The phorid fly, Pseudacteon tricuspis Borgmeier (Diptera: Phoridae) has been released in many parts of southern United States for biological control of red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae). However, little is known about the nutritional ecology and foraging behavior of phorid flies, and the impact of sugar feeding on parasitoid fitness. We investigated the ability of P. tricuspis to utilize sucrose solution, buckwheat nectar, and cotton aphid honeydew as food sources. We used a series of biochemical assays to quantify the amounts of fructose, body sugars, glycogen, and lipid in individual flies subjected to different diet treatments. Adult P. tricuspis emerged with no gut sugars, and only minimal amounts of body sugars and glycogen. Levels of body sugars and glycogen declined gradually in sugar-starved flies, whereas high levels of these nutrients were maintained in female and male phorid flies fed sucrose continuously over the observation period. Honeydew-fed phorid flies also showed a slight increase in the levels of body sugars. Lipid levels in sugar-fed flies did not differ significantly from levels in newly emerged individuals, suggesting that adult P. tricuspis were capable of converting dietary sucrose to body sugars and glycogen, but not lipids. These results suggest that conservation of naturally occurring sugar sources in the field may promote P. tricuspis lifespan and its impact as a biological control agent against imported fire ants.