In the current context of climate change insects are tracking the increase of temperature along the elevation gradient consequently, the fragile alpine plant flora will not only have to cope with climatic disruption but also with an increase of the herbivory pressure. In this project we are investigating the trophic interactions between grasshoppers and their food plants and we use this knowledge to predict the future of alpine plant communities under higher herbivory pressure. We selected our study sites along six elevational gradients in the Swiss Alps. at each of these sites we take measurements of environmental variables and perform vegetation surveys. To document the plant-insect-interaction networks we survey grasshoppers on the field and collect their feces. After having released them, we bring the faeces sample to the lab to analyse the plant DNA they contain using a technique called DNA metabarcoding. The first step of this lab procedure consists in extracting plant DNA from the insect feces. The ITS2 plant genetic marker is then amplified by a PCR and the success of the PCR is verified with an electrophoresis. After a few additional preparatory steps, the DNA is ready to be sequenced on the Illumina sequencing platform. DNA sequences are cleaned and sorted using bioinformatic tools and the sequences of each faeces sample are attributed to plant species. This is how networks can be reconstructed. The structure can then be compared along the elevation gradient. But describing network variation won’t be enough to predict the future interaction. We also have to understand them. This can be done by testing the match between plant and insect functional traits at both mechanical and chemical levels. To test these relationships at the mechanical level we measure different plant functional traits associated with leaf structural resistance and we quantify grasshopper mandibular strength. Finally, we evaluate the matching of these traits and how this relates to the insect diet. Similarly, to address this question at the chemical level we analyse the chemical plant defenses and the richness of the insect microbiome and then we test if a richer microbiome is associated with the ingestion of more toxic plants. Using this information, we aim at predicting the interaction between the alpine plants and the lowland migratory grasshoppers to forecast the future of alpine plant communities under climate change.