1. Parasitoids are common natural enemies of planthoppers and leafhoppers and often contribute substantial mortality to host populations. High mortality in itself does not, however, provide evidence for population regulation or control.
2. We review the interactions between the Auchenorrhyncha and their parasitoids in terms of their effect on stability or population persistence. Our review concentrates on parasitoid searching behavior and the spatial and temporal patterns of parasitism with respect to host density.
3. Direct studies of parasitoid functional response and interference are few and provide equivocal evidence for the regulatory power of parasitoids. On the other hand, spatial and temporal relationships between host density and parasitism are predominantly density independent (> 70% of the studies reviewed), indicating no or weak regulation by parasitoids.
4. Other potentially stabilizing factors, such as heterogeneous parasitism rates, the presence of refugia for hosts, host switching by parasitoids, and less traditional nonequilibrial strategies by parasitoids, have received very little consideration.
5. The critical data needed to assess the regulatory power of planthopper and leafhopper parasitoids are largely unavailable. It is imperative that long-term manipulative field experiments over many generations and spatial scales, coupled with detailed examination of parasitoid searching behavior, be performed if we hope to resolve this issue.