Population phenologies of the whitefly, Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae), in young cassava crops in Côte d'Ivoire, West Africa, are described for three field seasons. Populations of all stages were consistently greatest 6–12 weeks after the crop was planted. The number of adults on plants as well as on attractive and non-attractive sticky traps displayed cycles of buildup and decline each year, the periodicity of these cycles corresponding to the generation time of B. tabaci under field conditions. Adult population declines were probably caused by emigration from the crop. Rainfall was negatively correlated with both nymph and adult populations, possibly due to reduced oviposition after rain. B. tabaci is the vector of African cassava mosaic geminiviruses (ACMV) and the observed B. tabaci population trends fit well with the pattern of ACMV buildup in the crop.