A Comprehensive Guide to
Safe Biological Pest Control
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EFFECTIVE CONTROL OF WHITEFLY
Encarsia was one of the first biological control agents developed. This minute (< 1mm, 1/25 inch long) parasitic wasp is probably tropical in origin. It does not sting humans.
With the exception of the adult, all stages of Encarsia occur within the whitefly host. Adults are tiny wasps that lay eggs inside 2 week old whitfly scales (second and third whitfly larval stages). Each egg will kill one whitefly scale. Adults lay up to 200 eggs. The parasite then develops inside the whietfly scale, and midway through the development of Encarsia within the whitefly, the scale turns dark. It becomes black for greenhouse whitefly, and transparent brown for sweet potato whitefly.
This occurs after 10 days at normal greenhouse temperatures. Another 10 days is required before adults emerge. Adult Encarsia emerge from the parasitized scale by chewing a hole in the top of the scale.Adults also kill whitefly scales by direct feeding. Otherwise, they feed on honeydew secreted by the whiteflies. Adults can live for 30 days but normally are active for about 10 days. The complete life cycle requires nearly 28 days in commercial greenhouses.
METHOD OF APPLICATION
Encarsia are sold as black parasitized scales that have been fixed onto cards. Each card contains 150 developeing parasites. A strip of 10 cards contains 1,500 Encarsia whitefly parasites. It is important to hang the cards from lower leaves in the shade, and avoid wetting them while watering. Apply 1-5 Encarsia per 10 square feet or 1-5 per infested plant BI weekly or until control is achived. Double rates are necessary for the sweet potato whitefly. For greenhouse tomatoes or sweet peppers, 1 Encarsia per 4 plants BI weekly. For greenhouse cucumbers use 1 Encarsia per 2 plants BI weekly. Once the percentage of dark-color, parasitized whitefly scales on leaves exceeds 80%, the numbers of Encarsia in the greenhouse should limit further spread of greenhouse whitefly.