Whiteflies are an economically important group of insects infesting a wide range of host plants. The whitefly egg has a stalk or pedicel at one end, with which it attaches itself to the leaf. Some polyphagous whitefly species vary in their puparia depending on the host plant cuticle on which they develop, and this has caused a considerable amount of misidentification. Vasiform orifice on the dorsal surface of the caudal segment of the abdomen is characteristic of the Aleyrodidae, and within the family, it is taxonomically diagnostic because it varies in shape according to the species. Most whitefly species have a narrow range of host plants, but the ones that are considered pests may feed on and damage many vegetable and field crops, greenhouse, and nursery crops and house plants. Advances in molecular biology as well as new techniques enabling the discovery of morphological characters will further assist in the resolution of problems in whitefly systematics.