Transport of Water Vapor by Tenebrionid Beetles. II. Regulation of the Osmolarity and Composition of the Hemolymph

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Abstract
Water content was determined for hydrated and dehydrated larvae of Onymacris marginipennis. In addition, the volume and osmolarity of the hemolymph were measured, as were the major components of the hemolymph: sodium, potassium, magnesium, chloride ions, amino acids, and trehalose. There is a positive linear relationship between the water content (mg H₂O/mg dry weight) and the volume of the hemolymph (μl/mg dry weight). The osmolarity of the hemolymph is regulated between 320 and 450 mosmol/liter. The concentrations of the ions, amino acids, and trehalose are relatively constant despite changes in the volume of the hemolymph. The quantity of each of the major components increases as the volume of the hemolymph increases. These increases account for the observed regulation of the osmolarity of the hemolymph. All the major components of the hemolymph participate in the regulation.