1. The original purpose of the present work was to confirm a previous finding that, in unfed adult Xenopsylla, longevity varies according to the humidity during the cocoon period, and to find whether this is due to differential loss of water during the prepupal period. The previous finding has been confirmed, but the cause is shown to lie in loss of water during the pupal and not the prepupal period.2. Prepupae are shown to gain in weight by the absorption of water vapour from the air if kept at 24°C. and any relative humidity from 50–90 per cent. If kept below 45 per cent. R.H. they rapidly dry and fail to pupate.3. During this period (about three and a half days from cocoon spinning to pupation at 24°C.) the dry weight decreases by about 2 per cent, of the original total weight, and the total weight increases by from 4–29 per cent., with a mean of 14 per cent.4. The amount of water absorbed is independent of relative humidity within the range 50–90 per cent., and is approximately equal to the increase in total weight.5. The critical relative humidity, below which the insects die and above which they absorb water, is shown to be substantially the same (from 45 to 50 per cent. R.H.) at 12°, 24° and 35°C.6. After pupation the insects begin to lose water and continue to do so throughout the period. The rate of loss increases with decreasing humidity, though the effect of humidity is not very great.7. Adults emerging from pupae kept at higher humidities weigh more, have higher percentage water contents, and live longer without food, than those emerging from pupae kept at lower humidities.8. The results are discussed in the light of previous work, and suggestions as to the mechanism of the process of absorption of water are made.
Calculating the Critical Relative Humidity from the Solubility of Electrolyte According to Extended Non-random Two Liquid Model
