Fatty acids are crucial primary metabolites for virtually all creatures on earth. Most organisms thus do not rely exclusively on a nutritional supply containing fatty acids, but have the ability to synthesize fatty acids and triacylglycerides de novo from carbohydrates in a process called lipogenesis. The ubiquity of lipogenesis has been questioned by a series of studies reporting that many parasitic wasps (parasitoids) do not accumulate lipid mass despite having unlimited access to sugar. This has been interpreted as an evolutionary metabolic trait loss in parasitoids. Here, we demonstrate de novo biosynthesis of fatty acids from 13 C-labelled α- d -glucose in 13 species of parasitoids from seven families. We furthermore show in the model organism Nasonia vitripennis that lipogenesis occurs even when lipid reserves are still intact, but relative 13 C-incorporation rates increase in females with widely depleted fat reserves. We therefore conclude that the presumed ‘lack of lipogenesis' in parasitoids needs to be re-evaluated.

No abstract

Fatty acids are crucial primary metabolites for virtually any creature on earth. Therefore, most organisms do not rely exclusively on nutritional supply with fatty acids but have the ability to synthesize fatty acids and triacylglycerides de novo from carbohydrates, a process called lipogenesis. The ubiquity of lipogenesis has been questioned by a series of studies reporting that many parasitic wasps (parasitoids) do not accumulate lipid mass despite having unlimited access to sugar. This has been interpreted as an evolutionary metabolic trait loss in parasitoids. Here, we demonstrate de novo biosynthesis of fatty acids from 13C-labeled α-D-glucose in eleven species of parasitoids from six families. We furthermore show with the model organism Nasonia vitripennis that lipogenesis occurs even when lipid reserves are still intact, but relative 13C-incorporation rates increase in females with widely depleted fat reserves. Therefore, we conclude that the presumed "lack of lipogenesis" in parasitoids needs to be re-evaluated.

Linoleic acid (C18:2 Δ9,12 , LA) is an important metabolite with numerous essential functions for growth, health, and reproduction of organisms. It has long been assumed that animals lack Δ12-desaturases, the enzymes needed to produce LA from oleic acid (C18:1 Δ9 , OA). There is, however, increasing evidence that this is not generally true for invertebrates. In the insect order Hymenoptera, LA biosynthesis has been shown for only two parasitic wasp species of the so-called "Nasonia group," but it is unknown whether members of other taxa are also capable of synthesizing LA. Here, we demonstrate LA biosynthesis in 13 out of 14 species from six families of parasitic wasps by gas chromatography-mass spectrometry analysis using two different stable isotope labeling techniques. Females of the studied species converted topically applied fully 13 C-labeled OA into LA and/or produced labeled LA after feeding on fully 13 C-labeled α-D-glucose. These results indicate that Δ12-desaturases are widespread in parasitic Hymenoptera and confirm previous studies demonstrating that these insects are capable of synthesizing fatty acids de novo.