Can the plant‐mediated impacts on aphids of elevated CO 2 and drought be predicted?

The effects of drought and elevated CO 2 on the performance of sap‐feeding aphids is considered. It is assumed that, for these stressors, the major influence will act through altering host plant composition and therefore diet. Changes in the plant may affect the ability to locate phloem tissues, while changes in composition of the sieve element forming the aphid diet may have more direct effects. It is concluded that plant response to conditions where carbon is present in excess (elevated CO 2 ) or its consumption is exceeded by its availability (drought) is heterogeneous at the cellular level. The complexities of the response of the plant to components of climate change are paralleled by the diversity of the responses of aphids to drought and elevated CO 2 . Potential control points are discussed and it is concluded that current knowledge, both descriptive and mechanistic, supports the view that it is unreasonable to expect that a single plant component can predict the general response of aphids to climate change. Instead, it is more likely that aphids use a variety of cues when interacting with their host plants, and individual species respond to changes in their diet differently. Further work examining the response of both plant and aphid transcriptome and metabolome will support or contradict this hypothesis.