This research was about how life history traits were influenced by the nutrient components in the juvenile diet. The aim of this study was to provide more understanding about the function and the purpose of nutrients consumption. The first chapter addresses how essential and non-essential amino acids in the juvenile diet influence the juvenile performance and adult morphological traits. The second chapter addresses the effects of additional vitamin E in the protein-unrestricted juvenile diets on adult fitness and longevity. Both chapters had used Telostylinus angusticollis, neriid flies as the experimental organism. This was because this species is exceptionally plastic in adult morphology to its larval diet. The experimental larvae in the first chapter were raised in the nutrient-poor diet with the combination of extra essential amino acids, non-essential amino acids and sugar. The adult body size and relative head, antenna, wing and foreleg length were boosted by the presence of extra essential amino acids while the relative hind leg length was not affected, but the cost of such benefit was the decrease of larval viability. In contrast, the viability was significantly reduced to almost none by the non-essential amino acids. This may be caused by the large change in pH associated with the addition of non-essential amino acids. The development time was not affected by either essential or non-essential amino acids. The larvae in chapter two were raised in treatments with three levels (1, 3, 5μg/mL) of vitamin E and the presence of an additional amount of protein to the nutrient-poor base diet in the first experiment. The larvae in the second experiment were raised in treatments of the nutrient-poor base diet with the addition of 3μg/mL of vitamin E and the poor base diet as the control. The first experiment provided little evidence of a vitamin E by protein interaction. The second experiment showed that vitamin E itself had a positive effect on body size, but this effect was dependent to the sterilization of the larval environment. The presence of vitamin E in the juvenile diet decreased adult longevity and activity, especially in males. Nonetheless, it did not have any effects on juvenile development time, adult relative head length and adult relative antenna length. In conclusion, the effect of amino acids and the effect of vitamin E on life history traits were complex, indicating a need for further study.