An aboveground–belowground herbivore interaction in a woody perennial crop and its response to elevated atmospheric CO2

Interactions between aboveground and root-feeding herbivores can be influenced by changes in plant traits, such as tissue chemistry and morphology. Environmental heterogeneity and perturbations also affect these plant-mediated interactions. Climate change is a multi-faceted phenomenon; increases in atmospheric carbon dioxide (CO2) concentrations lead to increased global mean temperature and an associated higher frequency of extreme weather events. These factors can potentially perturb ecosystem function by altering both plant–herbivore and herbivore–herbivore interactions. A detailed understanding of whether above–belowground interactions are affected by climate change remains lacking. In an attempt to fill knowledge gaps in this understudied area of ecology, this thesis investigates, through a series of glasshouse experiments, the effects of elevated CO2 and other aspects of climate change, such as altered phenology, on the interspecific interaction between the aboveground large raspberry aphid (Amphorophora idaei) and the root feeding larvae of the vine weevil (Otiorhynchus sulcatus), mediated by the shared raspberry (Rubus idaeus) host-plant. Under ambient climate conditions, reciprocal feeding facilitation was observed to occur between aphids and vine weevil larvae feeding on raspberry, with the presence of one increasing the abundance of the other herbivore, and vice versa. This occurred regardless of plant cultivar and order of herbivore arrival on the plant. It is likely that this facilitative relationship is driven by over-compensatory plant growth in response to herbivory. Although tougher, adult vine weevils show a feeding preference for leaves grown in elevated CO2. Herbivory may be more influential than CO2 in determining plant–herbivore interaction outcomes. Aphids affect plant intraspecific competition to a greater extent than elevated CO2 by altering plant biomass of both infested and non-infested plants. In conclusion, this particular plant–herbivore system would seem to be relatively robust in the face of possible future CO2 concentration scenarios