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. aldrichi's range has greatly expanded across North America, particularly in Quebec and Ontario, Canada, and in the Midwest United States. In Minnesota, parasitism of Japanese beetles by I. aldrichi was documented in commercial apple orchards in 2021 and has since spread to multiple locations, highlighting its importance as a natural enemy. To facilitate research on I. aldrichi and other tachinid flies, we present a haploid reference genome generated from a single unsexed 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 tachinids as a whole have undergone rapid copy number changes in 935 gene families, largely related to metabolism and morphogenesis. 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. The I. aldrichi reference genome will further research opportunities on these parasitic flies, including their potential for biocontrol of P. japonica.