Superparasitism of second instar Ceratitis capitata (Wiedemann) larvae by naive females of Psyttalia concolor (Szepligeti) was compared for a range of three different exposure times of the host to the parasitoid (1-hour, 6-hours and 12-hours) at a constant 1/10 parasitoid/host ratio. In addition, the superparasitism effect on the emerging wasp and host progenies was examined. The percentage of host larvae parasitized ([gtoreq] 1 parasitoid egg/parasitized host) was not significantly different between 1-hour and 6-hours exposure, whereas a difference (F = 5.67; P < 0.05) in the amount of parasitized larvae was found after 12-hours of exposure. The shortest exposure time (1-hour) resulted in the highest level of larvae (32.7%) containing only 1 parasitoid egg (single parasitized hosts). This value was significantly different from the other two values (F = 6.04; P < 0.05), while no significant differences were observed between the percentage of single parasitized hosts recorded at the exposure times of 6-hours and 12-hours (24.6% and 21.4%, respectively). The amount of superparasitized hosts was found to increase with increasing exposure time. Thus the lowest level of superparasitized larvae (4%) was obtained at the minimum exposure time (1-hour), while the amount of superparasitized hosts recorded at the exposure time of 6-hours and 12-hours was 16% and 31.3%, respectively. These values were all significantly different from one another (F = 11.89; P < 0.05). The number of parasitoid progeny obtained at 1-hour and 6-hours was not significantly different (11% and 12%, respectively). In contrast, the highest exposure time resulted in the lowest rate of parasitoid progeny (7.5%). This latter value was significantly different from the other two values (F = 6.90; P < 0.05). Host progeny was found to decrease with increasing exposure times. Thus, 55.5%, 25.3% and 19% C. capitata emergence was observed after 1-hour, 6-hours and 12-hours of exposure respectively. Statistical differences were found between 1-hour and the other two treatments (F = 34.57; P < 0.05), but no differences were recorded between the C. capitata progenies obtained at 6-hours and 12-hours. Overall, it was concluded that P. concolor can successfully parasitize second instar larvae of C. capitata. Moreover, superparasitism of second instar larvae of C. capitata by P. concolor is very common in the given laboratory conditions. The duration of exposure of the host to the parasitoid was found to play a very important role in determining superparasitization of the host. Thus it was observed a high level of single parasitized hosts after the shortest exposure time (1-hour). The percentage of parasitoid progeny obtained after 1-hour of exposure indicates that the laying of a single egg on second instar C. capitata larvae is sufficient to secure a high level of offspring. The same result as regards parasitoid progeny was obtained with 6-hour exposure, but significantly higher host mortality was observed. The finding that the same results were obtained for parasitoid progeny after 1-hour as after 6-hours exposure, at a mean number of parasitoid eggs/parasitized host ranging between 1.1 and 1.49, suggests a possible difference in response of young host larvae as a function of their relative difference in size (3 [plus/minus] 0.3 mm), unavoidable in this experiment. The results of this study suggest the convenience to release the parasitoid in the field when the host population is mostly constituted by first and second instar larvae. none