page_title: Parasitoid wasp
hierarchical_section_title: Parasitoid wasp
caption_attribution_description: These wasps (Megarhyssa macrurus lunator) are commonly seen at our northern hardwoods cross country ski trail area on American beech trees suffering from beech bark disease. These wasps use their long ovipositor (egg laying structure) to lay eggs inside the holes insects make into the dying beech trees. It should be noted that these wasps do not sting and are really cool to see up close. Photo: Mike McCarthy
context_page_description: Parasitoid wasps are a large group of hymenopteran superfamilies, with all but the wood wasps being in the wasp-waisted Apocrita. As parasitoids, they lay their eggs on or in the bodies of other arthropods, sooner or later causing the death of these hosts. Different species specialise in hosts from different insect orders, most often Lepidoptera, though some select beetles, flies, or bugs; the spider wasps exclusively attack spiders.
  Parasitoid wasp species differ in which host life-stage they attack: eggs, larvae, pupae, or adults. They mainly follow one of two major strategies within parasitism: either they are endoparasitic, developing inside the host, and koinobiont, allowing the host to continue to feed, develop, and moult; or they are ectoparasitic, developing outside the host, and idiobiont, paralysing the host immediately. Some endoparasitic wasps of the superfamily Ichneumonoidea have a mutualistic relationship with polydnaviruses, the viruses suppressing the host's immune defenses.
context_section_description: Parasitoid wasps are a large group of hymenopteran superfamilies, with all but the wood wasps (Orussoidea) being in the wasp-waisted Apocrita. As parasitoids, they lay their eggs on or in the bodies of other arthropods, sooner or later causing the death of these hosts. Different species specialise in hosts from different insect orders, most often Lepidoptera, though some select beetles, flies, or bugs; the spider wasps (Pompilidae) exclusively attack spiders.
  Parasitoid wasp species differ in which host life-stage they attack: eggs, larvae, pupae, or adults. They mainly follow one of two major strategies within parasitism: either they are endoparasitic, developing inside the host, and koinobiont, allowing the host to continue to feed, develop, and moult; or they are ectoparasitic, developing outside the host, and idiobiont, paralysing the host immediately. Some endoparasitic wasps of the superfamily Ichneumonoidea have a mutualistic relationship with polydnaviruses, the viruses suppressing the host's immune defenses.
  Parasitoidism evolved only once in the Hymenoptera, during the Permian, leading to a single clade, but the parasitic lifestyle has secondarily been lost several times including among the ants, bees, and yellowjacket wasps. As a result, the order Hymenoptera contains many families of parasitoids, intermixed with non-parasitoid groups. The parasitoid wasps include some very large groups, some estimates giving the Chalcidoidea as many as 500,000 species, the Ichneumonidae 100,000 species, and the Braconidae up to 50,000 species.
  Host insects have evolved a range of defences against parasitoid wasps, including hiding, wriggling, and camouflage markings.
  Many parasitoid wasps are considered beneficial to humans because they naturally control agricultural pests. Some are applied commercially in biological pest control, starting in the 1920s with Encarsia formosa to control whitefly in greenhouses. Historically, parasitoidism in wasps influenced the thinking of Charles Darwin.
caption: Megarhyssa macrurus (Ichneumonidae), a parasitoid, ovipositing into its host through the wood of a tree. The body of a female is c. 2 inches (50 mm) long, with an ovipositor c. 4 inches (100 mm) long.
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