Amino acids as respiratory substrates in aphids:: an analysis of Aphis fabae reared on plants and diets

The fate of radioactively labelled amino acids injected into the haemolymph of the aphid Aphis fabae was investigated. Radioactivity from each of L-[U-C-14]-glutamic acid, L- [U-C-14] -serine and L- [U-C-14]-threonine in the aphid tissues declined exponentially, at rates of 32, 9.3 and 1.0 pmol/aphid/min, respectively. For C-14-glutamic acid, radioactivity lost from the aphids was recovered quantitatively as carbon dioxide, and radioactivity in aphid saliva and honeydew was undetectable. When expressed on a per unit aphid biomass basis, the rate of respiratory loss of glutamic acid from aphids reared on chemically-defined diets was more than double that of aphids reared on the host plant, Vicia faba. It is concluded that respiration is a quantitatively important component to the aphid metabolism of glutamic acid and other amino acids.