Developmental rates from egg to adult for a uniparental race ofEncarsia perniciosi(Tower), an endoparasitoid of the San Jose scaleQuadraspidiotus perniciosus(Comstock), were determined using first instar hosts at 20°C, and using second instar hosts at 15, 20, 25, 28, 29.5, and 31°C under a regime of 16:8 (L:D) photoperiod. Parasitoids developed in male and female San Jose scale. Development rate was highest in male second instars, intermediate in females second instars, and lowest in first instar nymphs. Temperature versus development rate data were used to estimate parameters for both linear and nonlinear models of parasitoid development in male, female, and male and female hosts combined. Simulated adult flight peaks, based on linear and nonlinear models, were compared with peaks of adult parasitoid activity in three orchards during 1986 and 1987, and adult activity was measured using San Jose scale pheromone-baited and colored sticky traps. Modeled peaks agreed well with the spring flight peaks (F2and F3), but were generally earlier than peaks occurring during the summer generations (F4and F5) and later than those of autumn generations (F6and F7). The linear model for parasitoids developing in male and female hosts combined simulated 8 of 13 parasitoid peaks within ±7 d, whereas the nonlinear model was accurate for 7 of 13 peaks. Up to seven parasitoid flight periods per season were detected.