Free amino acids, ions, and osmotic pressure of the hemolymph of three species of blackflies

Analysis of haemolymph samples from field-collected larvae of Simulium venustum Say, S. vittatum Zett. and either Prosimulium mixtum Syme & Davies or P. fuscum Syme & Davies or a mixture of the two showed the haemolymph of all species to be essentially similar with respect to amino-acid pool, ionic composition and osmotic pressure. A variety of ninhydrin-positive substances was recorded from the blood of all species. The most abundant amino acids were glutamic acid (and its amide glutamine), alanine, proline, glycine, serine, histidine, phenylalanine (and derivative dihydroxyphenylalanine) and lysine. Phosphatide components and several specialised amino compounds normally associated with higher plants and vertebrates were present in the haemolymph. The ionic composition was atypical for Diptera, as potassium and calcium were relatively abundant. Sodium was found to be the major cation in the haemolymph of all 3 species. The osmotic pressures of the blood samples were within the range of values recorded for other aquatic Diptera..