The role of lipid physical properties in cuticular water loss was examined in model membranes and intact insects. In model experiments, pure hydrocarbons of known melting point (T(m)) were applied to a membrane, and the effects of temperature on permeability were quantified. Arrhenius plots of permeability were biphasic, and transition temperatures for water loss (T(c)) were similar to T(m). In grasshoppers Melanoplus sanguinipes, changes in cuticular water loss were measured using flow-through respirometry. Transition temperatures were determined and compared with T(m) values of cuticular lipids, determined using Fourier transform infrared spectroscopy, for the same individuals. Individual variation in T(m) was highly correlated with T(c), although 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 greatly increased cuticular permeability.

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