Chromosome-level de novo genome assembly of two conifer-parasitic waspsMegastigmus duclouxiana and Megastigmus sabinae reveals genomic imprints of adaptation to hosts.

Conifers consist of about 1/3 of global forests but are threatened by seed parasitoid wasp species. Many of these wasps belong to the genus Megastigmus, yet little is known about their genomic background. In this study, we provide chromosome-level genome assemblies for two oligophagous conifer parasitoid species of Megastigmus, which represent the first two chromosome-level genomes of the genus.The assembled genomes of M. duclouxiana and M. sabinae are 878.48 Mb (scaffold N50 of 215.60 Mb), and 812.98 Mb (scaffold N50 of 139.16 Mb), respectively, which are larger than the genome size of most hymenopterans due to the expansion of transposable elements. Expanded gene families highlight the difference in sensory-related genes between the two species, reflecting the difference in their hosts. We further found that these two specieshave less family members while more single-gene duplications than polyphagous congeners in the gene families of ATP-binding cassette transporter (ABC), cytochrome P450 (P450) and olfactory receptors (OR). These findings shed light on the pattern of adaptation to a narrow spectrum of hostsin oligophagous parasitoids.Our finding suggests potential drivers underlying the genome evolution and parasitism adaptation, provides valuable resources for understanding the ecology, genetics and evolution of Megastigmus, as well asfor the research and biological control of global conifer forest pests.