Local adaptation of insect herbivores to grasses by mediation of the soil community

Background/Question/Methods

Plants are intimately associated with soil microbes and foliar feeding insects. This gives rise to three-way interactions that have important consequences for the functioning and evolution of the organisms involved. While above- and below- ground interactions have received considerable attention over the last decade, the consequences of plant-soil interactions on insect evolution still remains largely unexplored. To shed light on this matter, I addressed experimentally whether insect herbivores could be adapted to local plant populations by mediation of the soil community. Using the dune grass Ammophila arenaria and the aphid Schizaphis rufula, I conducted a reciprocal inoculation experiment comparing the multiplication rate of this aphid species on different plant populations. To test whether the soil community could be mediating this interaction with the aphid, the performance of the insect herbivore was compared for plants grown in sterilized soil, in locally inoculated soil, or with soil inoculated with non-local soil communities. 

Results/Conclusions

The results not only confirm the soil community to be important for aphid performance, but also its origin (i.e. local vs. non-local soil communities). In general, local combinations of plants and soil communities had a greater influence on aphid multiplication than non-local combinations. These results highlight the importance of the soil biota in understanding plant insect interactions from an evolutionary perspective.