Sugar consumption increases the fecundity and longevity in many species of parasitic wasps (parasitoids) but whether these insects use sugars to synthesize significant amounts of fatty acids and storage fat de novo (lipogenesis) is discussed controversially. It has long been assumed that parasitic wasps lost this ability during evolution, mainly because in several species wasps with ad libitum access to sugar did not increase teneral lipid levels. Recent studies demonstrated that many species are nonetheless capable of synthesizing fatty acids de novo from glucose. It is unclear, however, whether also other sugars are used for fatty acid biosynthesis and whether an increase of sugar concentration to levels occurring in natural sugar sources translates into higher fatty acid production. Furthermore, it has been suggested that fatty acid production in parasitoids is negligible compared to species increasing teneral fat reserves such as Drosophila melanogaster. Here we show by stable isotope labeling experiments that females of Nasonia vitripennis convert D-glucose, D-fructose, sucrose, and α,α-trehalose, major sugars consumed by adult parasitoids in nature, equally well to palmitic, stearic, oleic, and linoleic acid. Lipogenesis from D-galactose occurs as well albeit to a lesser extent. Sugar concentration is crucial for lipogenic activity, and almost 80% of de novo synthesized fatty acids were incorporated into storage fat (triacylglycerides). Comparison of fatty acid biosynthesis within a 48-h feeding period with D. melanogaster revealed that N. vitripennis produced approximately half as many fatty acids per body mass unit. Both species fed equal amounts of the glucose offered. We conclude that lipogenesis is far from negligible in N. vitripennis and plays an important role for the energy balance when teneral lipid reserves deplete.