Natal rearing experience of animals may affect their behaviors,such as habitat selection and oviposition decision.As part of the overall fitness of insect parasitoids,successful host discrimination (distinguishing parasitized hosts from unparasitized hosts)is of paramount importance.In this study we examined whether and how parasitoids’ natal rearing experience would affect their host discrimination ability according to host availability.We established separate colonies ofAphidius gifuensis Ashmead by continual rearing on two hosts,Sitobion avenae F.and Myzus persicae (Suzler),and quantified self superparasitism and self superparasitism versus parasitism ratio for the four combinations of parasitoid colonies and host species (S.aveane and M.persicae) at four host densities (30,50,100 or 150 per plant).Results showed that self superparasitism ofM.persicae by A.gifuensis reared on S.avenae was significantly higher than by those reared on M.persicae,no matter whether the host densities were 30,50,100 or 150.Aphidius gifuensis reared on M.persicae significantly superparasitized more S.avenae than those reared on S.aveane only when host density was 30.Self superparasitism versus parasitism ratio of A.gifuensis from both colonies was always lower on natal hosts than on new hosts,and the difference was more pronounced as the host density decreased.These results suggested that natal rearing effects is important on host discrimination and oviposition decision of the parasitoid A.gifuensis.These effects promoted the parasitoid’s host adaptation and made them confer greater fitness.