|Diphyus sp., Rhône (France)|
The Ichneumonidae are a parasitoid wasp family within the order Hymenoptera. They are important parasitoids of other invertebrates; common hosts are larvae and pupae of Coleoptera, Hymenoptera, and Lepidoptera. Over 24000 species have been described worldwide. Estimates of the total species range from 60000 to over 100000 - more than any other hymenopteran family.
The distribution of the ichneumonids has traditionally been one of the most notable exceptions to the common latitudinal gradient in species diversity, since the family was thought to be at its most species rich in the temperate zone instead of the tropics. This view has recently been questioned after the discovery of numerous new tropical species.
Insects in the family Ichneumonidae are commonly called ichneumon wasps or ichneumonids. Less exact terms are ichneumon flies (they are not closely related to true flies), or scorpion wasps due to the extreme lengthening and curving of the abdomen (scorpions are arachnids). Simply but ambiguously, these insects are commonly called ichneumons, which is also a term for the Egyptian mongoose (Herpestes ichneumon).
The name is derived from Latin 'ichneumon', from Ancient Greek ἰχνεύμων (ikhneúmōn, "tracker"), from ἴχνος (íkhnos, "track, footstep"). It apparently refers to the ichneumonids' habit of searching leaves, leaf litter or the ground for hosts.
Adult ichneumonids superficially resemble other wasps. They have a slender waist, two pairs of wings, a pair of large eyes on the side of the head and three ocelli on top of the head. Their size varies considerably from a few millimetres to seven or more centimetres.
The ichneumonids differ from typical, aculeate wasps (Aculeata: Vespoidea and Apoidea), in that the antennae have more segments; typically 16 or more, while most other wasps have 13 or fewer. Unlike the aculeate wasps, which sting in defense and do not pass their eggs along the stinger, ichneumonid females have an ovipositor (homologous to the stinger) which they use to lay eggs inside or on their host. Ichneumonids generally inject venom along with the egg, but only larger species with relatively short ovipositors use the ovipositor in defense. Males do not possess stingers or ovipositors in either lineage.
Ichneumonids are distinguished from their sister group Braconidae mainly on the basis of wing venation. The fore wing of 95% of ichneumonids has vein 2m-cu, 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 in Aphidiinae).
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. Recently this belief has been questioned, after the discovery of numerous new tropical species.
Reproduction and diet
Some ichneumonid species lay their eggs in the ground, but most inject them either directly into their host's body or on its surface. After hatching the ichneumonid larva eats its host alive. The most common hosts are larvae or pupae of Lepidoptera, Coleoptera and Hymenoptera, but some species also parasitise spiders. Hyperparasitoids such as Mesochorinae oviposit inside the larvae of other ichneumonids. The hosts of many species are unknown; host information has been summed up by e.g. Aubert, Perkins. and Townes.
Ichneumonids use both idiobiont and koinobiont parasitising strategies. Idiobionts paralyse their host and prevent it from growing while it is eaten. Koinobionts let their host grow and develop while they feed on it. In both strategies, the host typically dies after some weeks, after which the ichneumonid larva emerges and pupates.
Adult ichneumonids feed on a diversity of foods, including plant sap, nectar and other insects. They spend much of their active time searching, either for hosts (female ichneumonids) or for emerging females (male ichneumonids).
The predation pressure exerted by ichneumonids can be tremendous, and they are often one of the major regulators of invertebrate populations. 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).
Taxonomy and systematics
The taxonomy of the ichneumonids is still poorly known. The family is highly diverse, containing 24000 described species. Approximately 60000 species are estimated to exist worldwide, though some estimates place this number at over 100000. 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 the phylogeny of the ichneumonids. Even the relationships between subfamilies are unclear. The sheer diversity also means DNA sequence data is only available for a tiny fraction of the species, and detailed cladistic studies require major computing capacity.
Extensive catalogues of the ichneumonids include those by Aubert, Gauld, Perkins, and Townes. Due to the taxonomic difficulties involved, however, their classifications and terminology are often confusingly contradictory. Several prominent authors have gone as far as to publish major reviews that defy the International Code of Zoological Nomenclature.
Ichneumonid evolutionary history is even worse known than the modern day taxonomy. The family has existed since at least the Jurassic (ca. 150 mya), but may have appeared some time before. It diversified during the Oligocene.
At the time of writing, the ichneumonids are divided into 39 subfamilies, whose names and definitions have varied considerably. The phylogenetic relationships between the subfamilies are still unclear.
- Anomalinae (= Anomaloninae)
- Brachycyrtinae (sometimes included in Labeninae)
- Campopleginae (= Porizontinae)
- Cryptinae (= Gelinae, Hemitelinae, Phygadeuontinae)
- Ctenopelmatinae (= Scolobatinae)
- Cylloceriinae (= Oxytorinae, sometimes included in Microleptinae)
- Diacritinae (sometimes included in Pimplinae)
- Eucerotinae (sometimes included in Tryphoninae)
- Labeninae (= Labiinae)
- Lycorininae (sometimes included in Banchinae)
- Neorhacodinae (sometimes included in Banchinae)
- Orthocentrinae (sometimes included in Microleptinae)
- Paxylommatinae (sometimes not placed in Ichneumonidae at all)
- Pimplinae (= Ephialtinae)
- Poemeniinae (sometimes included in Pimplinae)
- Rhyssinae (sometimes included in Pimplinae)
- Stilbopinae (sometimes included in Banchinae)
- Tatogastrinae (sometimes included in Microleptinae or Oxytorinae)
Famous ichneumonologists include:
- Carl Gustav Alexander Brischke
- Peter Cameron
- Arnold Förster
- Johann Ludwig Christian Gravenhorst
- Alexander Henry Haliday
- August Emil Holmgren
- Joseph Kriechbaumer
- Thomas Ansell Marshall
- Constantin Wesmael
Darwin and the Ichneumonidae
The grisliness and apparent cruelty (at least, from a human perspective) of the ichneumonids troubled philosophers, naturalists, and theologians in the 19th century, who found the parasitoid life style inconsistent with the notion of a world created by a loving and benevolent God. Charles Darwin found the example of the Ichneumonidae so troubling, it contributed to his increasing doubts about the nature and existence of a Creator. In an 1860 letter to the American naturalist Asa 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.
Megarhyssa macrurus female
A female Ichneumoninae (Phaegonini, Lusius tenuissimus?) from Kibale rain forest
A female Campoleginae from Kibale
A female Banchinae (Syzecteus sp.), from Kibale
A female Metopinae (Exochus sp.) from Kibale
Morphology of the head and its processes: (А) head capsule; (В) antenna; (С) mandible
Morphology of the thorax (D)
Morphology of the abdomen and processes of the thorax: (E) front wing; (F) leg III; (G) abdomen of female
- Sime, K. R.; Brower, A. V. Z. (1998). "Explaining the latitudinal gradient anomaly in ichneumonid species richness: Evidence from butterflies". Journal of Animal Ecology 67 (3): 387. doi:10.1046/j.1365-2656.1998.00198.x. JSTOR 2647379.
- Veijalainen, A.; Wahlberg, N.; Broad, G. R.; Erwin, T. L.; Longino, J. T.; Saaksjarvi, I. E. (2012). "Unprecedented ichneumonid parasitoid wasp diversity in tropical forests". Proceedings of the Royal Society B: Biological Sciences 279 (1748): 4694. doi:10.1098/rspb.2012.1664.
- Quicke, D. L. J. (2012). "We Know Too Little about Parasitoid Wasp Distributions to Draw Any Conclusions about Latitudinal Trends in Species Richness, Body Size and Biology". PLoS ONE 7 (2): e32101. doi:10.1371/journal.pone.0032101.
- 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.
- Aubert, J. F. (1969): Les Ichneumonides ouest-palearctiques et leurs hotes 1. Pimplinae, Xoridinae, Acaenitinae ["The Western Palearctic ichneumon wasps and their hosts. 1. Pimplinae, Xoridinae, Acaenitinae"]. Laboratoire d'Evolution des Etres Organises, Paris. (French)
- Aubert, J. F. (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"]. Laboratoire d'Evolution des Etres Organises, Paris & EDIFAT-OPIDA, Echauffour. (French)
- Aubert, J. F. (2000): Les ichneumonides oeust-palearctiques et leurs hotes. 3. Scolobatinae (=Ctenopelmatinae) et suppl. aux volumes precedents [The West Palaearctic ichneumonids and their hosts. 3. Scolobatinae (= Ctenopelmatinae) and supplements to preceding volumes]. Litterae Zoologicae 5: 1-310. (French) (with English abstract)
- Perkins, J. F. (1959): Ichneumonidae, key to subfamilies and Ichneumoninae – 1. Handbook for the Identification of British Insects 7(part 2ai): 1–116.
- Perkins, J. F. (1960): Hymenoptera: Ichneumonoidea: Ichneumonidae, subfamilies Ichneumoninae 2, Alomyinae, Agriotypinae and Lycorininae. Handbook for the Identification of British Insects 7(part 2aii): 1–96.
- Townes, H. T. ; Momoi, S. A. & Townes, M. (1965): Catalogue and Reclassification of Eastern Palearctic Ichneumonidae Memoirs of the American Entomological Institute 5: 1-661 pages.
- Várkonyi G, Hanski I, Rost M et al. 2002: Host-parasitoid dynamics in periodic boreal moths — Oikos 98: 421--430.
- Hawkins BA, Cornell HV & Hochberg ME 1997: Predators, parasitoids, and pathogens as mortality agents in phytophagous insect populations — Ecology 78: 2145--2152.
- Memmott J, Godfray HCJ & Gauld ID 1994: The Structure of a Tropical Host-Parasitoid Community — Journal of Animal Ecology 63: 521--540.
- Várkonyi G & Roslin T 2013: Freezing cold yet diverse: dissecting a high-Arctic parasitoid community associated with Lepidoptera hosts — The Canadian Entomologist: 1--26.
- Gauld, I. D. (1976): The classification of the Anomaloninae (Hymenoptera: Ichneumonidae). Bulletin of the British Museum of Natural History (Entomology) 33: 1-135.
- Townes, H. T. (1969a): Genera of Ichneumonidae, Part 1 (Ephialtinae, Tryphoninae, Labiinae, Adelognathinae, Xoridinae, Agriotypinae). Memoirs of the American Entomological Institute 11: 1-300.
- Townes, H. T. (1969b): Genera of Ichneumonidae, Part 2 (Gelinae). Memoirs of the American Entomological Institute 12: 1-537.
- Townes, H. T. (1969c): Genera of Ichneumonidae, Part 3 (Lycorininae, Banchinae, Scolobatinae, Porizontinae). Memoirs of the American Entomological Institute 13: 1-307.
- Townes, H. T. (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 (new edition) 2: 1-49.
- Wahl, David (1999): Classification and Systematics of the Ichneumonidae (Hymenoptera). Version of 1999-JUL-19. Retrieved 2008-JUN-18.
- "Nonmoral Nature". Retrieved 2011-04-05.
- "Letter 2814 — Darwin, C. R. to Gray, Asa, 22 May ". Retrieved 2011-04-05.
- Tereshkin, 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. PDF
- Checklist of Japanese Ichneumonidae
- Fauna Europaea
- Ichneumonidae:Classification of afrotropical ichneumonid wasps. Extensive use of images.
Taxonomy and Systematics
- Ichneumonidae:Classification of afrotropical ichneumonid wasps. Extensive use of images.
- Key to Subfamilies found in Britain and Ireland. Extensive use of images.
- Aramel. Overview. In French.
- Important Systematic Literature
- Family Ichneumonidae at EOL Comprehensive image database
- Images of Ichneumonidae species in New Zealand
- Reference large-format photos of 15 different species of Ichneumonidae
- Photo Essay: Giant Ichneumon Wasps Ovipositing
- Reference Photos: Giant Ichneumon Wasps - Male Megarhyssa sp.
- Ichneumonidae as Biological Control Agents of Pests with Bibliography long download pdf
- Ichneumonid Types in Entomological Institute of Hokkaido University In Japanese but a pulldown menu of Subfamilies by clicking bottom box.
- Ichneumonidae Database In Korean but with images and type repositories in English.
- Diagnostic features of subfamilies
- Key to subfamilies in Spanish and not all the families, but good photos.
- Diadegma insulare on the University of Florida / Institute of Food and Agricultural Sciences Featured Creatures website
- Taiwan Digital Insects 401 species imaged.
- Galerie Insecte French Images by subfamily and genus.
- Hymis De Images 47 on 6 pages of authority (expert) named Ichneumonidae. Ongoing.
- W.Rutkies Images. Authority id.
- Camille Thirion Image Gallery
- Hymatol Subfamily Key Powerpoint pdf Excellent photos, figures and text. Note that it is 300MB in size.
- A.Tereshkin: Information about different species of Ichneumonidae (Hymenoptera), first of all Ichneumoninae Stenopneusticae, collected by author (taxonomic, faunistic and biological data, original images, methods of Ichneumonidae collecting etc.) and PDF collection of some G. Heinrich’s articles.