Effects of host plant resistance on insect pests and its parasitoid: A case study of wheat-aphid–parasitoid system

Host plant resistance can effectively reduce pest insect populations, but a concern is whether plant resistance could also negatively affect the natural enemies of the insect pests. In this paper the effect of three wheat cultivars on the population of an aphid species, Sitobion avenae (F.) and it’s parasitoids, Aphidius spp., were investigated in the field experiments in 2004 and 2005. Percentage of parasitized aphids at peak sampling date was also recorded. Both the aphid and parasitoid populations varied in the three wheat cultivars at the sampling dates. The density peak of parasitoid population in all the three wheat cultivars was 9–12 days behind the density peak of the aphid population. At the population peaks both the aphid and parasitoid densities were significantly higher in the susceptible than in the resistant cultivars. Furthermore, the accumulative parasitism was significantly higher in the resistant than in the susceptible cultivar, and level of resistance of the wheat cultivars had no effect on aphid mummy weight parasitized by A. spp. These results suggested that the host plant resistance against aphids enhanced the parasitism of aphid species S. avenae (F.) by its parasitoid A. spp. in wheat field.