Transpiration Through the Cuticle of Insects

The cuticle of most insects is an effective barrier to the evaporation of water. Since the work of Kühnelt (1928,1939) it has been known that this impermeability is a property of the outermost layer. It is usually ascribed to the epicuticle—defined as the layer, of the order of 1 μ in thickness, that is not penetrated by the pore canals, contains no chitin, and resists solution in cold concentrated hydrochloric or sulphuric acids. From chemical tests Kühnelt concluded that the epicuticle contained fatty acids and cholesterol-like bodies. He therefore refers to it as a ‘lipoid cuticula’.