Water limitation and host specificity modulate aphid parasitoid specialization through bottom-up effects

Freshwater resources available for agricultural production are in decline due to global change. Bottom-up forces due to abiotic stress such as water limitation may modulate parasitoid host range by modifying both adult preference and offspring performance defining parasitoid efficiency and safety in biocontrol programmes. In such context, we evaluated the impact of water limitation on 7 plant traits, 3 aphid performance traits, and parasitoid preference and performance of Aphidius ervi when encountering 6 plant-aphid complexes. The majority of the plants tested were smaller, had reduced stomatal conductance, and reduced leaf transpiration and photosynthesis rates under water limitation. The generalist aphids Macrosiphum euphorbiae, Myzus persicae, and Sitobion avenae were negatively affected by water limitation and showed increased generation time and reduced growth rate. By contrast, the specialist aphids Acyrthosiphon pisum, Aphis nerii, and Rhopalosiphum padi were not, or only slightly, impacted by bottom-up effects. Parasitoid choosiness was not drastically affected by bottom-up effects while aphid host suitability for parasitoid offspring development was decreased in the three generalist aphid species tested but not in the specialist ones. Aphid specificity (generalist vs. specialist) was a key factor explaining the bottom-up effect of water limitation on aphid performance and parasitoid efficacy as a biological control agent. Prediction of the impact of global change on the effectiveness of parasitoids could be useful to select the organisms best adapted to environmental conditions.

Automated summary

Freshwater resources for agriculture are decreasing due to global change. Abiotic stress such as water limitation affects parasitoid host range and performance, determining their effectiveness and safety in biocontrol programs. The impact of water limitation on plants, aphids, and parasitoids varies, with specialist and generalist aphids responding differently. Understanding these bottom-up effects is crucial for predicting the effectiveness of parasitoids as biological control agents under changing environmental conditions.