The population dynamics of the woolly whitefly,Aleurothrixus floccosus(Maskell), and its parasites on citrus were studied in an interior valley citricultural region of California. The development of populations was followed by leaf sampling and field observation from the initial pest colonization of the study site through 3 consecutive yr. The two major natural enemies found wereCales noackiHoward andEretmocerussp. Early in the study,C. noackidisplacedEretmocerussp. as the dominant parasite present. Parasitism byC. noackiwas responsible for substantial reductions in the whitefly population. High summer temperatures appeared to have a disruptive effect on biological control of the woolly whitefly by inhibiting the increase of parasite populations while pest population growth continued. However,C. noackipopulations recovered during cooler weather and apparently were able to effect rapid suppression of the whitefly outbreak.