An improved water content model for Periplaneta cuticle: Effects of epidermis removal and cuticle damage

All previously reported integumental permeabilities to water for Periplaneta at 20°C have been shown to be overestimates by at least an order of magnitude. Cuticle damage, apparently due to mechanical contact, is a common occurrence in cockroach cultures. Damage is increased by handling during experimental manipulation. Repair of the damage is readily observed in isolated individuals as cuticle permeability declines over a few days. Repaired cuticle permeability is not humidity dependent, but damage affecting a few per cent of the cuticle area, renders it so. Cuticle-water contents are slightly influenced by sex related size differences. Cuticle-water contents are unaffected by variations in ambient activity. Epidermal removal initiates a drop in cuticle-water content, apparently not involving active processes. Cuticle-water contents can be accurately predicted in any ambient vapour pressure using a two-layered model combining equilibrium water contents and component permeabilities. Incorporating a parallel unprotected endocuticle pathway into the model successfully simulates the observed humidity dependence of damaged permeabilities. Epidermal permeability cannot be less than 2× 10⁻⁵ cm.s⁻¹; 2000 times more permeable than the overlying cuticle.