ABSTRACT
Water content varies from 64 to 73 % of the total body weight and 72−76 % of the fatless body weight of 24 hr. old unflown alatae of Aphis fabae.
Water loss during flight may be attributed to evaporation and excretion. A mean of 0-07 mg. water is lost per aphid during a 6 hr. tethered flight at 25−26°C. and 57−82% R.H., corresponding to c. 9% body weight; at least 66% of the loss (c. 1 % body weight/hr.) is by evaporation.
Excretion during flight is not affected by relative humidity differences over the range 41−75 % at 25−26°C., but the relative amounts of water lost during prolonged flight are inversely related to relative humidity, because of the effect of humidity on evaporation.
Proportion of water in the body does not change significantly during tethered flight. Mean percentage water to total body weight increases from c. 68−69 % during 6 hr. ; mean percentage water to fatless body weight decreases from c. 74 to 73 %.
Water loss is evidently not a limiting factor to flight in atmospheres of saturation deficit less than c. 23 mm. Hg.
