Proportion of free amino acids during pea aphid development. Free amino acid contents of early, intermediate and late embryos, and in the first larval stage taken at two distinct times of development (early L1 ≤ 6 hours and late L1 ≥ 13 hours). Values (n = 4) are expressed as a percentage of the total amount of amino acids in the different samples. Among the 18 amino acids analysed, only those varying the most (P < 0.0001) and phenylalanine (P = 0.0015), the precursor of tyrosine, are represented. In particular among the significant changes (see Table S8 for details) it is worth noting: a decrease of aspartic acid from 16.3% in the early embryos (EE) to 0.7% in L1 larvae; a glutamic acid decrease from IE (35.2%) to the L1 stages (around 17.4%); an accumulation of tyrosine during development from 1.9% in early embryos (EE) to 12.1% in the late embryo group (LE), accumulation that continues in early first larval stage (17.6%) to decrease rapidly to 6.8% for the late larvae L1.