Effect of pH on the uptake of sodium in the waterbugs Corixa dentipes (Thoms.) and Corixa punctata (Illig.) (hemiptera, heteroptera)

1. 1. Sodium uptake in the adults of two species of waterbugs Corixa dentipes (Thoms.) and Corixa punctata (Illig.) is investigated, with regard to the pH of the external medium. 2. 2. Sodium exchange uptake was followed over a period of 160hr, at different external pH. 3. 3. In the range pH 3-4 important differences in the sodium exchange uptake rate are noticed between both species. 4. 4. Sodium uptake as a function of the external sodium concentration follows enzyme-saturation kinetics (Michaelis relation) in both species. 5. 5. The affinity of the sodium uptake mechanism strongly depends on the external pH. 6. 6. The maximum influx value depends also on the external pH. 7. 7. These findings are related to data on the distribution of both species in Belgian surface waters.