Hymenoptera is a largeorder ofinsects, comprising thesawflies,wasps,bees, andants. Over 150,000 living species of Hymenoptera have been described,[2][3] in addition to over 2,000 extinct ones.[4] Many of the species areparasitic. Females typically have a specialovipositor for inserting eggs into hosts or places that are otherwise inaccessible. This ovipositor is often modified into astinger. The young develop throughholometabolism (completemetamorphosis)—that is, they have a wormlike larval stage and an inactive pupal stage before they reach adulthood.
The name Hymenoptera refers to the wings of the insects, but the original derivation is ambiguous.[5]: 42 All references agree that the derivation involves theAncient Greekπτερόν (pteron) for wing.[6] The Ancient Greekὑμήν (hymen) for membrane provides a plausibleetymology for the term because species in this order have membranous wings.[6] However, a key characteristic of this order is that thehindwings are connected to theforewings by a series ofhooks. Thus, another plausible etymology involvesHymen, the Ancient Greek god of marriage, as these insects have "married" wings in flight. Another suggestion for the inclusion of Hymen is the myth ofMelissa, a nymph with a prominent role at the wedding of Zeus.[citation needed]
Hymenoptera originated in theTriassic, with the oldest fossils belonging to the familyXyelidae. Social hymenopterans appeared during theCretaceous.[8] The evolution of this group has been intensively studied byAlex Rasnitsyn,Michael S. Engel, and others.[9]
Phylogenetic relationships within the Hymenoptera, based on both morphology and molecular data, have been intensively studied since 2000.[10] In 2023, a molecular study[10] based on the analysis ofultra-conserved elements confirmed many previous findings and produced a relatively robust phylogeny of the whole Order. Basal superfamilies are shown in the cladogram below.
Hymenopterans range in size from very small to large insects, and usually have two pairs of wings. Theirmouthparts are adapted for chewing, with well-developedmandibles (ectognathous mouthparts). Many species have further developed the mouthparts into a lengthyproboscis, with which they can drink liquids, such asnectar. They have largecompound eyes, and typically three simple eyes,ocelli.
The forward margin of the hind wing bears a number of hooked bristles, or "hamuli", which lock onto the fore wing, keeping them held together. The smaller species may have only two or three hamuli on each side, but the largest wasps may have a considerable number, keeping the wings gripped together especially tightly. Hymenopteran wings have relatively few veins compared with many other insects, especially in the smaller species.
In the more ancestral hymenopterans, theovipositor is blade-like, and has evolved for slicing plant tissues. In the majority, however, it is modified for piercing, and, in some cases, is several times the length of the body. In some species, the ovipositor has become modified as astinger, and theeggs are laid from the base of the structure, rather than from the tip, which is used only to injectvenom. The sting is typically used to immobilize prey, but in some wasps and bees may be used in defense.[8]
Hymenopteran larvae typically have a distinct head region, three thoracic segments, and usually nine or 10 abdominal segments. In the suborderSymphyta, theeruciform larvae resemblecaterpillars in appearance, and like them, typically feed on leaves. They have large chewing mandibles, three pairs of thoracic limbs, and, in most cases, six or eight abdominalprolegs. Unlike caterpillars, however, the prolegs have no grasping spines, and the antennae are reduced to mere stubs. Symphytan larvae that are wood borers or stem borers have no abdominal legs and the thoracic legs are smaller than those of non-borers.
With rare exceptions, larvae of the suborderApocrita have no legs and aremaggotlike in form, and are adapted to life in a protected environment. This may be the body of a host organism, or a cell in a nest, where the adults will care for the larva. In parasitic forms, the head is often greatly reduced and partially withdrawn into the prothorax (anterior part of the thorax). Sense organs appear to be poorly developed, with no ocelli, very small or absent antennae, and toothlike, sicklelike, or spinelike mandibles. They are also unable to defecate until they reach adulthood due to having an incomplete digestive tract (a blind sac), presumably to avoid contaminating their environment.[8] The larvae of stinging forms (Aculeata) generally have 10 pairs of spiracles, or breathing pores, whereas parasitic forms usually have nine pairs present.[11]
Among most or all hymenopterans, sex isdetermined by the number ofchromosomes an individual possesses.[12] Fertilized eggs get two sets of chromosomes (one from each parent's respectivegametes) and develop intodiploid females, while unfertilized eggs only contain one set (from the mother) and develop intohaploid males. The act of fertilization is under the voluntary control of the egg-laying female, giving her control of the sex of her offspring.[8] This phenomenon is calledhaplodiploidy.
However, the actual genetic mechanisms of haplodiploid sex determination may be more complex than simple chromosome number. In many Hymenoptera, sex is determined by a single gene locus with many alleles.[12] In these species, haploids are male and diploids heterozygous at the sex locus are female, but occasionally a diploid will be homozygous at the sex locus and develop as a male, instead. This is especially likely to occur in an individual whose parents weresiblings or other close relatives. Diploid males are known to be produced by inbreeding in many ant, bee, and wasp species. Diploid biparental males are usually sterile but a few species that have fertile diploid males are known.[13]
One consequence of haplodiploidy is that females on average have more genes in common with their sisters than they do with their daughters. Because of this, cooperation among kindred females may be unusually advantageous and has been hypothesized to contribute to the multiple origins ofeusociality within this order.[8][14] In many colonies of bees, ants, and wasps, worker females will remove eggs laid by other workers due to increased relatedness to direct siblings, a phenomenon known asworker policing.[15]
Another consequence is that hymenopterans may be more resistant to the deleterious effects ofinbreeding. As males are haploid, any recessive genes will automatically be expressed, exposing them to natural selection. Thus, thegenetic load of deleterious genes is purged relatively quickly.[16]
Some hymenopterans take advantage ofparthenogenesis, the creation ofembryos withoutfertilization.Thelytoky is a particular form of parthenogenesis in which female embryos are created (without fertilisation). The form of thelytoky in hymenopterans is a kind of automixis in which two haploid products (proto-eggs) from the samemeiosis fuse to form a diploid zygote. This process tends to maintainheterozygosity in the passage of the genome from mother to daughter. It is found in several ant species including the desert antCataglyphis cursor,[17] the clonal raider antCerapachys biroi,[18] the predaceous antPlatythyrea punctata,[19] and the electric ant (little fire ant)Wasmannia auropunctata.[20] It also occurs in the Cape honey beeApis mellifera capensis.[21]
Single queen colonies of the narrow headed antFormica exsecta illustrate the possible deleterious effects of increased homozygosity. Colonies of this species which have more homozygous queens will age more rapidly, resulting in reduced colony survival.[22]
Different species of Hymenoptera show a wide range of feeding habits. The most primitive forms are typically phytophagous, feeding on flowers, pollen, foliage, or stems. Stinging wasps are predators, and will provision their larvae with immobilised prey, while bees feed on nectar andpollen.
A huge number of species areparasitoids as larvae. The adults inject the eggs into a host, which they begin to consume after hatching. For example, the eggs of the endangeredPapilio homerus are parasitized at a rate of 77%, mainly by Hymenoptera species.[23] Some species are evenhyperparasitoid, with the host itself being another parasitoid insect. Habits intermediate between those of the herbivorous and parasitoid forms are shown in some hymenopterans, which inhabit the galls or nests of other insects, stealing their food, and eventually killing and eating the occupant.[8]
The suborderSymphyta includes thesawflies,horntails, andparasitic wood wasps. The group may beparaphyletic, as it has been suggested that the familyOrussidae may be the group from which theApocrita arose. They have an unconstricted junction between the thorax and abdomen. The larvae are herbivorous, free-living, anderuciform, usually with three pairs of true legs,prolegs (on every segment, unlikeLepidoptera) andocelli. The prolegs do not havecrochet hooks at the ends unlike the larvae of the Lepidoptera.[4] The legs and prolegs tend to be reduced or absent in larvae that mine or bore plant tissue, as well as in larvae ofPamphiliidae.[24]
Thewasps,bees, andants together make up the suborder (and clade)Apocrita, characterized by a constriction between the first and second abdominal segments called a wasp-waist (petiole), also involving the fusion of the first abdominal segment to thethorax. Also, the larvae of all Apocrita lack legs, prolegs, or ocelli. The hindgut of the larvae also remains closed during development, with feces being stored inside the body, with the exception of some bee larvae where the larval anus has reappeared through developmental reversion.[clarification needed] In general, the anus only opens at the completion of larval growth.[4]
Hymenoptera as a group are highly susceptible to habitat loss, which can lead to substantial decreases in species richness and have major ecological implications due to their pivotal role as plant pollinators.[25]
^abcdefHowell, H.V.; Doyen, J.T.; Purcell, A.H. (1998).Introduction to Insect Biology and Diversity (2nd ed.). Oxford University Press. p. 320.ISBN978-0-19-510033-4.
^Baine, Q.; Looney, C.; Monckton, S. K.; Smith, D. R.; Schiff, N. M.; Goulet, H.; Redford, A. J. (April 2022)."Biology and behavior".idtools.org. RetrievedFebruary 15, 2024.
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