Haemolymph amino acids and related compounds during cocoon production by the larvae of the fly, Rhynchosciara americana

A qualitative and quantitative analysis of free amino acids and related compounds in the haemolymph of Rhynchosciara americana was carried out for different periods of the fourth larval instar. Threonine, serine, proline, and glutamic acid make up 50 per cent of the total free amino acids in R. americana haemolymph just before the larvae start spinning the communal cocoon; after this the titre of most of the amino acids declines continuously. There are few peptides but these are present in high titres; they consist of two to three amino acid residues, of which the most important are histidine and aspartic acid. The fall in the haemolymph amino acid and peptide titres is insufficient to account for the silk protein which accumulates on the communal cocoon during the same period. The results are consistent with a silk protein origin from haemolymph proteins and haemolymph free amino acids. The origin and metabolic rôle of some haemolymph ninhydrin-positive compounds are discussed.