show differences between male, female, gravid and non-gravid parasitoids. Also, the methods used to trap parasitoids at distances from the flowers can also affect the results and their interpretation. These aspects are discussed in this talk, using field data from the 2003/2004 New Zealand field season.