Transpiration and the Structure of the Epicuticle in Ticks

Abstract

The passage of water through the cuticle of living ticks is greatly influenced by the activities of the underlying epidermal cells. In a previous paper (Lees, 1946) it was shown, for example, that unfed ticks reach a state of equilibrium at a relative humidity of about 90%; and if their water balance is depleted they will take up water through the cuticle when exposed to higher humidities. Furthermore, although exposure to humidities below the equilibrium results in water loss through the cuticle, evaporation is much less rapid than it becomes subsequently if the tick is killed or asphyxiated. It was therefore argued that at low humidities secretion assists in the retention of water. These active processes are only well developed in the unfed tick and become imperceptible after the blood meal has been ingested.In considering the mechanisms involved in the exchanges of water through the cuticle the assumption was made that, in addition to active secretion, the passage of water, and particularly its retention, is also influenced by the presence of lipoid material in the cuticle. Ticks show great diversity in their powers of resisting desiccation, and this was thought to be accounted for by the specific nature of the waterproofing lipoid. Nevertheless, no direct evidence of such a component was advanced in this paper.