Genome Assembly and Comparative Analysis of the Egg Parasitoid Wasp Trichogramma dendrolimi Shed Light on the Composition and Evolution of Olfactory Receptors and Venoms

SIMPLE SUMMARY: Trichogramma wasps are minute egg parasitoids that are one of the most used biocontrol agents to manage lepidopteran pests. Given the great success in industrializing a mass-rearing method for the cost-effective production of Trichogramma dendrolimi, this parasitoid wasp has been used extensively to control agricultural and forestry pests in China. So far, while the biology and ecology of T. dendrolimi have been intensively studied to provide successful biological control, the limited genome information constrains the interpretation of the molecular mechanism underlying its host recognition and parasitism. Here, we assembled a high-quality reference genome for T. dendrolimi and identified the repetitive sequences and protein-coding genes. A phylogenomic tree constructed for T. dendrolimi and 24 hymenopteran species places the family Trichogrammatidae sister in the remaining Chalcidoidea species. We found that significantly expanded and contracted gene families are involved in the development, regulation and transport processes in T. dendrolimi, respectively. Additionally, 24 odorant binding proteins, 100 olfactory receptors, 27 gustatory receptors, 27 ionotropic receptors and 87 venom genes were identified in the genome of T. dendrolimi. Our study provides a foundation for future studies on the molecular mechanism underlying host recognition and parasitism in the Trichogramma species. ABSTRACT: Trichogramma dendrolimi is one of the most successfully industrialized Trichogramma species used to control agricultural and forestry pests in China. However, the molecular mechanisms underlying its host recognition and parasitism remain largely unknown, partially due to the limited genome information of this parasitoid wasp. Here, we present a high-quality de novo assembly of T. dendrolimi through a combination of Illumina and PacBio sequencing technologies. The final assembly had a length of 215.2 Mb and contains 316 scaffolds with a scaffold N50 size of 1.41 Mb. Repetitive sequences with a length of 63.4 Mb and 12,785 protein-coding genes were identified. Significantly expanded gene families were identified to be involved in the development and regulatory processes, while remarkably contracted gene families were involved in the transport processes in T. dendrolimi. The olfactory and venom-associated genes were identified in T. dendrolimi and 24 other hymenopteran species, using uniform methods combining BLAST and HMM profiling. The identified venom genes of T. dendrolimi were enriched in antioxidant activity, tricarboxylic acid cycle, response to oxidative stress and cell redox homeostasis. Our study provides an important resource for comparative genomics and functional studies to interpret the molecular mechanisms underlying host recognition and parasitism of Trichogramma species.