Young adults ofOoencyrtus kuvanae(Howard) were held at different photoperiods and periodically supplied with gypsy moth,Lymantria dispar(L.), eggs while their progeny production and longevity were noted. Females reared at 10:14 (L:D) and 12:12 photoperiods produced fewer progeny but lived longer than those held at 14:10 or 16:8 photoperiods. Switching females from a 10:14 to a 16:8 photoperiod after 12 days (or vice versa) did not influence progeny production; females continued to reproduce as they would have if photoperiods had not been changed. This suggests that the initial photoperiod environment of the adult is important. Dissections showed that number of mature eggs in ovaries of females held at a 16:8 photoperiod increased more than that in ovaries of females held at a 10:14 photoperiod, corroborating progeny production results. Females preconditioned to long or short photoperiods for 2 weeks did not differ in longevity when held subsequently at low temperatures.