Whiteflies (Trialeurodes vaporariorum)

Whiteflies:  Trialeurodes vaporariorum.  Whiteflies are 1550 species strong and feed on the underside of plant leaves.  The diseases that are spread and carried by the whitefly have largest impact on global food production.  In subtropical and tropical locations the whitefly is the most serious crop protection problem.  Whitefly crop losses are estimated to be in the hundreds of millions of dollars yearly.

Whitefly species include
     •    Greenhouse whitefly (Trialeurodes vaporariorum) a major fruit, vegetable, ornamental crop pest.  This type of whitefly is very common in greenhouses.
     •    Citrus blackfly (Aleurocanthus woglumi) – a citrus crops pest.
     •    Silverleaf whitefly (Bemisia argentifolii) – an agricultural and ornamental crop pest

Whiteflies can cause severe plant damage by feeding directly on the plants or by transmitting plant diseases.  Crops are especially susceptible of whitefly damage from the transmission of plant diseases.  Whiteflies attack a wide assortment of herbs, vegetable and floral crops.  Ornamental plants are also at risk for whitefly infestation.  A single whitefly can infect all of the these types of plants.   The worst whitefly virally transmitted disease, tomato yellow-leaf curl, was discovered in Florida in 1997.  Whiteflies are known to transmit at least 60 viral plant diseases.  Whiteflies damage the flow of water through the cells of plants sucking the saps or juices from the plant. This type of damage is considered damage by feeding.  Whiteflies secrete honeydew which is a major contributor to mold.  Their secretions and the lack of water in the plant cells can leave the plant in danger of spotting and yellowing leaves and increases the susceptibility to disease.  Since whiteflies travel in large groups it is easy to overwhelm individual plants and crops quickly.

Detection is a key factor in controlling and eliminating whiteflies.  In the early spring females lay their eggs in a circular pattern on the underside of the newer leaf growth near the top of the plant. Eggs are initially white but darken as they get close to hatching.  The newly hatched pupae look like little scales.  Mature white adults fly upward and outward to find a mate and repeat the cycle.  Plant infestation spreads at a rapid rate since new leaf growth continues on the top and the older growth further down the plant is now infested as well.   These cycles are often used to assess the age of the infestation and the seriousness of the problem.

Whiteflies can be controlled by an initial pesticide application.  Repeated pesticide applications can cause resistant strains to emerge.  Pesticide applications in conjunction with cultural and biological methods are recommended to sustain whitefly control.  Since whiteflies are attracted to the color yellow; yellow sticky paper can serve as a trap to monitor infestations.  Dead leaves should be removed and burned to avoid spreading the disease to healthy plants.  Control can also be obtained through the planting of companion plants.  These plants are known to repel or trap whiteflies.  Pot marigolds and Nasturtiums release a chemical that repels whiteflies.  Mint is thought to serve as either a repellent plant or could be used as a trap crop.