Genome report: Genome sequence of tuliptree scale, Toumeyella liriodendri (Gmelin), an ornamental pest insect.

Abstract

Scale insects are of interest both to basic researchers for their unique reproductive biology and to applied researchers for their pest status. In spite of this interest, there remain few genomic resources for this group of insects. To begin addressing this lack of data, we present the genome sequence of tuliptree scale, Toumeyella liriodendri (Gmelin) (Hemiptera: Coccomorpha: Coccidae). The genome assembly spans 536Mb, with over 96% of sequence assembled into one of 17 chromosomal scaffolds. We characterize roughly 66% of this sequence as repetitive and annotate 16,508 protein coding genes. Then we use the reference genome to explore the phylogeny of soft scales (Coccidae) and evolution of karyotype within the family. We find that T. liriodendri is an early-diverging soft scale, less closely related to most sequenced soft scales than a species of the family Aclerdidae is. This molecular result corroborates a previous, morphology-based phylogenetic placement of Aclerdidae within Coccidae. In terms of genome structure, T. liriodendri has nearly twice as many chromosomes as the only other soft scale assembled to the chromosome level, Ericerus pela (Chavannes). In comparing the two, we find that chromosome number evolution can largely be explained by simple fissions rather than more complex rearrangements. These genomic natural history observations lay a foundation for further exploration of this unique group of insects.