The reproductive potential of Microplitis rufiventris Kok. females resulted from Spodoptera littoralis (Boisd.) larvae topically treated by a constant dose (70 mu g/5 pl) of the growth regulator precocene II at different intervals of post-parasitism was studied in the laboratory. The obtained results showed that the effects of PII vary according to the timing of treatment relative to larval development of the parasitoid. Reduction in reproductive capacity of the parasitoid occurred when PII was applied on host larvae containing young parasitoid larvae. Workers should be aware from the delayed effects of precocenes which may occur in later stages of the non-target insects. none