The major foliar pest of poinsettia in U. This insect first became a greenhouse pest in the U. The current problem with B. Sweetpotato whitefly had been in the U. To distinguish this new, damaging form of sweet potato whitefly, from the pre-existing, less damaging strain, the old strain was referred to as strain A, and the new strain damaging poinsettia, field crops, and vegetables, was called strain B.
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Before , it was only an occasional pest of cultivated crops. However, in in Florida, the insect we called Bemisia tabaci became an extreme economic pest. It was found attacking crops that it had not infested previously, such as poinsettia, and was resistant to many formerly effective insecticides.
It transmitted new plant-pathogenic viruses that had never affected cultivated crops and induced plant physiological disorders, such as tomato irregular ripening and squash silverleaf disorder. This whitefly was thought to be a new biotype of Bemisia tabaci designated variously as B biotype, Florida biotype, or poinsettia biotype , possibly introduced from the Middle East.
It quickly moved into other southern states with intensive agricultural and horticultural industries Texas, Arizona, and California , and displaced the original Bemisia tabaci A biotype , which can no longer be found in the United States. Its common name is the silverleaf whitefly, because of its unique ability to induced silverleaf disorder in squash. Figure 1. Photograph by Shahab Hanif-khan, University of Florida.
Figure 2. Photograph by Yasmin Cardoza, University of Florida. Distribution Back to Top Bemisia is primarily a pest of cultivated plants in tropical and warm temperate regions of the world. It is found throughout the southern United States and can overwinter outdoors as far north as South Carolina.
It is found infesting greenhouses in more northern latitudes in the United States and Canada. It is present throughout much of southern Europe, Africa, India, and has recently moved into Australia. Description and Life History Back to Top Infestations of whiteflies, especially in greenhouses, may occasionally be a mixture of Bemisia and Trialeurodes vaporariorum Westwood , the greenhouse whitefly. They can be differentiated at the adult stage based on the position in which the wings are held over the body while alive see example in Whitefly Knowledgebase , close to the body and tent-like in Bemisia, and more loosely in Trialeurodes vaporariorum.
Another way to differentiate adult Bemisia and Trialeurodes vaporariorum is to examine the compound eyes using a microscope. The upper and lower compound eyes of Trialeurodes vaporariorum are completely divided whereas they are joined by one ommatidium in Bemisia. Adult Bemisia are soft and whitish-yellow when they first emerge from their nymphal exuvia. Within a few hours, their two pairs of wings become iridescent white due to the deposition of a powdery wax.
The body remains light yellow with a light dusting of wax. The body of the female measures 0. Figure 3. Adult whiteflies emerge through a T-shaped slit in the integument of the last nymphal instar. The remaining white, transparent "shell" is called the exuvia. If the exuvia has a round hole in it rather than a slit, an adult parasitoid emerged.
Adults that emerge may simply fly up the same plant or over to another plant. These are called trivial flights. Some individuals however, are primed for short-distance migration of up to several kilometers. Migrating individuals usually develop on plants that are senescing. These migrations can often be massive and can lead to severe infestation of newly planted crops. Figure 4. Exuvia of Bemisia with characteristic T-shaped whitefly adult emergence slit left , and exuvia of Bemisia with round emergence hole through which an adult parasitoid emerged right.
Photograph by Jane C. Medley,University of Florida. As far as we know, the sexes do not rely on pheromones to locate one another. Mating can occur as soon as the whiteflies have expanded and hardened their wings, usually within a few hours. Bemisia has arrhenotokous parthenogenetic reproduction where virgin females can only lay haploid eggs which give rise to males. Mated females can produce haploid and diploid female eggs.
There is usually a pre-oviposition period of less than a day to a few days, depending on the temperature. The female lands on a plant, using visual stimuli such as plant color, and walks or flies to the lower surface of a leaf. She tests the suitability of the plant by probing the leaf with her piercing-sucking mouthparts and ingesting a small amount of sap. If the host plant is deemed acceptable, she will insert her mouthpart stylets into the phloem from where she sucks plant sap. While she is feeding she may lay eggs, often in a semi-circular arrangement as she swivels her body around her feeding site.
Female longevity can range from 10 to 24 days during which time she can lay between 66 and eggs, depending on host plant and temperature. Whitefly eggs are oval in shape and somewhat tapered towards the distal end. The broader end has a short stalk, 0. The egg obtains moisture through this stalk. The egg is approximately 0. The egg is pearly white when first laid but darkens over time. The distal end of the egg becomes dark brown just before the first nymphal instar ecloses.
Figure 5. Newly laid eggs of Bemisia are pale yellow while those about to hatch are dark brown. Photograph by James Castner, University of Florida. The first nymphal instar is capable of limited movement and is called the crawler. It is oval in shape and measures approximately 0.
The dorsal surface of the crawler is convex while the ventral surface, appressed to the leaf surface, is flat. The crawler has three pairs of well-developed four-segmented legs, three-segmented antennae, and small eyes. It is whitish-green in color and has two yellow spots, the mycetomes, visible in the abdomen through the integument skin.
The mycetomes house several species of endosymbiotic bacteria that may play an important role in whitefly nutrition. The crawlers usually move only a few centimeters in search of a feeding site but can move to another leaf on the same plant. They initiate feeding on the lower surface of a leaf, also feeding in the phloem. After they have begun feeding, they will molt to the second nymphal instar, usually two to three days after eclosion from the egg.
The second, third and fourth nymphal instars are immobile with atrophied legs and antennae, and small eyes. The nymphs secrete a waxy material at the margins of their body that helps adhere them to the leaf surface. Nymphs are flattened and oval in shape, greenish-yellow in color, and range from 0. The mycetomes are yellow.
The second and third nymphal instars each last about two to three days. Figure 6. Various nymphal instars of Bemisia. The red-eyed nymphal stage is sometimes called the "pupal stage". There is no molt between the fourth nymphal instar and the red-eyed nymphal stage but there are morphological differences.
The fourth and red-eyed nymphal stages combined lasts for five to six days. The stage gets its name from the prominent red eyes that are much larger than the eyes of earlier nymphal instars. The red-eyed nymphal stage is also less flattened and more convex in shape.
This stage is more yellow than the fourth instar and the mycetomes are less visible. The red-eyed nymphal stages of Bemisia and Trialeurodes vaporariorum can be distinguished easily in a mixed infestation.
The sides of Bemisia red-eyed nymphs are boat-shaped or wedged see example in Whitefly Knowledgebase while those of Trialeurodes vaporariorum are perpendicular to the leaf surface.
Figure 7. Red-eyed nymphal or "pupal" stage of Bemisia. Hosts Back to Top Bemisia is widely polyphagous, feeding on over species of plants in 74 families. Its hosts include vegetable, field, and ornamental crops. Of the important vegetables crops grown in Florida, Bemisia is a major pest of tomato, peppers, squash, cucumber, beans, eggplant, watermelon, and cabbage. The Florida-grown field crops of potato, peanut, soybean and cotton are heavily attacked by Bemisia.
The ornamental host plants of Bemisia are too numerous to list, but include poinsettia, hibiscus, and chrysanthemum. Damage Back to Top Bemisia can cause economic damage to plants in several ways. Heavy infestations of adults and their progeny can cause seedling death, or reduction in vigor and yield of older plants, due simply to sap removal.
When adult and immature whiteflies feed, they excrete honeydew, a sticky excretory waste that is composed largely of plant sugars. The honeydew can stick cotton lint together, making it more difficult to gin and therefore reducing its value. Sooty mold grows on honeydew-covered substrates, obscuring the leaf and reducing photosynthesis, and reducing fruit quality grade.
Figure 8. Sooty mold developing on soybean leaves covered with Bemisia honeydew. Feeding by immature Bemisia, but not adults, has been associated with several developmental physiological disorders of plants.
Tomato irregular ripening was first noted in Florida tomatoes in Tomatoes that develop on plants that are heavily infested with whiteflies may incompletely develop external color, resulting in streaking.
Even if fruits appear normal externally, the internal tissue may be white, hard, and unripe. Squash silverleaf disorder is another developmental disorder caused by feeding of immature whiteflies, also first noted in Florida in This disorder affects many Cucurbita species, including the squashes and pumpkins of Cucurbita pepo, Cucurbita moschata, and Cucurbita mixta.
It attacks over species of plants USDA, Crop hosts that support large populations include alfalfa, broccoli, cabbage, cantaloupe, cauliflower, cotton, cucumber, tomato, squash, peanut, pepper, beans, and watermelon Perring, et. Ornamental hosts that support large populations include poinsettia, hibiscus, lantana, garden mum, Gerber daisies, mandevilla, and verbena Gruenhagen, et. Other preferred ornamental hosts include canna lilies, bearded iris, crepe myrtle, petunia, rose, and bottle brush.
EPPO Global Database
Before , it was only an occasional pest of cultivated crops. However, in in Florida, the insect we called Bemisia tabaci became an extreme economic pest. It was found attacking crops that it had not infested previously, such as poinsettia, and was resistant to many formerly effective insecticides. It transmitted new plant-pathogenic viruses that had never affected cultivated crops and induced plant physiological disorders, such as tomato irregular ripening and squash silverleaf disorder. This whitefly was thought to be a new biotype of Bemisia tabaci designated variously as B biotype, Florida biotype, or poinsettia biotype , possibly introduced from the Middle East. It quickly moved into other southern states with intensive agricultural and horticultural industries Texas, Arizona, and California , and displaced the original Bemisia tabaci A biotype , which can no longer be found in the United States. Its common name is the silverleaf whitefly, because of its unique ability to induced silverleaf disorder in squash.