Nutritional Evidence for the Absence of the Complete Ornithine-Urea Cycle in the Insect, Argyrotaenia velutinana (Lepidoptera: Tortricidae)

Abstract

Studies were made of the ornithine-urea cycle in the plant-feeding insect, Argyrotaenia velutinana (Walker), by replacing dietary arginine with intermediaries involved in the cycle. Axenic rearing on graded concentrations of arginine showed that arginine is a dietary requirement. This was in agreement with previous studies using the radioactive tracer technique which demonstrated that arginine was not synthesized by the insect. Likewise, the optimum dietary concentration of arginine found in this study was between 0.10 and 0.15% at a 2.0% dietary amino acid mixture level, which agreed with previous studies of the dietary quantitative amino acid requirements based on the pattern of amino acids found in the carcass of the insect. The dietary arginine requirement could be satisfied by substituting twice the equimolecular amount of citrulline: ornithine, creatine, or guanidoacetic acid could not replace arginine. Biological studies resulting from axenic rearing for three successive generations on a diet in which citrulline replaced arginine indicated that the conversion of citrulline to arginine was nutritionally adequate to satisfy the requirements for growth, development and reproduction of the insect.