Biotic and abiotic modulation of drought effects on aphids and plants

Interactions between environmental factors are a major source of ecosystem complexity. Here we re-analyse published data to define the type of relationships between drought and biotic and abiotic factors affecting plants and aphids from molecular to community scales. Out of 329 pair-wise relationships, 55% were additive, 36% antagonistic and 9% synergistic. The type of relationship varied with plant and aphid trait; plant and aphid genotype; timing, duration and intensity of stress in relation to plant and aphid developmental stage; intra- and inter-specific competition; and relations at higher trophic levels. We identify two aspects to make future research in this field more effective. First, frameworks are needed to scale from molecular cross-talk between stresses to the relevant traits: crop yield in agriculture and fitness in nature. Second, experiments require a shift from a nominal (e.g., well-watered, droughted) to a quantitative characterisation of stress, and realistic conditions to avoid artefacts from over-simplified settings, for example, roots confined to pots, insects confined to cages. In the absence of predictive frameworks, interventions in agriculture and conservation are needed that are robust to the uncertainty in the type of relationship, that is, antagonistic, additive or synergistic.