RESUMEN
The aphid parasitoid Aphelinus asychis Walker is an important biological control agent against many aphid species. In this study, we examined whether the rearing host aphid species (the pea aphid, Acyrthosiphon pisum and the grain aphid, Sitobion avenae) affect the performance of A. asychis. We found that A. pisum-reared A. asychis showed a significantly larger body size (body length and hind tibia length) and shorter developmental time than S. avenae-reared A. asychis. There was no difference in the sex ratio between them. The longevity of A. pisum-reared A. asychis was also significantly longer than that of S. aveane-reared A. asychis. Furthermore, A. pisum-reared A. asychis presented stronger parasitic capacity and starvation resistance than S. aveane-reared A. asychi. In addition, host aphid alteration experiments showed that A. asychis only takes two generations to adapt to its new host. Taken together, these results revealed that A. pisum is a better alternative host aphid for mass-rearing and releasing of A. asychis. The body size plasticity of A. asychis is also discussed.