The parasitic wasp Encarsia formosa is used in many countries to control an important glasshouse pest, Trialeurodes vaporariorum. Increasing energy costs initiated research about breeding tomato varieties that can be grown at lower glasshouse temperatures than usual. Encarsia formosa is, however, not sufficiently efficient in controlling whitefly at these low temperatures. The great success of this biocontrol method forces us to search for a solution either by selecting cold-resistant E. formosa strains, or by screening of other parasites and predators. In this paper the current situation with regard to control of whitefly is evaluated, the knowledge about factors influencing the relationship between host and parasite is reviewed, data about other parasites and predators are given, and evaluation procedures of natural enemies are discussed.