Encarsia formosa has been used since the 1920s throughout the world in commercial vegetable greenhouses. It can successfully control whiteflies on vegetable crops, including cucumber and tomatoes, and several ornamental crops, such as poinsettia. There are also many other promising natural enemies that can be used alone or in conjunction with Encarsia wasps. The best time to introduce Encarsia is when the whitefly population is low. Wasp efficiency is seriously impaired when whitefly nymphs are too numerous (5-10/cm2). The wasps spend more time cleaning the excessive honeydew from themselves than searching for and parasitizing whiteflies.
This wasp does best at between 61 and 83F. A daytime air temperature around 75F is the optimum for greenhouse whitefly control. Encarsia is not very efficient under cool, cloudy conditions. Higher release rates, or auxiliary natural enemies, may be required to maintain control under these conditions. Yellow sticky traps can also be used along with Encarsia to reduce whitefly populations. The whiteflies are strongly attracted to the yellow sticky traps, while the parasites are not, as long as sufficient whitefly nymphs are present.
Encarsia wasps are shipped in the pupal stage, on leaves or glued to small cards that can be hung directly on the plants. Release rates vary considerably depending on the whitefly density, the crop, and the time of year. Most suppliers provide detailed instructions for the release and use of Encarsia and can make recommendations about the number of wasps to release based on specific situations. In general, for very low initial infestations (less than 1 whitefly per 50 to 100 plants) rates of 1-5 parasite/ft2) are recommended for each release. Release rates are better established for vegetable crops than for ornamentals.
Susan Mahr, Universityof Wisconsin - Madison
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