UTILIZATION OF AMMONIA AS A NITROGEN-SOURCE IN THE SILKWORM, BOMBYX-MORI

This study evaluated the relative effectiveness of ammonium salt in co mparison to non-essential amino acids for growth of the silkworm larva e, Bornbyx mori. Newly ecdysed 5th-instar larvae were fed chemically d efined diets containing only the ten essential amino acids supplemente d with diammonium citrate (DAC), potassium glutamate (K-Glu) or a mixt ure of acidic plus non-essential amino acids (NEA), Alterations in lar val growth and the haemolymph components as a result of the supplement ed diet were used to investigate the utilization of nitrogen sources b y this species, Promotion of growth of larvae and silk glands was achi eved by the addition of DAC or K-Glu, but NEA was most effective, Haem olymph protein content increased with increased levels of nitrogen in the supplemented diet, The composition of free amino acids in the haem olymph was altered as the level of DAC or K-Glu in the diet increased, Among the essential amino acids, valine, methionine, isoleucine, leuc ine and phenylalanine decreased, whereas almost all non-essential amin o acids except for tyrosine and ornithine greatly increased, To confir m that dietary ammonia was used as a nitrogen source, 5th-instar larva e were fed a diet containing N-15 ammonium acetate, Mass spectroscopic analysis revealed that a large amount of N-15 was incorporated into l arval protein fractions, especially the silk glands, These results ind icate that dietary ammonium nitrogen is converted by silkworm larvae i nto amino acid nitrogen and utilized for protein synthesis in the same manner as nonessential amino acids. Copyright (C) 1996 Elsevier Scien ce Ltd