There are a number of signifi cant reasons why many more of the 1,200 described species of whitefl ies (Homoptera: Aleyrodidae) (Mound and Halsey 1978) deserve attention. Nevertheless, few have been the subjects of careful examination. This is likely because many of the unstudied species are found in remote habitats or because they lack economic impact. Most that have been examined do have economic importance. Consequently, one

of the best studied species is the cotton, sweet potato or tobacco whitefl y, Bemisia tabaci (Gennadius).1 This is because B. tabaci is one of the principal insect pests found on plants grown for food and fi ber (Byrne et al. 1990). Most of these hosts are herbaceous. B. tabaci causes problems as a result of direct feeding damage (Riley and Palumbo 1995) and by acting as a vector of several viral pathogens, e.g., squash leaf curl virus, tomato yellow leaf curl virus and lettuce infectious yellows virus (Brown and Nelson 1986, Duffus 1996). Additionally problems resulting from the deposition of B. tabaci honeydew (excreta) and the associated sooty mold fungi (i.e., stickiness and staining) have become critical for growers (Hector and Hodkinson 1989). Finally, its feeding results in a plant disorder known as squash silverleaf with certain members of Cucurbitaceae (Costa et al. 1993). Other species, e.g., the greenhouse whitefl y, Trialeurodes vaporariorum, is also considered signifi cant crop pests of herbaceous crops, in some situations (Johnson et al. 1992).