The present study was conducted to investigate the preferred host age for oviposition by the two parasitoid species and the relationship between parasitoid fitness and host age. The aim was to provide some of the information needed in order to use parasitoid more efficiently in integrated pest management. Interspecific analysis shows that the parasitoid, A. colemani produced significantly more mummies than D. rapae in two and four day old aphid (Myzus persicae Sulzer), whereas D. rapae produced more mummies in six and eight day old aphids. Increasing host age increased the number of mummified aphids, which was more profitable in terms of fitness for D. rapae than A. colemani. Both the parasitoid species are capable of successfully ovipositing in any developmental stage of M. persicae. Yet these species preferred different ages of the host. With this host preference by the two parasitoid species, a better parasitism is expected at the beginning of the aphid infestation season from A. colemani, because of the fact that early stages are more numerous than older hosts are. Whereas at the end of aphid infestation season the better parasitization from the D. rapae should the expected when the older hosts are more numerous than the young ones. none