Water Balance In Ilyocoris Cimicoides (L.) (Heteroptera; Naucoridae): the Rate of Net Water Uptake Through the Cuticle

1. Measurements have been made of the rate of net water uptake through the cuticle of adult females of Ilyocoris cimicoides (L). 2. With a method that consisted in recording the increase in weight after sealing the external openings of the gut a value of about 10% of the body weight per day was obtained for the rate of net water uptake through the cuticle at a temperature of 18° C. The Arrhenius equation appeared to hold over the temperature range 4-26° C. and an approximate value of 10,530 cals was obtained for the temperature characteristic, µ, of the rate of net water uptake over this range of temperatures. However, the values obtained for the rate of net water uptake at 1° C. (1.8% of the body weight per day) were less than straightline expectation between log, uptake and 1/T over the temperature interval 1-26° C. would indicate. 3. The results obtained by recording the increase in weight after sealing the external openings of the gut agreed well with those obtained by determining the difference between the intake of drinking water and output of rectal fluid, were somewhat less than the values obtained with a method that consisted in recording the increase in weight after death by ammonia poisoning, and were some four to five times greater than the theoretical values derived on a diffusional basis from the rate of entry of D 2 O. 4. The results confirm previous evidence that adult waterbugs are typical fresh-water animals in the sense that the excretory system must work continuously to eliminate water gained unavoidably and in appreciable amount by osmotic uptake through the cuticle.