Non-reproductive effects of two parasitoid species on the oriental armyworm Mythimna separata on wheat and maize plants

Non-reproductive effects of parasitoids on their hosts and their associated mechanisms are poorly known. We carried out laboratory studies to measure non-reproductive mortality (NRM) and reproductive mortality (RM) caused by two different larval parasitoids to the oriental armyworm Mythimna separata (Walker) that fed on either wheat or maize plants. We then examined non-lethal effects of the parasitoids on developmental performances of the surviving hosts on the two plant species. We found that NRM was as high as RM for Meteorus pulchricornis (Wesmael) while lower than RM for Microplitis mediator (Haliday), on both wheat and maize plants. The exposure of the host larvae to either of the two species of parasitoids had non-lethal effects on the surviving hosts on both wheat and maize plants, impairing some of host developmental performances as measured by larval developmental time, larval body weight, pupal duration, pupal body weight, and adult longevity. These non-lethal effects did not vary between the two parasitoid species: they varied somewhat between the two plant species. The results from the present study suggest that different parasitoid species in the same guild can have different levels of non-reproductive effects on the same host, and such effects may vary somewhat across host’s food plant species.