Stilwell, P. A. | bioRxiv Science

bioRxiv2026

Asymmetry and niche partitioning shape the infection dynamics of co-transmitted Wolbachia symbionts

Wolbachia is an incredibly widespread maternally transmitted bacterium in arthropods that can alter host physiology, nutrition, reproduction, and immunity. In some cases, multiple Wolbachia strains infect the same host and are stably transmitted alongside each other. This raises the question of how multiple intracellular symbionts interact with each another and with the host to ensure stable transmission. Here, we use fluorescence in situ hybridizations and confocal microscopy to investigate co-transmission in a naturally occurring co-infection of two Wolbachia strains in Drosophila simulans: wHa and wNo. We find significant differences in spatial occupancy and abundance between the co-transmitted strains across stages of oogenesis and embryogenesis. We show that wHa and wNo have biases for different niches during oogenesis, and their strain-specific abundance is driven by egg chamber development, mating status, and their interaction. After differential curing of the co-infection, we find that wNo is dependent on wHa for vertical transmission, but not vice versa. Additionally, while wHa localization patterns are unchanged by loss of co-infection, abundance of wHa in the ovaries increases when wNo is removed. Understanding how symbiont co-infections achieve stability has important implications for the ongoing use of Wolbachia as a tool for insect management programs, but also for our understanding of the ecology of intracellular communities more broadly.

microbiology↗

bioRxiv2025

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.

genomics↗