Water balance in the firebrat, Thermobia domestica (Packard). Exchanges of water with the atmosphere.

Abstract

ABSTRACT Uptake of water from the atmosphere by previously desiccated, starved Thermobia domestica is related to the % relative humidity, and occurs in and above 63% R.H. between 17 and 37 ° C. Losses occur in and below 43% R.H. Uptake is often, though not invariably, arrested during even brief periods of locomotor activity. Recovery from desiccation proceeds to the same level of body-water content in all humidities above the ‘critical’ value. Equilibrium is reached more rapidly in the higher temperatures and humidities. The equilibrium level attained is the same as that found in control insects, and it does not change when the insect is transferred from one high humidity to another. During periods of relatively large dry-weight losses, a greater proportion of water is retained in the body, providing some volume regulation. The living insect restricts its water loss in low humidities by means of a permeability barrier which is disrupted during uptake in high humidities and is progressively lost on death. This restriction is not dependent upon the continued activity of the uptake mechanism.