A quantitative analysis of the osmolytes in the hemolymph of the larval gypsy moth, Lymantria dispar

In spite of the growing number of in vitro studies conducted with the gypsy moth there are no reports which describe its hemolymph composition. For this reason we have conducted a quantitative analysis of the osmolytes in the hemolymph of the fifth-instar gypsy moth larva reared on a wheat-germ diet. The osmotic pressure of hemolymph is 313 mOsm/kg water and the hemolymph pH is 6.6. The dominant inorganic cations are potassium (29.1 mM), magnesium (25.9 mM), calcium (6.8 mM) and sodium (5.0 mM). The dominant inorganic anions are chloride (14.9 mM), sulfate (12.3 mM), and phosphate (5.7 mM). The electrical conductivity of the hemolymph (4.52 ms/cm) is equivalent to the conductivity of a 98.8 mOsm/kg water NaCl solution. Since the sum of the measured hemolymph cations and anions approaches this osmolality, more than 200 mOsm/kg water of hemolymph solutes are non-electrolytes. Among these non-electrolytes we have identified 18 amino acids (112.0 mM), trehalose (21.1 mM), glucose (2.4 mM) and urea (4.8 mM). Organic solutes such as arginine (0.9 mM), histidine (3.9 mM), lysine (13.9 mM), tyrosine (2.5 mM), aspartic acid (0.3 mM), glutamic acid (1.6 mM), organic phosphates (29.6 mM) and uric acid (0.2 mM) are expected to exist in ionized forms at the hemolymph pH. Together the identified electrolytes and non-electrolytes account for nearly 85% of the measured hemolymph osmolality.