Whiteflies are small Hemipterans that typically feed on the undersides of plant leaves. They comprise the family Aleyrodidae, the only family in the superfamily Aleyrodoidea. They can be as small as 1/12 of an inch, somewhat triangular in shape, and are often found in clusters on the undersides of leaves. They are active during the daytime, so they are easier to spot than some other nocturnal pests. More than 1550 species have been described. Whiteflies develop rapidly in warm weather, and populations can build up quickly in situations where natural enemies are ineffective and when weather and host plants favor outbreaks. Large colonies often develop on the undersides of leaves. The most common pest species such as greenhouse whitefly and sweet potato whitefly have a wide host range that includes many weeds and crops. These species breed all year round in warmer parts of California, moving from one host to another as plants are harvested or dry up. Another species of whitefly with a broad host range is the giant whitefly, Aleurodicus dugesii. It is now found in coastal areas and interior valleys in much of the state on a number of tropical and semi-tropical ornamental species.
Adult whiteflies are moth-like insects with powdery white wings and short antenna. They are easily recognized and often found near the tops of plants or on stem ends. Wingless nymphs are flattened, oval and almost scale-like in appearance. The full life cycle of the whitefly lasts between 15 to 40 days, depending on environmental conditions, particularly the temperature, as eggs will turn into adults more quickly when the temperature is higher. The whitefly usually lays its eggs on the underside of the leaves and the eggs stick to them by means of a pedicel. The larva or nymphs emerge from the eggs and in their first stage of development, they are mobile enough to move along the leaf until they find the right place to insert their stylus and begin to feed off the sap of the phloem, which is rich in sugars. The nymphs then pass through several more stages of development, during which they remain in the same place and continue to feed off the plant until the adult emerges from the last nymph stage. Non-fertilized eggs produce males while the fertilized eggs produce females.
The whitefly feeds on more than 500 species of host plants. Common targets include ornamental plants, houseplants, hibiscus, coleus, fuchsia, sweet potato (edible and ornamental), tomato, grape, citrus and squash-family plants. Whiteflies use their piercing, needle like mouth parts to suck sap from phloem, the food-conducting tissues in plant stems and leaves. Large populations can cause leaves to turn yellow, appear dry, or fall off plants. Like aphids, whiteflies excrete sugary liquid called honeydew, so leaves may be sticky or covered with black sooty mold that grows on honeydew. The honeydew attracts ants, which interfere with the activities of natural enemies that may control whiteflies and other pests.
Feeding by the immature sweet potato whitefly, Bemisia tabaci, can cause plant distortion, discoloration, or silvering of leaves, and may cause serious losses in some vegetable crops. Some whiteflies transmit viruses to certain vegetable crops. These include the TYLCV (Tomato yellow leaf curl virus), the ToCV (Tomato chlorosis crinivirus) or the TYMV (Tomato Yellow Mosaic Virus). Whiteflies are not normally a problem in fruit trees although their populations can build up in citrus, pomegranate and avocado. In warm or tropical climates and especially in greenhouses, whiteflies present major problems in crop protection. Worldwide economic losses are estimated at hundreds of millions of dollars annually.
Let us look at some news articles pertaining to the damage caused by whiteflies.
Whitefly pest attacks cotton crop in Punjab
July 11 2016, India
Whitefly pest has again attacked cotton crop, now in the flowering stage, in Punjab, posing a threat to the kharif crop even as the opposition Congress lambasted the Shiromani Akali Dal (SAD)-Bharatiya Janata Party (BJP) alliance for its “failure” in preventing the pest attack. “Whitefly has attacked cotton crop in several fields of about 15 villages of Khuian Sarwar block in Abohar,” an official of Punjab Agriculture department said on Monday.
Also in the year 2015, about two-third of Punjab’s cotton crop was destroyed by whiteflies causing an estimated loss of Rs 4,200 crore. There were reports of at least 15 cotton farmers committing suicide.
The damage and loss caused by these tiny whiteflies are huge! We cannot afford this significant amount of crop damage caused by pests like whiteflies. There is an urgent need for a sustainable solution.
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