Informantion About Greenhouse Whiteflies

The greenhouse whitefly, Trialeurodes vaporariorum, is a common insect pest that attacks plants in greenhouses and indoor environments during the summer months. It feeds on approximately 250 different species of plants, including grape, hibiscus, poinsettia and aster, among many others. Greenhouse growers and homeowners control infestations with a combination of chemical and mechanical methods.

Identification and Life Cycle

Greenhouse whiteflies are approximately 0.06 inches long, with light-colored bodies and four waxy white wings. Adult female whiteflies lay between 200 and 400 eggs at a time. The eggs hatch approximately a week later. The young whiteflies, called crawlers, have flattened, rounded bodies and vary in color from clear to black. The nymphs lose their legs after molting and spend several weeks attached to the undersides of leaves in a pupa stage. Adult whiteflies live for about a month after emerging.

Effects

Adult and immature greenhouse whiteflies congregate on the undersides of foliage and drain sap from plant tissues. Severe infestations stunt plant growth, and damaged leaves may turn yellow and fall to the ground. Whiteflies excrete large amounts of a sticky-sweet, watery material called honeydew that drips on the surrounding foliage. An unsightly grayish-black fungus called sooty mold forms on the honeydew deposits, interfering with photosynthesis. Greenhouse whiteflies also transmit viruses from one plant to another.

Prevention and Mechanical Controls

Carefully inspect the upper and lower surfaces of leaves before bringing a plant home from the nursery. Quarantine new plants for several days before placing them near existing household or greenhouse plants. Lance Greer from the National Sustainable Agriculture Information Service recommends trapping whiteflies in greenhouses using between one and four yellow sticky cards for every 1,000 square feet of space. Place the traps near openings such as doors at approximately the same height as vulnerable plants.

Biological and Chemical Controls

Greenhouse growers can purchase small parasitic wasps called Encarsia formosa from commercial suppliers. These insects prey on whiteflies. Discontinue the use of sticky traps when incorporating Encarsia wasps, however, since they are also attracted to the traps. Insects such as the lady beetle, Delphastus pusillus, feed on both adult whiteflies and crawlers. A commercially available fungus called Beauvaria bassiana infects and kills whiteflies. Many greenhouse whiteflies are resistant to traditional chemical insecticides, but insecticidal soaps, neem oil and horticultural oil help control the pests.

References

• Colorado State University Extension: Greenhouse Whitefly; W.S. Cranshaw; January 2007
• University of California Statewide Integrated Pest Management Program: Caneberry -- Greenhouse Whiteflies
• University of Florida Entomology & Nematology Department: Greenhouse Whitefly
• University of Missouri Extension: Managing Whiteflies on Indoor and Outdoor Plants; Bruce A. Barrett; June 2010
• University of Connecticut Integrated Pest Management: Whiteflies in the Greenhouse; Leanne Pundt
• National Sustainable Agriculture Information Service: Sustainable Whitefly Control; Lance Greer; 2000