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

Keywords: Mermithidae; blood-feeding pests; genetics; host–parasite relationship; insect parasitism; stable fly.

Figure 1.

(A) Sampling location of adult stable flies (Stomoxys calcitrans). (B—F) Larval form of the mermithid nematode from Gifu. (B) Whole body. (C, D) Anterior part and its extremity. (E, F) Posterior part and its extremity with a tail appendage (arrowhead).

Figure 2.

Phylogenetic trees of Mermithidae with known genus-level identifications based on 18S (A) and 28S (B) rDNA using the maximum-likelihood method. Arrowheads indicate the mermithids sequenced in this study. Bootstrap values above 50% are indicated at the phylogenetic tree node.

Figure 3.

Phylogenetic tree of Mermithidae with known hosts based on 18S rDNA sequences using the maximum-likelihood method. Arrowheads indicate the mermithids sequenced in this study. The red frame includes mermithids recorded from Japan. Bootstrap values above 65% are indicated at the phylogenetic tree node.

Figure 4.

Phylogenetic tree of unidentified species of mermithid nematodes parasitizing insects in Japan based on 18S rDNA sequences (A) using the maximum-likelihood method and (B) distribution map of mermithids included in Ovomermis sinensis, Hexamermis sp., and Amphimermis sp. clusters. Ovomermis sinensis (KU177046), Hexamermis agrotis (DQ530350), Hexamermis popilliae (MF040823), Romanomerimis sichuanensis (EF612769), and Amphimermis enzoni (MT021436) have been identified in other countries and used as reference species in the phylogenetic tree. Arrowheads indicate the mermithids isolated in Gifu and sequenced in this study. Bootstrap values above 65% are indicated at the phylogenetic tree node.