The most cost effective biological control for the greenhouse whitefly (Trialeurodes vaporarium) is the whitefly parasite (Encarsia formosa), a tiny parasitic wasp similar to the trichogramma. This aggressive beneficial insect is attracted to its host by the smell of honeydew produced by the pest, and is capable of detecting this from several feet away. Adult parasites not only feed on this honeydew, but also on whitefly body fluids through a hole made in the pest larvae. Egg laying of E. formosa can take place in all four whitefly larval instars and the pupae of the pest. The female whitefly parasite lays an average of 50 – 100 eggs. Most parasitization will occur at humidities of 50% – 80% and a high light intensity. A major factor affecting whitefly control with E. formosa is temperature. At temperatures below 62°F, the parasites will not fly and consequently will not seek out new hosts. When half of the development of the whitefly parasite is completed, the host turns black and the parasite finally emerges through a hole in the back of the “black scale.”
Having trouble with greenhouse whiteflies? Give whitefly parasites a try! These non-stinging parasitic wasps have been used by pest control professionals for years and are the #1 biological control for the job.
Depending on pest levels, the following release rates have been established:
2-4 per square foot of infested area
1-2 per plant when pests are first noticed
Whitefly parasites are shipped as mature pupae in host eggs, glued to a paper card and almost ready to hatch as adult parasitic wasps. If pest levels are high, use a least-toxic, short-lived natural pesticide (insecticidal soap, botanical insecticide) to establish control, then release beneficials 2-3 weeks later to maintain control. Learn about Greenhouse IPM here.
A Word About the Target Pest:
The greenhouse whitefly is a major pest problem in commercial greenhouses, attacking cucumber, paprika, tomato and many ornamentals. The female lays her eggs on the undersides of young apical leaves, often in circles on hairless hosts. The eggs hatch after about 8 days while further development consists of 1st, 2nd, 3rd, and 4th instars and pupae whose development occupies an average of 20 days. The newly hatched larvae are initially mobile. They move for a few hours only and then settle down. After inserting their mouthparts into the leaf tissue, they lose their functional legs and remain static throughout the remainder of their development.
Once the whitefly emerges, it will start laying eggs within 1 to 2 days, thus repeating the cycle. Egg production increases with increasing density of whiteflies per leaf; it is also greater at higher temperatures. A temperature of 70° Fahrenheit and humidity of 75% – 80% are considered optimal conditions for the pest.
• Managing Whiteflies on Indoor and Outdoor Plants – University of Missouri
• Midwest Biological Control News – University of Wisconsin, Madison
• Encarsia formosa – Cornell University
• Natural Enemies Gallery – University of California Statewide IPM Program