| Abstract: | Many experiments have tested the hypothesis that stress‐induced changes in plant quality enhance insect performance. Data available for insects feeding on woody plants indicate that phloem‐feeding insects’ response is stronger (i.e. enhanced performance) than that of chewing leaf‐feeding insects. However, with the exception of one study, performance data for these two insect groups emanate from separate experiments. Here we report on the performance of a phloem‐feeding aphid (Cinara costata) and larvae of a folivorous sawfly (Gilpinia hercyniae) feeding on drought‐stressed mature Norway spruce (Picea abies). Sawfly larvae did not survive or grow any better on drought stressed trees than on control trees. Surprisingly, there was no significant difference in the build‐up of aphid densities between trees of the two treatments, in contrast to most other stress experiments. Our experiment involved mature trees, while most other studies have used seedlings. It is possible that there are fundamental differences between seedlings and mature trees in their response to environmental stress. Possible mechanisms for such differences are discussed. |
