Development of the sweetpotato whitefly, Bemisia tabaci (Gennadius) was studied on in-field cotton plants at the University of California's Imperial Valley Agricultural Research Center in 1984 and 1985, using clip cages to restrict insect movement in or out of the infested leaf areas. Counts of eggs and nymphal instars from the cages were made every 2 to 4 days. These values were plotted in terms of physiological time. Accumulated-degrees days ( D) between developmental thresholds of 10 C (min.) and 32 C (max.) were calculated using the double-sine-wave method. B. tabaci developmental stages studied were eggs, 1st through 4th instar nymphs, and empty pupal cases which represents emergence of adults. Developmental rates for both years followed very similar patterns. Developmental rates for the period from egg to adult stage in this study were comparable to earlier observations of generation times from peaks in adult activity in several cotton fields over a three year period.