De novo biosynthesis of linoleic acid is widespread in parasitic wasps.

Linoleic acid (C18:2∆9,12 , LA) is an important metabolite with numerous essential functions for growth, health, and reproduction of organisms. It has long been assumed that animals lack ∆12-desaturases, the enzymes needed to produce LA from oleic acid (C18:1∆9 , 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 ∆12-desaturases are widespread in parasitic Hymenoptera and confirm previous studies demonstrating that these insects are capable of synthesizing fatty acids de novo.

Functional characterisation of two Δ12-desaturases demonstrates targeted production of linoleic acid as pheromone precursor in Nasonia.

Insect pheromones are often derived from fatty acid metabolism. Fatty acid desaturases, enzymes introducing double bonds into fatty acids, are crucial for the biosynthesis of these chemical signals. Δ12-desaturases catalyse the biosynthesis of linoleic acid by introducing a second double bond into oleic acid, but have been identified in only a few animal species. Here, we report the functional characterisation of two Δ12-desaturases, Nvit_D12a and Nvit_D12b, from the parasitic wasp Nasonia vitripennis. We demonstrate that Nvit_D12a is expressed in the rectal vesicle of males where they produce a linoleic acid-derived sex pheromone to attract virgin females. 13C-labelling experiments with Urolepis rufipes, a closely related species belonging to the 'Nasonia group', revealed that females, but not males, are able to synthesise linoleic acid. U. rufipes males produce an isoprenoid sex pheromone in the same gland and do not depend on linoleic acid for pheromone production. This suggests that Δ12-desaturases are common in the 'Nasonia group', but acquired a specialised function in chemical communication of those species that use linoleic acid as a pheromone precursor. Phylogenetic analysis suggests that insect Δ12-desaturases have evolved repeatedly from Δ9-desaturases in different insect taxa. Hence, insects have developed a way to produce linoleic acid independent of the omega desaturase subfamily which harbours all of the eukaryotic Δ12-desaturases known so far.