Whitefly Killer is supplied as a number of cards with tiny parasitized whitefly pupae attached to them. These contain the tiny parasitic wasp of whitefly; Encarsia formosa. These minute wasps emerge from the pupae on the cards to search for whitefly pupae to parasitize. Once they have located them, they lay an egg inside the whitefly pupae, which turns it black in colour and kills the whitefly. The parasitized whitefly pupae then go on to produce a new Encarsia formosa wasp. This process is one of the oldest forms of biological control and has been used for many years, especially by tomato growers. It has a huge advantage over traditional chemical pesticide control in that the whitefly are not able to become resistant to attack by these tiny parasites.
Encarsia formosa are only active at temperatures of 17.c plus. Do not expect much activity from the parasites at temperatures below this. Temperatures above this will increase their activity and effectiveness. Even at higher temperatures their life cycle is still quite long, so it may take time before you see black scale on the underside of leaves [parasitized whitefly scale], so some patience is required.
Introduce Whitefly Killer before whitefly are in high numbers. A programme of introductions is the most effective way of getting good results from Whitefly Killer. If temperatures are low but whitefly are still present, use yellow sticky traps and SB Plant invigorator sprays on a regular basis until it is warm enough to introduce Whitefly Killer. Once you start cease sprays and take down sticky traps.