Abstract
Changes in the concentrations of free amino acids, sugars and cations in the hemolymph of Bombyx mori were examined in relation to the change of hemolymph osmotic pressure during the fifth instar of larval development. The osmotic pressure of about 280 mOsmol/kg at day 0 increased to about 320 mOsmol/kg at day 5, then rapidly declined to about 240 mOsmol/kg at day 9. The concentration of amino acids also increased until day 5 and then began a decline parallel to the change in the osmotic pressure. Among the major amino acids in the hemolymph, the concentrations of threonine and histidine changed during development, whereas those of serine and glycine did not. The contribution of sugars to the osmotic pressure was small compared with that of the animo acids. The concentration of sodium ions began to decrease at day 4, prior to the decrease in the osmotic pressure and in the concentration of amino acids. The concentrations of potassium, magnesium and calcium remained relatively constant during the fifth instar. These results indicate that the change in the osmotic pressure during silkworm development is mainly attributable to the change in the concentration of amino acids.
