Abstract: 【Aim】To identify fatty acid desaturase (FAD) genes in the whole genome of Hermetia illucens, and to investigate their spatiotemporal expression patterns and evolutionary pattern in representative dipteran insects. 【Methods】 The amino acid sequences of FAD genes of Drosophila melanogaster were downloaded from FlyBases and used as seed sequences to search for FAD genes in H. illucens and several other representative species of Diptera by the local Blastp program across the whole genome. The phylogenetic tree of the FAD genes across several dipteran species was constructed by a neighbor-joining method (NJ) with MEGA7. 0. The expression patterns of FAD genes in representative tissues and developmental stages were determined based on the transcriptome data of H. illucens and were further verified using RT-PCR. 【Results】 In this study, a total of 13 FAD genes in the whole genome of H. illucens were identified and annotated with general characteristics. The phylogenetic analysis revealed that gene duplication occurs in partial H. illucens FAD genes, such as HillFAD-10 and HillFAD-12, and HillFAD-9 and HillFAD-11. In contrast, we also found that partial FAD genes, such as HillFAD-5 and HillFAD-6, present a consistent evolutionary pattern in dipteran species, suggesting that they are relatively conserved and may play general roles in dipteran species. Transcriptome data analyses and RT-PCR results revealed that most FAD genes showed different expression patterns during the growth and development of H. illucens, e.g., HillFAD-2 and HillFAD-6 were expressed in embryo, larval, pupal and adult stages, HillFAD-3 were mainly expressed during the late embryo and the 4th instar larval stage while HillFAD-4 showed low expression levels in the whole developmental satge, suggesting that the FAD genes may play distinctive roles in the metamorphosis development process of H. illuences. 【Conclusion】 Our study not only identified the whole set of FAD genes in the whole genome of H. illucens, but also reconstructed their evolutionary pattern across dipteran species, enabling us to better understand the role of FAD in the ecological adaptation in Diptera. The expression patterns of FAD genes uncovered in this study also provide preliminary insights into the lipid metabolism in this important resource insect species.

Key words: Hemetia illucens, fatty acid desaturase, Diptera, phylogenetic analysis, evolution, spatiotemporal expression