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The whiteflies, comprising only the family Aleyrodidae, are small hemipterans. More than 1550 species have been described. Whiteflies typically feed on the underside of plant leaves.

Agricultural threat

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 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.

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.
Video of infestation of whiteflies on an American Beech
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. The video to the right which shows a severe infestation can be enlarged for better viewing.

Control

Whitefly control is difficult and complex as whiteflies rapidly gain resistance to chemical pesticides. The USDAmarker 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 . For heavy infestations, an initial insecticide application may be necessary to reduce the population of whiteflies before using other control methods. Care should be taken to insure 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 nenonicotinoids. Products containing nenonicotinoid 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). Nenocotinoid can be harmful if ingested . Nenocotinoid are also extremely toxic to bees which are essential to the pollination of flowering plants, and are seen as one of the cause behind their 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 and other methods have also been proposed to control whiteflies infestation, but multiple options may be needed, as well as repeated application. 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.

Several predators and parasitoids may be effective in controlling at least to some degree whiteflies. It should be noted that not all such predators are equally effective at controlling the different types of whiteflies, or equally effective outdoors as well as under controlled conditions, such as in green houses. These predators include green lacewings, lady beetles, bugs, minute pirate bugs, big eyed bugs, and damsel bugs.

Green lacewings larvae have a voracious appetite. They will attack whiteflies as well as other pests including aphids, mealybugs, spider mites, leafhopper nymphs, moth eggs, scales and thrips. The also can attack other insects including caterpillars. They are available in the form of eggs from commercial insectaries and will stay in a larveal stage after they hatch for 1 to 3 weeks. The adult insect can fly and will feed only on pollen, honey and nectar to reproduce. Repeated application may be necessary and the eggs could be eaten before they hatch by their natural predators, such as ants or mature green lacewings.

Lady bugs, aka lady beatles, also have a healthy appetite. They eat mostly insect eggs, but will eat as well beetle larvae, scale crawlers and young caterpillars. These are collected often when in a dormant state in the wild and shipped as insects. While they can be effective at controlling whiteflies, they may not stay in the location where they are released. They do however live for about a year and will continuously lay eggs and reproduce. Spraying the bug's wing with a sticky substance before release may hinder their ability to fly.

Companion plants

Various companion plants are reputed to repel or trap white flies. Calendula like 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.

See also



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.


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