Whiteflies
Order: Hemiptera
Family: Aleyrodidae
Description
Whiteflies are a common pest of plants, particularly greenhouse plants, and a vector of several plant diseases. Despite their name, whiteflies are not true flies. Rather, they are in the order Hemiptera along with many other plant pests such as aphids, mealybugs, and scales. There are multiple species of whitefly that can damage ornamental plants and vegetable crops or become established in greenhouses. Several species of whiteflies are of particular importance in Colorado: the greenhouse whitefly (Trialeurodes vaporariorum), and sweetpotato whitefly (Bemisia tabaci), and bandedwinged whitefly (Trialeurodes abutiloneus). A fourth species, Bemisia argentifolii, has recently become established in Colorado and is endemic to southwestern US and Florida where it causes severe damage to ornamentals and crops.
The exact appearance of whiteflies depends on the species. Generally, adult whiteflies measure 1.6-2.5 mm (1/16-1/10 in) long and have four wings covered in white wax. The wings are usually white, sometimes with gray markings. All immature stages are wingless, and the first nymphal stage, called a crawler, is barely visible as it moves around the leaf before settling to feed. Later instar nymphs are immobile and flattened with reduced legs, resembling small scale insects, and may be visible on the underside of leaves. The eggs are oblong and very small at 0.2 mm long and 0.08 mm wide.
The greenhouse whitefly produces nymphs with very long filaments of wax and adults that have white wings and a yellow body. Nymphs of the sweetpotato whitefly do not have waxy filaments and adults have yellow bodies with white wings, held slightly tilted to the surface. The bandedwinged whitefly produces nymphs with short waxy filaments and adults that have grey bodies and brown bands across the wings.
Quick Facts
- There are around 1300 described whitefly species, some of which are common pests of many plants and can become especially injurious in greenhouse production. In greenhouses, some preferred vegetable hosts include cucumber, tomato, and eggplant.
- In summer, whiteflies can become established in the garden and impact vegetable and flower production. Whiteflies can attack a wide variety of garden vegetables including bean, cucumber, eggplant, potato, squash, cabbage, sweet potato, lettuce, and tomato.
- Whiteflies do not survive outdoors in areas with freezing temperatures, such as Colorado. Winter infestations may persist on plants grown indoors.
- Colored sticky traps and certain biological controls are effective tactics in whitefly monitoring and control.
Adult greenhouse whiteflies on a zucchini leaf. Whiteflies are a common pest of plants, particularly greenhouse plants, and a vector of several plant viruses. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Nymph (left) and adult (right) of the greenhouse whitefly. Note the waxy filaments on the nymph, and the white wings and yellow body of the adult. Image credit: David Cappaert, Bugwood.org.
Infestation of greenhouse whiteflies on zucchini leaf with a penny for size comparison. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Adult sweetpotato whitefly. Note the tilted white wings and yellow body. Image credit: W. Billen, Pflanzenbeschaustelle, Weil am Rhein, Bugwood.org
Mature nymph of the sweetpotato whitefly. Image credit: W. Billen, Pflanzenbeschaustelle, Weil am Rhein, Bugwood.org
Adult of the bandwinged whitefly. Note the grey body and brown bands on the wings. Image credit: Nancy Gregory, University of Delaware, Bugwood.org
Nymph of the bandedwinged whitefly. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Cucurbit leaf with silver coloration caused by feeding of whiteflies. Image credit: David B. Langston, University of Georgia, Bugwood.org
Adult of E. formosa, which is a commercially available parasitoid of whiteflies. Image credit: David Cappaert, Bugwood.org
Greenhouse whitefly nymphs, black forms are parasitized. Image credit: David Cappaert, Bugwood.org
Life history and habits
Whiteflies are a common insect pest in greenhouses and on house plants. They can also become established on garden plants during the summer. New infestations arise from the winged adult females moving to new plants. The female will lay eggs in a semicircular pattern on the undersides of leaves while they feed. Adults and nymphs feed by penetrating the phloem with their proboscis and sucking plant fluids. Whiteflies can also transmit viruses of economic importance. Nymphs emerge from the eggs in five to seven days and move a short distance before flattening themselves against the leaf to feed. All remaining immature stages are immobile. Under favorable conditions, one generation of whiteflies takes three to four weeks to complete its development. Each female can lay 400 eggs over a period of two months.
Whiteflies develop rapidly in warm weather and can produce multiple generations. Year-round infestations are possible indoors, and whiteflies can produce up to 13 generations per year in greenhouses. Large populations often develop on the undersides of leaves. Collectively, these whitefly species have a very wide range of host plants. Whiteflies are considered tropical/subtropical insects that have a host range of more than 250 ornamental and vegetable plants. The greenhouse whitefly can attack most vegetables and may occur on fuchsia, gardenia, lantana, and redbud. The sweet potato whitefly also has a very broad host range that includes cole crops, cucurbits, tomatoes, and peppers. The bandedwinged whitefly attacks cucurbits and other vegetables.
All three species can transmit plant viruses. For example, the sweetpotato whitefly is a vector of 111 different plant viruses. Of these, Begomoviruses are the most numerous and can cause 20%-100% yield loss in infected tomatoes and other crops. The greenhouse whitefly can spread a phoretic pest called the broad mite, Polyphagotarsonemus latus (Acari: Tarsonemidae), which can attack many greenhouse crops.
Injury
Whiteflies feed on phloem and heavy infestations cause a decline of plant vigor. Symptoms of injury include stippling and yellowing of leaves, drying, stunted growth, and premature leaf drop. On cucurbits, phytotoxins injected by the sweetpotato whitefly can cause a condition called “silver leaf”. Some common symptoms of viral infection include yellow mosaics, yellow veins, leaf curling, stunted growth, and vein thickening. Whiteflies also excrete excess sugars in a sticky waste called honeydew, which can interfere with photosynthesis and promote growth of sooty mold.
Monitoring
Whiteflies are attracted to yellow sticky traps, which can be used to monitor adult densities and are useful in early detection of whiteflies. The traps should be deployed with the yellow surface at the same level as the infestation on the host plant. Research has shown that traps with reduced translucency and printed black patterns can increase whitefly captures. Since whiteflies are not strong fliers, it is recommended that one trap be deployed for every two large plants to help increase the capture rate.
Cultural control
Sufficiently watering plants can reduce the hot, dry, dusty conditions conducive to outbreaks. Infestations in the field and greenhouse frequently originate from infested plant materials. Removing leaves or entire plants that are heavily infested with whiteflies is recommended. All plants should be carefully inspected and, if necessary, quarantined before moving them into a greenhouse with susceptible plants or before planting in the field. Once whiteflies are established in a greenhouse, establishing a host-free period can be an effective management strategy. This may mean removing susceptible plants for at least two weeks. Weed control in the greenhouses is an effective preventative tactic as well. In addition, using a syringe to spray water can dislodge adults.
The use of metallic-coated construction paper or reflective plastic mulches can help repel whiteflies from small plants. For this to be effective in gardens, all weeds should be removed, and 3- to 4-inch diameter holes should be cut for planting seeds or single transplants. An added benefit of plastic mulches is that they reduce the prevalence of weeds and can also decrease the incidence of viruses.
Biological control
There are several insects that will feed on whiteflies, including lacewings, bigeyed bugs, minute pirate bugs, and several species of lady beetle, such as Harmonia axyridis (Coleoptera: Coccinellidae). Some of these, such as minute pirate bugs, can be effective predators of whitefly nymphs in greenhouses.
In addition to predators, a small parasitic wasp, Encarsia formosa (Hymenoptera: Aphelinidae) is an effective parasitoid of whiteflies. These wasps are commercially available and are one of the most widely used biological control agents for greenhouse whiteflies in greenhouse production systems. Releasing these wasps outdoors is not recommended as they are not adapted for survival in temperate zones. Female wasps lay eggs in immature stages of greenhouse whitefly except for eggs and the mobile first instars, with the third and fourth instars among the most susceptible immature stages. In some instances, the parasitized nymphs turn black. When parasitized, the whitefly nymph dies within several days. The degree of parasitoid activity can be evaluated by inspecting plants for empty whitefly pupal cases, which will have a round or oval exit hole produced by emerging wasps, or a T-shaped exit hole produced by emerging adult whiteflies.
Conserving populations of natural enemies is highly recommended to help suppress whitefly densities. Controlling the amount of dust and ants in greenhouses is also recommended, as both protect whiteflies from natural enemies.
Chemical control
Insecticidal soaps, neem oil, or petroleum-based oils are less toxic to beneficial insects than synthetic insecticides and can be effective against whiteflies. However, thorough coverage of plants is necessary since these formulations must come in direct contact with insects to kill them. Repeat applications may be necessary. To prevent damage to plants, soaps or oils should be used in situations where plants are not drought-stressed and temperatures are below 32°C (90°F). In some areas whiteflies are frequently controlled with synthetic insecticides.
CSU Extension Fact Sheet
Download or view the CSU Extension’s PDF fact sheet for your reference.
References
Delahaut, K. 2019. Whiteflies. University of Wisconsin Extension. Available https://hort.extension.wisc.edu/articles/whiteflies/
Jones, D. 2003. Plant viruses transmitted by whiteflies. European Journal of Plant Pathology. 109: 195-219. Available https://link.springer.com/content/pdf/10.1023/A:1022846630513.pdf
UC IPM. 2015. Whiteflies. University of California – Agriculture and Natural Resources. Available https://ipm.ucanr.edu/PMG/PESTNOTES/pn7401.html
University of California. 2015. Pests in Gardens and Landscapes: Whiteflies. University of California Agriculture & Natural Resources. Available http://ipm.ucanr.edu/PMG/PESTNOTES/pn7401.html
University of Maryland. 2021. Whiteflies – Vegetables. University of Maryland Extension. Available https://extension.umd.edu/resource/whiteflies-vegetables
Walia, A., S. Verma, P. Sharma, N. Sharma, and S. Palial. 2021. Relative preference and demographic parameters of Encarsia formosa Gahan against Trialeurodes vaporariorum (Westwood). Egyptian Journal of Biological Pest Control. 31(79): 1-7. Available https://ejbpc.springeropen.com/counter/pdf/10.1186/s41938-021-00424-3.pdf