Editing Parasitoid (section)

{{Use British English|date=January 2017}}
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{{short description|Organism that lives with its host and kills it}}
[[File:CSIRO ScienceImage 2357 Spotted alfalfa aphid being attacked by parasitic wasp.jpg|thumb|upright=1.2|A [[parasitoid wasp]] (''Trioxys complanatus'', [[Aphidiinae]]) [[ovipositing]] into the body of a spotted alfalfa [[aphid]] (''Therioaphis maculata'', [[Calaphidinae]]), a behaviour that is used in [[biological pest control]]{{efn|The species has been introduced to Australia to control the spotted alfalfa aphid.<ref name="WilsonSwincer1982">{{cite journal |last1=Wilson |first1=C. G. |last2=Swincer |first2=D. E. |last3=Walden |first3=K. J. |title=The introduction of ''Trioxys complanatus'' Quilis (Hymenoptera: Aphidiidae), an internal parasite of the Spotted Alfalfa Aphid, into South Australia |journal=Australian Journal of Entomology |volume=21 |issue=1 |year=1982 |pages=13–27 |doi=10.1111/j.1440-6055.1982.tb01758.x|s2cid=84996305 }}</ref>}}<ref>{{Cite web |title=Spotted Alfalfa Aphid / Alfalfa / Agriculture: Pest Management Guidelines / UC Statewide IPM Program (UC IPM) |url=https://ipm.ucanr.edu/agriculture/alfalfa/spotted-alfalfa-aphid/ |access-date=2023-09-22 |website=ipm.ucanr.edu}}</ref>]]

In [[evolutionary ecology]], a '''parasitoid''' is an [[organism]] that lives in close association with its [[host (biology)|host]] at the host's expense, eventually resulting in the death of the host. Parasitoidism is one of six major [[evolutionarily stable strategy|evolutionary strategies]] within [[parasitism]], distinguished by the fatal [[prognosis]] for the host, which makes the strategy close to [[predation]].

Among parasitoids, strategies range from living inside the host (''endoparasitism''), allowing it to continue growing before emerging as an adult, to [[Paralysis|paralysing]] the host and living outside it (''ectoparasitism''). Hosts can include other parasitoids, resulting in [[hyperparasitism]]; in the case of [[oak gall]]s, up to five levels of parasitism are possible. Some parasitoids [[Behavior-altering parasite|influence their host's behaviour]] in ways that favour the propagation of the parasitoid.

Parasitoids are found in a variety of [[Taxon|taxa]] across the [[insect]] superorder [[Endopterygota]], whose complete [[metamorphosis]] may have [[pre-adapted]] them for a split lifestyle, with parasitoid [[Larva|larvae]] and free-living adults. Most are in the [[Hymenoptera]], where the [[Ichneumonidae|ichneumons]] and many other [[parasitoid wasp]]s are highly specialised for a parasitoidal way of life. There are parasitoids, too, in the [[Diptera]], [[Coleoptera]] and other [[Order (biology)|order]]s of [[endopterygota|endopterygote insects]]. Some of these, usually but not only wasps, are used in [[biological pest control]]. 

The 17th-century zoological artist [[Maria Sibylla Merian]] closely observed parasitoids and their hosts in her paintings. The biology of parasitoidism influenced [[Charles Darwin]]'s beliefs and has inspired [[science fiction]] authors and [[scriptwriter]]s to create numerous parasitoidal aliens that kill their human hosts, such as the [[Alien (creature in Alien franchise)|alien species]] in [[Ridley Scott]]'s 1979 film ''[[Alien (film)|Alien]]''.