Effect of temperature on emergence, survival and infectivity of cercariae of the marine trematode Renicola roscovita (Digenea: Renicolidae)

Marine bivalves harbour a diversity of trematode parasites affecting population and community dynamics of their hosts. Although ecologically and economically important, factors influencing transmission between first (snail) and second (bivalve) intermediate hosts have rarely been studied in marine systems. In laboratory experiments, the effect of temperature (10, 15, 20, 25 degrees C) was investigated on (1) emergence from snails, (2) survival outside hosts and (3) infectivity in second intermediate hosts of cercariae of the trematode Renicola roscovita (Digenea: Renicolidae), a major parasite in North Sea bivalves. Emergence of cercariae peaked at 20 degrees C (2609 +/- 478 cercariae snail(-1) 120 h(-1)) and was considerably lower at 10 degrees C (80 +/- 79), 15 degrees C (747 +/- 384) and 25 degrees C (1141 +/- 334). Survival time decreased with increasing temperature, resulting in 50% mortality of the cercariae after 32.8 +/- 0.6 h (10 degrees C), 26.8 +/- 0.8 h (15 degrees C), 20.2 +/- 0.5 h (20 degrees C) and 16.6 +/- 0.3 h (25 degrees C ). Infectivity of R. roscovita cercariae in cockles Cerastoderma edule increased with increasing temperature and was highest at 25 degrees C (42.6 +/- 3.9%). However, mesocosm experiments with infected snails and cockle hosts in small aquaria, integrating cercarial emergence, survival and infectivity, showed highest infection of cockles at 20 degrees C (415 +/- 115 metacercariae host(-1)), indicating 20 degrees C to be the optimum temperature for transmission of this species. A field experiment showed metacercariae of R. roscovita to appear in C. edule with rising water temperature in April; highest infection rates were in August, when the water temperature reached 20 degrees C. Since another trematode species (Himasthla elongata; Digenea: Echinostomatidae) occurring at the experimental site showed a similar temporal pattern, trematode transmission to second intermediate bivalve hosts may peak during especially warm (> or = 20 degrees C) summers in the variable climate regime of the North Sea.     

Vertical migration of cercariae of the littoral trematode Renicola thaidus (Trematoda: Renicolidae) in the water layer

Vertical dispersion of the cercariae Renicola thaidus in the water layer was examined in experiments. Dispersion of larvae of 1 and 6 hours old were investigated in different conditions of illumination. It was found out that in the first hour of life the larvae both in light and dark conditions display a negative geotaxis. 6 hours later, the reaction alternates. Both in light and dark condition, the larvae show a positive geotaxis. This changes of vertical dispersion is the result of inversion of the reaction onto the gravitation, that depends on biology of cercariae examined.     

The occurrence of metacercariae of Bucephaloides gracilescens (Digenea: Gasterostomata) in an intermediate host, the four-bearded rockling, Enchelyopus cimbrius (Gadidae)

Infections with metacercariae of Bucephaloides gracilescens in the four-bearded rockling Enchelyopus cimbrius were studied for a year in a Norwegian fjord. The prevalence was at all times high, but abundance showed a marked decline in spring to a low level during summer. A rise in abundance, variance-to-mean ratio and frequency of smaller metacercariae in early autumn (August-September) shows infection to have occurred mainly in autumn. There were no differences in level of infection between host sexes, but a highly significant positive correlation of parasite burden with host length. No influence on the condition factor of the host was revealed, the parasite cysts in the central nervous system are believed to have low pathogenicity. A detailed account of the distribution of metacercarial cysts is given. No support for infection being via the lateral line canals is revealed, cercarial penetration is believed to be through the general surface of the head and through the unpaired fins of the trunk and tail.     

A new species,new host records and life cycle data for lepocreadiids (Digenea) of pomacentrid fishes from the Great Barrier Reef,Australia

A new species of lepocreadiid, Opechonoides opisthoporus n. sp., is described infecting 12 pomacentrid fish species from the Great Barrier Reef, Australia, with Abudefduf whitleyi Allen & Robertson as the type-host. This taxon differs from the only other known member of the genus, Opechonoides gure Yamaguti, 1940, in the sucker width ratio, cirrus-sac length, position of the testes, position of the pore of Laurer’s canal, and relative post-testicular distance. The new species exhibits stenoxenic host-specificity, infecting pomacentrids from seven genera: Abudefduf Forsskål, Amphiprion Bloch & Schneider, Neoglyphidodon Allen, Neopomacentrus Allen, Plectroglyphidodon Fowler & Ball, Pomacentrus Lacépède and Stegastes Jenyns. Phylogenetic analyses of 28S rDNA sequence data demonstrate that O. opisthoporus n. sp. forms a strongly supported clade with Prodistomum orientale (Layman, 1930) Bray & Gibson, 1990. The life cycle of this new species is partly elucidated on the basis of ITS2 rDNA sequence data; intermediate hosts are shown to be three species of Ctenophora. New host records and molecular data are reported for Lepocreadium oyabitcha Machida, 1984 and Lepotrema amblyglyphidodonis Bray, Cutmore & Cribb, 2018, and new molecular data are provided for Lepotrema acanthochromidis Bray, Cutmore & Cribb, 2018 and Lepotrema adlardi (Bray, Cribb & Barker, 1993) Bray & Cribb, 1996. Novel cox1 mtDNA sequence data showed intraspecific geographical structuring between Heron Island and Lizard Island for L. acanthochromidis but not for L. adlardi or O. opisthoporus n. sp.

     

Effect of temperature on the infectivity of metacercariae of Zygocotyle lunata (Digenea: Paramphistomidae)

As a test of the energy limitation hypothesis (ELH), we predicted that temperature would have a significant influence on the infectivity of metacercariae of the digenetic trematode Zygocotyle lunata. Snails infected with Z. lunata were collected from ponds near Crawfordsville, Indiana, isolated at room temperature, and examined for the release of cercariae. Newly encysted metacercariae were collected and incubated 1-30 days at 1 of 5 temperatures (0, 3, 25, 31, 37 C). Twenty-five cysts were fed to each of 5 or 10 mice per treatment group (temperature). At 17 days postinfection, mice were killed and worms were recovered; data were collected on levels of infection in each group and the total body area of each worm. No worms were found in mice fed cysts that had been held at 0 C or 37 C (after 30 days). There were no differences in prevalence, infectivity, or mean intensity among the 3, 25, and 31 C treatments. Infectivity of metacercariae incubated at 37 C for 1 day was significantly greater than in all other treatments, while infectivity of metacercariae in the 37 C/15-day treatment was significantly lower than in all others. Mean body area of worms at 37 C/15 days was significantly greater than at other temperatures, suggesting density-dependent increases in growth. These results, particularly those from the 37 C treatments, are consistent with the ELH; infectivity was lower at high temperatures or when incubated for more time at 1 temperature (fewer energy reserves). It is suggested that microhabitat conditions experienced by metacercariae of Z. lunata could contribute to longer larval life, thus influencing this parasite's temporal dispersal.     

Holostephanus metorchis (Digenea: Cyathocotylidae) from chicks experimentally infected with metacercariae from a fish, Pseudorasbora parva, in the Republic of Korea

Holostephanus metorchis (Digenea: Cyathocotylidae) is a parasite of birds, transmitted by freshwater fishes. H. metorchis adults were recovered from chicks experimentally infected with metacercariae collected from freshwater fishes, Pseudorasbora parva. The metacercariae were oval, surrounded with thick fibrous capsules. In adult flukes, the holdfast organ occupied the ventral concavity, and the anterior testis did not reach the level of the ventral sucker. Based on these morphological characteristics, these flukes were identified as H. metorchis.     

Cultivation of Clinostomum marginatum (Digenea: Clinostomatidae) metacercariae in vitro, in chick embryo and in mouse coelom

Metacercariae of Clinostomum marginatum obtained from naturally infected Perca flavescens were cultured by 5 methods. In vitro cultivation at 37 C in twice daily changes of Tyrode's, Na-poor Tyrode's, and Eagle's media failed to produce ovigerous adults after 4-5 days. Metacercariae placed on the chorioallantois of week-old chick embryos at 37 C migrated to the albumen. Only 8 of 123 worms recovered were ovigerous after 4-7 days in ovo. Best success occurred with metacercariae injected in groups of 4 or 6 into the abdominal cavities of male A/J mice. Despite liver lesions and strong inflammatory responses in the host, all 174 worms recovered were ovigerous after 4-8 days. None of 41 mice died prematurely from the procedure or the parasites.     

Paracrias pluteus (Hymenoptera, Eulophidae) in Brazil: new distribution and host records, and with a new host group for Paracrias

Bruchines damage agricultural crops and trees, reducing the quantity and quality of the seeds. The aim of this study is to record, for the first time, Paracrias pluteus as a parasitoid on the immature stages of Sennius spodiogaster and Sennius cupreatus on seeds of Melanoxylon brauna in Teixeiras, Minas Gerais State, Brazil. Paracrias pluteus is a parasitoid without previous host records and known only from Costa Rica. Specimens obtained in this study add to knowledge of the biology of Paracrias species with a new host group (Chrysomelidae: Bruchinae), and the first host record and a new distribution for Paracrias pluteus.     

A new neodiplostomid (Digenea) from the intestine of chicks infected with metacercariae from the grass snake, Rhabdophis tigrina

Three species of neodiplostomula are known to inhabit the European grass snake, Rhabdophis tigrina, in the Republic of Korea: Pharyngostomum cordatum (large-sized neodiplostomula), an intestinal trematode of cats; Neodiplostomum seoulense (small-sized neodiplostomula), an intestinal trematode of humans and rodents; and Neodiplostomum leei (small-sized neodiplostomula), which migrates to the livers of rodents and is an intestinal trematode of birds. The present study describes a fourth species, Neodiplostomum (Conodiplostomum) boryongense n. sp. (Digenea: Neodiplostomidae), based on adult flukes recovered from the small intestines of chicks experimentally infected with small-sized neodiplostomula from the grass snake. The new species differs from 13 previously known species. It also differs from N. seoulense in its larger body size, severely bilobed testes, and smaller genital atrium, and from N. leei in its larger body size, smaller ventral sucker, presence of a genital cone, and vitelline follicles distributed chiefly in the forebody. The new species does not migrate to the livers of rodents nor does it develop to adulthood in the rodent intestines. However, the neodiplostomula of the new species are indistinguishable from those of the other 2 species. Results show that at least 4 species of neodiplostomula inhabit the grass snake in the Republic of Korea.     

Morphological and molecular differentiation of Clinostomum complanatum and Clinostomum marginatum (Digenea: Clinostomidae) metacercariae and adults

The separation of Clinostomum complanatum Rudolphi, 1814 and Clinostomum marginatum Rudolphi, 1819 has long been unclear. Recent data confirm the validity of the junior species, C. marginatum , by ～ 1% differences in its 18S rDNA sequences. We collected adults and metacercariae of C. complanatum and C. marginatum and found reliable morphological differences in the genital complex at both developmental stages. In addition, we identified basic morphometrics (distance between suckers, body width) in metacercariae that may be useful for discriminating the species. The morphological differences were supported by the comparison of sequences of internal transcribed spacers of ribosomal DNA and of the mitochondrial gene cytochrome c oxidase I (COI) from 39 specimens. In 36 specimens, the average divergence between the species was 7.3% in ITS and 19.4% in COI sequences. Two specimens from North America and 1 from Europe had sequences that did not allow them to be clearly allied with either species.     

Redescription of Closterocerus cruy (Girault) (Hymenoptera: Eulophidae: Entedoninae), with new geographical and host records

Abstract  Closterocerus cruy (Girault) is newly recorded, both from New Zealand and as a parasitoid of lepidopteran leafminers. The species is redescribed from the Girault type and from New Zealand material. Diagnostic character states are provided for the separation of C. cruy from the closely related Australian agromyzid parasitoid C. mirabilis Edwards and LaSalle.     

The ruddy turnstone, Arenaria interpres interpres, a new definitive host for Gynaecotyla squatarolae (Digenea: Microphallidae)

The ruddy turnstone, Arenaria interpres interpres, a migratory Korean bird, was proved to be a natural definitive host for Gynaecotyla squatarolae (Digenea: Microphallidae). The ruddy turnstone was found dead at the seashore of Okgueup, Gunsan-si, Jeollabuk-do. The intestinal tract was examined, and 98 unknown flukes were recovered. The worms were 600 284 micrometer in size, and had 2 ventral suckers. The seminal vesicle was large, the genital atrium was prominent, and the average egg size was 20 12.5 micrometer. Based on these results, the worms were identified as G. squatarolae. This is the first report on the ruddy turnstone as a natural definitive host of G. squatarolae in the Republic of Korea.     

Infection patterns in white sea blue mussels Mytilus edulis of different age and size with metacercariae of Himasthla elongata (Echinostomatidae) and Cercaria parvicaudata (Renicolidae)

Infection of mussels Mytilus edulis L. by 2 trematode species was studied in a natural intertidal population in the Chupa inlet of the White Sea. The prevalence of metacercariae of Himasthla elongata (Mehlis, 1831) and Cercaria parvicaudata (Stunkard & Shaw, 1931) in mussels reached 100% in 3 to 4 yr old molluscs and remained at this level in older individuals. Infection intensity increased evenly with the age of the molluscan host, showing a tendency to decrease only in the oldest (9 yr old) mussels. These patterns of age dynamics of prevalence and infection intensity were associated with accumulation of trematode larvae in the course of the molluscs' lives. Ability of metacercariae to exist in mussels for long periods (at least 2.5 yr) was verified in the course of an experiment, during which infected molluscs were kept in a subtidal net cage. Decrease of infection intensity in the oldest individuals may reflect selective mortality of the most severely infected molluscs. Among mussels of the same age, higher infection intensity values occurred in larger individuals. This may be due to an enhanced pumping rate in large molluscs, which increases the probability of cercariae, free-living trematode larvae, infecting them via water currents.     

Gynaecotyla squatarolae (Digenea: Microphallidae) from rats experimentally infected with metacercariae from the shore crab, Macrophthalmus dilatatus

Metacercariae of Gynaecotyla squatarolae (Digenea: Microphallidae) were discovered from the shore crab, Macrophthalmus dilatatus, purchased at a market in a coastal town of Taean-Eup, Chungcheongnam-do, Republic of Korea. Their adult flukes were confirmed by experimental infection of rats. The metacercariae of G. squatarolae were elliptical (391.1 x 362.5 micrometer), and the excysted metacercariae had progenetic genital organs, including the ovary and testes. To obtain adult flukes, 6 Sprague-Dawley rats were fed 500 metacercariae each, and killed at days 2, 4, and 6 post-infection. The adult flukes were identified as G. squatarolae (Yamaguti, 1934) Yamaguti, 1939, based on morphological characters, including 2 ventral suckers (1 large and 1 small), a large genital atrium equipped with the cirrus and the metraterm, separated male and female genital pores, a transversely long cirrus pouch, and extensive vitelline follicles. In the present study, it has been first proven that the shore crab M. dilatatus is a second intermediate host for G. squatarolae in the Republic of Korea.     

Melanoides tuberculata (Mollusca: Thiaridae) harboring renicolid cercariae (Trematoda: Renicolidae) in Brazil

Melanoides tuberculata , naturally infected by gymnocephalous cercariae, were found in aquatic collections from Belo Horizonte, Minas Gerais, Brazil. After morphological characterization, larvae were used for experimental infection of Poecilia reticulata. Metacercariae were obtained from the liver of these fish, which were also found to be naturally infected in the same locality. The morphology and biology of the developmental stages of trematodes we obtained were characteristic of Renicola sp. This is the first record of renicolid cercariae and metacercariae in Brazil.     

Seasonal occurrence of Dollfustrema vaneyi (Digenea: Bucephalidae) metacercariae in the bullhead catfish Pseudobagrus fulvidraco in a reservoir in China

The seasonal population dynamics of metacercariae of the bucephalid Dollfustrema vaneyi (Tseng, 1930) Echmann, 1934 in the bullhead catfish Pseudobagrus fulvidraco (Richardson) were investigated in Jiangkou reservoir, Jiangxi Province, east China, during the period from April 1990 to August 1991. In total, 523 fish were obtained, and the overall prevalence of the metacercariae was 89.87% and mean abundance 136.25 +/- 308.09 (mean +/- SD). A pattern of seasonal changes in prevalence and mean abundance was observed, with higher levels of metacercariae infection in late spring and summer. An analysis of the distribution of D. vaneyi in different organs of P. fulvidraco suggested that the eyes might be a suitable location for the parasite. Furthermore, the possible role of metacercariae in bullhead catfish was discussed in relation to the life cycle of this parasite.