WHITEFLIES
General Description
Adult whiteflies resemble tiny white moths. However, they are not closely related to moths but are related to scale insects. They are only about 1/16 to 1/8 inch long and have four wings. The wings and body are covered with a fine white powdery wax. The immature stages (nymphs), which are found on the underside of leaves, are flat, oval in outline, and slightly smaller than a pin head. They are light green to whitish and somewhat transparent.
Important Species
Approximately 100 species of whiteflies occur in the United States and Canada. There are over 1,150 species world-wide, mostly in the tropics. The most common whiteflies in Florida are:
Detailed Information
For more detailed information on whiteflies, click your cursor on this sentence. If you are not currently connected to the WWW then access this URL later:
http://entomology.ifas.ufl.edu/fasulo/whiteflies/
Biology
The female silverleaf whitefly deposits 100-300 eggs on the lower leaf surface of the host plant. Eggs hatch in five to seven days into the first nymphal stage known as a crawler. Crawlers are pale green in color and move about the leaf seeking a suitable feeding site. They locate a site, insert their long thread-like mouthparts into the lower leaf surface, become immobile and soon molt, loosing their legs and antennae. The resulting larvae are flat, oval, pale-green and nearly transparent. They resemble pale-green scales. After two additional molts, they pupate and the adults emerge. The life cycle from egg to adult requires 21 days at 80 degrees F and over 30 days at 65 degrees F. They do not develop at temperatures below 50 degrees F. There are several generations per year.
Citrus whitefly development is similar except it lays fewer eggs and there are three major generations per year. In the Gainesville, FL area, these occur in late March, mid-June and late August (these are the times when adults will be noticed). In south Florida, they will be approximately two to three weeks earlier and one week later in north Florida.
Host Plants
Host range varies greatly with different species. The silverleaf whitefly feeds on approximately 700 species of plants, poinsettia being the most common host. The citrus whitefly commonly attacks citrus, allamanda, chinaberry, gardenia, poinsettia and many other annual, perennial and woody plants.
Seasonal Abundance
Some whiteflies are present year-round. The largest numbers occur in late summer and early fall.
Damage
Both adults and immature whiteflies feed on the leaves of plants, but the larvae inflict the most damage. Their withdrawal of sap reduces plant vigor and causes leaves to turn yellow or chlorotic. Heavy infestations will cause the plant to wilt and eventually die. Larvae excrete large amounts of honeydew causing sooty mold.
Sampling
Observe for sooty mold. Tap plants to disturb adults. Inspect the undersides of leaves for larvae and pupal cases. Use a 10X magnifying glass if needed. Observe for evidence of predators or parasitoids as discussed under biological control. Whiteflies are attracted to yellow sticky cards.
Yellow Sticky Card
Whiteflies in general, are attacked by several species of predators and parasitoids. These include several small wasp parasites, lady beetles, lacewings, a thrips, some mites and ants.
Citrus whitefly nymphs are highly parasitized by a small wasp, Encarsia lahorensis. These parasitoids were first released in Gainesville and Winter Haven in 1972.
Carefully examine plants susceptible to whitefly infestations with the aid of a hand lens for evidence of the parasitoids. Parasitized whitefly nymphs will contain the larva or pupa of the parasitoid, or the parasitoid emergence hole can be seen in the whitefly nymph. The parasitoid does not attack the adult whitefly. If parasitism is evident, do not apply a pesticide. Chemical control will delay increase of the parasitoid which will eventually control the pest.
During recent years, the silverleaf whitefly has replaced the citrus whitefly as the predominant species attacking ornamental plants. This species is difficult to control with insecticides. At the present time, research is being conducted to find parasitoids that will aid in control. The wasp Encarsia pergandiella appears to be one very promising parasitoid.
Chemical Control
Insecticide soaps and oils should be carefully considered when a pesticide is required. They are effective against whiteflies and the least toxic to people, other non-target organisms and the environment.
For the most current insecticide recommendations to control these pests, please contact the local county office of the Cooperative Extension Service. If you have access to the World Wide Web you can consult the University of Florida's Insect Management Guide at:
http://edis.ifas.ufl.edu/TOPIC_GUIDE_Insect_Management_Guide
Back to Insect and Mite Menu or Back to Main Menu
Copyright © University of Florida