Greenhouse Whitefly Fact Sheet No. 5.587 Insect Series|Home and Garden by W.S. Cranshaw* The greenhouse whitefly,Trialeurodes Quick Facts vaporariorum, can be a common insect pest in greenhouses and on house plants and • Greenhouse whitefly is a garden plants during the summer. This insect common pest of house plants has a host range of more than 250 ornamental and greenhouse plants. and vegetable plants including poinsettia, In summer, it can become begonia, nicotiana, aster, calendula, established in the garden, cucumber, lantana, tomato, grape, ageratum, affecting vegetables and and hibiscus. flowers. The greenhouse whitefly sucks sap from the plant, primarily from the phloem. Heavy • It does not survive outdoors infestations cause decline of plant vigor. Figure 1: Adult greenhouse whitefly. in areas of freezing winters, Stunting, yellowing of foliage and premature such as Colorado. Winter leaf drop are among the symptoms of injury. infestations come from adult females moving infestations may persist on Whiteflies excrete sticky honeydew during to new plants. When they find a suitable indoor plants. feeding. This detracts from plant appearance plant, they insert their mouthparts into the and allows gray sooty mold fungi to grow on phloem. They usually remain in place for • Horticultural oils and neem the foliage. several hours as they lay a series of eggs in a are two of the best controls In recent years, a second whitefly has semicircular pattern on the plant surface. The for the immature stages. become established in some Colorado creamy yellow eggs darken after 24 hours. Pyrethrins and related greenhouses: the silverleaf whitefly,Bemisia Most eggs are laid on the newest leaves. pyrethroid insecticides are argentifolii. This species is sometimes known Nymphs emerge within five to seven days. recommended for control of as the sweetpotato whitefly Strain B or the They move a short distance before flattening adults. “poinsettia whitefly.” It has become endemic themselves against the leaf to feed. All in the southwestern United States and in remaining immature stages of the greenhouse • Colored sticky traps and Florida. There it causes serious damage whitefly are immobile. certain biological controls can to crops and ornamental plants. It is far There are three nymphal stages that assist in whitefly control. less common on house plants than the feed on the plant, spaced at two- to four- greenhouse whitefly. day intervals. A nonfeeding pupal stage follows, lasting almost a week. All the immature stages are inconspicuous and easily Life History and Habits overlooked. They are usually pale, almost The greenhouse whitefly is a tropical/ translucent, and are superficially similar to subtropical species that cannot overwinter certain scale insects. Late-stage nymphs and outdoors in Colorado. Freezing temperatures pupae may also have thin, waxy threads that kill it and the lack of host plants prevents can resemble those produced by mealybugs. its survival except under highly protected Adult whiteflies emerge from a slit that conditions. Although whiteflies produce develops along the back of the pupal skin. several generations on a variety of garden Ratios of male to female whiteflies vary. More plants during the summer (notably tomato, females occur in late spring than in winter. pepper and cucumber), year-round Under favorable conditions, a generation of infestations are possible only indoors. the greenhouse whitefly takes three to four © Colorado State University The familiar form is the white, winged weeks to complete. Each female can lay 400 Extension. 3/03. Revised 6/13. adult. Because of the insect’s mobility, most eggs over a period of up to two months. www.ext.colostate.edu Usually they produce many fewer eggs. *Colorado State University Extension entomologist and professor, bioagricultural sciences and pest management. 6/2013 Control of Whiteflies whiteflies turn black and die in several Prevention is the best management. days. However, temperatures must average Infestations originate only from infested (day plus night) 72 degrees F. Many garden plant materials. Carefully check all new catalogs carry whitefly parasites. plants and quarantine them before moving More recently, another parasitic them into a room with susceptible plants. wasp has been marketed, Eretmocerous Once the insects are established in a californicus. It appears to have some greenhouse, a host-free period can starve advantages over Encarsia formosa. Adults them. This might mean removing for at of E. californicus kill many whiteflies in least two weeks any plants on which the the process of “blood feeding.” This occurs whitefly can survive. Pay careful attention when the whitefly nymphs are punctured Figure 2: Greenhouse whitefly, hatched eggs to weed control, because weeds may allow with the wasps’ ovipositors. Instead of and nymphs. whiteflies to survive even if suitable crops laying an egg, the adult feeds on blood from are not present. the wound. E. californicus is also much more effective against the silverleaf whitefly. Traps Insecticides Adult whiteflies are highly attracted to yellow and white. They often are found Insecticidal control can be difficult on lighter colored foliage. To capture the because the insect is resistant to most winged whiteflies, place appropriately insecticides. Furthermore, egg and the colored sticky traps just above susceptible nonfeeding pupal stages are generally plants or around edges of plantings. These not susceptible to insecticides that can traps usually are flat sheets or tape coated kill adults and nymphs. Thus repeated with a sticky material that can hold the applications are usually required. insects. Several commercial products The most effective insecticide for designed specifically for insect capture whiteflies is imidacloprid. This has systemic are available from garden catalogs and properties and is usually used as a soil greenhouse suppliers. Trade names include application, taken into the plant via the R R roots. It is not registered for most home Figure 3: Greenhouse whitefly nymphs. Black Tanglefoot , Stick-em Special and Tack- forms are parasitized. trapR. A heavy-weight oil or grease is an grown vegetables but can be used in flower acceptable alternative. Some manufacturers beds and houseplants. make yellow sticky cards or tapes. Horticultural oils (e.g., SunSpray) are Yellow sticky traps are used both to one of the most effective whitefly controls monitor whitefly populations and to help available for use on house plants. Applied suppress populations. Monitoring is the as dilute sprays (e.g., 2 percent), they most common use, to detect movement of smother the immature forms and eggs. whiteflies into a greenhouse or increases Other products effective against nymphs in populations. For whitefly control, place are neem-based insecticides and some many sticky tape or other traps around insecticidal soaps. Because of the potential the planting. for plant injury, test them first on a few plants or on a small area of a plant. Adult Biological Controls whiteflies are usually best controlled with pyrethrins or various pyrethroid The small parasitic wasp,Encarsia insecticides labeled for use on house formosa, has long been used as a biological plants (e.g., permethrin, tetramethrin, control for greenhouse whitefly. It develops bifenthrin, resmethrin). within the whitefly nymphs. Young

Colorado State University, U.S. Department of Agriculture and Colorado counties cooperating. CSU Extension programs are available to all without discrimination. No endorsement of products mentioned is intended nor is criticism implied of products not mentioned.