Green peach aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae), is a serious and global pest of vegetables and greenhouses. Developing a strategy for the control of this pest and creating a mass-rearing program of its parasitoid wasp Aphidius platensis (Hymenoptera: Braconidae) requires that host plant preference, host stage preference and switching of A. platensis were investigated. Host stage experiment and switching carried on using third and fourth instar green peach aphid nymphs and host plant preference was studied by sweet pepper and eggplant as host plant for M. persicae. All experiments were conducted at 25 ± 1°C, 70 ± 5% RH and 16:8 h L:D photoperiod. Data analysis showed that A. platensis parasitized all nymphal stages of M. persicae, however it preferred third and fourth green peach aphid nymphs. Furthermore, it was shown that the parasitism rate of A. platensis on pepper-reared aphids (85.5%) was significantly higher than eggplant- reared aphids (28.5%). It was also shown that the number of parasitized nymphs varied at different ratios of host stages (mixture of third instar and fourth instar nymphs) and the number of hosts parasitized increased with increasing the contribution of that stage in host stage ratio. These results revealed could be useful to develop a mass-rearing program of A. platensis.
