The genome of Istocheta aldrichi (Diptera: Tachinidae), a parasitoid of the Japanese beetle, Popillia japonica (Coleoptera: Scarabaeidae)

Istocheta aldrichi Mesnil 1953 (Diptera: Tachinidae), is native to Japan, and has recently become an important biological control agent of the Japanese beetle, Popillia japonica (Coleoptera: Scarabaeidae), a pest with >300 host plants, including roses, linden trees, and numerous agricultural crops. During the past decade, I. aldrichis range has greatly expanded across North America, particularly in Quebec and Ontario, Canada, and in the Midwest U.S. In many areas, including Minnesota, 15-60% of Japanese beetles are parasitized by I. aldrichi, highlighting its importance as a natural enemy. To facilitate research on I. aldrichi and other tachinid flies we present a reference genome generated from a single individual. The final genome assembly is 875.3 Mbp contained in 1,041 scaffolds, with an N50 of 4.77 Mbp, and 99.5% complete Diptera BUSCOs present. We also present a complete mitogenome and use comparative genomics across 19 tachinid species to identify unique features of I. aldrichi. Specifically, we find that while many tachinid lineages have experienced contractions in gene families, I. aldrichi is characterized by a relatively high number of gene family expansions, many of which are predicted to function in metal ion transport. Tachinids as a whole have undergone rapid copy number changes in 935 gene families, largely related to metabolism and morphogenesis. The I. aldrichi reference genome will further research opportunities on these parasitic flies, including their potential for biocontrol of P. japonica. ARTICLE SUMMARYThe parasitic fly Istocheta aldrichi attacks and kills the Japanese beetle (Popillia japonica), a pest of more than 300 plants. There is potential to leverage I. aldrichi for biological control of the beetle, but application is hindered by a limited understanding of this flys biology. This reference genome for I. aldrichi will enhance research future efforts and our ability to manage P. japonica.