INTRODUCTION:The aphid Rhopalosiphum padi L. is a vector of Barley yellow dwarf virus (BYDV) in wheat and other economically important cereal crops. Increased atmospheric CO2 has been shown to alter plant growth and metabolism, enhancing BYDV disease in wheat. However, the biochemical influences on aphid metabolism are not known. OBJECTIVES:This work aims to determine whether altered host-plant quality, influenced by virus infection and elevated CO2, impacts aphid weight and metabolism. METHODS:Untargeted 1H NMR metabolomics coupled with multivariate statistics were employed to profile the metabolism of R. padi reared on virus-infected and non-infected (sham-inoculated) wheat grown under ambient CO2 (aCO2, 400 µmol mol-1) and future, predicted elevated CO2 (eCO2, 650 µmol mol-1) concentrations. Un-colonised wheat was also profiled to observe changes to host-plant quality (i.e., amino acids and sugars). RESULTS:The direct impacts of virus or eCO2 were compared. Virus presence increased aphid weight under aCO2 but decreased weight under eCO2; whilst eCO2 increased non-viruliferous (sham) aphid weight but decreased viruliferous aphid weight. Discriminatory metabolites due to eCO2 were succinate and sucrose (in sham wheat), glucose, choline and betaine (in infected wheat), and threonine, lactate, alanine, GABA, glutamine, glutamate and asparagine (in aphids), irrespective of virus presence. Discriminatory metabolites due to virus presence were alanine, GABA, succinate and betaine (in wheat) and threonine and lactate (in aphids), irrespective of CO2 treatment. CONCLUSION:This study confirms that virus and eCO2 alter host-plant quality, and these differences are reflected by aphid weight and metabolism.