Technical Abstract: Ambient temperature is an abiotic factor that has been studied extensively in insect biology and population dynamics while relatively little investigations have been carried out on the impact of ambient moisture. Whiteflies cause major agricultural problems in environments ranging from arid to humid climates on a global scale. A study was conducted on the effects of vapor pressure deficit (VPD) on oviposition, hatching, body size, and survival of immature Bemisia tabaci (Gennadius). Comparative tests were conducted among VPD conditions of 0.5, 1.7 and 2.7 kPa to represent low, medium and high VPD environments. All experiments were conducted at 26oC. The study was conducted using the B-biotype sweetpotato whitefly, B. tabaci, which was reared on collard, Brassica oleracea ssp. acephala de Condolle. The rate of oviposition was decreased at the highest VPD treatment when using adults which were obtained from the same colony. Yet, egg hatch was not significantly affected by the treatments even though it tended to be lower at the high VPD treatment. However, the rate of oviposition and survival to the adult stage were decreased at the highest VPD. Sizes of males and females were different, as is well known, but VPD had little significant effect on adult body size (length and width). The size effect was erased when the F1 generations from the different treatments were reared under a common environment. Insect population models that include the most relevant parameters can offer the best estimation of life history events. These results help elucidate the ecology of B. tabaci and indicate that extremes in ambient moisture can have an impact on populations.