Quantifying the symbiont contribution to essential amino acids in aphids:: the importance of tryptophan for Uroleucon ambrosiae

A complete amino acid budget was constructed using the aphid Uroleucon ambrosiae (Strecker), feeding on a suboptimal host, Tithonia fruticosa . The availability of amino acids was estimated from phloem analyses and phloem intake rates at each stage of development. Requirements for amino acids were estimated from gravimetric studies and from analyses of body amino acids. Because the budget was found to be well balanced, estimates of specific needs and shortfalls of essential amino acids were calculated, thus quantifying the role of symbiotic bacteria in fulfilling needs for these amino acids. The most dramatic shortfall was for tryptophan, consistent with the amplification of relevant genes in the symbiont.