The influence of salinity on the cuticular permeability of Cenocorixa bifida hungerfordi Lansbury (Hemiptera: Corixidae)

Abstract

The cuticular permeabilities of individual Cenocorixa bifida hungerfordi Lansbury collected over a wide range of salinities were determined. Corixids from low salinity water (0–2000 μmhos∙cm−1 surface conductivity at 25 °C) exhibited low cuticular permeability, whereas those from moderately saline water bodies (7000 – 11 000 μmhos∙cm−1) were much more permeable. However, at higher salinities cuticular permeability was again low; corixids from a lake with a surface conductivity of 16 000 μmhos∙cm−1 (approximately half that of seawater) had cuticular permeabilities comparable with those of corixids from freshwater lakes. This phenomenon was shown to be acclimatory, since permeability decreased over time when corixids from moderately saline lakes were placed into distilled water. The biological reasons for these results are not clear, but it appears that cuticular permeability of C. bifida increases as problems of ion regulation diminish, and then begins to decrease, seemingly at the salinity at which it becomes difficult for the corixid to maintain a constant haemolymph osmotic pressure. The biological implications of this phenomenon are discussed.