ABSTRACT
It has been felt for some time that the relations between insects and atmospheric humidity must often be responsible for determining the places and seasons at which particular species can exist, or be abundant. But it is not easy to devise experimental methods of testing this view, and investigating the water balance of an insect. One way of approaching the problem is explored in the present paper. I have set myself to delimit the precise conditions of temperature and humidity which are fatal to a particular insect: I hope to discover whether evaporation into dry air cools the insect and so allows it to survive higher air temperatures than it can in moist air; or whether evaporation kills the insect by causing undue loss of water; or whether the humidity of the air has little effect on the insect, even at temperatures which are nearly fatal. A serious objection to the method is that it is so laborious; allowing for preliminary work with imperfect apparatus, and for experiments with an exposure of 5 minutes which are not reported in full, I have performed over 200 experiments, using ten insects in each; as the rate of reproduction of Rhodnius (Buxton, 1930) is not very high, the work has occupied a part of my time for three years.
