| Whitefly | |
|---|---|
| Whiteflies (Trialeurodes vaporariorum) | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Hemiptera |
| Suborder: | Sternorrhyncha |
| Superfamily: | Aleyrodoidea |
| Family: | Aleyrodidae |
| Subfamilies[1] | |
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.
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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 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 environmentally-friendly integrated pest management systems, with the goal of reducing insecticide use aim to 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 whiteflies, and to the plant diseases carried by them. A major problem is the fact that whiteflies and the viruses they carry can infect many different host plants, including agricultural crops, palms,[2] 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 was discovered in Florida, USA. This is the worst viral disease transmitted by the whitefly, Bemisia argentifolii. The whitefly has also been shown to transmit almost 60 other viral plant diseases.
Whiteflies feed by tapping into the phloem of plants, introducing toxic saliva and decreasing the plants' overall turgor pressure. Since whiteflies congregate in large numbers, susceptible plants can be quickly overwhelmed. Further harm is done by mold growth encouraged by the honeydew whiteflies secrete. This may also 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 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."[3] 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,[4] 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.[5] Care should be taken to ensure that the insecticide used will not kill the natural predators of whitefly. 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.[6] 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.[7] 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. 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.[8] Whiteflies are also attracted by the color yellow so yellow sticky paper can serve as traps to monitor infestations.[9] 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.
Early detection in combination with hosing or vacuuming of diseased portions as well as removal of any section that is heavily infested. Pesticide use is not ideal in the case of controlling whitefly and widespread contamination can be costly; it is best to avoid this problem with aggressive preventive measures.
Several predators and parasitoids may be effective in controlling whitefly infestations. These predators include green lacewings, ladybirds, minute pirate bugs, big eyed bugs, and damsel bugs.[8]
Integrated management of whitefly can as well be done using Biopesticides based on microbials such Beauveria bassiana (effective on nymphs and adults) or Paecilomyces fumosoroseus.
Green lacewing 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. They also can attack other insects including caterpillars. They are available in the form of eggs from commercial insectaries and will stay in a larval stage after they hatch for one to three weeks. The adult insects 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.
Ladybirds are also used. They eat mostly insect eggs, but will also feed on beetle larvae, aphids, scale insects and young caterpillars. Adults are often collected when in a dormant state in the wild and shipped for use in pest control, however, they may not stay in the location where they are released. They do live for about a year and will continuously lay eggs and reproduce. Spraying the bug's wings with a sticky substance before release may hinder their ability to fly.
The greenhouse whitefly, Trialeurodes vaporariorum, is a major pest of many fruit, vegetable and ornamental crops, frequently being found in glasshouses.
The citrus blackfly, Aleurocanthus woglumi, is a pest of citrus crops.
The silverleaf whitefly, Bemisia argentifolii, is a pest of a number of agricultural and ornamental crops.
The cabbage whitefly, Aleyrodes proletella is a pest of various Brassica species.
Various companion plants are reputed to repel or trap white flies. Calendula, such as pot marigolds do so by producing chemicals that repel them. Nasturtiums are thought to have a similar effect, while mint may serve either as a repellent or trap crop.