Ceraphron sp., copyright Pierre Bornand.

Belongs within: Unicalcarida.
Contains: Aculeata, Megalyridae, Evanioidea, Platygastridae, Cynipoidea, Proctotrupoidea, Ichneumonoidea.

The Apocrita are a clade of wasps characterised by the development of a narrow waist between the first and second abdominal segments with the first abdominal segment being incorporated into the mesosoma as the propodeum (Grimaldi & Engel 2005). Molecular analysis supports recognition of a major clade of parasitoid forms, including the Proctotrupomorpha, Ichneumonoidea and Ceraphronoidea, as the sister taxon of the remaining members (Peters et al. 2017). The Proctotrupomorpha are a diverse clade of small, often minute, wasps united by the lack of a median mesoscutal sulcus and a number of characters relating to reduction in wing venation (Rasnitsyn 2002).

The Ceraphronoidea are minute wasps characterised by two protibial spurs, an enlarged second metasomal segment, and fore wings with the costal and subcostal + radial veins fused into a bar running along the anterior margin. The Stigmaphronidae, a Mesozoic family possibly related to the Ceraphronoidea, have similarly fused anterior wing veins but have a single protibial vein and the second metasomal segment is not enlarged (Grimaldi & Engel 2005). Ceraphronoids are divided between the families Ceraphronidae and Megaspilidae, with Megaspilidae possessing two spurs on the mid tibia and an enlarged pterostigma in winged forms whereas Ceraphronidae have a single mid tibial spur (Naumann 1991).

Other members of the Apocrita include the Trigonalidae, hyperparasitoid wasps within caterpillars or sawfly larvae whose females lay their eggs within incisions in leaves where they are ingested by the primary host when feeding. The Stephanidae are slender wasps with a mobile, globular head bearing a crown of rasp-like teeth that parasitise larvae of wood-boring insects (Naumann 1991). Eostephanites tenuis is a species described from Chinese Eocene amber by Hong (2002) that resembles a stephanid but has fewer teeth on the crown and bears longer maxillary palps.

A bunch of apocrites
Published 17 February 2012
An unidentified male of Megalyridae, a family of ‘evaniomorphs’ parasitic on wood-boring beetles, from here.

During the late nineteenth century, many women attempted to achieve a ‘wasp waist’, using corsets to tighten their waist to as narrow a diameter as possible. The style was so-called, of course, because of its resemblance to the body of a wasp, with a sharp constriction dividing the body. However, this feature is not universal among wasps: rather, it characterises a distinct clade within the wasps, the Apocrita.

Basal members of the Hymenoptera possess a broad junction between thorax and abdomen like that seen in other insects. In apocritan wasps, the first segment of the abdomen became incorporated into the body of the thorax (where it is referred to as the propodeum) and the characteristic wasp waist developed at the front of the second abdominal segment. Because the major divisions of the body in Apocrita therefore do not correspond directly to the thorax and abdomen of other insects, workers on Apocrita instead refer to the mesosoma and metasoma (or ‘altitrunk’ and ‘gaster’). So narrow is the connection between mesosoma and metasoma, in fact, that members of the Apocrita are incapable of taking solid food: only liquids can pass through the waist. This limitation is believed to have later been significant in the development of the social wasps and ants: because mature ants cannot themselves eat solids, they must feed any solid food they collect to their larvae. The larvae then regurgitate the semi-digested food in a liquid form that the adults can handle. This dependance on their larvae induced the formation of stable colonies. Mature wasps that do not form colonies feed on naturally-occurring liquids such as nectar.

An unidentified wasp of the Stephanidae ovipositing, from Singapore Nature.

Ancestrally, the Apocrita are a lineage of larval parasites, and the majority of species remain so today. The wide distribution of parasites of wood-boring beetles among basal apocritans, and in their sister group the Orussidae among the non-waisted wasps, suggests that this was probably the original lifestyle for the apocritans (Grimaldi & Engel 2005). Living Apocrita can be divided between five main groups: the Stephanidae, the Aculeata (stinging wasps, including all the social forms such as ants and bees), the Ichneumonoidea (ichneumons and braconids), the Proctotrupomorpha, and the Evaniomorpha (though the monophyly of the latter group is debatable). The Stephanidae are a family of long slender beetle parasites that are most diverse in tropical parts of the world.

An evaniid of the genus Hyptia, from Kurt Schaefer.

The evaniomorphs have been suggested to form a group on the basis of the form of the inner articulation of the coxa (the basal segment) of the middle pair of legs, but the polarity of this feature is debatable (Ronquist 1999). The type superfamily, the Evanioidea, includes a group of families characterised by having the articulation of the metasoma to the mesosoma positioned high up on the propodeum rather than low down as in most other wasps. The hatchet wasps of the Evaniidae have a particularly distinctive body form: the mesosoma is boxy, often almost square in side view; the first segment of the metasoma is developed into a long and narrow petiole; and the remainder of the metasoma is relatively small and hangs off the petiole like the head of the eponymous hatchet. Evaniids are parasites of cockroaches, laying their eggs on the cockroaches’ egg cases.

Female trigonalyid of the genus Trigonalys, photographed by Simon van Noort. Note the hooked end to the metasoma; when ovipositing, the female will stand on one side of a leaf and hook her metasoma around to lay her eggs on the other side of the leaf.

Females of another evaniomorph family, the Trigonalyidae, lay large numbers of eggs inserted into incisions on a plant leaf. When a piece of leaf containing a trigonalyid egg is eaten by a caterpillar, the egg hatches out and the trigonalyid larva emerges, then burrows into the body of the caterpillar. However, the larva’s target is not the caterpillar itself. Instead, the trigonalyid is looking for the parasitic larva of another wasp that may be inside the caterpillar: it is what is called a hyperparasite (that is, a parasite of a parasite). Trigonalyids are also known as parasites of the larvae of social wasps: when the social wasp feeds its larvae on a caterpillar containing a trigonalyid, the trigonalyid may infect the larva to which it is fed (Grimaldi & Engel 2005).

To give Lovecraft nightmares
Published 8 October 2007
Various Chalcidoidea, from the Natural History Museum.

Many of you will probably be aware of the existence of parasitoid* wasps—Hymenoptera that lay their eggs inside insects and other animals so that when the larvae hatch out they can devour the unfortunate host from the inside out (in some situations, you can’t help but say “devour”). The most well-known examples of parasitoid wasps are the large ichneumons**, but I’ll be dealing today with a different group—the micro-wasps of the Proctotrupomorpha.

*Not a typo. Technically speaking, “parasitism” implies that the parasite feeds off the host without (ideally) actually killing it. “Parasitoid” Hymenoptera are referred to as such because the growth of the larva almost invariably results in the death of the host. As such, they are better described as internal predators rather than parasites. All the same, I apologise in advance for when I’m going to inevitably slip back into referring to them as parasites later on.

**Not to be confused with the mongooses also known as ichneumons. The two are easily distinguished—mongooses are much harder to fit into a collection vial.

Inostemma, from here.

Proctotrupomorphs are a spectacularly diverse group. The image at the top of this section shows an array of examples from only one of the component superfamilies, the Chalcidoidea. Proctotrupomorphs also include the Proctotrupoidea, Platygastroidea and Cynipoidea. Most are exceedingly small—according to the Natural History Museum, the smallest chalcidoid (also the world’s smallest insect) reaches a maximum adult size of 0.11mm. There are proctotrupomorphs with wings, there are ones without. There are species with relatively enormous ‘horns’ arising from the front of the abdomen that allow space for ovipositors considerably longer than the remainder of the insect (as shown above). Most emerge from eggs or juveniles of other arthropods, but some have taken to living in galls or pollinating figs. Some are even parasitoids of other parasitic wasps. And a few are even aquatic.

Encarsia formosa, from Cornell University.

A number of proctotrupomorphs exhibit what is called polyembryony. A single egg is laid within a host which then divides into a number of larvae—up to two thousand in Copidosoma floridanum. The latter species also has a remarkable characteristic in that some of the polyembryonically produced individuals, the precocious larvae, develop enlarged mandibles and seek out and destroy other larvae of the same species but from different eggs (Zhurov et al. 2004). These precocious larvae never mature and die along with the host, leaving their identical siblings (the reproductives) to emerge as adults. In another species, Encarsia formosa, the gift from one larva to another is even more significant though perhaps less willing. Most E. formosa larvae are female, and develop within greenhouse white-flies. Males are much rarer, and actually have a different host (Askew 1971)—they develop as hyperparasites of the female larvae! As with the marine fly Pontomyia, this demonstrates the dangers potentially inherent in reading morals of human society into the biology of other organisms.

In many cases, however (particularly with egg parasites), there is often no room at the inn for more than one larva—if two larvae attempted to grow within the one host, food supplies would be exhausted before either could complete development. Therefore, most parasitic wasps have measures to prevent competition within the host. As already mentioned for Copidosoma, larvae may kill each other off within the host. There are a number of cases where development of supernumerary larvae halts terminally once one has hatched out or pupated (Askew 1971) though the mechanisms of this termination may be unclear. Some species act to prevent supernumerary oviposition from happening at all. Trissolcus basalis (image above from SARE) is a parasite of shield bug eggs. After the female has laid within an egg, she scratches the ovipositor over the cap of the egg in a figure-eight movement to leave a mark indicating that the egg has already been parasitised. As a contrast to all this, though, Tetrastichus giffardianus is an obligate superparasite of the fruit fly Dacus cucurbitae. Larvae of T. giffardianus can only avoid encapsulation* by the host if said host has already been parasitised by another wasp, the braconid Opius fletcheri.

*Encapsulation is the formation of a hard capsule around the parasite larva by the host’s natural defenses, which isolates and kills the parasite.

Finally, a number of proctotrupomorphs have abandoned parasitism to become herbivores. Fig wasps are a number of families of chalcidoids that lay their eggs within fig flowers. Fig flowers are produced entirely enclosed within an immature fig, and can only be accessed by a single small hole in the fig. The female wasp crawls within the fig and lays her eggs in the flowers. The hatching larvae feed on the inside of the fig (though ovules are deep enough to escape the depredations of the larvae) before maturing. Once mature, they mate within the fig, and the males chew an exit path for the females before expiring without dispersing. The females become covered in pollen as they escape the fig (some species apparently actively collect pollen into special pockets), which they carry to the fig they will lay in. Figweb is a website with all the information on the fig-wasp interaction you could possibly want, as well as some pretty good images.

Systematics of Apocrita
<==Apocrita [Clistogastra, Ichneumonides, Proctotrupii, Terebrantes]PK17
    |  |  `--+--MegalyridaeHR11
    |  |     `--Trigonalidae [Archiglossata, Ichneumomimidae, Trigonaloidea, Trigonalyidae]HR11
    |  |          |--MimelogonalosN91
    |  |          |--Orthogonalys pulchellaHR11
    |  |          |--Pseudogonalos hahniiPK17
    |  |          |--Darbigonalus capitatus Rasnitsyn 1986RJ93
    |  |          |--Lycogaster pullata [incl. L. pullata nevadensis]S96
    |  |          |--Bareogonalos canadensisS96
    |  |          |--Poecilogonalos thwaitesiiRD77
    |  |          |--Cretogonalys taimyricus Rasnitsyn 1977P92
    |  |          |--TrigonalysB11
    |  |          |    |--T. maculatusRD77
    |  |          |    |--T. micanticepsB11
    |  |          |    `--T. pervetus Cockerell 1917P92
    |  |          `--TaeniogonalosHR11
    |  |               |--T. gundlachii [incl. Poecilogonalos costalis]S96
    |  |               |--T. maculataB11
    |  |               `--T. venatoriaR70
    |  `--+--EvanioideaPK17
    |     `--StephanoideaH02
    |          |--Eostephanites Hong 2002 [Eostephanitidae]H02
    |          |    `--*E. tenuis Hong 2002H02
    |          `--StephanidaeHR11
    |               |  i. s.: MegischusHR11
    |               |           |--M. basalis Aguiar 2005A05
    |               |           `--M. furcatus (Lepeletier & Serville 1825) [incl. M. annulator Brullé 1846]A05
    |               |         Protostephanus ashmeadiA05
    |               |         ElectrostephanusA05
    |               |           |--E. brevicornisA05
    |               |           `--E. neovenatusA05
    |               |         HemistephanusA05
    |               |--StephanusPK17 [StephaninaeGE05]
    |               |    |--S. coronatorB35 [=Bracon (Stephanus) coronatusG20, Ichneumon coronatusL02, Pimpla coronatorB35]
    |               |    `--S. serratorPK17
    |               `--SchlettererinaeGE05
    |                    |--Archaeostephanus coraeGE05
    |                    `--Schlettererius cinctipesN91
         |--Proctotrupomorpha [Cinipserae, Cynipsera, Diplolepariae]PK17
         |    |  i. s.: ProctorenyxidaeGE05
         |    |         NeotelenomusG17
         |    |           |--N. anthereae Dodd 1913GM79
         |    |           `--N. javae Girault 1917G17
         |    |         Eulagynodes Girault 1917G17
         |    |           `--*E. bicolor Girault 1917G17
         |    |         AcoloidesG17
         |    |           |--A. arachnophagus Girault 1917GM79
         |    |           |--A. fasciatipennis Girault 1917G17
         |    |           |--A. javensis Girault 1917G17
         |    |           `--A. trispinosus Girault 1917G17
         |    |         MesoserphusGE05 [MesoserphidaeR02, Mesoserphinae]
         |    |           `--M. karatavicusGE05
         |    |--PlatygastridaeMH11
         |    `--+--CynipoideaMH11
         |       `--ProctotrupoideaMH11
               |    |--Aphrostigmon vitimense Rasnitsyn 1991RJ93
               |    |--Stigmaphron Kozlov 1975P92
               |    |    `--*S. orphne Kozlov 1975P92
               |    |--Elasmomorpha Kozlov 1975P92
               |    |    `--*E. melpomene Kozlov 1975P92
               |    `--Hippocoon Kozlov 1975P92
               |         `--*H. evadne Kozlov 1975P92
                    |  i. s.: Libanophron astartePK17
                    |    |--Lagynodes Forster 1841GM79 [LagynodinaeN91]
                    |    `--MegaspilinaeN91
                    |         |--Megaspilus fuscipennisMH11
                    |         |--Dendrocerus carpenteriN91, M83
                    |         `--ConostigmusN91
                    |              |--C. dolicharthrusP92
                    |              `--C. lazarosPP19
                    `--Ceraphronidae [Calliceratidae]GE05
                         |--Lygocerus dubitatus Brues 1937P92
                         |--Allocotidus bruesi Muesebeck 1963P92
                         |--Prolagynodes pennigerP92
                         `--Ceraphron Jurine 1807GM79 [incl. CallicerasP92]
                              |--C. achilles Dodd 1914GM79
                              |--C. bispinosusMH11
                              |--C. javensis Girault 1917G17
                              `--C. sulcatusR26 [=Sparasion (Ceraphron) sulcatumG20]

*Type species of generic name indicated


[A05] Aguiar, A. P. 2005. A new and unusual species of Stephanidae (Hymenoptera), with a discussion on its phylogenetic implications. Journal of Hymenoptera Research 14 (1): 1–6.

Askew, R. R. 1971. Parasitic Insects. Heinemann Educational Books: London.

[B35] Boisduval, J. B. 1835. Voyage de Découvertes de l’Astrolabe. Exécuté par ordre du Roi, pendant les années 1826–1827–1828–1829, sous le commandement de M. J. Dumont d’Urville. Faune entomologique de l’océan Pacifique, avec l’illustration des insectes nouveaux recueillis pendant le voyage vol. 2. Coléoptères et autres ordres. J. Tastu: Paris.

[B11] Brothers, D. J. 2011. A new Late Cretaceous family of Hymenoptera, and phylogeny of the Plumariidae and Chrysidoidea (Aculeata). ZooKeys 130: 515–542.

[G17] Girault, A. A. 1917. New Javanese Hymenoptera. Privately published (reprinted: Gordh, G., A. S. Menke, E. C. Dahms & J. C. Hall. 1979. The privately printed papers of A. A. Girault. Memoirs of the American Entomological Institute 28: 59–71).

[G20] Goldfuss, G. A. 1820. Handbuch der Naturgeschichte vol. 3. Handbuch der Zoologie pt 1. Johann Leonhard Schrag: Nürnberg.

[GM79] Gordh, G., A. S. Menke, E. C. Dahms & J. C. Hall. 1979. The privately printed papers of A. A. Girault. Memoirs of the American Entomological Institute 28: 1–400.

[GE05] Grimaldi, D., & M. S. Engel. 2005. Evolution of the Insects. Cambridge University Press: New York.

[HR11] Heraty, J., F. Ronquist, J. M. Carpenter, D. Hawks, S. Schulmeister, A. P. Dowling, D. Murray, J. Munro, W. C. Wheeler, N. Schiff & M. Sharkey. 2011. Evolution of the hymenopteran megaradiation. Molecular Phylogenetics and Evolution 60: 73–88.

[H02] Hong Y. 2002. Amber Insect of China. Beijing Scientific and Technological Publishing House.

[L02] Latreille, P. A. 1802. Histoire Naturelle, générale et particulière des crustacés et des insectes vol. 3. Familles naturelles des genres. F. Dufart: Paris.

[M83] Martin, N. A. 1983. Miscellaneous observations on a pasture fauna: an annotated species list. DSIR Entomology Division Report 3: 1–98.

[MH11] Munro, J. B., J. M. Heraty, R. A. Burks, D. Hawks, J. Mottern, A. Cruaud, J.-Y. Rasplus & P. Jansta. 2011. A molecular phylogeny of the Chalcidoidea (Hymenoptera). PLoS One 6 (11): e27023.

[N91] Naumann, I. D. 1991. Hymenoptera (wasps, bees, ants, sawflies). In: CSIRO. The Insects of Australia: A textbook for students and research workers 2nd ed. vol. 2 pp. 916–1000. Melbourne University Press: Carlton (Victoria).

[PP19] Palencia, L., E. Peñalver, C. E. Prieto & F. J. Poyato-Ariza. 2019. First fossil harvestmen (Arachnida: Opiliones) from Spain and notes on the fossil record of Opiliones. Palaeontologica Electronica 22.1.5A: 1–18.

[PK17] Peters, R. S., L. Krogmann, C. Mayer, A. Donath, S. Gunkel, K. Meusemann, A. Kozlov, L. Podsiadlowski, M. Petersen, R. Lanfear, P. A. Diez, J. Heraty, K. M. Kjer, S. Klopfstein, R. Meier, C. Polidori, T. Schmitt, S. Liu, X. Zhou, T. Wappler, J. Rust, B. Misof & O. Niehuis. 2017. Evolutionary history of the Hymenoptera. Current Biology 27 (7): 1013–1018.

[P92] Poinar, G. O., Jr. 1992. Life in Amber. Stanford University Press: Stanford.

[R02] Rasnitsyn, A. P. 2002. Superorder Vespidea Laicharting, 1781. Order Hymenoptera Linné, 1758 (=Vespida Laicharting, 1781). In: Rasnitsyn, A. P., & D. L. J. Quicke (eds) History of Insects pp. 242–254. Kluwer Academic Publishers: Dordrecht.

[RD77] Richards, O. W., & R. G. Davies. 1977. Imms’ General Textbook of Entomology 10th ed. vol. 2. Classification and Biology. Chapman and Hall: London.

[R70] Riek, E. F. 1970. Hymenoptera (wasps, bees, ants). In: CSIRO. The Insects of Australia: A textbook for students and research workers pp. 867–959. Melbourne University Press.

[R26] Risso, A. 1826. Histoire naturelle des principales productions de l’Europe méridionale et particulièrement de celles des environs de Nice et des Alpes maritimes vol. 5. F.-G. Levrault: Paris.

Ronquist, F. 1999. Evolution of the Hymenoptera (Insecta): the state of the art. Zoologica Scripta 28: 3–11.

[RJ93] Ross, A. J., & E. A. Jarzembowski. 1993. Arthropoda (Hexapoda; Insecta). In: Benton, M. J. (ed.) The Fossil Record 2 pp. 363–426. Chapman & Hall: London.

[S96] Smith, D. R. 1996. Trigonalyidae (Hymenoptera) in the eastern United States: seasonal flight activity, distribution, hosts. Proceedings of the Entomological Society of Washington 98 (1): 109–118.

Zhurov, V., T. Terzin & M. Grbić. 2004. Early blastomere determines embryo proliferation and caste fate in a polyembryonic wasp. Nature 432: 764–769.

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