TheIchneumonidae, also known asichneumon wasps,ichneumonid wasps,ichneumonids, orDarwin wasps, are afamily ofparasitoid wasps of the insect orderHymenoptera. They are one of the most diverse groups within the Hymenoptera with roughly 25,000 species described as of 2016[update].[2] However, this likely represents less than a quarter of their truerichness as reliable estimates are lacking, along with much of the most basic knowledge about theirecology,distribution, andevolution.[1] It is estimated that there are more species in this family than there are species ofbirds andmammals combined.[3] Ichneumonid wasps, with very few exceptions, attack the immature stages ofholometabolous insects and spiders, eventually killing their hosts.[4] They play an important role as regulators of insect populations, both in natural and semi-natural systems, making them promising agents forbiological control.[5]
Male ichneumonid wasp
The distribution of the ichneumonids was traditionally considered an exception to the commonlatitudinal gradient in species diversity, since the family was thought to be at its most species-rich in the temperate zone instead of the tropics, but numerous new tropical species have now been discovered.
Insects in the family Ichneumonidae are commonly calledichneumon wasps, orichneumonids. However, the termichneumon wasps can refer specifically to thegenusIchneumon within the Ichneumonidae and thus can cause confusion. A group of ichneumonid specialists have proposedDarwin wasps as a better vernacular name for the family.[5] Less exact terms areichneumon flies (they are not closely related totrue flies) andscorpion wasps due to the extreme lengthening and curving of the abdomen (scorpions are arachnids, not insects).
The name is derived from Latin 'ichneumon', from Ancient Greek ἰχνεύμων (ikhneúmōn, "tracker"), from ἴχνος (íkhnos, "track, footstep"). The name first appeared inAristotle's "History of Animals", c. 343 BC. Aristotle noted that the ichneumon preys upon spiders, is a wasp smaller than ordinary wasps, and carries its prey to a hole which they lay their larvae inside, and that they seal the hole with mud.[6] Aristotle's writing, however, more accurately describes themud daubers than the true ichneumon wasps, which do not construct mud nests and do not sting.
Adult ichneumonids superficially resemble otherwasps. They have a slender waist, two pairs of wings, a pair of largecompound eyes on the side of the head and threeocelli on top of the head. Their size varies considerably from a few millimetres to seven or more centimetres.
The ichneumonids have more antennal segments than typical, aculeate wasps (Aculeata:Vespoidea andApoidea): ichneumonids typically possess 16 or more, while most other wasps have 13 or fewer. Unlike aculeate wasps, which have anovipositor modified for prey capture and defense, and do not pass their eggs along thestinger, ichneumonid females have an unmodified ovipositor which they use to lay eggs inside or on their host. Ichneumonids generally inject venom along with the egg, but only larger species (some in the generaNetelia andOphion) with relatively short ovipositors use the ovipositor in defense. Males do not possess stingers or ovipositors in either lineage.
Head (Ichneumon xanthorius). Antennae with many segments
FemaleXanthopimpla punctata. Ovipositor longer and more slender than stingers of aculeate wasps
Ichneumonids are distinguished from theirsister groupBraconidae mainly on the basis of wing venation. The fore wing of 95% of ichneumonids has vein 2m-cu (in theComstock–Needham system), which is absent in braconids. Vein 1rs-m of the fore wing is absent in all ichneumonids, but is present in 85% of braconids. In the hind wing of ichneumonids, vein rs-m joins Rs apical to (or rarely opposite) the split between veins Rs and R1. In braconids, vein rs-m joins basal to this split. The taxa also differ in the structure of the metasoma: about 90% of ichneumonids have a flexible suture between tergites 2 and 3, whereas these tergites are fused in braconids (though the suture is secondarily flexible inAphidiinae).[7]
Ichneumonid fore wing (Syzecteus sp.). The presence of vein 2m-cu and absence of vein 1Rs+M distinguish the wing from that of braconids.
Ichneumonid hind wing. Vein rs-m joins Rs after the split between veins Rs and R1.
Braconid hind wing. Vein rs-m joins Rs before the split between veins Rs and R1.
Ichneumonids are found on all continents with the exception of Antarctica. They inhabit virtually all terrestrial habitats, wherever there are suitable invertebrate hosts.
The distribution of ichneumonid species richness is subject to ongoing debate. Long believed to be rare in the tropics, and at its most species rich in the temperate region, the family became a classic textbook example of an 'exceptional'latitudinal diversity gradient.[8] Recently this belief has been questioned, after the discovery of numerous new tropical species.[9][10][11]
A very few ichneumonid species lay their eggs in the ground, but the vast majority inject eggs either directly into theirhost's body or onto its surface, and this may require penetration of substrate around the host, as in wood-boring host larvae that live deep inside of tree trunks, requiring the ichneumon to drill its ovipositor through several centimeters of solid wood (e.g.,Megarhyssa species). After hatching, the ichneumonid larva consumes its still living host. The most common hosts are larvae or pupae ofLepidoptera,Coleoptera andHymenoptera. Some species in the subfamilyPimplinae also parasitise spiders. Hyperparasitoids such asMesochorinae oviposit inside the larvae of other ichneumonoids. The hosts of some species are agricultural pests, therefore ichneumons are sometimes valuable forbiological pest control, but the hosts of most species are unknown; host information has been reviewed and summarized by various researchers, e.g. Aubert,[12][13][14] Perkins.[15][16] andTownes.[17]
Ichneumonids use both idiobiont and koinobiont strategies. Idiobionts paralyze their host and prevent it from moving or growing. Koinobionts allow their host to continue to grow and develop. In both strategies, the host typically dies after some weeks, after which the ichneumonid larva emerges and pupates.[18]
Adult ichneumonids feed on a diversity of foods, including plant sap and nectar; females of some species also feed on their hosts by sipping body fluids released during oviposition, or even stabbing host and non-host insects to imbibe their body fluids. They spend much of their active time searching, either for hosts (female ichneumonids) or for emerging females (male ichneumonids).[19]The parasitism pressure exerted by ichneumonids can be tremendous, and they are often one of the major regulators of invertebrate populations.[20][21] It is quite common for 10-20% or more of a host's population to be parasitised (though reported parasitism rates often include non-ichneumonid parasitoids).[22][23]
An ichneumonid caught in amber 15-20 million years ago.
The taxonomy of the ichneumonids is still poorly known. The family is highly diverse, containing 24,000 described species. Approximately 60,000 species are estimated to exist worldwide, though some estimates place this number at over 100,000. They are severely undersampled, and studies of their diversity typically produce very high numbers of species which are represented by only a single individual.[24][25] Due to the high diversity, the existence of numerous small and hard to identify species, and the majority of species being undiscovered, it has proven difficult to resolve thephylogeny of the ichneumonids. Even the relationships between subfamilies are unclear. The sheer diversity also meansDNA sequence data is only available for a tiny fraction of the species, and detailedcladistic studies require major computing capacity.
The large number of species in Ichneumonidae may be due to the evolution of parasitoidism in Hymenoptera, which occurred approximately 247 million years ago.[33][34] Ichneumonidae is the basal branch ofApocrita, which together withOrussoidea makes up the lineage in which parasitoidism in Hymenoptera evolved, and some ichneumonids are thought to have been in stasis for millions of years and closely resemble the common ancestor in which parasitoidism evolved. This common ancestor was likely anEctoparasitoid woodwasp that parasitized wood-boring beetle larvae in trees.[35] However, this has been disputed as early fossil ichneumonoids (such asPraeichneumonidae,Tanychorinae,Eoichneumoninae, andProtorhyssalinae) have ovipositors that are only a few millimeters long. Therefore, it has been proposed that they make unlikely candidates for parasitoids of wood-boring hosts.[1] The family has existed since at least theEarly Cretaceous (c. 125 mya),[36][37] but probably appeared already in theJurassic (c. 181 mya), soon after the appearance of its major host groups.[38] It diversified during the Oligocene.
In 1999, the extant ichneumonids were divided into 39 subfamilies,[39][40] whose names and definitions have varied considerably. In 2019, combined morphological and molecular phylogenetic analysis of the family resulted in the following 41 subfamilies being recognized, in addition to the extinctLabenopimplinae.[41]
The perceived cruelty of the ichneumonids troubled philosophers, naturalists, and theologians in the 19th century, who found the parasitoid life cycle inconsistent with the notion of a world created by a loving and benevolent God.[42]Charles Darwin found the example of the Ichneumonidae so troubling that it contributed to his increasing doubts about the nature and existence of a Creator. In an 1860 letter to the American naturalistAsa Gray, Darwin wrote:
I own that I cannot see as plainly as others do, and as I should wish to do, evidence of design and beneficence on all sides of us. There seems to me too much misery in the world. I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of Caterpillars, or that a cat should play with mice.[43]
^abcQuicke, D. L. J. (2015).The braconid and ichneumonid parasitoid wasps: biology, systematics, evolution and ecology. Chichester: John Wiley & Sons, Ltd.
^Yu, D. S.; van Achterberg, C.; Horstmann, K. (2016). Taxapad 2016. Ichneumonoidea 2015 (Biological and taxonomical information), Taxapad Interactive Catalogue Database on flash-drive. Nepean, Ottawa, Canada.
^J. LaSalle; Ian David Gauld (1993). "Hymenoptera: Their Diversity, and Their Impact on the Diversity of Other Organisms".Hymenoptera and biodiversity. Wallingford, Oxon, UK: C.A.B. International. p. 1.ISBN9780851988306.OCLC28576921.
^Broad, G. R.; Shaw, M. R.; Fitton, M. G. (2018). "Ichneumonid wasps (Hymenoptera: Ichneumonidae): their classification and biology".Handbooks for the Identification of British Insects, 7(12): 1-418.
^Aristotle (2015) [343 BC].The Complete Aristotle. Booklassic. p. section 87, chapter 20.ISBN978-963-525-370-8.The wasps that are nicknamed 'the ichneumons' (or hunters), less in size, by the way, than the ordinary wasp, kill spiders and carry off the dead bodies to a wall or some such place with a hole in it; this hole they smear over with mud and lay their grubs inside it, and from the grubs come the hunter-wasps. ... The eagle and the snake are enemies, for the eagle lives on snakes; so are the ichneumon and the venom-spider, for the ichneumon preys upon the latter.
^Sharkey, M.J. (1993),Family Braconidae, pp. 362-394. In: Goulet, H. and J. Huber (eds.).Hymenoptera of the World, an Identification Guide to Families, Agriculture Canada Research Branch Monograph No. 1894E.
^abAubert, Jacques (1969).Les Ichneumonides ouest-palearctiques et leurs hotes 1. Pimplinae, Xoridinae, Acaenitinae [The Western Palearctic ichneumon wasps and their hosts. 1. Pimplinae, Xoridinae, Acaenitinae] (in French). Paris: Laboratoire d'Evolution des Etres Organises.OCLC773541612.[page needed]
^abAubert, Jacques François (1978).Les Ichneumonides ouest-palearctiques et leurs hotes 2. Banchinae et Suppl. aux Pimplinae [The Western Palearctic ichneumon wasps and their hosts. 2. Banchinae and supplement to the Pimplinae] (in French). Paris & EDIFAT-OPIDA, Echauffour: Laboratoire d'Evolution des Etres Organises.OCLC461814920.[page needed]
^abAubert, Jacques (2000).Les Ichneumonides ouest-paléarctiques et leurs hôtes. 3. Scolobatinae (=Ctenopelmatinae) et suppl. aux volumes précédents [The West Palaearctic ichneumonids and their hosts. 3. Scolobatinae (= Ctenopelmatinae) and supplements to preceding volumes]. Litterae Zoologicae (in French). Vol. 5.OCLC716442080.[page needed]
^abTownes, Henry; Momoi, Setsuya; Townes, Marjorie (1965).A catalogue and reclassification of the eastern Palearctic Ichneumonidae. Memoirs of the American Entomological Institute. Vol. 5.OCLC669390657.[page needed]
^Gauld, Ian D. (1988). "Evolutionary patterns of host utilization by ichneumonoid parasitoids (Hymenoptera: Ichneumonidae and Braconidae)*".Biological Journal of the Linnean Society.35 (4):351–377.doi:10.1111/j.1095-8312.1988.tb00476.x.ISSN0024-4066.
^Hawkins, Bradford A.; Cornell, Howard V.; Hochberg, Michael E. (October 1997). "Predators, parasitoids, and pathogens as mortality agents in phytophagous insect populations".Ecology.78 (7):2145–52.doi:10.1890/0012-9658(1997)078[2145:PPAPAM]2.0.CO;2.JSTOR2265951.
^Gauld, I. D. (1976). "The classification of the Anomaloninae (Hymenoptera: Ichneumonidae)".Bulletin of the British Museum (Natural History) Entomology.33:1–135.
^abTownes, H. K. (1969a). "Genera of Ichneumonidae, Part 1 (Ephialtinae, Tryphoninae, Labiinae, Adelognathinae, Xoridinae, Agriotypinae)".Memoirs of the American Entomological Institute.11:1–300.
^abTownes, H. K. (1969b). "Genera of Ichneumonidae, Part 2 (Gelinae)".Memoirs of the American Entomological Institute.12:1–537.
^abTownes, H. K. (1969c). "Genera of Ichneumonidae, Part 3 (Lycorininae, Banchinae, Scolobatinae, Porizontinae)".Memoirs of the American Entomological Institute.13:1–307.
^abTownes, H. K. (1971). "Genera of Ichneumonidae, Part 4 (Cremastinae, Phrudinae, Tersilochinae, Ophioninae, Mesochorinae, Metopiinae, Anomalinae, Acaenitinae, Microleptinae, Orthopelmatinae, Collyriinae, Orthocentrinae, Diplazontinae)".Memoirs of the American Entomological Institute.17:1–372.
^Oehlke, J (1966). "Die westpaläarktische Arte der Tribus Poemeniini (Hymenoptera, Ichneumonidae) ["The Western Palearctic species of the tribe Poemeniini"]".Beiträge zur Entomologie.15:881–892.
^Oehlke, J (1967). "Westpaläarktische Ichneumonidae 1, Ephialtinae".Hymenopterorum Catalogus.2 (new ed.):1–49.
^Wahl, David; Gauld, Ian."American Entomological Institute".Genera Ichneumonorum Nearcticae. The American Entomological Institute.Archived from the original on 9 June 2017. Retrieved9 August 2017.
^abcTereshkin, A. (2009): Illustrated key to the tribes of subfamilia Ichneumoninae and genera of the tribe Platylabini of world fauna (Hymenoptera, Ichneumonidae).Linzer biol. Beitr.41/2: 1317-1608.PDFArchived 2018-04-10 at theWayback Machine
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![Morphology of the head and its processes: (А) head capsule; (В) antenna; (С) mandible[44]](/mt/?noimg=&dark=on&url=https%3a%2f%2fwikipedia.org%2fwiki%2fFile%3a2-Morphology-of-head.png)
![Morphology of the thorax (D)[44]](/mt/?noimg=&dark=on&url=https%3a%2f%2fwikipedia.org%2fwiki%2fFile%3a3-Morphology-of-thotax.png)
![Morphology of the abdomen and processes of the thorax: (E) front wing; (F) leg III; (G) abdomen of female[44]](/mt/?noimg=&dark=on&url=https%3a%2f%2fwikipedia.org%2fwiki%2fFile%3a4-Morphology-of-abdomen-and.png)
