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PubMed1995

Measurement of water and carbon dioxide loss from insects using radioactive isotopes

A method is described for investigating the rate of loss of water and carbon dioxide from terrestrial insects by absorbing tritiated water and 14CO2 from a gas stream flowing past the insect. The loss of water and carbon dioxide can be studied simultaneously with a time resolution (nominal) down to 2 min. The theoretical and experimental bases of analysing the data are considered in detail. The determination of the efflux rate constant for water is straightforward and, if an estimate of surface area is available, the efflux rate constant can be converted to a permeability coefficient. In the case of 14CO2 loss, the interpretation is complicated by the presence of other compartments within the body that can be labelled with 14C. A multicompartment model of 14C exchange is developed and a method of obtaining the efflux rate constant of 14CO2 is described. The efflux rate constant for 14CO2 can be used to estimate CO2 output.

Journal Article↗
PubMed1995

Water and carbon dioxide loss from the cockroach Periplaneta americana (L.) measured using radioactive isotopes.

Tritiated water (THO) loss from Periplaneta americana is used to measure cuticular permeability (Pd). In dry air, following various periods of predesiccation, the values of Pd lie around 0.5 x 10(-9) ms-1, with the lowest values below 0.3 x 10(-9) ms-1, close to the lowest permeabilities previously reported. There is no obvious relationship between permeability and initial mass of the insect. A significant lowering of Pd was found after 72 h of predesiccation. A marked sudden decrease in permeability occurred when the airstream flowing over an insect was changed from humid air to dry air. Labelling the bicarbonate pool using 14CO3(2-) enabled the output of CO2 to be estimated. An average output of about 390 microliters g-1 h-1 was found. Simultaneous measurement of THO and 14CO2 loss showed that tracheal water loss is only a small component of total water loss, with an average value of 3.8%. The total water loss can therefore be used to make close estimates of cuticular permeability in Periplaneta americana. 2min sampling periods clearly show the pulsatile nature of 14CO2 release but, even when the effect is most discernible, the periodic release of CO2 has only a small effect on water loss.

Animals↗