ABSTRACT
Predators and parasites control pests in distinctly different ways. The following biological control agents include both types, but should be considered with reference to their practical use in horticulture. For example, the use of the parasitic wasp Encarsia formosa is only effective if introduced early at a density of one wasp scale per plant, when the whitefly pest problem is no greater than one whitefly per twenty plants. They also require a minimum temperature of 20°C, otherwise they do not fly around from plant to plant, and walking gives less effective control.
