The effects of abiotically induced changes in host plant quality (and morphology) on a salt marsh planthopper and its parasitoid

1. In this study, the effects of shading and fertilisation on the density of the salt marsh planthopper Pissonotus quadripustulatus (Homoptera: Delphacidae), which is monophagous on Borrichia frutescens (Asteraceae), were assessed. The effects of these abiotic factors on the rate at which Pissonotus eggs were parasitised by Anagrus sp. nr armatus (Hymenoptera: Mymaridae) were also examined. 2. Field plots were shaded by shade cloth suspended above the plots, and fertilised by the application of NH4NO3 fertiliser. Both shading and fertiliser increased plant foliar nitrogen levels significantly. Both shading and fertiliser also increased the density of Pissonotus, presumably because of their effect on plant quality. 3. In addition, both shading and fertiliser increased the percentage of Pissonotus eggs parasitised by Anagrus. This increase in parasitism is probably attributable to changes in host plant morphology induced by the treatments. 4. The results of this study suggest that in stressful environments such as salt marshes, changes in the abiotic environment may play an important role in shaping the community by directly affecting organisms on multiple trophic levels.