Biological characteristics (oviposition and survival rates) and esterase banding patterns were investigated to evaluate the extent of variation among three test populations of Bemisia tabaci Gennadius (Homoptera. Aleyrodidae). In terms of reproductive capabilities, whiteflies from the cotton (Gossvviurn hirsutum L.) and pumpkin (Cucurbita maxima Duchesne) populations performed similarly on the three host plant species tested. Both populations, which originated from the same wild-type field population, reproduced to higher levels on either cotton and pumpkin hosts than on a poinsettia (Euahorbia vulcherrirna Willdenow) host. In contrast, whiteflies from the poinsettia population differed from cotton- and pumpkin-reared populations in that reproductive capabilities were relatively similar for the three host species tested. For whiteflies from pumpkin and cotton populations a similar and characteristic esterase banding pattern ("A-type") was observed, while whiteflies from the poinsettia population yielded a different banding pattern ("B- type"). In transmission studies, whiteflies from cotton or pumpkin sources did not induce silverleaf (SL) or white stem (WS) symptoms in Cucurbita spp. tested. In contrast, poinsettia population whiteflies were routinely associated with SL and WS symptom phenotypes which developed in Cucurbita spp. following exposure to whitefly adults. From these data, it is possible to correlate a specific esterase banding pattern (A or B) with reproductive capabilities and either the ability or inability to induce SL and WS symptoms.