# First Report of Mermithidae (Enoplea: Mermithida) Parasitizing Adult Stable Flies in Japan

## TL;DR

This paper reports the first case of Mermithidae nematodes parasitizing adult stable flies in Japan, based on morphological and genetic analysis.

## Contribution

The first documented report of Mermithidae parasitizing adult stable flies in Japan, with genetic insights into the nematode species involved.

## Key findings

- Three adult stable flies in Japan were found to be parasitized by Mermithidae nematodes.
- Phylogenetic analysis grouped the mermithids with known species like Ovomermis sinensis and Amphimermis sp.
- The findings suggest the presence of genetically distinct mermithid species across Japan.

## Abstract

Mermithidae is a family of nematodes that parasitize a wide range of invertebrates worldwide. Herein, we report nematodes that were unexpectedly found in three of 486 adult stable flies (Stomoxys calcitrans) captured from three farms (F1, F2, and F3) in different regions of Gifu Prefecture, Japan. We aimed to characterize these nematodes both at the morphological and molecular level. Morphological studies revealed that the nematodes were juveniles of Mermithidae. Phylogenetic analysis based on 18S and 28S rDNA indicated that the mermithids from farms F1 and F2 could be categorized into the same cluster as Ovomermis sinensis and Hexamermis sp., whereas the mermithid from farm F3 clustered with Amphimermis sp. Additionally, these mermithids could be categorized within the same clusters as related mermithids detected in Japan that parasitize various arthropod orders. Our findings suggest that these stable flies may have been parasitized by mermithids already present in the region and that genetically distinct species of mermithids occur across Japan. To the best of our knowledge, this is the first report of mermithids parasitizing adult stable flies in Japan.