Unfed 2- to 5-day-old females of different species of Florida mosquitoes were fed a meal of 50% glucose solution and analyzed for quantities of glucose ingested, duration of survival, rate of glucose depletion, and accumulation and depletion of energy reserves. Another group of females was maintained from the time of emergence on 10% sucrose solution ad lib. and analyzed for fluctuations in the level of total energy reserves during their life span. No direct correlation was evident in the wet weight of females, the calories imbibed and the duration of survival on a meal of 50% glucose. A. aegypti and A. taeniorhynchus survived for 80 hr/cal. of glucose, and sollicitans and P. confinnis survived for 37 and 49 hr/cal., respectively. In general, lighter mosquitoes (1.5 to 2.1 mg/♀) utilized glucose much more efficiently than heavier mosquitoes (2.4 to 3.6mg/♀). The rate of disappearance of glucose followed the exponential law of decline in A. sollicitans, A. taeniorhynchus and M. titillans, but in other species this law was followed only 72 hr. The duration of survival of mosquitoes was directly related to the rate of disappearance of glucose. Absorption of glucose was followed by synthesis of glycogen and triglycerides. Their accumulation varied with species, and they prolonged the survival of females after sugar was depleted. Females of different species maintained on sucrose ad lib. accumulated specific levels of energy reserves, which achieved maximum levels after 2 weeks. These levels of energy reserves were maintained for the major portion of the life span, after which they declined, coincident with the 50% survival age. It is concluded that sugar is necessary for the prolonged survival of female mosquitoes of all species investigated.