De novo genome assembly of Bradysia cellarum (Diptera: Sciaridae), a notorious pest in traditional special vegetables in China.

Bradysia cellarum (Diptera: Sciaridae) is a destructive vegetable insect pest infesting more than 30 species of host plants from seven families in Asia and Europe. B. cellarum causes grave problems in Chinese chive, which originated in China and is cultivated widely in East Asia. The B. cellarum infestation results in economic losses and subsequent severe food safety problems in farm productions, insecticide resistance and environmental pollution. The genomic and molecular information of B. cellarum to delineate the biological features, insecticide resistance, evolution remains poorly understood. Herein, we decode the whole genome of B. cellarum to delineate the underlying molecular mechanisms causing insecticide resistance. We constructed a highly reliable genome for B. cellarum using PacBio, Illumina and 10X Genomics sequencing platforms. The genome size of B. cellarum was 375.91 Mb with a contig N50 of 1.57 Mb. A total of 16,231 genes were identified, among which 93.8% were functionally annotated, and 42.06% were repeat sequences. According to phylogenetic analysis, B. cellarum diverged from the common ancestor of Drosophila melanogaster and Musca domestica ~139.3-191.0 million years ago. Moreover, some important genes responsible for significant insecticide resistance, such as cytochrome P450s, ABC transporters and those involved in glutathione metabolism, were expanded in B. cellarum. We assembled a high-quality B. cellarum genome to provide valuable insights into their life history strategies, insecticide resistance and biological behaviours. It also lays the foundation for exploring gene structure and functional evolution, as well as comparative genomics of B. cellarum and other model insect species.