Hydrophilic Cuticle - The Basis for Water Vapour Absorption by the Desert Burrowing Cockroach, Arenivaga Investigata

Abstract

ABSTRACT A micro-method has been developed for measuring the water content of materials over a range of humidities. A vapour pressure osmometer measures the equilibrium humidity in a sealed chamber containing the sample and an accurately known volume of water. The cuticle of the hypopharyngeal bladders, which are the sites for atmospheric water absorption in Arenivaga, has a water affinity much greater than that of unspecialized cuticle from this and other species. This difference is also found in washed samples. The hydrophilic properties of the bladder cuticle are therefore not due to dissolved salts in the frontal body fluid which is applied to the bladders during absorption in vivo. Dissolved salts reduce cuticle water affinity. The basis for this effect is discussed with reference to known properties of polyelectrolytes. A model of in vivo absorption is proposed. It is suggested that the cyclical addition of frontal body fluid alters the water affinity of bladder cuticle so that condensed water is released. Some of the water is then swallowed.