The whiteflies, comprising only the family Aleyrodidae, are small hemipterans (true bugs). More than 1550 species have been described. Whiteflies typically feed on the underside of plant leaves.
The ability of the whitefly to carry and spread disease is the widest impact they have had on global food production. In the tropics and subtropics, whiteflies (Hemiptera: Aleyrodidae) have become one of the most serious crop protection problems. Economic losses are estimated in the hundreds of millions of dollars. While several species of whitefly cause crop losses through direct feeding, a species complex, or group of whiteflies in the genus Bemisia are important in the transmission of plant diseases. Bemisia tabaci and B. argentifolii, transmit African cassava mosaic, bean golden mosaic, bean dwarf mosaic, bean calico mosaic, tomato yellow leaf-curl, tomato mottle, and other Begomoviruses, in the Family: Geminiviridae. The worldwide spread of emerging biotypes, such as B. tabaci biotype B, also known as, 'B. argentifolii', and a new biotype Q, continue to cause severe crop losses which will likely continue to increase, resulting in higher pesticide use on many crops (tomatoes, beans, cassava, cotton, cucurbits, potatoes, sweet potatoes). Efforts to develop integrated pest management, IPM, systems aimed at environmentally friendly strategies to also reduce insecticide use will help re-establish the ecological equilibrium of predators, parasitoids, and microbial controls that were once in place. New crop varieties are also being developed with increased tolerance to the whiteflies, and to the whitefly-transmitted plant diseases. A major problem is the fact that the whiteflies and the viruses they carry can infect many different host plants, including agricultural crops and weeds. This is complicated by the difficulty in classifying and detecting new whitefly biotypes and Begomoviruses. Proper diagnosis of plant diseases depends on using sophisticated molecular techniques to detect and characterize the viruses and whiteflies which are present in a crop. A team of researchers, extension agents and growers working together are needed to follow disease development, using dynamic modeling, to understand the incidence of disease spread.
Whitefly control is difficult and complex as whiteflies rapidly gain resistance to chemical pesticides. The USDA recommends "an integrated program that focuses on prevention and relies on cultural and biological control methods when possible." While an initial pesticide application may be necessary to control heavy infestations, repeated applications may lead to strains of whiteflies that are resistant to pesticides, so only use of selective insecticides is advised. Specific insecticide information and guidance for the fig whitefly is available from the University of Florida, Davie. Care should be taken to ensure that the insecticide used will not kill the whiteflies' natural predators. For effective use of biological method after application of pesticide, plant washing is advised prior to release of predators or parasitoids.
Pesticides used for whiteflies control are neonicotinoids. Products containing neonicotinoid compounds have one of these four active ingredients: clothianidin (commercial), dinotefuran (over the counter and commercial), imidacloprid (over the counter and commercial) and thiamethoxam (commercial). Neocotinoids can be harmful if ingested. Neocotinoids are also extremely toxic to bees which are essential to the pollination of flowering plants, and are seen as probably one of the causes behind the dramatic decrease in their numbers. Rotation of insecticides from different families may be effective at preventing the building of tolerance to the product. Clothianidin and Dinotefuran are of the same family.
Biological methods have also been proposed to control whitefly infestation, and may be paired with chemical methods as well. Washing the plant, especially the underneath of leaves may help reduce the number of the pests on the plants and make their management by other methods more effective. Spraying the leaves using Safer-Soap following manufacturer instructions is one option. Whiteflies are also attracted by the color yellow so yellow sticky paper can serve as traps to monitor infestations. Dead leaves or leaves that have been mostly eaten by whiteflies can be removed and burned or carefully placed in closed bins to avoid reinfestation and spreading of the disease.
Various companion plants are reputed to repel or trap white flies. Calendula like pot marigolds do so for documented reason, producing chemicals that repel them. Nasturtiums are thought to have a similar effect, while mint may serve either as a repellant or trap crop.
For more information: http://en.wikipedia.org/wiki/Whitefly
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