The Systematic Entomology Laboratory (SEL), a laboratory of the Plant Sciences Institute (PSI) at the Henry A. Wallace Beltsville Agricultural Research Center (BARC) , belongs to the Agricultural Research Service (ARS), which is the main in-house research arm of the United States Department of Agriculture (USDA).

    Whiteflies (family Aleyrodidae) belong to the group of insects called the Sternorrhyncha.  This group includes other economically important insects such as scales (Coccoidea), aphids (Aphidoidea), and jumping plantlice (Psylloidea).  Whiteflies are not only injurious to their host plants through feeding, but are also capable of transmitting numerous plant-viral diseases.  Worldwide, there are approximately 1,200 described species of whiteflies.  Adults are minute insects, 2-3 mm in length.  The body is either pale, partially pigmented, or completely pigmented.  The two pairs of wings have reduced venation and are covered with white powdery wax.  The wings are either completely pale or with brown markings, or greyish brown with pale markings; some species have reddish pigments in a pattern.  The body is completely covered with minute spinules.  Antennae are elongate and are 7-segmented.  The compound eyes are either completely divided into dorsal and ventral eyes or are joined by one ommatidium.  Mouthparts are elongate and developed for piercing and sucking plant tissue.  

    Whitefly eggs are ovoid and have a pedicel.  Eggs are inserted either into the plant stomata or in a cut in the leaf surface that has been made with the ovipositor.  Eggs may be scattered on the plant or laid in a distinctive pattern such as the spirals of the citrus blackfly, Aleurocanthus woglumi Ashby.  First-instar larvae have developed legs and are the only mobile instar.  The legs of the second instar, third instar, and fourth instar are reduced.  The fourth instar is also known as the "pupal case" or "puparium."   It is within this structure that the adult whitefly develops and from which it later emerges.  Although immature whiteflies are often mistaken for soft scales (Coccidae), they can be distinguished from other sternorrhynchous insects by the presence of structures such as a vasiform orifice, an operculum, and a lingula.  Larvae and pupae of some species are either covered or fringed with various types and forms of wax, while others are devoid of wax. 

    Taxonomy of the whiteflies is based almost entirely on characters found on the pupa.  After specimens are mounted on microscope slides, pupal characters can be studied with a high-powered microscope.  The U.S. National Collection of Aleyrodidae is maintained by the USDA's Systematic Entomology Laboratory but is part of the Smithsonian's National Museum of Natural History. This collection represents one the world's best collection of whiteflies.  It includes more than 1,000 species represented by over 32,000 specimens mounted on microscope slides, an extensive collection of dry-preserved material, and over 300 types.

 Last updated:  5 July 2001