NITROGEN RECYCLING IN THE ENDOSYMBIOTIC SYSTEM OF THE PEA APHID, ACYRTHOSIPHON-PISUM

In an effort to investigate the metabolic importance of amide amino acids glutamine and asparagine in the endosymbiotic system of aphids, symbiotic and aposymbiotic pea aphids, Acyrthosiphon pisum, were maintained on a holidic diet, and the effects of omission of these amides from the diet on the aphid performance, in terms of growth and reproduction, were investigated. While omission of amides depressed the growth and reproduction of symbiotic aphids, the omission of glutamine improved the performance of aposymbiotic aphids. In the honeydew excreted by aposymbiotic aphids on the control diet, glutamine and asparagine were the most abundant amino acid constituents, while the honeydew from symbiotic aphids contained these amides only in trace amounts. In addition, aposymbiotic aphids excreted these amides, especially glutamine, even when kept on diets not containing the amides. The tissues of symbiotic and aposymbiotic aphids contained the same level of glutamine synthetase activity. It was suggested that: (1) amides are important nitrogen sources for symbiotic aphids, but not for aposymbiotic ones; (2) aposymbiotic aphids excrete amides as nitrogenous wastes that are reutilized by symbiotic ones.