SHORT COMMUNICATION CONTROL OF CUTICULAR WATER PERMEABILITY IN INSECTS

In a recent note (Croghan and Noble-Nesbitt, 1989), it was shown that water permeability of the cockroach epicuticle could not be explained in terms of what was known about the properties of the components of the system. Additionally, there are further observations in need of explanation. Coenen-Stass and Kloft (1976), using both weight loss and tritiated water, showed that the rate of water loss from the cockroach (Periplaneta) was lower in living animals than in dead animals and suggested that this could indicate an active reduction of cuticular permeability. There is evidence that cuticular water loss is under endocrine control (Treherne and Willmer, 1975; Noble-Nesbitt and Al-Shukur, 1987) and the progressive reduction in cuticular water permeability under desiccating conditions has been interpreted as an expression of this control (Noble-Nesbitt and Al-Shukur, 1987). It is not immediately obvious how the epicuticular permeability could be controlled. Also, Winston and Beament (1969) have shown that, in pieces of cuticle removed from the living cockroach and locust, the chemical potential of water is significantly less than in the blood. In the cockroach, the cuticular wate