Methods for Releasing Encarsia formosa to Control Greenhouse Whitefly

This article by Cathy Thomas, Integrated Pest Management Program, Pennsylvania Department of Agriculture, appeared in the "Vegetable and Small Fruit Gazette," September 2000, Vol. 4, No. 9.

Four methods of releasing Encarsia formosa to control Greenhouse whitefly listed below have been developed in Europe, and are used by commercial vegetable producers. The effectiveness and success of these programs are based on the level of honeydew- and sooty-mold development on foliage and fruit. If sooty-mold levels are acceptable for a marketable product, control of greenhouse whitefly has been achieved.

1. Pest in First.
With this method, adult whiteflies are introduced into the crop at a fixed rate when transplants are installed in production houses. Encarsia formosa is then introduced at regular intervals when whitefly nymphs develop. This method has not been widely adopted because of the concern of releasing pests into the crop.

2. Banker Plants.
The bank plant system uses established colonies of parasitoids, reared on whitefly-infested plants, that are introduced into the crop. Mesh screens can be used to cage banker plants to contain whiteflies, and allow only the tiny parasitoids to disperse into the production area. Using this method may require other facilities (greenhouses or growth chambers) to establish the pest and biocontrol on the banker plant; however, there would be the advantage of having a sustainable, on-site supply of parasitoids.

3. Inundative.
With inundative introductions, high numbers of E. formosa are introduced on a regular basis. This method might be used when establishment and reproduction of the biocontrols are not expected. Inundative releases are used in ornamental crops or short-term crops. Inundative introduction of biocontrols may not be cost effective.

4. Dribble method.
With the dribble method, weekly parasitoid introductions begin at planting, in anticipation of naturally-developing whitefly populations, or introduction of E. formosa can be made when whiteflies are first observed. Parasitoids are introduced every two weeks until there is a high level of parasitized whitefly pupae in the crop. This is usually more cost effective than introducing E. formosa every week of the crop cycle. The dribble method is the most common introduction method used in Pennsylvania greenhouses.

These introduction methods should be discussed with your supplier, who can also advise you on the number of E. formosa needed for your crop. These numbers will be based on whitefly populations; hence, the need for careful crop observation and scouting. These introduction methods can also be used for other parasitoids and predators.