Osmoregulation in the Larvae of Odontomyia cincta (Diptera: Stratiomyidae)

Larvae of Odontomyia cincta tolerate osmotic concentrations ranging from 3 to 5,415 mOsm. Hypoosmotic regulation occurs above an external osmotic concentration of 290 mOsm; hyperosmotic regulation occurs below an external osmotic concentration of 270 mOsm. Animals subjected to hyperosmotic stress (4-5,415 mOsm) lost 35% of their original weight within 48 days; animals subjected to hypoosmotic stress (5,415-4 mOsm) maintained their original weight. The hemolymph osmotic concentration accounted for by sodium ranged from 27% to 37%; there is no correlation between these percentages and external osmotic concentration. The hemolymph osmotic concentration accounted for by chloride between external osmotic concentrations of 30 and 5,415 mOsm ranged from 25% to 36%; these percentages are not correlated with external osmotic concentration. However, in animals acclimated to 3 mOsm, chloride accounted for only 17% of the hemolymph osmotic concentration. There is no correlation between external osmotic concentration and the concentration of hemolymph amino acids. There was no difference in the content of tissue free amino acids in animals acclimated to either 3 or 5,415 mOsm; thus cellular volume regulation is not mediated by free amino acids.