The strain B sweetpotato whitefly (SPWF) (Bemisia tabaci) became a predominant pest in the Lower Rio Grande Valley of TX on vegetables, ornamentals and various agronomic crops in 1990-1992. Cotton (Gossypium spp.) production in the Lower Rio Grande Valley occurs during the warmest period of the year and in relatively large acreage (300,000 to 400,000 acres) compared to other host crops for the SPWF. Consequently, the populations of SPWF in the summers of 1991 and 1992 were associated with cotton crop development. Conversely, decline in SPWF populations in the fall and winter of 1991 and 1992 began after cotton stalk destruction and was associated with smaller acreage of available host crops and cooler weather in the fall of both years. Crop sequencing appears to play a critical role in SPWF population dynamics.