SEM image of endoparasitoid ciliates of the genus Collinia, which can cause mass mortality in affected krill populations. The scanning electron microscope ( SEM) is a type of Electron microscope that images the sample surface by scanning it with a high-energy beam of Electrons The ciliates are one of the most important groups of Protists common almost everywhere there is water — lakes ponds oceans rivers and soils with many ectosymbiotic Krill are a type of Shrimp -like marine Invertebrate animal These small Crustaceans are important organisms of the Zooplankton, particularly

A parasitoid is an organism that spends a significant portion of its life history attached to or within a single host organism which it ultimately kills (and often consumes) in the process. A life cycle is a period involving 1 Generation of an Organism through means of Reproduction, whether through Asexual reproduction or Sexual In Biology, a host is an organism that harbors a Virus or Parasite, or a mutual or Commensal Symbiont, typically providing nourishment Thus they are similar to typical parasites except in the certain fate of the host. Parasitism is a type of symbiotic relationship between Organisms of different Species. In a typical parasitic relationship, the parasite and host live side by side without lethal damage to the host. Typically, the parasite takes enough nutrients to thrive without preventing the host from reproducing. A nutrient is food or chemicals that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment Reproduction is the Biological process by which new individual Organisms are produced In a parasitoid relationship, the host is killed, normally before it can produce offspring. When treated as a form of parasitism, the term necrotroph is sometimes (though rarely) used. Parasitism is a type of symbiotic relationship between Organisms of different Species.

This type of relationship seems to occur only in organisms that have fast reproduction rates, such as insects, or (rarely) mites. Reproduction is the Biological process by which new individual Organisms are produced Insects ( Class Insecta) are a major group of Arthropods and the most diverse group of Animals on the Earth with over a million described Mites, along with Ticks belong to the subclass Acarina (also known as Acari and the class Arachnida Mites are among the most diverse and successful Parasitoids are also often closely coevolved with their hosts. In a broad sense biological co-evolution is "the change of a biological object triggered by the change of a related object" Most biologists use the term parasitoids to refer only to insects with this type of life history, but some argue the term should be used more embrasively to include parasitic nematodes, seed weevils, and certain bacteria and viruses (e. g. bacteriophages) all of which obligately destroy their host.

Types of parasitoids

Idiobiont parasitoids are those which prevent any further development of the host after initial parasitization, and this typically involves a host life stage which is immobile (e. g. , an egg or pupa), and almost without exception they live outside the host. A pupa ( Latin pupa for doll pl pupae or pupas) is the life stage of some Insects undergoing transformation Koinobiont parasitoids allow the host to continue its development and often do not kill or consume the host until the host is about to either pupate or become an adult; this therefore typically involves living within an active, mobile host. Koinobionts can be further subdivided into endoparasitoids, which develop inside of the prey, and ectoparasitoids, which develop outside the host body, though they are frequently attached or embedded in the host's tissues.

It is not uncommon for a parasitoid itself to serve as the host for another parasitoid's offspring. The latter is commonly termed a hyperparasite but this term is slightly misleading, as both the host and the primary parasitoid are killed. A better term is secondary parasitoid, or hyperparasitoid; most such species known are in the insect order Hymenoptera. Hymenoptera is one of the larger orders of Insects comprising the sawflies, Wasps Bees and Ants The name refers to

Insects

About 10% of described insect species are parasitoids,^[1] but as many parasitoid groups are poorly known taxonomically the true figure is probably nearer 20%. There are four insect orders that are particularly renowned for this type of life history. By far the majority are in the order Hymenoptera. Hymenoptera is one of the larger orders of Insects comprising the sawflies, Wasps Bees and Ants The name refers to The largest and best known group comprises the so-called "Parasitica" within the Hymenopteran suborder Apocrita: the largest subgroups of these are the chalcidoid wasps (superfamily Chalcidoidea) and the ichneumon wasps (superfamily Ichneumonoidea), followed by the Proctotrupoidea and Platygastroidea. Hymenoptera is one of the larger orders of Insects comprising the sawflies, Wasps Bees and Ants The name refers to Chalcid wasps (superfamily Chalcidoidea) belong to the Insect order Hymenoptera, and are one of the largest groups within the order with some 22000 known The Hymenopteran superfamily Proctotrupoidea is a somewhat confusing assemblage of taxa with new families being added (or removed with surprising frequency and very little The Hymenopteran superfamily Platygastroidea (sometimes incorrectly spelled Platygasteroidea) has in the past often been treated as a lineage within the superfamily Outside of the Parasitica there are many other Hymenopteran lineages which include parasitoids, such as most of the Chrysidoidea and Vespoidea, and the rare Symphytan family Orussidae. The superfamily Chrysidoidea or Bethyloidea is a very large cosmopolitan group (some 6000 described species and many more undescribed of Parasitoid or cleptoparasitic Vespoidea is a superfamily of order Hymenoptera of class Insecta, although older taxonomic schemes may vary in this Symphyta redirects here For the Moth Genus, see Symphyta (genus. The family Orussidae (the sole living member of the superfamily Orussoidea) is the only Symphytan group which is parasitic, thus giving them the common The flies (order Diptera) include several families of parasitoids, the largest of which is the family Tachinidae, and also smaller families such as Pipunculidae, Conopidae, and others. True flies are Insects of the Order Diptera ( Greek: di = two and pteron = wing possessing a single pair of Tachinidae is a large and rather variable family of true flies within the Insect order Diptera with more than 8200 known species and many more to be discovered Pipunculidae are a family of flies ( Diptera) commonly termed Big-Headed Flies a reference to the large eyes, which cover nearly the entire Conopidae, usually known as the thick-headed flies, is a family of flies within the Brachycera suborder of Diptera. The other two orders are the "twisted-wing parasites" (order Strepsiptera), which is a small group consisting entirely of parasitoids, and the beetles (order Coleoptera), which includes at least families, Ripiphoridae and Rhipiceridae, that are largely parasitoids, and rove beetles (family Staphylinidae) of the genus Aleochara. The Strepsiptera (known in older literature as twisted-winged parasites) are an order of Insects with nine families making up about 600 species Beetles are the group of Insects with the largest number of known Species. The family Ripiphoridae (formerly spelled Rhipiphoridae) is a cosmopolitan group of Beetles commonly known as wedge-shaped beetles containing some 450 species The rove beetles are a large family ( Staphylinidae) of Beetles primarily distinguished by their short Elytra that leave more than half of their Rove beetles of the genus Aleochara are among the only insect parasites in the Beetle family Staphylinidae Occasional members of other orders can be parasitoids; one of the more remarkable is the moth family Epipyropidae, which are ectoparasitoids of planthoppers. A moth is an Insect closely related to the Butterfly, both being of the order Lepidoptera. Epipyropidae is a small family of Insects in the Lepidoptera order A planthopper is any Insect in the infraorder Fulgoromorpha within the Hemiptera.

See also: Parasitic wasp

In fact and fiction

The term parasitoid was coined in 1913 by the German writer O. M. Reuter (and adopted in English by his reviewer, W. M. Wheeler) to describe the strategy in which during its development, the parasite lives in or on the body of a single host individual, eventually killing that host, the adult parasitoids being free-living.

Many "parasites" portrayed in fiction are actually parasitoids; these include;

• The Xenomorphs from the Alien films. The alien, also called the xenomorph, or a thing and by Ellen Ripley in a deleted scene from Alien³. The Alien film series is a science fiction horror film franchise, focusing on Lieutenant Ellen Ripley (played by Sigourney
• The X Parasites and Metroids from the Metroid series. is a series of Science fiction adventure Video games conceived by designer Gunpei Yokoi and produced by Nintendo. is a series of Science fiction adventure Video games conceived by designer Gunpei Yokoi and produced by Nintendo.
• Several of the symbiotes from the Spider-Man comics. A symbiote, in Marvel Comics ' fictional universe is a living sentient alien organism that bonds with other living organisms in order to survive Spider-Man is a Fictional character appearing in Comic books published by Marvel Comics.
• The Flood from the Halo video game series. The Flood are fictional parasitic alien life forms in Bungie 's Halo video game series Halo is a Science fiction Video game franchise created by Bungie and owned and published by Microsoft Game Studios.
• The Headcrabs from the game Half Life. A headcrab is a fictional alien Parasitoid found in the Half-Life and Half-Life 2 computer game series Half-Life is a Science fiction First-person shooter computer game developed by Valve Software and the company's debut product
• The "shit-weasels" from Stephen King's novel, Dreamcatcher. Stephen Edwin King (born September 21, 1947) is an American Author, Screenwriter, Musician, Columnist, This is about the novel by Stephen King For other uses see Dreamcatcher (disambiguation.
• The Magog from the television series Gene Roddenberry's Andromeda. The Magog are an alien race in the television series Andromeda The Species The origins of the Magog are unknown See Andromeda (disambiguation for other uses of "Andromeda"
• The Black Oil alien virus from The X-Files. Black Oil is a creation of the TV series The X-Files, starring David Duchovny and Gillian Anderson. The X-Files is a Peabody, Golden Globe and Emmy Award -winning American Science fiction television series created by Chris Carter
• The Las Plagas creatures from Resident Evil 4
• The Broodlings from the Starcraft games

References