A Chromosome-Level Genome Assembly of the Parasitic Wasp Chelonus formosanus Sonan 1932 (Hymenoptera: Braconidae)

Abstract

Chelonus formosanus Sonan 1932 (Hymenoptera: Braconidae) is a wasp capable of parasitizing a variety of lepidopteran pests at the "egg-larval" stage which distributes throughout Taiwan, Guangdong, Zhejiang, and Hainan provinces of China. This wasp has been successfully used to control pests such as Spodoptera litura Fabricius, 1775, Spodoptera frugiperda (JE Smith, 1797), Spodoptera exigua (Hübner, 1808), and Helicoverpa armigera (Hübner, 1808). So far, there is only one genome assembled from the Chelonus genus [Chelonus insularis (Cresson, 1865)] and it is fragmented with 455 scaffolds. Here, we report a chromosome-level genome assembly of C. formosanus, which was sequenced using PacBio, Illumina, and Hi-C technologies. The long reads were 35.4 Gb (∼150× coverage) with an average length of 15.23 kb. The size of the genome assembly was 139.59 Mb. More than 99.46% of the assembled sequences were anchored to seven pseudochromosomes (138.84 Mb). The Benchmarking University Single-Copy Orthologs (BUSCO) assessment results showed 99.0% of the 1,367 genes (insect_odb10 database) were completely present. We annotated 11,242 protein-coding genes including 98.6% of BUSCO complete genes that were recovered. Nearly one-fourth of the genome assembly (22.25%) was annotated as repetitive sequences and 324 noncoding RNAs were predicted. There were 58 gene families found with significant expansion including allelopathic families (odorant receptors and ionotropic receptors), which may play a crucial role in efficiently locating a wide range of hosts. This high-quality genome assembly and annotation could provide a highly valuable resource of parasitic wasp for the biological control of Lepidoptera pest.

Keywords: comparative genomics; gene family evolution; genome; parasitic wasp.