Apocrita is a suborder of insects in the order Hymenoptera. It includes wasps, bees, and ants, and consists of many families. It contains the most advanced hymenopterans and is distinguished from Symphyta by the narrow "waist" (petiole) formed between the first two segments of the actual abdomen; the first abdominal segment is fused to the thorax, and is called the propodeum.[2] Therefore, it is general practice, when discussing the body of an apocritan in a technical sense, to refer to the mesosoma and metasoma (or gaster) rather than the "thorax" and "abdomen", respectively.[3] The evolution of a constricted waist was an important adaption for the parasitoid lifestyle of the ancestral apocritan, allowing more maneuverability of the female's ovipositor.[4][5] The ovipositor either extends freely or is retracted, and may be developed into a stinger for both defense and paralyzing prey. Larvae are legless and blind, and either feed inside a host (plant or animal) or in a nest cell provisioned by their mothers.
Apocrita has historically been split into two groups, Parasitica and Aculeata. Aculeata is a clade whose name is in standard use.[6] "Parasitica" is not a clade, as it is paraphyletic: the clade would contain the Aculeata.[7] "Parasitica" is therefore a rankless grouping in many present classifications, if it appears at all.[8]Parasitica comprises the majority of hymenopteran insects, its members living asparasitoids.[9][10] Most species are small, with the ovipositor adapted for piercing. In some hosts, the parasitoids inducemetamorphosis prematurely, and in others it is prolonged. There are even species that arehyperparasites, or parasitoids on other parasitoids.[11] The Parasitica lay theireggs inside or on another insect (egg, larva or pupa) and their larvae grow and develop within or on that host. The host is nearly always killed. Manyparasitic hymenopterans are used asbiological control agents to control pests, such ascaterpillars,true bugs and hoppers,flies, andweevils.[12]
Aculeata is amonophyletic group that includes those species in which the female'sovipositor is modified into astinger to injectvenom. Groups within Aculeata include the familiar ants, bees, and various types of parasitic and predatory wasps; it also includes all of thesocial hymenopterans.[13]Among the nonparasitic and nonsocial Aculeata, larvae are fed with captured prey (typically alive and paralyzed) or may be fed pollen and nectar. Thesocial Aculeata feed their young prey (paper wasps andhornets), orpollen andnectar (bees), or perhaps seeds,fungi, or nonviable eggs (ants).
The Apocrita contains a large number of families. Some traditional taxa such as theParasitica (containing many families ofparasitoid wasps) have been found on molecular analysis to beparaphyletic.Parasitoidism evolved once, and it is found today across most Apocritan families, though it has been secondarily lost several times. Thephylogenetic tree gives a condensed overview of the phylogeny, illustrated with major groups. The sawflies are paraphyletic as the Apocrita evolved inside that group. The tree is not fully resolved.[13][14][2][9]
Cladogram of Apocrita after Peters et al.(2017)[9]
