Category Archives: Parasites

Friday Fellow: Grasshopper Nematode

by Piter Kehoma Boll

About one and a half year ago, I presented the long and thread-like wood cricket’s worm, a parasite that can control the behavior of the wood cricket and leaves its body once becoming an adult. The wood cricket’s worm belongs to the phylum Nematomorpha, commonly known as horsehair worms. They are closely related to phylum Nematoda, the roundworms. And just like horsehair worms, roundworms also love to infect crickets and grasshoppers.

One of those species is Mermis nigrescens, known as the grasshopper nematode. This worm can be found all over the world where grasshoppers exist, although they seem to be more common in Eurasia and the Americas.

An adult, gravid female. Photo by wikimedia user Beentree.**

Adults of the grasshopper nematode live in the soil and are very large for a nematode. Males measure about 5 cm in length and females can reach 20 cm, which is much larger than most nematodes that infect insects. They are, therefore, very similar to horsehair worms in appearance and behavior. The body has a smooth surface and a pale brown color, with females having a red spot on their head, the chromatopore, which functions like an eye.

After adults mate in spring or summer, males usually die but females remain in the soil through fall and winter and emerge in the following spring after a rainfall. They show a black stripe running along the body that is caused by thousands of eggs inside. They climb the nearby vegetation, up to 3 m above the ground, and lay their eggs, which measure about 0.5 mm in length, on it.

A female climbing the vegetation. Photo by Wikimedia user Notafly.**

In order to be able to climb the vegetation, female grasshopper nematodes show positive phototaxis, i.e., they are attracted by light sources, which is the opposite of what happens with most nematodes that have eyes. In fact the female’s eye, the chromatopore, is a single structure, like a single eye, and seems to have evolved independently from other nematode eyes. Its red color is caused by a hemoglobin, like the one that makes our blood red, but in this case it seems to function as a light receptor.

A closeup of the female eye and a transverse section through it. Extracted from Burr et al. (2000).*

When the eggs are ingested by an orthopteran insect (usually a grasshopper but sometimes a katydid), they hatch almost immediately. The young worm pierces the grasshopper’s gut and enters its hemocoel, the “blood cavity” of the body.

An adult around its dead host, a katydid. Photo by Wikimedia user Beentree.**

There, the worm develops by absorbing nutrients from the insect’s blood directly through its cuticle. This leads to serious depletion in the insect’s levels of blood sugar, especially trehalose (the insect storage sugar) and body proteins. After reaching 5 cm or more in size, they leave the insect, killing it in the process, and continue their development in the soil until reaching the adult stage and starting the cycle all over again.

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References:

Burr AHJ, Babinzski CPF, Ward AJ (1990) Components of phototaxis of the nematode Mermis nigrescens. Journal of Comparative Physiology A 167: 245–255. doi: 10.1007/BF00188117

Burr AHJ, Hunt P, Wagar DR, Dewilde S, Blaxter ML, Vanfleteren JR, Moens L (2000) A Hemoglobin with an Optical Function. Journal of Biological Chemistry 275: 4810–4815. doi: 10.1074/jbc.275.7.4810

Burr AHJ, Schiefke R, Bollerup G (1975) Properties of a hemoglobin from the chromatrope of the nematode Mermis nigrescens. Biochimica et Biophysica Acta (BBA) – Protein Structure 405(2): 401–411. doi: 10.1016/0005-2795(75)90105-1

Gordon R, Webster JM (1971) Mermis nigrescens: Physiological relationship with its host, the adult desert locust Schistocerca gregaria. Experimental Parasitology 29(1): 66–79. doi: 10.1016/0014-4894(71)90012-9

Rutherford TA, Webster JM (1974) Transcuticular Uptake of Glucose by the Entomophilic Nematode, Mermis nigrescens. Journal of Parasitology 60(5): 804–808. doi: 10.2307/3278905

Rutherford TA, Webster JM (1978) Some effects of Mermis nigrescens on the hemolymph of Schistocerca gregaria. Canadian Journal of Zoology 56(2): 339–347. doi: 10.1139/z78-046

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Friday Fellow: European Beewolf

by Piter Kehoma Boll

Among the species of the highly diverse insect order Hymenoptera, many are known to be parasites or parasitoids of a variety of animals and plants. Commonly known parasited species include spiders and caterpillars, but some hymenopterans parasitize other hymenopterans.

One of such species is Philanthus triangulum, known as the European beewolf. The name beewolf refers to the fact that this wasp species hunts bees, particularly the common honey bee Apis mellifera. This species occurs throughout Europe and Africa, having several subspecies.

A female European beewolf in Gran Canaria, Spain. Photo by Juan Emilio.**

The European beewolf has about the same length as its prey, the common honey bee, but its body has a more typical wasp look. The abdomen and the legs are predominantly yellow, while the head and the thorax are mainly black and brown. The yellow abdomen has black transversal stripes that are typical in many wasp species but their width can vary. Males are smaller than females and have a characteristic trident-shaped light mark between the eyes that is absent or very small in females.

A male in Andalucia, Spain. See the trident-shaped mark between the eyes. Photo by flickr user gailhampshire.*

In colder regions, where the winter is harsh, adult European beewolves emerge as adults in early summer. Both male and female adults feed on the nectar of several plants. Females create large and sometimes complex burrows in sandy soils in open sunny places. The burrows may have up to a meter in length and have between 3 and 34 short tunnels, the brood cells, at the end, each of which will be used to raise one larva. Once finishing the burrow, the female searches for honeybees to hunt. When attacking the bee, the beewolf stings it behind the front legs and paralyzes it, and then flies back to the nest carrying the paralyzed bee below her between her legs. Up to five honeybees can be provided for each larva and serve as their only food during their development.

A female with a paralyzed bee in England. Photo by Martin Cooper.*

Males tend to live near female burrows and use sex pheromones to attract them. Although they are territorial, they can sometimes tolerate other males nearby because the increased release of feromones increases the chances of them being detected by the females.

After the female has provided each egg with enough food, it closes the burrow and leaves. However, since the larvae will remain several months in that closed and humid environment, they can end up suffering from mold growth that can destroy themselves or their food. Females seem to have developed several strategies to reduce this problem. First, before laying the egg on the bee, the wasp licks most of the bee’s surface, applying a secretion from a postpharyngeal gland. Although this secretion has no antimycotic properties, it seems to delay water condensation on the bee’s surface, which also delays the development of fungi, and at the same time prevents water loss from the bee’s body, ensuring that the larvae will have the necessary amount of water to survive.

Carrying a bee into the burrow in England. Photo by Charlie Jackson.*

Female beewolves also live symbiotically with bacteria of the genus Streptomyces, which they cultivate in specialized glands in their antennae. They “secrete” the bacteria into the brood cells before leaving and later, when the larvae hatch, they collect the bacteria and apply them on the surface of a coccoon that they build to overwinter. These bacteria thus prevent fungi or other bacteria from growing on the coccoon, protecting the larvae from infections.

Nature never stops amusing us with its wonderful strategies so beautifully built by natural selection.

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References:

Herzner G, Schmitt T, Peschke K, Hilpert A, Strohm E (2007) Food Wrapping with the Postpharyngeal Gland Secretion by Females of the European beewolf Philanthus triangulum. Journal of Chemical Ecology 33:849–859. doi: 10.1007/s10886-007-9263-8

Herzner G, Strohm E (2008) Food wrapping by females of the European Beewolf, Philanthus triangulum, retards water loss of larval provisions. Physiological Entomology 33:101–109. doi: 10.1111/j.1365-3032.2007.00603.x

Kaltenpoth M, Goettler W, Dale C, Stubblefield JW, Herzner G, Roeser-Mueller K, Strohm Erhard (2006) ‘Candidatus Streptomyces philanthi’, an endosymbiotic streptomycete in the antennae of Philanthus digger wasps. International Journal of Systematic and Evolutionary Microbiology 56: 1403–1411. doi: 10.1099/ijs.0.64117-0

Wikipedia. European beewolf. Available at < https://en.wikipedia.org/wiki/European_beewolf >. Access on 20 February 2020.

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Friday Fellow: Common Fish Louse

by Piter Kehoma Boll

We all know that crustaceans comprise the most morphologically and ecologically diverse group of arthropods. One peculiar clade is that of the arguloids or fish lice.

As you may infer from the common name, the fish lice are parasites of fish, and eventually other vertebrates. One of the most common an well-known species is Argulus foliaceus, known as the common fish louse.

The common fish louse is found in freshwater bodies of Europe and parasitizes many different fish species. Their only food is fish blood, so they are forced to look for a host as soon as they hatch from their eggs. Once they find a fish, they attach firmly to its skin and remain there for most of their life. They only leave the host to mate or if the host dies and they need to find a new one. Trouts, perches, roaches and sticklebacks are some common hosts of the common fish louse.

Watch some eggs hatching and the larvae that come out of them.

The first and only larval stage, called metanauplius, measures less than 1 mm in length and has long and plumose antennae and palps but relatively short legs. The thoracic legs have claws, though, and help them to attach to the host. In the second stage, already a young adult, the antennae became much shorter but the legs grow more, especially the abdominal legs, which became plumose like the antennae used to be. From there on, the body remains with a more or less constant shape but increases in size, reaching about 6 mm at the 11th stage.

Several common fish lice parasitizing a brown trout in Denmark. Photo by iNaturalist user mikkel65.*

In natural environments, the number of common fish lice per fish is usually small and they do not harm the host that much. However, in confined habitats, such as fish farms, they can reach high densities and end up causing a high fish mortality.

Just like many other external parasites or other types of blood-sucking animals, the common fish louse can serve as an intermediary host for some nematode parasites that infect freshwater fish. The larval stages of the worm reach the fish louse when he feeds on infected fish and remain in its body, eventually infecting a new fish when the crustacean abandons its current home and searches for another one.

Thus, sometimes the main problem that fish face is not the fish louse itself, but rather its hitchhikers.

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More maxillopods:

Friday Fellow: Glacial calanus (on 1 July 2016)

Friday Fellow: Common Goose Barnacle (on 31 May 2019)

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References:

Harrison AJ, Gault NFS, Dick JTA (2006) Seasonal and vertical patterns of egg-laying by the freshwater fish louse Argulus foliaceus (Crustacea: Branchiura). Diseases of Aquatic Organisms 68:167–173.

Molnár K, Székely C (1998) Occurrence of skrjabillanid nematodes in fishes of Hungary and in the intermediate host, Argulus foliaceus. Acta Veterinaria Hungarica 46(4): 451-463.

Pasternak AF, Mikheev VN, Valtonen ET (2000) Life history charactheristics of Argulus foliaceus L. (Crustacea: Branchiura) populations in Central Finland. Annales Zoologici Fennici 37: 25–35.

Rushton-Mellor SK, Boxshall GA (1994) The developmental sequence of Argulus foliaceus (Crustacea: Branchiura). Journal of Natural History 28(4): 763–785. doi: 10.1080/00222939400770391

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Should we save or should we get rid of parasites?

by Piter Kehoma Boll

Parasites are special types of organisms that live on or inside other lifeforms, slowly feeding on them but usually not killing them, just reducing their fitness to some degree. This is a much more discrete way to survive than killing or biting entire parts off, as predators (both carnivores and herbivores) do. However, different from these creatures, parasites are often regarded as unpleasant and disgusting. Yet parasitism is the most common way to get food in nature.

When I introduced the rhinoceros tick in a recent Friday Fellow, I mentioned the dilemma caused by it. Since the rhinoceros tick is a parasite of rhinoceroses, and rhinoceroses are threatened with extinction, a common practice to improve the reproductive fitness of rhinos is removing their ticks, but this may end up leading the rhinoceros tick to extinction.

This actually happened already with other parasites, such as the louse Coleocephalum californici, which was an exclusive parasite of the California condor Gymnogyps californianus. In order to save the condor, a common practice among veterinarians working with conservationists was to delouse the birds and, as a result, this louse is now extinct. The harm that the louse caused to the condor was so little, though, that its extinction was not at all necessary, being nothing more than a case of negligence and lack of empathy for a small and non-charismatic species.

The California condor louse Coleocephalum californici was extinct during a poorly managed campaign to save the California condor Gymnogyps californianus. Image extracted from https://www.hcn.org/blogs/goat/the-power-and-plight-of-the-parasite

The louse Rallicola (Aptericola) pilgrimi has also vanished forever during the conservation campaigns to save its host, the little spotted kiwi, Apteryx owenii, in another failed work.

The efforts to save the little spotted kiwi, Apteryx owenii, from extinction led to the extinction of its louse. Photo by Judi Lapsley Miller.*
The now extinct Rallicola (Aptericola) pilgrimi. Credits to the Museum of New Zealand.***

Another group of parasites that is facing extinction are fleas. The species Xenopsylla nesiotes was endemic to the Christmas Island together with its host, the Christmas Island rat, Rattus macleari. The introduction of the black rat, Rattus rattus, in the island led to a quick decline in the population of the Christmas Island rat, which went extinct at the beginning of the 20th century and, of course, the flea went extinct with it. The flea Acanthopsylla saphes has likely become extinct as well. It was a parasite of the eastern quoll, Dasyurus viverrinus, in mainland Australia. The eastern quoll today is only found in Tasmania, as the mainland Australia’s population went extinct in the mid-20th century. However, the flea was never found in the Tasmanian populations, so it is likely that it died away in mainland Australia together with the local population of its host.

The Manx shearwater flea Ceratophyllus (Emmareus) fionnus. Photo by Olha Schedrina, Natural History Museum.*

But things have been changing lately and fortunately the view on parasites is improving. A recent assessment was made on the population of another flea, the Manx shearwater flea, Ceratophyllus (Emmareus) fionnus. This flea is host-specific, being found only on the Manx shearwater Puffinus puffinus. Although the Manx shearwater is not at all a threatened species and has many colonies along the North Atlantic coast, the flea is endemic to the Isle of Rùm, a small island off the west coast of Scotland. Due to the small population of its host in this island, the flea has ben evaluated as vulnerable. If the Manx shearwater population in the Island were stable, things would be fine but, as you may have guessed already, things are not fine. Just like it happened in Christmas Island, the black rat was also introduced in the Isle of Rúm and has become a predator of the Manx shearwater, attacking its nests.

The Manx shearwater, Puffinus puffinus, is the sole host of the Manx shearwater flea. Photo by Martin Reith.**

Some ideas have been suggested to protect the flea from extinction. One of them is to eradicate the black rat from the Isle or at least manage its population near the Manx shearwater colonies. Another proposal is to translocate some fleas to another island to create additional populations in other Manx shearwater colonies.

But why bother protecting parasites? Well, there are plenty of reasons. First, they comprise a huge part of the planet’s biodiversity and their loss would have a strong impact on any ecosystem. Second, they are an essential part of their host’s evolutionary history and are, therefore, promoters of diversity by natural selection. Removing the parasites from a host would eventually decrease its genetic variability and let it more vulnerable to other new parasites. Due to their coevolution with the host, parasites are also a valuable source of knowledge about the host’s ecology and evolutionary history, helping us know their population dynamics. We can even find ways to deal with our own parasites by studying the parasites of other species, and parasites are certainly something that humans managed to collect in large numbers while spreading across the globe.

Parasites may be annoying but they are necessary. They may seem to weaken their host at first but, in the long run, what doesn’t kill you makes you stronger.

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References:

Kirst ML (2012) The power and plight of the parasite. High Country News. Available at < https://www.hcn.org/blogs/goat/the-power-and-plight-of-the-parasite >. Access on 3 November 2019.

Kwak ML (2018) Australia’s vanishing fleas (Insecta: Siphonaptera): a case study in methods for the assessment and conservation of threatened flea species. Journal of Insect Conservation 22(3–4): 545–550. doi: 10.1007/s10841-018-0083-7

Kwak ML, Heath ACG, Palma RL (2019) Saving the Manx Shearwater Flea Ceratophyllus (Emmareus) fionnus (Insecta: Siphonaptera): The Road to Developing a Recovery Plan for a Threatened Ectoparasite. Acta Parasitologica. doi: 10.2478/s11686-019-00119-8

Rózsa L, Vas Z (2015) Co-extinct and critically co-endangered species of parasitic lice, and conservation-induced extinction: should lice be reintroduced to their hosts? Oryx 49(1): 107–110. doi: 10.1017/S0030605313000628

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Filed under Conservation, Ecology, Evolution, Extinction, Parasites

Friday Fellow: Eucalyptus Gall Wasp

by Piter Kehoma Boll

Galls are a common abnormal growth on plant tissues, being similar to animal warts, and can be caused by several different parasites, including viruses, bacteria, fungi, arthropods and sometimes even other plants. Sometimes galls can be harmless but they are often able to affect the plant’s fitness to a degree that harms it.

In several species of eucalyptus, including the river red gum presented here last week, a common agent causing galls is Ophelimus maskelli, known as the eucalyptus gall wasp. As its name suggests, this species is a wasp, more precisely a chalcid wasp, therefore related to several parasitoid wasps and the fig wasps.

An adult female eucalyptus gall wasp. Extracted from https://bicep.net.au/pests/ophelimus-maskelli/

The eucalyptus gall wasp is very small, measuring, as an adult, only about 1 mm in length and having a black body. After mating, the female looks for immature eucalyptus leaves, 15–90 days old, growing in the lower tree canopy because leaves are larger there. A female lays about 100 eggs and has a preference for the area close to the leaf’s petiole. As soon as the eggs are laid, a reaction on the leaf tissues leads to the formation of the galls, with one larva growing inside each gall. In heavily infested trees, the whole leaf can be covered and there may be as much as 36 galls per cm². The larva pupates inside the gall and leaves after reaching the adult stage.

A heavily infested eucalyptus leaf with numerous galls. Credits to NHMLA Community Science Program.**

After the adults emerge, the leaves start to desiccate, especially the heavily infested ones, and die, weakening the tree. As a result, the eucalyptus gall wasp is considered a serious eucalyptus pest and can have devastating effects on eucalyptus plantations.

The eucalyptus gall wasp is native from Australia, since most eucalyptus species come from there, but was accidentally introduced in several other countries together with the eucalyptus trees, especially in the last decades. The galls are easily identified as very small, somehow oval eruptions, not very tall, seen from both the upper and lower sides of the leaf. After the adult emerge, there is a visible hole on the gall and the surroundings start to dry.

Several methods to reduce the infections are used, including pesticides and biological control, especially of other chalcid wasps such as the parasitoid Closterocerus chamaeleon. Considering that this pest is a relatively novel nuisance in a global scale, effective control methods are still being developed.

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More hymenopterans:

Friday Fellow: Bullet Ant (on 27 May 2016)

Friday Fellow: Jataí Bee (on 12 August 2019)

Friday Fellow: Turnip Sawfly (on 17 May 2019)

Friday Fellow: Chinese Banyan Wasp (on 5 July 2019)

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References:

Branco M, Boavida C, Durand N, Franco JC, Mendel Z (2009) Presence of the Eucalyptus gall wasp Ophelimus maskelli and its parasitoid Closterocerus chamaeleon in Portugal: First record, geographic distribution and host preference. Phytoparasitica 37(1): 51–54. doi: 10.1007/s12600-008-0010-7

Burks RA, Mottern JL, Waterworth R, Paine TD (2015) First report of the Eucalyptus gall wasp, Ophelimus maskelli (Hymenoptera: Eulophidae), an invasive pest on Eucalyptus, from the Western Hemisphere. Zootaxa 3926(3): 448–450. doi: 10.11646/zootaxa.3926.3.10

Dhahri S, Ben Jamaa ML, Lo Verde G (2010) First record of Leptocybe invasa and Ophelimus maskelli eucalyptus gall wasps in Tunisia. Tunisian Journal of Plant Protection 5: 231–236.

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Filed under Entomology, Friday Fellow, Parasites

Friday Fellow: Rhinoceros Tick

by Piter Kehoma Boll

Parasites exist everywhere and, although most of us see them as hateful creatures, more than half of all known lifeforms live as a parasite at least in part of their life. And there are likely many more yet unknown parasites around there. Today I’m going to talk about one of them, which is found in large portions of Africa.

Its name is Dermacentor rhinocerinus, known as the rhinoceros tick. As its name suggests, it is a tick, therefore a parasitic mite, and its adult stage lives on the skin of the white rhinoceros (Ceratotherium simum) and the critically endangered black rhinoceros (Diceros bicornis).

A male rhinoceros tick attached to the skin of a rhinoceros in South Africa. Credits to iNaturalist user bgwright.**

Male and female rhinoceros ticks are considerably different. In males, the body has a black background with many large orange spots. In females, on the other hand, the abdomen is mainly black with only two round orange spots and the plate on the thorax is orange with two small dark spots. Males and females mate on the surface of rhinoceroses. After mating, the female starts to increase in size while the eggs develop inside her and then drops to the ground, laying the eggs there.

A female rhinoceros tick patiently waiting for a rhinoceros to come close. Photo by Martin Weigand.**

The larvae, as soon as they hatch, start to look for another host, usually a small mammal such as rodents and elephant shrews. They feed on this smaller host until they reach the adult stage, when they drop to the ground and climb on the surrounding vegetation, waiting for a rhinoceros to pass by and then attaching to them.

Conservation efforts to preserve biodiversity are mainly focused on vertebrates, especially mammals and birds. Rhinoceroses, which are an essential host for the rhinoceros tick to survive, are often part of conservation programs and, in order to increase their reproductive success, the practice of removing parasites from their skin is common. This is, however, bad for the rhinoceros ticks. If their host is endangered, they are certainly endangered too, and removing them worsens their condition. Are parasites less important for the planet? Don’t they deserve to live just as any other lifeform? We cannot forget that nature needs more than only what we consider cute.

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More mites and ticks:

Friday Fellow: Giant Red Velvet Mite (on 22 June 2016)

Friday Fellow: Cuban-Laurel-Thrips Mite (on 28 June 2019)

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References:

Horak IG, Fourie LJ, Braack LEO (2005) Small mammals as hosts of immature ixodid ticks. Onderstepoort Journal of Veterinary Research 72:255–261.

Horak IG, Cohen M (2001) Hosts of the immature stages of the rhinoceros tick, Dermacentor rhinocerinus (Acari, Ixodidae). Onderstepoort Journal of Veterinary Research 68:75–77.

Keirans JE (1993) Dermacentor rhinocerinus (Denny 1843) (Acari: Ixodida: Ixodidae): redescription of the male, female and nymph and first description of the larva. Onderstepoort Journal of Veterinary Research 60:59–68.

Mihalca AD, Gherman CM, Cozma V (2011) Coendangered hard ticks: threatened or threatening? Parasites & Vectors 4:71. doi: 10.1186/1756-3305-4-71

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Filed under Arachnids, Conservation, Friday Fellow, Parasites, Zoology

Friday Fellow: Salmon Fluke

by Piter Kehoma Boll

Leia em Português

Everybody knows salmons, especially the Atlantic salmon, Salmo salar, and many of us love to eat this fish species as well. However, I’m not here to talk about the Atlantic salmon itself, but to talk about one of its closes companions and antagonists, the salmon fluke.

Scientifically known as Gyrodactylus salaris, the salmon fluke is a flatworm of the clade Monogenea, a group of ectoparasites that infect mainly fish. As its name suggests, the salmon fluke infects salmons, such as the Atlantic salmon, and closely related species, such as the rainbow trout Onchorhynchus mykiss.

Several salmon flukes on a host. Photo by Tora Bardal. Extracted from https://www.drivaregionen.no/no/Gyrodactylus-salaris/

The salmon fluke was first discovered in 1952 in salmons from a Baltic population that were kept in a Swedish laboratory. Measuring about 0.5 mm in length, the salmon fluke attaches to the skin of the fish and is too small to be seen with the naked eye. The attachment happens using a specialized organ full of tiny hooks, called haptor, located at the posterior end of the body. When feeding, the salmon fluke attaches its mouth to the surface of the fish using special glands in its head and everts its pharynx through the mouth, releasing digestive enzymes on the fish, dissolving its skin, which is then ingested. The wounds caused by the parasite’s feeding activity can lead to secondary infections that can seriously affect the salmon’s health.

Artificially colored SEM micrograph of five specimens of Gyrodactylus salaris. Credits to Jannicke Wiik Nielsen. Extracted from https://www.vetinst.no/nyheter/kan-gyrodactylus-salaris-utryddes-i-drammensregionen

Different from most parasitic flatworms, monogeneans such as the salmon fluke have a single host. During reproduction, the hermanophrodite adults release a ciliated larva called oncomiracidium that infects new fish. A single fluke can originate an entire population because it is able to self fertilize.

During the 1970’s, a massive infection by the salmon fluke occurred in Norway following the introduction of infected salmon strains. This led to a catastrophic decrease in the salmon populations in the country, affecting many rivers. Due to this evident threat to such a commercially important species, several techniques have been developed to control and kill the parasite. The first developed methods included the use of pesticides in the rivers, but those ended up having a negative effect on many species, including the salmons themselves. Currently, newer and less aggressive methods have been used.

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References:

Jansen, P. A., & Bakke, T. A. (1991). Temperature-dependent reproduction and survival of Gyrodactylus salaris Malmberg, 1957 (Platyhelminthes: Monogenea) on Atlantic salmon (Salmo salar L.). Parasitology, 102(01), 105. doi:10.1017/s0031182000060406

Johnsen, B. O., & Jenser, A. J. (1991). The Gyrodactylus story in Norway. Aquaculture, 98(1-3), 289–302. doi:10.1016/0044-8486(91)90393-l

Meinilä, M., Kuusela, J., Ziętara, M. S., & Lumme, J. (2004). Initial steps of speciation by geographic isolation and host switch in salmonid pathogen Gyrodactylus salaris (Monogenea: Gyrodactylidae). International Journal for Parasitology, 34(4), 515–526. doi:10.1016/j.ijpara.2003.12.002

Wikipedia. Gyrodactylus salaris. Available at < https://en.wikipedia.org/wiki/Gyrodactylus_salaris >. Access on December 26, 2018.

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Filed under flatworms, Friday Fellow, Parasites, Zoology