Molecular characterization of Thelastomatoidea (Nematoda: Oxyurida) from cockroaches in Australia

Redescription of three pinworms of the genus Cephalobellus Cobb, 1920 (Nematoda: Oxyuridomorpha: Thelastomatidae) from scarab beetle grubs from Hungary

Larvae of European rose chafer Cetonia aurata (Linnaeus, 1758) and cockchafer Melolontha sp. beetles were collected in Hungary for parasitological study. Intestinal examination revealed the presence of three well-known thelastomatid nematodes belonging to the genus Cephalobellus Cobb, 1920. We report for the first-time Cephalobellus cuspidatum (Rudolphi, 1814) Leibersperger, 1960, C. osmodermae Leibersperger, 1960, and C. potosiae Leibersperger, 1960 in Hungary, all found in scarab beetle larvae. Due to incomplete original descriptions, a comprehensive redescription with detailed morphological data is presented. Additionally, an identification key for closely related Cephalobellus, Thelastoma and Severianoia species infesting scarab beetles worldwide is provided. Newly generated 18S and 28S rDNA gene sequences of C. osmodermae place it as one of the early branches within Thelastomatidae.

Morphological and molecular characterization of Desmicola ryukyuensis n. sp. (Nematoda: Oxyuridomorpha: Thelastomatidae) from the wood-feeding cockroach Panesthia angustipennis yayeyamensis Asahina, 1988 (Blattaria: Blaberidae) in the Ryukyu Archipelago, Japan

Desmicola ryukyuensis n. sp. (Nematoda: Oxyuridomorpha: Thelastomatidae) is described from the wood-feeding cockroach Panesthia angustipennis yayeyamensis Asahina, 1988 (Blattaria: Blaberidae) in Iriomote Island, Japan. The males of D. ryukyuensis n. sp. are similar to D. lamdongensis Sokolova, 2019 but differ by the length of the spicule and the extension of the lateral alae. The females of D. ryukyuensis n. sp. resemble those of D. ornata Jex, Schneider, Rose & Cribb, 2005, but can be differentiated by the shape of the sensilla in the interlabial space and the presence of lateral alae in D. ryukyuensis n. sp. that are absent in D. ornata. The females of D. ryukyuensis n. sp. are similar to D. lamdongensis. However, they differ in the morphology of the lips and the size of the eggs. The phylogeny of D. ryukyuensis n. sp. is inferred by the D2-D3 domains of the 28S rDNA. The new species forms a clade with another sequence of an unidentified Desmicola species from a Vietnamese wood-feeding cockroach.

Leidynemella shahi n. sp. (Nematoda: Thelastomatidae) from wood-eating cockroaches (Insecta: Blaberidae) in the Yunnan Province, China

Leidynemella shahi n. sp. is described based on material from Panesthia angustipennis cognata Bey-Bienko and Salganea raggei Roth in the Yunnan Province, China. The new species is very similar to L. fusiformis Cobb in Chitwood & Chitwood, 1934, but differs from the latter in the position of the nerve-ring and vulva, and in the length of the eggs. In addition, molecular analysis of partial 28S rDNA sequences also supported the distinct status of the new species.

Ectosymbiotic bacterial microbiota densely colonize the surface of thelastomatid nematodes in the gut of the wood-feeding cockroach Panesthia angustipennis

Cockroaches generally harbor thelastomatid nematodes (pinworms) in their gut. In this study, we discovered that the surfaces of two undescribed thelastomatid species in the hindgut of the wood-feeding cockroach Panesthia angustipennis were consistently and densely colonized by bacteria. Epifluorescence microscopy using 4',6-diamidino-2-phenylindole and transmission electron microscopy revealed that several distinct morphotypes of bacteria covered almost the entire body surface of the nematodes in single or multiple layers. Sequencing analysis of 16S rRNA amplicons of either entire nematodes or sections of nematode body surfaces indicated that the associated bacterial microbiota consisted of several dominant phylotypes belonging to either Dysgonomonadaceae (Bacteroidales termite cluster V), Rikennellaceae or Ruminococcaceae. These phylotypes formed clades with sequences previously obtained from cockroach and/or termite guts. Comparisons of the bacterial community structure of the entire cockroach hindgut microbiota vs the nematode-associated microbiota suggested that these dominant bacterial phylotypes preferentially colonized the nematode surface. The two nematode species shared most of the dominant bacterial phylotypes, but the bacterial community structures differed significantly. Colonization by five predominant phylotypes was confirmed by fluorescence in situ hybridization analysis using phylotype-specific probes. Our study provides fundamental information on this previously unknown ectosymbiosis between gut bacteria and thelastomatid pinworms.

Broad infectivity of Leidynema appendiculatum (Nematoda: Oxyurida: Thelastomatidae) parasite of the smokybrown cockroach Periplaneta fuliginosa (Blattodea: Blattidae)

Host specificity of parasites is important for the understanding of evolutionary strategies of parasitism that would be a basis of predictions of the disease expansion when parasitized hosts invade new environments. The nematode order Oxyurida is an interesting parasite group for studying the evolution of parasitism as it includes parasites of both invertebrates and vertebrates. In our survey, we found that the smokybrown cockroach Periplaneta fuliginosa was primarily infected with only one nematode species Leidynema appendiculatum. In two cases, L. appendiculatum was isolated from two additional cockroach species Pycnoscelus surinamensis, sold in Japan as a reptile food, and Blatta lateralis, captured in the field and cultured in the laboratory. Inoculation of L. appendiculatum into three additional cockroach species P. japonica, Blattella nipponica, and P. surinamensis also resulted in parasitism. Infection prevalence was high, and timing of postembryonic development from hatched nematode larva to mature adult in these hosts was identical with that in P. fuliginosa. While ecological interactions strongly determine the host range, such broad infectivity is still possible in this parasitic nematode.

Morphological, molecular and developmental characterization of the thelastomatid nematode Thelastoma bulhoesi (de Magalhães, 1900) (Oxyuridomorpha: Thelastomatidae) parasite of Periplaneta americana (Linnaeus, 1758) (Blattodea: Blattidae) in Japan

The American cockroach Periplaneta americana (Linnaeus, 1758) (Blattodea: Blattidae) has been spreading worldwide by commerce and has successfully adjusted to living with humans. There are many reports of thelastomatid parasitic nematode isolated from P. americana in many countries including USA, Canada, India, Argentina, Bulgaria, but not in Japan. We have investigated the parasitic nematodes in P. americana lab strain and field-captured individuals in Japan and found that Thelastoma bulhoesi (de Magalhães, 1900) (Oxyuridomorpha: Thelastomatidae) parasitizes with high infection rates. We described morphological, molecular, and developmental characters of the parasitic nematode because such information was missing despite it has been discovered more than one hundred years ago. We described morphometrics with DIC microscopy and fine structure of male and female adult with SEM observation. We also reveal the embryonic and postembryonic development of this nematode. This is the first report of a thelastomatid nematode isolated from American cockroach in Japan, and the data showed here is also very useful and fundamental for further analysis of the cockroach and parasite relations.

Molecular characterization of two insect nematode species (Oxyurida: Thelastomatidae) using small subunit (18S) ribosomal DNA sequence and secondary-structure analyses

Nematodes of the family Thelastomatidae are parasitic in the alimentary tract of many arthropods, includingPeriplaneta americanaL. In Meerut, Uttar Pradesh, India, two nematode species, namelyHammerschmidtiella indicusandThelastoma icemi, belonging to this family have been reported. In the present study, the molecular phylogeny of these two nematode species was derived using small subunit (18S) sequence and secondary-structure analyses. The small subunit sequence analyses were carried out to explore the validation and systematics of these species. Phylogenetic analyses were performed for primary sequence data as well as using neighbour-joining and maximum-parsimony approaches. In contrast, the inferred secondary structures for the two species, using free-energy modelling, showed structural identities. As well as this, motif sequences were also found to be a promising tool for nematode species identification. The study provides molecular characterization based on primary sequence data of the 18S ribosomal DNA region of the nematodes along with secondary-structure data and motif sequences for inferences at higher taxonomic levels.

The systematics and evolution of pinworms (Nematoda: Oxyurida: Thelastomatoidea) from invertebrates

The nematode order Oxyurida is unique in including species for which definitive host ranges are broad and may include vertebrate or invertebrate hosts. The superfamily Thelastomatoidea is a highly diverse assemblage of oxyurids occurring in cockroaches, diplopods, hydrophilid beetles, passalid beetles, several other coleopteran larvae, mole crickets, and, with few representative species documented, other arthropod hosts. Published research and revision of the Thelastomatoidea, particularly in the 1980s and 1990s, provided several interesting hypotheses on the systematics and evolution of this group. In this review, these hypotheses are examined in the context of recent advances in taxonomy, discovery of additional species diversity and distribution, and preliminary phylogenetic hypotheses that have been proposed. There continues to remain a paucity of phylogenetic data that explore the phylogenetic relationships of the Thelastomatoidea and their relationships to vertebrate-parasitizing pinworms. A combination of mitochondrial and nuclear DNA sequences for representative species across all of the major lineages will be important for more robust phylogenetic hypotheses. Much broader geographical and host taxon sampling is necessary to determine true diversity of the Thelastomatoidea. Modern approaches to species descriptions, such as improvements in light and scanning electron microscopy and the use of molecular approaches to matching male and female nematodes, can also be applied to improve our understanding of the evolution of these fascinating parasites.

Nucleotide alterations in the D3 domain of the large subunit of ribosomal DNA among 21 species of equine strongyle

The expansion segments or divergent (D) domains in the large subunit (LSU) of the ribosomal DNA have been suggested as genetic markers for taxonomic and/or phylogenetic studies of parasites. In the present study, we assessed the degree of sequence variation in the D3 domain and flanking core regions of the LSU for 21 species of equine strongyles (Strongylida: Strongylidae) and determined which positions in the secondary structure of the LSU were associated with the nucleotide alterations. No intraspecific sequence variation was detected in 17 species, for which multiple individual worms were available. Mutations in sequence among species were detected at 19 nucleotide positions, most of which were located in the D3 domain. Fifteen alterations were transitions, three were transversions and one represented a site of multiple mutations. In relation to the secondary structure element of D3, 26% of these mutations were located in unpaired regions (i.e., end of loops, or in bulges of helices) and thus did not appear to alter the pairing arrangement in the helices of the secondary structure. Many of the other mutations represented partial or complete compensatory base pair changes. The magnitude of interspecific nucleotide variation in the D3 domain (0-4%) was considerably less than that recorded for some other nematode groups (enoplids and thelastomatoids), indicating that this region alone is of limited value for taxonomic and phylogenetic studies for strongyles of equids but is interesting in relation to the evolution of ribosomal DNA.