Dear Editor, The pinewood nematode （PWN） Bursaphelenchus xylophilus （Steiner and Buhrer, 1934） Nickle, 1970, the causal agent of Pine Wilt Disease （PWD）, is an invasive species known to have originated from North America, where it was not re- ported to cause large-scale outbreaks （Wingfield et al., 1984）. Ecological conditions encountered by B. xylophilus in China are different from conditions in its native North American range. Ecological differences, together with short generation times, improve the chances that changes in developmental traits may occur during lengthy invasive processes.
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 E and Myzuspersicae (Suzler),and quantified self superparasitism and self superparasitism versus parasitism ratio for the four:combinations ofparasitoid 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.
