Parasitic wasps usually are more effective at low pest population densities, whereas predators are more effective at high population densities. However, parasitism is often more responsive to changes in host populations and therefore more able to regulate these populations at some equilibrium level. Parasitism can be quantified by counting the number of empty whitefly pupal cases with a circular exit hole (created by the emerging adult wasp) rather than a "T" shaped split (created by the normal adult whitefly emergence).
The ability of naturally occurring parasites and predators to reduce whitefly populations to low levels in unsprayed weeds and crops has been demonstrated in Florida and Texas. Such is not yet the case in the desert regions of California and Arizona where the parasites and their refuge areas are less abundant. Numbers and activity of whitefly parasites and predators can be encouraged by avoiding broad-spectrum insecticides, planting of refuge crops, and augmentative releases.
Whitefly mortality from pathogenic fungi often reach high levels in greenhouses where relative humidity is constantly high and spores naturally accumulate. Pathogenic fungi can be applied as a spray treatment and are effective at any population density. Insect pathogens used for sweetpotato whitefly control must be applied with good coverage and under proper environmental conditions (high relative humidity) to be effective. These products are being tested in commercial production fields and commercial greenhouses, but the economic feasibility of their use has yet to be determined.