Whitefly should be very easy to control so ling as they are not the species that transmit plant viruses. In the UK, the Glasshouse Whitefly (Trialeurodes vaporariorum) is the main pest and does not have any damaging viruses associated with it. Across the channel in southern Europe though, the Tobacco whitefly (Bemisia tabaci) is causing horrendous problems within many of the crops that produce fruit and veg for our supermarkets because they are transmitting damaging viruses (particularly in tomato and cucumber). Inevitably growers are using all sorts of chemicals to try and control them!!! Parasitic wasps, such as encarsia formosa can indeed help by reducing the larval levels, but they are no where near as effective as a keen eyed gardener who removes the lower infested leaves and destroys (burns) them. Why spend money and time releasing little wasps, when less time can be involved in de-leafing the older leaves (where the larvae are found). Whitefly larvae cannot move from where they are developing once they have passed the first instar stage, then spend up to a month stuck on the leaf as the plant grows. New whitefly emerge from these larvae, fly to the new growth on the plant, lay eggs, then the cycle continues.