Effects of lipid phase transitions on cuticular permeability: Model membrane and in situ studies

The role of lipid physical properties in cuticular water loss was examined in model membranes and intact insects. In model experiments, pure hydrocarb ons of known melting point (T-m) were applied to a membrane, and the effect s of temperature on permeability were quantified. Arrhenius plots of permea bility were biphasic, and transition temperatures for water loss (T-c) were similar to T-m. In grasshoppers Melanoplus sanguinipes, changes in cuticul ar mater loss were measured using flow-through respirometry. Transition tem peratures were determined and compared with Tm values of cuticular lipids, determined using Fourier transform infrared spectroscopy, for the same indi viduals. Individual variation in T-m was highly correlated with T-c, althou gh T-m values were slightly higher than T-c values. Our results show that, in both intact insects and model membranes, lipid melting results in greatl y increased cuticular permeability.