Encarsia formosa is considered to be one of the most promising biological control agents for whitefly. This small, parasitic wasp is able to parasitise and feed on a number of different larval instars of whitefly making it a highly effective parasitoid.
Appearance and Biology
The adult female is a small (0.6mm) wasp with a black head and thorax and a yellow abdomen (figure 1). Wings are transparent. Males are completely black and very rarely seen.
Female Encarsia deposit a single egg into the whitefly larvae. Although instar 2-4 can be parasitised the female will preferably pick the 3rd and 4th instar. The Encarsia larva develops through 3 stages within whitefly larva. Between 13-15 days after the egg within the whitefly larva has hatched, the 3rd instar will pupate. As a result of this pupation, the parasitised whitefly larva turns black in colour (Figure 2). Between 13-15 days after pupation an adult Encarsia emerges. The majority of the Encarsia population are female with only 1-2% being male. Females feed on as well as parasitise, whitefly larvae. Females lay about 5 eggs per day for about 10 days after which they die out.
How to make use of Encarsia formosa as a control agent of whitefly
Encarsia very rarely fly at night so early morning releases are recommended. Ensure that no chemicals with long residues periods have been spayed.
Ensure the correct life stage of whitefly is available for Encarsia to parasitise. 30 000 Encarsia per ha per week should be released until 80% parasitism is seen. Once 80% parasitism is observed releases can be decreased to 30 000 every 2 weeks.
Releasing Encarsia formosa
Encarsia are sold on individual cards containing 60 pupae per card. Tear the cards along the perforation to separate them. Inspect 5 plants to assess where the highest whitefly infestation is on the plants (bottom, middle or top leaves). Place the card near the stem of the plant close to the area of highest infestation. Ensure that cards are spread as evenly as possible throughout the Greenhouse or land. After 2-3 weeks check plants for parasitised larvae (black in colour).
Encarsia can be stored at 15 °C for 1-2 days before releases. However, for optimum results releases should take place as soon as the insects are received. For most effective results use Encarsia in conjunction with other means of biological control such as applications of Beauveria bassiana (beneficial fungal agent).