Silverleaf whitefly

The silverleaf whitefly (Bemisia tabaci, also informally referred to as the sweet potato whitefly) is one of several species of whitefly that are currently important agricultural pests. A review in 2011 concluded that the silverleaf whitefly is actually a species complex containing at least 24 morphologically indistinguishable species. The silverleaf whitefly thrives worldwide in tropical, subtropical, and less predominately in temperate habitats. Cold temperatures kill both the adults and the nymphs of the species. The silverleaf whitefly can be confused with other insects such as the common fruitfly, but with close inspection, the whitefly is slightly smaller and has a distinct wing color that helps to differentiate it from other insects. While the silverleaf whitefly had been known in the United States since 1896, in the mid-1980s a virulent strain appeared in poinsettia crops in Florida. For convenience that strain was referred to as strain B (biotype B), to distinguish it from the milder infestation of the earlier known strain A. Less than a year after its identification, strain B was found to have moved to tomatoes, and other fruit and vegetable crops. Within five years, the silverleaf whitefly had caused over $100 million in damage to Texas and California agriculture industries. Female B. tabaci will lay 50 to 400 eggs ranging from 0.10 mm - 0.25 mm on the under part of leaves. Female whiteflies are diploid and emerge from fertilized eggs whereas male whiteflies are haploid and emerge from unfertilized eggs. Eggs are laid in groups, being small in size with dimensions of 0.2 mm wide and 0.1 mm in height. Eggs are initially whitish in color and change to a brown color near hatching, within 5 to 7 days. After hatching, the whitefly nymph develops through four instar stages. The first instar, commonly called a crawler, is the only mobile nymphal stage. The first instar nymph can grow to about 0.3 mm and is greenish in color and flat in body structure. The mobile nymph walks to find a suitable area on the leaf with adequate nutrients and molts into an immobile stage. The next three instars remain in place for 40–50 days, until molting into an adult. Silver exuvia, or shed skins are left on the leaves. The immobile instars appear opaquely white. Nymphs feed by stabbing into the plant with their mouth-parts and sucking up plant juices. After the fourth instar, the nymph transforms into a pupal stage where the eyes become a deep red color, the body color becomes yellow, and the body structure thickens. This is not a true pupal stage, as is found in the Endopterygota, but is similar in function. Adult whiteflies are approximately four times the size of the egg, with light yellow bodies and white wings, which is attributed by the secretion of wax across its wings and body. Adult silverleaf whiteflies can reach up to 0.9 mm in length. While feeding or resting the whitefly adult folds its wings tent-like over its body. Research indicates that the silverleaf whitefly likely came from India. Since the whitefly is predominately associated with areas exhibiting tropical/subtropical climates, the focus shifts to how these insects attained access to crops in habitats with temperate climates. One hypothesis suggests that the transfer of decorative plants from tropical regions may have aided in the spread of the silverleaf whiteflies to temperate environments. The ability of the whitefly to adapt to various plants facilitates the spread of dangerous plant viruses, which these insects are notorious for transmitting. Plants which are affected by the whitefly include: tomatoes, squash, poinsettia, cucumber, eggplants, okra, beans, and cotton. Other common plant damages of whitefly include: removing plant sap, breakdown of the leaves of the plant, and leaf shedding. The silverleaf whitefly is considered an invasive species in the United States as well as Australia, Africa, and several European countries. It was classified as an agricultural pest in Greece around 1889 and had a significant impact on tobacco crops there. The first silverleaf whitefly was found in the United States in 1897 on a crop of sweet potatoes. This tiny insect causes damage to plants through feeding and transmitting plant diseases. The silverleaf whitefly feeds on its host plants by piercing the phloem or lower leaf surfaces with its mouth and removing nutrients. Affected areas of the plant may develop chlorotic spots, whither, or drop leaves. Whiteflies also produce a sticky substance called honeydew, which is left behind on the host. Honeydew can induce the growth of sooty molds, which can then reduce the plants ability to absorb light. This results in slower growth, lower yield, and poor quality plants. It also requires that crops be thoroughly washed after harvesting, which raises processing costs for the grower.