Whitefly

The whiteflies, comprising only the family Aleyrodidae, are small homopterans. More than 1550 species have been described. Whiteflies typically feed on the underside of plant leaves. While feeding damage can cause economic losses, it is the ability of whiteflies to transmit or spread viruses that has had the widest impact 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 world-wide 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.

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In 1997 Tomato yellow leaf-curl begomovirus, TYLCV was discovered in the USA, in Florida. This plant disease is the worst viral disease of tomato. The disease is transmitted by the whitefly, Bemisia argentifolii. The whitefly is also been shown to transmit almost all of the 60 known whitefly transmitted plant viral diseases.

Whitefly damage by feeding: Whiteflies feed by tapping into the phloem of plants, exposing plants to the whiteflies' toxic saliva and decreasing the plant's overall turgor pressure. The damage is quickly elevated as whiteflies congregate in large numbers, quickly overwhelming susceptible plants. Damage is further exacerbated as whitesflies, like aphids, excrete honeydew as a waste product, which promotes mold growth and may seriously impede the ability of farms to process cotton harvests.

Whiteflies share modified form of hemimetabolous metamorphosis, in that the immature stages begin life as mobile individuals, but soon attach to a host plant. The stage before the adult is called a pupa, though it shares little in common with the pupal stage of holometabolous insects.

Whitefly control is difficult and complex, as they 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." [1] Use of yellow sticky traps to monitor infestations and only selective use of insecticides is advised.

See also

greenfly, aphid, leafhopper, thrips

References

• Hunter, WB, Hiebert, E, Webb, SE, Tsai, JH, & JE. Polston. 1998. Location of geminiviruses in the whitefly Bemisia tabaci (Homoptera: Aleyrodidae). Plant Disease, Vol. 82: 1147-1151.

• Hunter, WB, Hiebert, E, Webb, SE, & JE. Polston. 1996. Precibarial and cibarial chemosensilla in the whitefly, Bemisia tabaci (Gennadius)(Homoptera: Aleyrodidae). International Journal of Insect Morphology & Embryology. Vol. 25: 295-304. Pergamon Press, Elsevier Science Ltd., Great Britain.

• Sinisterra, XH., McKenzie, CL, Hunter, WB, Shatters, RG, Jr. 2005. Transcript expression of Begomovirus in the Whitefly Vector (Bemisia tabaci, Gennadius: Hemiptera: Aleyrodidae). J General Virology 86: 1525-32.