Silverleaf whitefly

Female B. tabaci will lay 50 to 400 eggs ranging from 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 wide and 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 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 Holometabola, 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 in length. While feeding or resting the whitefly adult folds its wings tent-like over its body. == Distribution ==

Native/original community 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. Plants which are affected by the whitefly include: tomatoes, squash, poinsettia, cucumber, eggplants, okra, beans, and cotton. == Commercial impact ==

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. Bemisia tabaci became a serious issue in crops across the southwestern United States and Mexico in the 1980s. Scientists speculate that this pest was introduced via infested ornamental plants brought into the United States at this time. Florida's poinsettia greenhouses were crippled by the pest beginning in 1986, and by 1991, the infestation had spread through Georgia, Louisiana, Texas, New Mexico, and Arizona to plague growers in California. California produces approximately 90% of the United States’ winter vegetable crop, and has incurred an estimated $500 million in crop damage due to silverleaf whitefly populations. ==Nuclear receptors==

B. tabaci like all arthropods has ecdysone receptors (EcRs) which may be useful for insecticide development. Carmichael et al., 2005 presents the X-ray crystal structure for the 1Z5X ligand-binding domain of the B. tabaci EcR. == Integrated pest management ==

Multiple methods of control can be used to combat these prevalent agricultural pests. Some major control methods include, application of oils, use of natural enemies such as Aphelinidae parasitoids, employment of trap crops, release of insect growth regulators, and implementation of traps. Most of these control tools have a minimal effect on plant and soil properties. Scientists are currently focusing on targeting the whitefly through mechanisms that do not cause pollution or contamination (i.e., mechanisms other than insecticides). It is important to be able to reduce the number of B. tabaci individuals that settle on plants to decrease plant damages such as those caused by viral transmissions. This can be accomplished by reducing settling, decreasing oviposition, and abating population development. Biological controls Classical biological control has been the best long-term, sustainable solution to controlling these exotic pests. However, success of this method can be unpredictable. Entomologists with the U.S. Arid-Land Agricultural Research Center identified the most common causes of death of the whitefly as predation by other insects, parasitism, and weather induced dislodgement. They emphasize the importance of exploiting the use of natural predators and have identified predators by the use of enzyme-linked immune sorbent assay (ELISA). It was found that the use of the biological controls and insect growth regulators produces a higher predator-to-prey ratio. Insect growth regulators, such as buprofezin and pyriproxyfen, conserve natural predators compared to conventional insecticides, which can indiscriminately kill both predator and pest populations. There are currently four species of predators that are commercially available for control of B. tabaci: Delphastus pusillus, Macrolophus caliginosus, Chrysoperla carnea, and C. rufilabris. This oil causes the silverleaf whitefly nymph to shrink in size and therefore detach from the tomato plant, leading to starvation. Sugar apple seed oil is not phytotoxic to tomato plants of any concentrations and reduces the survival rate of the pest. This hormone is a juvenile hormone analogue, which affects hormonal balance and chitin in immature insects, and causes deformation and death during molting and pupation. This insect growth regulator does not kill adult whiteflies, and has low toxicity to mammals, fish, birds and bumblebees. Mechanical controls Man-made traps and covers Traps offer a pesticide free method of control of B. tabaci. The Light-Emitting Diode Equipped CC trap (LED-CC) was developed by plant physiologist Chang-Chi Chu and Thomas Henneberry. Originally, the trap was used to monitor population of silverleaf whitefly populations, but as the trap was improved it was used in control programs to limit whitefly pest populations. The trap itself includes a green LED light that attracts and traps the whiteflies. The LED device works best at night, and is inexpensive and durable. In addition, the LED does not harm predators and parasitoids of the whitefly. Silverleaf whiteflies are actually more attracted to the squash crop than they are to the tomato plant. Good sanitation in winter and spring crops is also required for the maintenance and control of the fly population. The SqVYV virus discovered by plant pathologist Benny Bruton and Shaker Kousik is essentially a crippling disease of the watermelon, which leads to the vine of the watermelon to collapse, causing the death of the watermelon before harvest. Kousik and pathologist Scott Adkins at ARS Subtropical Plant Pathology Research Unit worked together in screening the watermelon germplasm for resistance to SqVYV as to search for potential sources of resistance in wild-type watermelon. Kousik examined different combinations of insecticides and silver plastic mulch that could be used to reduce the whitefly populations. ==References==