Reproductive failure and the free amino acid pools in pea aphids ( Acyrthosiphon pisum) lacking symbiotic bacteria

Abstract

Pea aphids ( Acyrthosiphon pisum) treated at birth with the antibiotic, rifampicin, to disrupt the symbiotic bacteria (i.e. aposymbiotic aphids) grow very slowly. The growth of embryos in the aposymbiotic aphids was particularly depressed, such that, by adulthood, the embryo fraction represented 65% of the total protein in symbiotic aphids, but just 12% of the protein in aposymbionts. Profile analysis of the free amino acid pools of the aphids and their embryos indicated that the concentrations of the aromatic amino acids phenylalanine and tryptophan were very low in the embryos of aposymbionts, and it is proposed that these amino acids may limit embryo growth in aposymbiotic aphids. There are also indications that lysine may be limiting to the growth of the maternal tissues of 4-day-old larval aposymbionts, and methionine may be in short supply in older aposymbiotic aphids.