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 a nd (CO2)-C-14 from a gas stream flowing past the insect, The loss of w ater and carbon dioxide can be studied simultaneously with a time reso lution (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 estim ate of surface area is available, the efflux rate constant can be conv erted to a permeability coefficient. In the case of (CO2)-C-14 loss, t he interpretation is complicated by the presence of other compartments within the body that can be labelled with C-14, A multicompartment mo del of C-14 exchange is developed and a method of obtaining the efflux rate constant of (CO2)-C-14 is described, The efflux rate constant fo r (CO2)-C-14 can be used to estimate CO2 output.