Answer: Whiteflies are smaller than 7 mm long, more often 2-3 mm, and are usually covered with a white waxy film.
Stages: Whiteflies go through an incomplete metamorphosis beginning as an egg that moves through a nymphal stage before becoming an adult.
Mouthpart: Like all members of the order Homoptera, the whitefly has a pierce-sucking mouthpart that is located at the back of the head.
Wings: The order Homoptera is characterized by a set of four transparent wings with visible veins. The wings of the whitefly appear opaque because they are covered in the white waxy scales that give this insect its color. The forewings are characterized by a simple major vein.
Unlike other insect orders that have wings that lay against the body when not in flight, the wings of the order Homoptera create a roof-like structure over the insect.
Though very weak, whiteflies have the ability to fly and are known to travel short distances when the host plant is disturbed. They also undertake a migratory flight and have been known to travel a distance greater than three miles. 
Antennae: During the larval stage the legs and the seven segmented antennae appear unusually long in relation to the size of the body. They will ultimately grow into both as they molt into adulthood.
 “Homoptera.” McGraw-Hill Concise Encyclopedia of Science and Technology. New York: McGraw-Hill, 2006. Credo Reference. 2 Nov. 2010. Web. 25 May 2011. <http://www.credoreference.com/entry/conscitech/homoptera>.
 “About Whiteflies.” UA Whitefly – Home. N.p., n.d. Web. 25 May 2011. http://whiteflytax.biosci.arizona.edu/about_wf/index.htm
 “Radcliffe’s IPM World Textbook | CFANS | University of Minnesota..” Radcliffe’s IPM World Textbook | CFANS | University of Minnesota.. N.p., n.d. Web. 25 May 2011. <http://ipmworld.umn.edu/chapters/ byrne.htm>