Analysis of extracts of the sweetpotato whitefly Bemisia tabaci (Gennadius) (= B. argentifolii Bellows and Perring) and cotton aphid, Aphis gossypii Glover, showed that both accumulated very large amounts of polyhedric alcohols (polyols) in their bodies during the warmest part of the day. The sweetpotato whitefly accumulated sorbitol and the cotton aphid accumulated mannitol. Mannitol accumulation in the cotton aphid followed the temperature of its environmnent much closer than did sorbitol accumulation in the sweetpotato whitefly, which only appeared in large amounts in extracts of insects collected during the hottest part of the day. These polyols do not appear in the honeydew of either insect, suggesting that a significant portion of their metabolism is dedicated to both the creation and to the breakdown of these polyols during the course of a day. Results of experiments with the sweetpotato whitefly suggest that the reason for this major metabolic commitment is that this polyol accumulation protects these insects against desiccation and dietary osmotic stress. The production of honeydew from both insects was found to vary during the day and to be maximal in the early afternoon for insects feeding in fields of cotton. Both honeydews contain significant amounts of glucose, fructose, sucrose, trehalulose and melezitose, but the ratio of different honeydew sugars was substantially different for the two insect genera. Preliminary results from experiments involving spraying known sugars on clean cotton suggest that honeydew from the sweetpotato whitefly may be more sticky than that from the cotton aphid.