Research Article |
Corresponding author: Shiuh-Feng Shiao ( sfshiao@ntu.edu.tw ) Academic editor: Andreas Schmidt-Rhaesa
© 2017 Ming-Chung Chiu, Chin-Gi Huang, Wen-Jer Wu, Shiuh-Feng Shiao.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Chiu M-C, Huang C-G, Wu W-J, Shiao S-F (2017) A new orthopteran-parasitizing horsehair worm, Acutogordius taiwanensis sp. n., with a redescription of Chordodes formosanus and novel host records from Taiwan (Nematomorpha, Gordiida). ZooKeys 683: 1-23. https://doi.org/10.3897/zookeys.683.12673
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A description of a new species of horsehair worm, Acutogordius taiwanensis sp. n., a redescription of Chordodes formosanus, and novel host records for the latter are provided. Acutogordius taiwanensis sp. n. is morphologically similar to A. protectus with moderately flat areoles on its tail tips, but is distinguishable by small mid-body ornamentations. Despite the distinct differences in the post-cloacal crescents between 14 male samples, their conspecific status, along with that of nine female samples, was upheld by a phylogenetic comparison of partial cytochrome oxidase subunit I (COI) sequences. Chordodes formosanus is another common horsehair worm species in Taiwan, which was previously believed to specifically parasitize Hierodula mantids. However, in this study, five C. formosanus were observed emerging from an Acromantis mantid, and two long-horned grasshopper hosts (Leptoteratura sp. and Holochlora japonica). These five worms showed high degrees of similarity in COI sequences and morphology, but one of these individuals bore abnormal crowned areoles, which has never been observed in C. formosanus, and may be attributed to the incomplete development of this particular individual.
Acutogordius taiwanensis , Chordodes formosanus , immature stage, new species, novel host
Horsehair worms (phylum Nematomorpha) are aquatic parasites whose life cycle typically contains a free-living, aquatic phase, including mating and early larval development, and two parasitic stages, including an aquatic paratenic host stage and a terrestrial definitive host stage (
The definitive hosts of C. formosanus are Hierodula mantids (
In the present study, the conspecific status of 23 Acutogordius samples is established according to minor differences observed in the sequences of their partial mitochondrial DNA cytochrome oxidase subunit I (mtDNA-COI) genes, collected from eleven species of orthopteran hosts, and the morphological differences among these samples is determined as intraspecific variation. Furthermore, the morphology of the immature stages of this species was also described. Five horsehair worm samples that had emerged from Acromantis mantids and two long-horned grasshopper species, i.e., Leptoteratura sp. and Holochlora japonica, were identified as C. formosanus based on morphological and molecular evidence, and thus added these insect species as novel definitive hosts of C. formosanus.
The morphologies and DNA sequences of 29 adult horsehair worms (24 Acutogordius and 5 Chordodes) were examined. Two pairs of Acutogordius were reared in the laboratory for two weeks to breed and lay eggs, and the morphology of the resulting larvae was examined using a light microscope (Olympus BH-2, PM-10AD, Tokyo, Japan). Specimens (partial bodies with their hosts) were preserved at the Department of Entomology, National Taiwan University, Taipei; National Museum of Natural Science, Taichung, Taiwan; and Lake Biwa Museum, Shiga, Japan. Specimen examination followed our previously published methods described in
Insect hosts infected with horsehair worms were hand-collected from a riparian environment. To determine if a host was infected with worms, its posterior was examined, and then the worms were collected by immersing the host in water or by host dissection. Except for the two pairs of Acutogordius that were kept for breeding, all other horsehair worms were killed with hot water (>80°C), fixed in a 75% alcohol solution with their hosts for few days, and preserved in a 95% alcohol solution. The collection and host data are given in Tables
Breeding Acutogordius pairs were reared in 800 mL aerated tap water and maintained at room temperature (~28°C). After mating, the males were removed and fixed and preserved in 75% followed by 95% alcohol solutions. After the mated females laid eggs for one month, they were also removed and fixed and preserved in 75% followed by 95% alcohol solutions. Egg strings were detected at approximately three days, and hatched larvae were detected at approximately 2–3 weeks after egg laying. Live larvae were observed under a light microscope.
Snails (Physa sp.) infected by horsehair worms were collected with nine other non-infected snails from a small pond in Wufengqi Waterfalls, Jiaushi Township, Yilan County, Taiwan, where free-living adult horsehair worms have been seen. Live snails were maintained together in 2000 mL aerated tap water and were dissected after five days.
Adult specimens. Fragments (~0.5 cm in length) of the anterior end, mid-body, and posterior end of the preserved adult horsehair worm samples were first examined under a stereomicroscope (Leica S8 APO, Leica, Wetzlar, Germany). The fragments were dehydrated with a series of ethanol and acetone solutions (95% and 100% ethanol (twice) and ethanol/acetone mixtures of 2:1, 1:1, 1:2, 0:1) and critical-point-dried and gold-sputter-coated before being examined under a scanning electronic microscope (SEM) (JEOL JSM-5600, Tokyo, Japan) at a magnification of 100–15,000×.
Immature stages. Eggs and newly hatched larvae were examined and photographed alive on microslides using a light microscope (Olympus BH-2, PM-10AD, Olympus, Tokyo, Japan) at magnifications of 200× and 400×. Larvae, for examination under SEM, were first killed, fixed by 75% alcohol solution, and collected in a paper envelope soaked in 75% alcohol solution. The protocol of dehydration, critical point drying, and gold sputter coating followed that applied in the examination of the adult fragments and they were examined at a magnification of 500–9,000×. To examine the cysts inside the snail hosts, the snail shells were removed, the soft tissue flattened by two glass slides, and the slides were examined under a light microscope at 200× magnification.
The measurements of each characteristic were performed using the segmented line function in ImageJ 1.47 (
Genomic DNA from adult horsehair worms was extracted using an ALS Tissue Genomic DNA Extraction Kit (Pharmigene, Kaohsiung, Taiwan). A set of universal primers (LCO1490 and HC02198) (
Pairwise genetic distances and phylogenic tree reconstruction using the neighbor-joining (NJ) method, which is based on Kimura’s 2-parameter model, were used to verify conspecific status of the horsehair worm samples. COI sequences (450 high-quality nucleotide base pairs) were first aligned using CLUSTALX 2.0.10 (
Wufengqi Waterfalls (24°49′55.62′′N, 121°44′50.10′′E), Jiaushi Township, Yilan County, Taiwan (holotype and allotype). Paratypes were collected from Sindian, New Taipei City, and the Fushan Botanical Garden, Yilan County. See Table
Partial bodies of the holotype and allotype were deposited with their hosts at the National Museum of Natural Science. Paratypes were deposited at the Department of Entomology, National Taiwan University, Taipei; the National Museum of Natural Science, Taichung, Taiwan; and Lake Biwa Museum, Shiga, Japan. See Table
Acutogordius taiwanensis sp. n. and Chordodes formosanus specimen information.
Horsehair worm | |||||||||
---|---|---|---|---|---|---|---|---|---|
Species | Collection date | GenBank no. | Locality | Longitude and latitude | Collector | Depository | Sex | Length (mm) | Host code |
A. taiwanensis | 16-XI-2014 | KX591947 | Xindian, New Taipei, Taiwan | 24°50'47.70"N 121°32'41.20"E | Shipher Wu | NTU | F | 283 | HAc23302 |
A. taiwanensis | 2-VIII-2009 | KX591922 | Jiaushi, Yilian, Taiwan | 24°49'55.62"N, 121°44'50.12"E | Ming-Chung Chiu | NTU | M | 334 | HAc26201 |
A. taiwanensis | 29-VII-2009 | KX591948 | Fushan botanical garden, Yilian, Taiwan | - | Ming-Chung Chiu | NTU | M | 278 | HAC26401 |
A. taiwanensis | 10-VII-2011 | KX591926 | Jiaushi, Yilian, Taiwan | 24°49'55.62"N, 121°44'50.12"E | Ming-Chung Chiu | NTU | M | 312 | HAc26206 |
A. taiwanensis | 5-VII-2011 | KX5919271 | Jiaushi, Yilian, Taiwan | 24°49'55.62"N, 121°44'50.12"E | Ming-Chung Chiu | NMNS | M | 410 | HAc26207 |
A. taiwanensis | 5-VII-2011 | KX591928 | Jiaushi, Yilian, Taiwan | 24°49'55.62"N, 121°44'50.12"E | Ming-Chung Chiu | NTU | M | 428 | HAc26208 |
A. taiwanensis | 18-VIII-2011 | KX591929 | Jiaushi, Yilian, Taiwan | 24°49'55.62"N, 121°44'50.12"E | Ming-Chung Chiu | NTU | F | 360 | HAc26209 |
A. taiwanensis | 20-VII-2010 | KX591930 | Jiaushi, Yilian, Taiwan | 24°49'55.62"N, 121°44'50.12"E | Ming-Chung Chiu | NTU | M | 387 | HAc26210 |
A. taiwanensis | 24-IX-2011 | KX591931 | Jiaushi, Yilian, Taiwan | 24°49'55.62"N, 121°44'50.12"E | Ming-Chung Chiu | LBM | M | 262 | HAc26211-12 |
A. taiwanensis | 24-IX-2011 | KX591932 | Jiaushi, Yilian, Taiwan | 24°49'55.62"N, 121°44'50.12"E | Ming-Chung Chiu | LBM | F | 272 | HAc26211-12 |
A. taiwanensis | 5-VIII-2012 | KX5919332 | Jiaushi, Yilian, Taiwan | 24°49'55.62"N, 121°44'50.12"E | Ming-Chung Chiu | NMNS | F | 288 | HAc26214 |
A. taiwanensis | 21-VII-2012 | KX591934 | Jiaushi, Yilian, Taiwan | 24°49'55.62"N, 121°44'50.12"E | Ming-Chung Chiu | NMNS | M | 133 | HAc26215 |
A. taiwanensis | 21-XI-2012 | KX591935 | Jiaushi, Yilian, Taiwan | 24°49'55.62"N, 121°44'50.12"E | Ming-Chung Chiu | NMNS | M | 241 | HAc26217 |
A. taiwanensis | 31-VIII-2012 | KX591937 | Jiaushi, Yilian, Taiwan | 24°49'55.62"N, 121°44'50.12"E | Ming-Chung Chiu | NMNS | M | 222 | HAc26219-20 |
A. taiwanensis | 31-VIII-2012 | KX591938 | Jiaushi, Yilian, Taiwan | 24°49'55.62"N, 121°44'50.12"E | Ming-Chung Chiu | NMNS | M | 216 | HAc26219-20 |
A. taiwanensis | 31-VIII-2012 | KX591939 | Jiaushi, Yilian, Taiwan | 24°49'55.62"N, 121°44'50.12"E | Ming-Chung Chiu | NMNS | F | 322 | HAc26221-21A |
A. taiwanensis | 31-VIII-2012 | NA3 | Jiaushi, Yilian, Taiwan | 24°49'55.62"N, 121°44'50.12"E | Ming-Chung Chiu | NMNS | F | 73 | HAc26221-21A |
A. taiwanensis | 31-VIII-2012 | KX591940 | Jiaushi, Yilian, Taiwan | 24°49'55.62"N, 121°44'50.12"E | Ming-Chung Chiu | NMNS | F | 285 | HAc26222 |
A. taiwanensis | 26-VII-2014 | KX591941 | Jiaushi, Yilian, Taiwan | 24°49'55.62"N, 121°44'50.12"E | Ming-Chung Chiu | LBM | M | 369 | HAc26223 |
A. taiwanensis | 26-VI-2015 | KX591942 | Jiaushi, Yilian, Taiwan | 24°49'55.62"N, 121°44'50.12"E | Ming-Chung Chiu | NTU | M | 164 | HAc26225-26 |
A. taiwanensis | 26-VI-2015 | KX591943 | Jiaushi, Yilian, Taiwan | 24°49'55.62"N, 121°44'50.12"E | Ming-Chung Chiu | NTU | F | 166 | HAc26225-26 |
A. taiwanensis | 17-VII-2015 | KX591944 | Jiaushi, Yilian, Taiwan | 24°49'55.62"N, 121°44'50.12"E | Ming-Chung Chiu | LBM | M | 280 | HAc26228 |
A. taiwanensis | 17-VII-2015 | KX591945 | Jiaushi, Yilian, Taiwan | 24°49'55.62"N, 121°44'50.12"E | Ming-Chung Chiu | LBM | F | 432 | HAc26231 |
A. taiwanensis | 17-VII-2015 | KX591946 | Jiaushi, Yilian, Taiwan | 24°49'55.62"N, 121°44'50.12"E | Ming-Chung Chiu | LBM | F | 237 | HAc26232 |
C. formosanus | 11-II-2015 | KX591949 | Taipei Zoo, Taipei City, Taiwan | 24°59'44.70"N, 121°34'49.49"E | Long-Chun Huang | NMNS | M | 58 | HCH11606-8 |
C. formosanus | 11-II-2015 | KX591950 | Taipei Zoo, Taipei City, Taiwan | 24°59'44.70"N, 121°34'49.49"E | Long-Chun Huang | NMNS | M | 125 | HCH11606-8 |
C. formosanus | 11-II-2015 | KX591951 | Taipei Zoo, Taipei City, Taiwan | 24°59'44.70"N, 121°34'49.49"E | Long-Chun Huang | NMNS | M | 115 | HCH11606-8 |
C. formosanus | 4-III-2015 | KX591952 | Jiaushi, Yilian, Taiwan | 24°49'55.62"N, 121°44'50.12"E | Ming-Chung Chiu | NTU | M | 43 | HCH26207 |
C. formosanus | 10-XI-2015 | KX591953 | Jiaushi, Yilian, Taiwan | 24°49'55.62"N, 121°44'50.12"E | Ming-Chung Chiu | NTU | M | 204 | HAc26216 |
Eugryllacris sp., Neanias magnus Matsumura and Shiraki, 1908 (Orthoptera: Gryllacrididae), Deflorita apicalis (Shiraki, 1930), Elimaea sp., Hexacentrus japonicus Karny, 1907, H. unicolor Serville, 1831, Isopsera sp., Mecopoda elongata (Linnaeus, 1758), Phaulula sp., Pyrgocorypha formosana Matsumura and Shiraki, 1908, Sinochlora longifissa (Matsumura and Shiraki, 1908) (Orthoptera: Tettigoniidae). See Table
Host code (see Table |
Host species | Host sex | Host length (mm) |
---|---|---|---|
HAc23302 | Mecopoda elongata | M | 31.5 |
HAc26201 | Eugryllacris sp. | M | 27.5 |
HAC26401 | Neanias magnus | F | 20.5 |
HAc26206 | Neanias magnus | M | 21.9 |
HAc26207 | Eugryllacris sp. | M | 27.2 |
HAc26208 | Eugryllacris sp. | M | 25.9 |
HAc26209 | Hexacentrus japonicus | F | 29.4 |
HAc26210 | Sinochlora longifissa | F | 33.5 |
HAc26211-12 | Hexacentrus unicolor | F | 28.8 |
HAc26214 | Elimaea sp. | F | 27.1 |
HAc26215 | Deflorita apicalis | M | 22.3 |
HAc26217 | Pyrgocorypha formosana | F | 41.3 |
HAc26219-20 | Phaulula sp. | F | 23.1 |
HAc26221-21A | Hexacentrus unicolor | F | 23.9 |
HAc26222 | Hexacentrus unicolor | F | 29.1 |
HAc26223 | Elimaea sp. | F | 27.2 |
HAc26225-26 | Neanias magnus | M | 17.9 |
HAc26228 | Hexacentrus unicolor | M | 28.4 |
HAc26231 | Eugryllacris sp. | F | 30.6 |
HAc26232 | Isopsera sp. | M | 24.1 |
HCH11606-8 | Acromantis japonica | F | 29.4 |
HCH26207 | Leptoteratura sp. | F | 9.6 |
HAc26216 | Holochlora japonica | F | 39.2 |
The specific name refers to the type locality, Taiwan.
Acutogordius taiwanensis sp. n. is morphologically similar to A. protectus Schmidt-Rhaesa and Geraci, 2006 with regards to the (1) distribution pattern of tiny bristles on the ventral posterior end, (2) moderately flat areoles (rounded in elevation) covering the tail tips, and (3) cone-shaped spines scattered on the base of the tail lobes of the male samples. However, it is distinct because of the small ornamentations on the mid-body.
Description (Figs
Anterior end columnar and slightly narrowed at tip; anterior tip white (white cap) with a dark-brown collar (Fig.
Anterior end of Acutogordius taiwanensis sp. n. A–C Images of the anterior end showing the (A) white cap and dark-brown collar and B–C white spots scattered on the brown collar D–FSEM images of the anterior end surface that is D smooth E smooth but wrinkled on the tip with holes scattered on the dark-brown collar, and F wrinkled A–F are images from the same individual, respectively. Scale bars 500 µm (A–C), and 200 μm (D–F).
Posterior end of male Acutogordius taiwanensis sp. n. A–C Images of the posterior end with the postcloacal crescent extending A, C over or B anterior to the starting point of the tail lobe bifurcation D–FSEM images of the posterior end with a D angled E slightly curved, and F semicircular postcloacal crescent A–F are images from the same individual, respectively. Scale bars 500 µm (A–C), and 200 μm (D–F).
Cuticle in mid-body smooth, slightly wrinkled, or cracked; short or cone-like bristles (Fig.
Posterior end divided into two tail lobes, each 360.25 ± 53.30 (303.70–489.58) µm in length; lobe tips generally tapered, wrinkled, or covered by moderately flat areoles with short spines amongst areoles; inner side of tail lobes smooth; tiny spines scattered around tip; cone-shaped spines or flat areoles scattered on base behind post-cloacal crescent.
Ventral side of posterior end structured with post-cloacal crescent, cloacal opening, and tiny bristles. One post-cloacal crescent not evident as it was covered by larval cuticle, post-cloacal crescent length (extension along longitudinal axis) 275.48 ± 68.84 (195.78–417.03) µm, width (widest) 44.81 ± 16.21 (18.73–83.01) µm, located near base of tail lobes; post-cloacal crescent slightly curved (Fig.
Detailed diagnostic characteristics of male Acutogordius taiwanensis sp. n. A Tiny bristles scattered anterior to postcloacal crescent B Tiny bristles scattered in concentrated groups on tail lobes C Lobe tips covered by moderately flat areoles with short spines amongst areoles D–E Short bristles scattered on the mid-body cuticle. Scale bars 200 µm (A–B), 100 µm (C–D), and 10 μm (E).
Female adults (n = 10) (Fig.
Morphological variation of the cuticle that may result from mucus. A Smooth cuticle B–C Wrinkled cuticle D–E Cracked surface of cuticle F Areole-like structures on the anterior end of the cuticle G–J Indentations on the G–I mid-body and J anterior end of the cuticle surface. Scale bars 100 µm (A), 10 µm (B), 50 µm (C–E), 100 µm (F), 20 µm (G), 100 µm (H), 10 µm (I), and 100 µm (J).
Eggs (Fig.
Larvae (Fig.
Under SEM (worm-form larvae), larvae superficially annulated with 13 segments on pre-septum and 35 on post-septum, ectodermal septum not distinguishable (Fig.
Field-collected cysts (Fig.
Immature stages of Acutogordius taiwanensis sp. n. A–B Live A cyst-form and B worm-form larvae in water C Posterior view of a worm-form larva D Cysts in an infected snail; E Worm-form larva under SEMF Anterior view of a larva showing the hook arrangement G Egg strings H Close-up of the proboscis. DS, dorsal spines; Ho, hooklet; LS, lateral spines; Peo, pseudointestine exterior opening; PostS, postseptum; PreS, preseptum; Pro, proboscis; PS, proboscis sheath; PsI, pseudointestine gland. Scale bars 50 µm (A–B), 2 µm (C), 50 µm (D), 10 µm (E), 5 µm (F), 1 cm (G), and 2 µm (H).
Except for one female with insufficient DNA for sequencing, the 23 AcutogordiusCOI sequences (GenBank numbers KX591922, KX591926–KX591935, KX591937–KX591948) contained eight haplotypes with 442 invariable sites, six singletons, and two parsimoniously informative sites. The genetic distance among them was 0.0025 with a range of 0.0000–0.0112. The phylogenetic tree had a polytomic topology in which some clades were not highly supported because of low bootstrap values and short genetic distances (Fig.
The 23 Acutogordius samples from orthopteran hosts were determined to be from a single species based on their low genetic distances, which was similar to the intraspecific pairwise distances found within G. cf. robustus (0.64–2.63%) (
All three morphological types of post-cloacal crescents identified in A. protectus were apparent in the Acutogordius taiwanensis sp. n. samples. Nevertheless, post-cloacal crescents significantly extending onto the tail lobes were only described in Acutogordius taiwanensis sp. n. and previously in A. acuminatus
Short bristles on the mid-body were a newly described character, which were first found in A. finni (
Taipei Zoo (24°59′44.70′′N, 121°34′49.49′′E), Taipei City, Taiwan (three males from an Acromantis japonica individual); Wufengqi Waterfalls (24°49′55.62′′N, 121°44′50.10′′E), Jiaushi Township, Yilan County, Taiwan (two males from two Tettigoniidae species). For specimen details, see Table
Acromantis japonica Westwood, 1889 (Mantodea: Mantidae). Leptoteratura sp., Holochlora japonica Brunner von Wattenwyl, 1878 (Orthoptera: Tettigoniidae). For host details, see Table
(Fig.
Except for one sample with the broken posterior end, which was not described, the posterior end of the other 4 samples (Fig.
Mid-body covered with areoles with some ornamentation on surface. Areoles characterized into five types (simple, tubercle, thorn, circumcluster, and crowned areoles). Simple areoles, most abundant, covering entire cuticle of mid-body, 9.70 ± 1.84 (8.18–12.51) μm in diameter, circular, surface smooth or uneven. Tubercle areoles and thorn areoles scattered among simple areoles, similar in shape, but with a tubercle (ca. 3.96–8.09 μm long) or a solid thorn (ca. 7.35–16.92 μm long), respectively, on the latter or on top of thorn areoles; thorn areoles less abundant than tubercle areoles and not found in one sample. Crowned areoles (Fig.
Male adult Chordodes formosanus from novel hosts. A Posterior end B Anterior end C–D Variable crowned areole morphologies from different individuals E Close view of (C) with typical C. formosanus crowned areoles; F Close view of (D) with smaller crowned areoles. Ca, crowned areole. Scale bars 100 µm (A), 10 µm (B), 100 µm (C–D), and 10 µm (E–F).
The genetic distances among all horsehair worms from Acromantis japonica (GenBank nos: KX591949- KX591951), Leptoteratura sp. (GenBank no.: KX591952), Holochlora japonica (GenBank no.: KX591953), and Hierodula mantid (sequences from
The five male horsehair worms were all determined to be C. formosanus because of the low genetic distances between their COI sequences and those of C. formosanus individuals as described in
The size of the bristlefields was smaller in individuals in the present study than in those described in
Another abnormal morphological feature was the similar-sized paired crowned areoles and their surrounding circumcluster areoles. These “abnormal crowned areoles” were only found in one extremely small individual, but not in the other horsehair worms, including the two large ones that emerged from the same host individual. Because the molecular data suggested that this individual was conspecific with C. formosanus, we believe the abnormal crowned areoles may have been caused by incomplete development during synchronized maturation (see Discussion for details).
In this article, a new species, Acutogordius taiwanensis sp. n. and its immature stages were described, and 11 species of orthopteran insect hosts of this new species were identified. In addition, three novel hosts of C. formosanus, Acromantis japonica, Leptoteratura sp., and Holochlora japonica, were identified.
Intraspecific variation. Finding stable diagnostic characters is a crucial step in distinguishing horsehair worm species (
Using SEM to describe nematormorph species has become standard practice (
Because of high intraspecific variation, the conspecific status of the 28 examined samples of Acutogordius taiwanensis sp. n. was primarily based on the comparison of DNA barcodes and secondarily supported by the similarity of hosts and habitat. DNA sequencing, with the application of SEM since 1980 (reviewed in
The immature stages of Acutogordius. Studies of the immature stages of horsehair worms have received more attention in recent years. Although morphological identification of the immature stage to the genus level is only now roughly possible (
Newly hatched larvae that fold their bodies outside of hosts have rarely been described (
Acutogordius taiwanensis sp. n. hosts. Prior to this study, the only reported host of Acutogordius was Acanthodis sp. (reviewed in Schmidt-Rhaesa 2013). In the case of Acutogordius taiwanensis sp. n., it was found to emerge from several families of Orthoptera with different foraging behaviors. Most of the hosts are obligate or facultative predators and are frequently found to prey on small insects in the field (e.g., Eugryllacris sp., Neanias magnus, Hexacentrus japonicus, and H. unicolor), but some of them are primarily herbivorous in Taiwan (e.g., Deflorita apicalis, Elimaea sp., Isopsera sp., and Phaulula sp.). Adult horsehair worms have emerged from non-carnivorous hosts, herbivores (Barbitistes serricauda, Leptophyes punctatissima), or detritivores (Cambala annulata) (
Novel hosts. The Acromantis mantid and Leptoteratura sp. are general predators that can easily ingest the cysts of C. formosanus in paratenic hosts, but C. formosanus was previously thought to develop specifically inside Hierodula mantids (
In the present study, we recorded long-horn grasshoppers and an Acromantis mantid as hosts of C. formosanus. However, we do not think these novel hosts are the general ones used by C. formosanus. Horsehair worm hosts have been recorded for most of horsehair worm genera (Schmidt-Rhaesa 2013), but knowledge of host preference, the extent to which a particular host taxon is used by a parasite (
Abnormal morphology of the smallest individual. Horsehair worm length is strongly correlated to the host’s size and to the number of individuals in a single host (
The possible reason causing incomplete development may be resource competition and synchronized maturation. Horsehair worms inside a host individual may compete for resources to increase their fecundity, or they may ensure their survival by synchronizing maturation before the host performs the suicide behavior. These actions would subsequently cause the horsehair worm, which may enter the host later than its neighbors, to mature without completing its development. Thus, we suggest that the abnormal crowned areoles may be a result of incomplete development rather than small size. This hypothesis could also be supported by another extremely small C. formosanus (43 mm in length) with crowned areoles that were more likely to be normal in this study. This small C. formosanus singly developed in a host individual. Without the influence from neighbor horsehair worms, its small size might have been the result of the small host (9.63 mm in length), instead of incomplete development.
We deeply appreciate the assistance provided by Shipher Wu and Long-Chun Huang for sample collection, Po-Wei Chen for host identification, and Jhih-Rong Liao for DNA sequencing.
This work was supported by the Ministry of Science and Technology, Taiwan (104-2313-B-002-017); the Bureau of Animal and Plant Health Inspection and Quarantine, Council of Agriculture, Taiwan (105AS-10.6.4-BQ-B1(1–2)); and the Yangmingshan National Park, Taiwan (20130740).