Using metabolic fingerprints to study insect-plant interactions

Metabolic fingerprinting is a biochemical method that takes an untargeted approach to measure a large number of metabolites and gain a ‘snapshot’ of an organism’s metabolome at a specific time. This thesis explores how metabolic fingerprinting can be used to study plant-insect interactions using Pieris rapae and its larval host plant species as model systems, and investigates how biotic and abiotic factors shape plant and insect metabolomes. I found that different Brassicales host plant species, as well as P. rapae larvae feeding on these plant species, had different metabolic fingerprints. A group of very abundant metabolites in the host plant Cleome spinosa were present in larvae feeding from this plant species, documenting a new occurrence of metabolite transfer between plants and insect herbivores. There was some evidence that the metabolic fingerprints of plants predicted the performance of insects, implying that the presence or absence of specific metabolites in host plants may determine the success of herbivores. Changes in metabolites measured in three host plant species following herbivory by P. rapae showed that herbivory changed the metabolic fingerprints of plants but there was little overlap in metabolites that were induced. I conclude that plants respond in a species-specific manner to herbivory, which implies that the evolution of plant defences has varied among the three species resulting in no similarities in induced metabolites. The metabolic fingerprints of the host plant Brassica oleracea as well as P. rapae larvae were changed by elevated temperature and to a lesser extent by elevated carbon dioxide (CO2). The larvae developed more quickly under elevated temperature but larval performance was not affected by elevated CO2 despite the diet of B. oleracea leaves grown under elevated CO2 containing less nitrogen. These findings provide a unique metabolite perspective of insects and plants and were facilitated by the wide breadth of metabolites studied using metabolic fingerprinting.