Temperature and the transpiration of water through the insect cuticle

The effervescence that occurs when an insect is immersed in a mixture of liquid paraffin and butanol indicates that the waterproofing barrier may be very close to the surface, that this barrier varies greatly in permeability in different areas, and that it is readily permeable in the newly moulted insect, but becomes far more resistant as the cuticle hardens. At the height of the effervescence the streams of expanding vesicles, that come from the surface, arise from fixed points—which suggests that the water is escaping from the terminations of the tubular filaments. It is shown that if the intact insect is warmed in a solution of ammoniacal silver at a succession of rising temperatures the argentaffin component of the extracuticular waterproofing layer is usually the first location of silver reduction, to be followed by the contents of the epicuticular channels piercing the outer epicuticle, the substance of the inner epicuticle, and the distal portions of the pore canals. The temperature at which this silver staining increases most rapidly parallels (approximately) the temperature at which transpiration in dry air begins to rise most steeply. It is inferred that both responses are probably dependent on the same temperature effects in the waterproofing lipids.