Encarsia, Welcome to the Dark Side
Encarsia formosa is a whitefly predator and parasitoid. The advantages of using Encarsia as a biocontrol agent were recognized over one hundred years ago when an English tomato grower observed whitefly pupae that turned from white to black, and Encarsia emerging from the darkened pupae. This tiny parasitoid not only eats its prey from the outside, but also lays an egg inside of the immature whitefly, eating them from the inside as it develops. Between host feeding and parasitism, Encarsia is a double threat. With this combined mode of predation, Encarsia can kill almost 100 whitefly during their lifetime, which varies between 10-30 days depending on temperature. As with their prey, Encarsia are most effective in temperatures over 68°F, with high light and humidity levels. Encarsia are extremely sensitive to insecticide residues that may persist on plants as well as greenhouse surfaces, so always keep this in mind when using this biocontrol agent.
Encarsia formosa is a thelytokous species, producing all females. They are infected by the bacteria Wolbachia which regulates this parthenogenesis. Once in a while a male slips into the picture, but this is rare. Having all females makes Encarsia an extremely effective parasitoid. All of them will lay eggs, not just half of the population. This tiny parasitoid is just over 1/2 mm long with a black head and thorax and a yellow abdomen. Parasitized greenhouse whitefly pupae turn black and parasitized silver leaf whitefly will darken only slightly. Being so tiny they are difficult to see, always in motion is the future.
Encarsia is a prime biocontrol agent to use preventatively. If there is a history of whitefly with certain crops or seasons, releasing at a low rate can prevent an infestation. Encarsia are excellent searchers and will locate their prey in a greenhouse, flying well over 150 ft as they search. If they are cold stored, this searching capability declines, as well as fecundity and hardiness. Fresh is best! On plants that are not pruned, they can build up a good population, but on plants that are heavily pruned or cycle quickly through the greenhouse, Encarsia should be applied on a consistent basis. This is the way.
Encarsia is shipped in its larval state, in a parasitized whitefly scale. These are attached to little cards that can be distributed throughout the greenhouse. The pupae on the cards are extremely delicate, try to avoid touching them. The cards are best placed on the lower leaves in the shade, as Encarsia have a tendency to fly upward. The cards often have a date which reminds growers to remove them after a few weeks. Adults will emerge from the pupae over 1-2 weeks at 68°-77°F. Never place Encarsia near yellow sticky cards as they will get trapped. Remove yellow sticky cards or place them under benches before releasing Encarsia.
It's always best to identify the pest species before releasing biocontrols. Many beneficial insects have a very specific prey and may need higher rates otherwise. Eliminate whitefly from alternate sources such as weeds or previous crops before releasing. High whitefly populations and the presence of honeydew can slow the movement of Encarsia. Spraying with water or insecticidal soap before releasing can reduce these problems. Encarsia tend to remain in regions where the whitefly is concentrated, so distribute them well throughout the greenhouse.
Rates for Encarsia will vary depending on the severity of the whitefly. Talk with a technical specialist at Sound Horticulture for more help. Suggested release rates are:
1-10 Encarsia/10ft2. Or 1-5 Encarsia /infested plant, every 1-2 weeks for at least 5 introductions, or until 80% of whitefly scales are parasitized.
Above rates for Encarsia must be at least doubled for control of silverleaf and/or sweet potato whitefly or if temperatures are less than 64°
May the Encarsia force be with you.
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