Amino acid composition of phloem sap and the relation to intraspecific variation in pea aphid ( Acyrthosiphon pisum) performance

Abstract

The performance of five clones of the pea aphid, Acyrthosiphon pisum, was evaluated on red clover, Trifolium pratense, alfalfa, Medicago sativa, broad bean, Vicia faba and five genotypes of pea, Pisum sativum. Phloem sap samples were collected from excised aphid stylets on plants of each species and analysed for amino acids. The pea aphid clones displayed large differences in performance patterns on the plant species, but more uniform patterns on the pea genotypes. Performance patterns of the aphid clones were related to the host plant species from which they had been collected originally. The total concentration of amino acids varied considerably between phloem samples, but there were no significant differences in the means between plant species or pea genotypes. Plant species differed distinctly in their amino acid composition, whereas pea genotypes did not. Several of the amino acids were present in similar compositions in all plant species and pea genotypes. The total concentration of amino acids in the phloem sap could not explain the differences in the performance of pea aphid clones on pea genotypes. However, differences in the performance of two out of five of the pea aphid clones could be explained by a part of the amino acid composition.