Fatty acid synthases and desaturases are essential for the biosynthesis of α‐linolenic acid and metamorphosis in a major mulberry pest, Glyphodes pyloalis walker (Lepidoptera: Pyralidae)

α-linolenic acid is an essential unsaturated fatty acid in organisms. However, there is a large gap between α-linolenic acid accumulation and its synthesis mechanism in insects. Fatty acid synthases (FASs) and desaturases (Desats) are vital enzymes required for the synthesis of unsaturated fatty acids.The pupae of Glyphodes pyloalis (Lepidoptera: Pyralidae), which is a destructive pest of mulberry trees, contain the highest level of α-linolenic acid compared to other life-history stages. To further explore the synthesis mechanism of α-linolenic acid in G. pyloalis pupae, we constructed a pupal transcriptome dataset and identified 106 genes related to fatty acid metabolism from it. Among these, two fatty acid synthases (GpylFAS) and five desaturases (GpylDesat) were identified. A qRT-PCR validation revealed that GpylFAS1 and GpylDesat1, 2, 3, 5 were expressed highest at pupal stages. Furthermore, the content of α-linolenic acid decreased significantly after silencing GpylFAS1 and GpylDesat5, respectively. Besides, knocking down GpylFAS1 or GpylDesat5 resulted in more malformed pupae and adults, as well as lower emergence rates. Meanwhile, silencing GpylFAS1 or GpylDesat5 affected the expressions of the other GpylFASs and GpylDesats.The present results illustrate the pivotal function of FASs and Desats in α-linolenic acid biosynthesis and metamorphosis in insects. Our research also broadens the sources of unsaturated fatty acids, especially for α-linolenic acid from insects, and provides novel insights for the management of mulberry insect pests from the perspective of utilization rather than control. © 2022 Society of Chemical Industry.