Whitefly

Whitefly is any sap-sucking member of the insect family Aleyrodidae (with the order - Homoptera). The nymphs, which resemble scale insects, are oval, flat, and normally covered in a cottony substance; the adults, which are 2–3 mm (0.08–0.12 inch) long and resemble tiny moths, are covered in an opaque white powder. The four wings will develop within the insect and ebert at the time the last molt. These pests are abundant in warm climates and can be found in greenhouses and houseplants.

Because it feeds on the sap of date and orange trees, the citrus whitefly (Dialeurodes citri) is commercially important because it produces honeydew, a tasty digestive by-product on which a sooty fungus grows and destroys the fruit. Whitefly control is by parathion sprays or oil. The citrus blackfly (called Aleurocanthus woglumi) is well established in the West Indies and Mexico. The host plant's ability to photosynthesize is reduced by a sooty fungus that thrives on the honeydew secreted by the citrus blackfly.

About Whitefly

These small sucking insects hold developed resistance to several synthetic whitefly pesticides making chemical control difficult.

The whitefly (Triaeurodes vaporariorum) is a sap-sucking bug that can be found in thick swarms on the undersides of leaves on tomatoes, indoor plants, and greenhouses. When infested plants are said to be disturbed and great clouds of the winged adults fly into the air. Plants are damaged by both adults and nymphs sucking the juices from new growth, resulting in stunted development, lower yields, and leaf yellowing. Plants become susceptible and weak to disease. Like aphids, whiteflies also secrete honeydew, so leaves may be covered or sticky with a black sooty mold. Also, they are responsible for transmitting many plant viruses.

The below figure indicates Whiteflies (Aleyrodidae).

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Whiteflies are found year-round in outdoor gardens in southern and coastal states. In northern areas, year-round infestations are possible only indoors. Host plants include 250 plus vegetable and ornamental plants. Squash, citrus, potato, poinsettia, grape, cucumber, hibiscus and tomato are commonly infested.

The below figure is citrus whitefly (Dialeurodes citri; order Homoptera).

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Botanical & Biological Whitefly Controls for Whiteflies

Whiteflies (also called "whitefly" or "white fly") are the common pests of indoor crops and greenhouses. Seasonal pests in most outdoor areas, whiteflies are found year-round either in enclosed growing areas (hoop houses, greenhouses, grow tents) or southern states. Their rapid reproduction rate makes them more difficult to control once established. Also, several varieties have developed chemical resistances, making certain chemical controls ineffective. In addition to the physical damage that they cause, whitefly infestations and the honeydew that they produce can harbor sooty molds, which reduce plant vigor, causing any unnecessary stress to the grower and plant.

Identification & Prevention

Often, growers spot them by the plume of whiteflies, which take flight after disturbing an infested plant. Whitefly control is difficult to achieve by this point. Place the yellow sticky traps around the developing region and keep an eye on the undersides of the leaves for early detection. Whiteflies tend to cluster and they are much easier to spot in groups. The other indicator, which whiteflies are around, is honeydew on the leaves. It is sticky to the touch and appears shiny. You can remove honeydew by wiping leaves either with a diluted alcohol solution or a Green Cleaner. An ash whitefly is also an example of a whitefly.

Controlling a Whitefly Problem

• Carefully inspect the new plants before transplanting. Dip root ball and foliage in soapy water to clean and kill the existing whitefly eggs, adults or nymphs, if any.

• Early in the season, release the Green Lacewing larvae to feed on whitefly nymphs or eggs before the infestation becomes severe.

• For high whitefly populations, they release specialized parasites and predators for pest control. E. eremicus and E. Formosa are species-specific parasites effective in most environments. A. swirskii are predatory mites effective in humid and warm areas.

• Beauveria bassiana sprays (which are the BioCeres and BotaniGard) are effective for whitefly control either in gardens (whiteflies in garden) or commercial growing. They use the fungus to slow reproduction or feeding and kill the infected pests. Using the bio-rational control sprays also helps in limiting the environmental impacts on non-target organisms like pollinators and bees.

• If it is necessary, knockdown sprays of contact insecticides will quickly reduce the whitefly numbers. Application repeat may be necessary as most sprays have a little residual impact.

• Neem is a feeding and growth inhibitor, which is commonly used by organic gardeners for general pest control.

• Pyrethrin sprays are excellent for a rapid reduction of large pest populations, but they should not be applied to flowering plants.

• Horticultural Oils are given as an effective knockdown for use in-season and for controlling the dormant or overwintering life stages.

• Make sure to clean everything in the greenhouse, either with SaniDate or OxiDate between growing seasons. Soil drenches, the whiteflies in soil, whiteflies in grass or white flying bugs on plants, may be required to control overwintering pests and/or diseases.

Identification and Life cycle

Whiteflies, white flying insects, despite their name, are not genuine flies (in the insect order Diptera), but rather belong to the Hemiptera family, which includes scales, aphids, and mealybugs. They derive their particular name from the mealy white wax covering the wings and body of the adults. Adults are tiny insects having four whitish wings and yellowish bodies. Several species can be differentiated in their last nymphal (immature) stage, which lacks visible legs and is wingless, despite the fact that adults of a few species have unique wing markings. Whitefly nymphs range in colour from practically transparent pale or yellow to black with a white fringe, depending on the species.

Whiteflies develop in warm weather rapidly, and their populations can build up quickly in situations where the natural enemies are ineffective and when host plants and weather favor outbreaks. Often, the large colonies develop on the undersides of leaves. The most common pest species­, such as the sweet potato whitefly (called Bemisia tabaci) and greenhouse whiteflies (called Trialeurodes vaporariorum) - have a wide host range that includes several crops and weeds. These species breed all year round in the warmer parts of California by moving from one host to the other as plants are harvested or dry up.

The Aleurodicus dugesii, or enormous whitefly (white flying insect), is another whitefly species with a wide host range, having entered Southern California in the early 1990s. Now, it is found in interior valleys and coastal areas in much of the state on numerous semi-tropical and tropical ornamental species. Other species of whiteflies, especially those living on the woody species, often contain a more limited host range.

Normally, the whiteflies (white flying insects) lay their tiny oblong eggs on the undersides of the leaves. The young whiteflies and the eggs hatch gradually increase in size through four nymphal stages known as instars. The first nymphal stage (called crawler) is barely visible even with a hand lens. The crawlers move around for many hours before settling to begin the feeding process. Later nymphal stages are oval, immobile and flattened, with great antennae and reduced legs, like small-scale insects. The last nymphal stage is completed, and the winged adult emerges (at times, referred to as pupa, although whiteflies do not have a truly complete metamorphosis). All the stages feed by sucking plant juices from the leaves and excreting excess liquid as drops of honeydew as they feed.

Damage

Whiteflies suck sap from the phloem, which is the food-conducting tissues of plant leaves and stems, with their piercing, which are needle-like mouthparts. Large populations can cause the leaves to appear dry, yellow, or fall off plants. Like aphids, whiteflies excrete a sugary liquid, which is known as honeydew, so leaves may be sticky or covered with black sooty mold that grows on the honeydew. The honeydew attracts ants that interfere with the activities of the natural enemies that may control whiteflies, including other pests.

Plant deformation, silvering of leaves, discoloration, and major losses in a few vegetable crops can all be caused by the juvenile sweet potato whitefly, Bemisia tabaci. Some of the whiteflies transmit viruses to certain vegetable crops. Normally, the whiteflies are not a problem in fruit trees, although their populations can build up in pomegranate, citrus, and avocado.

Many whitefly species can be found on shrubs and ornamental trees, however due to natural restrictions such as predators and parasites, the majority of them are uncommon. Most whiteflies on the trees hold limited host ranges. Usually, the low levels of whiteflies are not damaging. Adults will not do much harm unless they are transmitting the plant pathogen. In general, plant losses do not take place unless there is a significant population of whitefly nymphs.

Management

Management of the heavy whitefly infestations is not easy. The best strategy is to prevent the problems from developing in your landscape or garden (whiteflies in garden). In several situations, the natural enemies provide adequate control of whiteflies; outbreaks often take place when natural enemies are disrupted by dusty conditions, insecticide applications, or interference by ants. It is better to remove or avoid plants that repeatedly host high populations of whiteflies.

In gardens, the whitefly populations in the early stages of population development can be held down by the vigilant program of hosing down with water sprays or removing the infested leaves. Yellow sticky traps can be used to monitor or, at high levels, reduce whitefly numbers and the reflective mulches can repel the whiteflies from vegetable gardens. If you choose to use insecticides, oils or insecticidal soaps such as neem oil may reduce but not eliminate the populations. Maybe systemic insecticides are more effective but can have negative impacts on pollinators and beneficial insects.