The sweetpotato whitefly (SPWF) has become an increasingly severe problem of cotton in the desert Southwest. It reached severely damaging levels in most of western and central Arizona in 1992. Key factors identified as contributing to the problem in cotton are: mild winters (permitting greater survival), the new biotype B (or species?) with an expanded host range, and the year-round sequence of suitable hosts (both cultivated and weeds), thus, providing the bridge which permits populations to cycle from cotton season to cotton season by continuing to reproduce, albeit more slowly on less suitable hosts and in winter. The major cultivated hosts of the SPWF during the non-cotton season are vegetable crops such as broccoli, cauliflower, lettuce, and melons, particularly cantaloupes. Alfalfa is also a large-acreage crop which can serve as a host during the "off-season". Additionally, numerous weeds such as the mallows (alkali, Globe and Little), London rocket and spiny sowthistle provide host sites for overwintering populations.