Sweetpotato Whitefly
Bemisia tabaci (Gennadius)
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ADULT. The sweetpotato whitefly adult is small, about 0.8 mm (1/32") in length. At rest it holds its solid white wings rooflike over its pale yellow body. It inhabits and feeds on the undersurfaces of leaves by penetrating the tissue and removing the plant sap with its piercing-sucking mouthparts. The insect's snow-white color is attributed to the secretion of wax on its body and wings.
EGGS. The females deposit their eggs on the undersides of leaves, where they are usually clustered in groups. The number of eggs laid by the females ranges m approximately from 50 to 400, with an average of about 160. The eggs are very small, about 0.2 mm (1/125") long, and 0.1 mm (1/250") in diameter. Each egg is attached by a stalk to the leaf and is somewhat elliptical in shape, tapering towards the unattached end. Newly laid eggs are smooth and whitish-yellow. As the eggs approach hatching in about five to seven days, they turn brown.
NYMPHAL STAGES. This insect goes through four nymphal instars, ranging in approximate size from 0.3 mm (1/95") as first instars and/or crawlers, to 0.6 mm (1/40") as fourth instars. The first instar or crawler is a flattened, oval nymph which attaches itself to the underside of a leaf near the empty egg. It remains there through three more molts. Late third and fourth instars begin to develop distinctive eye spots and are often referred to as red-eyed nymphs. These immature stages are thin and flat, elliptical in shape, and greenish-yellow in color. In most infestations, all stages of the life cycle are present.
PUPAL STAGE. At the end of the nymphal cycle, the whitefly enters into what is commonly referred to as the pupal stage. It is yellow in color and about 0.7 mm (1/35") long. The pupa has very prominent eye spots and is oval and flat with a rounded outside margin, tapering toward the leaf surface as viewed from the side. In contrast, the pupae of Trialeurodes species, bandedwinged whitefly and greenhouse whitefly, have distinctly ridged outside margins with flat, vertical surfaces and waxy projections at the tops of the ridges as viewed from the side.
When the adult whitefly emerges from the pupa it leaves a distinctive T-shaped split in the pupal case. A pupa that was parasitized has a round emergence hole left by the emerging adult wasp.
ADULTS. The adult is a moth-like insect approximately 0.8 mm (1/32") in length. It inhabits and feeds on the undersurfaces of leaves by penetrating the tissue and removing plant sap with its piercing-sucking mouthparts. The insect's snow-white color is attributed to the secretion of wax on its body and wings. The adults fold their wings tent-like over their bodies when at rest or while feeding. Other species of whitefly usually hold their wings flatter. The females deposit their eggs on the undersides of leaves, where they are usually clustered in groups.
EGGS. The eggs are very small, about 0.2 mm (1/125") long, and 0.1 mm (1/250") in diameter. Each egg is attached by a stalk to the leaf and is somewhat elliptical in shape, tapering towards the unattached end. Newly laid eggs are smooth and whitish-yellow. As the eggs approach hatching in about five to seven days, they turn brown.
MOLTING. As the life cycle progresses from stage to stage, molting occurs and the cast skins (particularly from the pupae) remain on the leaves. These structures are empty, silver in color and resemble small fish scales on the leaves.
NYMPHAL STAGES. This insect goes through four nymphal instars, ranging in approximate size from 0.3 mm (1/95") as a first instar and/or crawler, to 0.6 mm (1/40") as a fourth instar/pupa. Immature stages are thin and flat, elliptical in shape, and greenish-yellow in color. In most infestations, all stages of the life cycle are present.
PUPAL STAGE. At the end of the nymphal cycle, the whitefly enters into what is commonly known as the pupal stage. The pupa has two conspicuous red eyes and the body is raised or convex in shape, but appearing oval and flat from above. It is yellow in color and about 0.7 mm (1/35") in length.
When the adult whitefly emerges from the pupal case it leaves a distinctive
T-shaped split. If the pupal case has a round emergence hole, it was probably left by an emerging adult parasitic wasp
ADULT INFESTATION. Adults congregate, feed, and mate on the undersurfaces of the leaves of the host plant. This can occur in such numbers as to create "clouds" when disturbed. They appear to be more active during the sunny daylight periods, and do not fly as readily during the early morning, late evening, or night hours.
NYMPHAL INFESTATION. The nymphal stages are sedentary, with the exception of the crawler, which after hatching moves a very short distance. Once a feeding site is selected the nymphs do not move. They suck juices from the plant with their piercing-sucking mouthparts. The nymphs are located on the undersides of the leaves and can become so numerous that they almost cover the entire undersurface area.
DAMAGE. Feeding damage by both the nymphs and adults results in the accumulation of honeydew on the leaves, and the subsequent growth of sooty black as well as other molds. Other forms of damage include the removal of plant sap; vine, leaf, and plant breakdown; chlorotic spots, yellowing, blanching of vegetative structures, leaf shedding, and irregular ripening (tomatoes) or other abnormalities of fruiting structures. It is believed that this insect injects foreign enzymes into the host plant while feeding, affecting the normal physiological processes. This insect is also known to vector virus diseases to a large number of crops.