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Hymenoptera is a large
order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...
of
insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pa ...
s, comprising the sawflies,
wasp A wasp is any insect of the narrow-waisted suborder Apocrita of the order Hymenoptera which is neither a bee nor an ant; this excludes the broad-waisted sawflies (Symphyta), which look somewhat like wasps, but are in a separate suborder ...
s,
bee Bees are winged insects closely related to wasps and ants, known for their roles in pollination and, in the case of the best-known bee species, the western honey bee, for producing honey. Bees are a monophyletic lineage within the superfami ...
s, and ants. Over 150,000 living species of Hymenoptera have been described, in addition to over 2,000 extinct ones. Many of the species are parasitic. Females typically have a special ovipositor for inserting eggs into hosts or places that are otherwise inaccessible. This ovipositor is often modified into a stinger. The young develop through
holometabolism Holometabolism, also called complete metamorphosis, is a form of insect development which includes four life stages: egg, larva, pupa, and imago (or adult). Holometabolism is a synapomorphic trait of all insects in the superorder Endopterygota ...
(complete
metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...
)—that is, they have a wormlike larval stage and an inactive pupal stage before they mature.


Etymology

The name Hymenoptera refers to the wings of the insects, but the original derivation is ambiguous. All references agree that the derivation involves the
Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic pe ...
πτερόν (''pteron'') for wing. The Ancient Greek ὑμήν (''hymen'') for membrane provides a plausible
etymology Etymology () The New Oxford Dictionary of English (1998) – p. 633 "Etymology /ˌɛtɪˈmɒlədʒi/ the study of the class in words and the way their meanings have changed throughout time". is the study of the history of the form of words ...
for the term because species in this order have membranous wings. However, a key characteristic of this order is that the hindwings are connected to the forewings by a series of hooks. Thus, another plausible etymology involves Hymen, the Ancient Greek god of marriage, as these insects have married wings in flight. Another suggestion for the inclusion of Hymen is the myth of
Melissa Melissa is a female given name. The name comes from the Greek word μέλισσα (''mélissa''), "bee", which in turn comes from μέλι (''meli''), "honey". In Hittite, ''melit'' signifies "honey". ''Melissa'' also refers to the plant '' ...
, a nymph with a prominent role at the wedding of Zeus.


Evolution

The cladogram of external relationships, based on a 2008 DNA and
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
analysis, shows the order as a
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...
, most closely related to endopterygote orders including the Diptera (true flies) and
Lepidoptera Lepidoptera ( ) is an order of insects that includes butterflies and moths (both are called lepidopterans). About 180,000 species of the Lepidoptera are described, in 126 families and 46 superfamilies, 10 percent of the total described speci ...
(butterflies and moths). Hymenoptera originated in the
Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest per ...
, with the oldest fossils belonging to the family Xyelidae. Social hymenopterans appeared during the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
. The evolution of this group has been intensively studied by Alex Rasnitsyn,
Michael S. Engel Michael S. Engel, FLS, FRES (born September 24, 1971) is an American paleontologist and entomologist, notable for contributions to insect evolutionary biology and classification. In connection with his studies he has undertaken field expedit ...
, and others. This clade has been studied by examining the mitochondrial DNA. Although this study was unable to resolve all the ambiguities in this clade, some relationships could be established. The
Aculeata Aculeata is a subclade of Hymenoptera containing ants, bees, and stinging wasps. The name is a reference to the defining feature of the group, which is the modification of the ovipositor into a stinger. However, many members of the group cannot ...
, Ichneumonomorpha, and
Proctotrupomorpha Proctotrupomorpha is a major subgrouping of the Apocrita within the Hymenoptera, containing mainly parasitic wasps. It contains the major groupings of Chalcidoidea, Diaprioidea, Proctotrupoidea, Cynipoidea and Platygastroidea, as well as the ...
were monophyletic. The Megalyroidea and Trigonalyoidea are sister clades as are the
Chalcidoidea Chalcid wasps (, , for their metallic colour) are insects within the superfamily Chalcidoidea, part of the order Hymenoptera. The superfamily contains some 22,500 known species, and an estimated total diversity of more than 500,000 species, me ...
+
Diaprioidea Diaprioidea is a hymenopteran superfamily containing five extant families, though in the past these families were included in the superfamily Proctotrupoidea. References Parasitica Apocrita superfamilies {{Apocrita-stub ...
. The
Cynipoidea The Cynipoidea are a moderate-sized hymenopteran superfamily that presently includes five modern families and three extinct families, though others have been recognized in the past. The most familiar members of the group are phytophagous, especia ...
was generally recovered as the sister group to
Chalcidoidea Chalcid wasps (, , for their metallic colour) are insects within the superfamily Chalcidoidea, part of the order Hymenoptera. The superfamily contains some 22,500 known species, and an estimated total diversity of more than 500,000 species, me ...
and
Diaprioidea Diaprioidea is a hymenopteran superfamily containing five extant families, though in the past these families were included in the superfamily Proctotrupoidea. References Parasitica Apocrita superfamilies {{Apocrita-stub ...
which are each other's closest relations. The cladogram is based on Schulmeister 2003.


Anatomy

Hymenopterans range in size from very small to large insects, and usually have two pairs of wings. Their
mouthparts Mouthparts may refer to: * The parts of a mouth ** Arthropod mouthparts The mouthparts of arthropods have evolved into a number of forms, each adapted to a different style or mode of feeding. Most mouthparts represent modified, paired append ...
are adapted for chewing, with well-developed
mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
s (ectognathous mouthparts). Many species have further developed the mouthparts into a lengthy
proboscis A proboscis () is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In invertebrates, the term usually refers to tubular mouthparts used for feeding and sucking. In vertebrates, a proboscis is an elong ...
, with which they can drink liquids, such as nectar. They have large compound eyes, and typically three simple eyes, ocelli. The forward margin of the hind wing bears a number of hooked bristles, or "
hamuli A hamus or hamulus is a structure functioning as, or in the form of, hooks or hooklets. Etymology The terms are directly from Latin, in which ''hamus'' means " hook". The plural is ''hami''. ''Hamulus'' is the diminutive – hooklet or little ...
", 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, the ovipositor 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 a stinger, and the eggs are laid from the base of the structure, rather than from the tip, which is used only to inject
venom Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a st ...
. The sting is typically used to immobilise prey, but in some wasps and bees may be used in defense. Hymenopteran larvae typically have a distinct head region, three thoracic segments, and usually nine or 10 abdominal segments. In the suborder Symphyta, the larvae resemble
caterpillar Caterpillars ( ) are the larval stage of members of the order Lepidoptera (the insect order comprising butterflies and moths). As with most common names, the application of the word is arbitrary, since the larvae of sawflies (suborder Sy ...
s 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 abdominal prolegs. 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 suborder Apocrita have no legs and are
maggot A maggot is the larva of a fly (order Diptera); it is applied in particular to the larvae of Brachycera flies, such as houseflies, cheese flies, and blowflies, rather than larvae of the Nematocera, such as mosquitoes and crane flies. En ...
like 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. The larvae of stinging forms (
Aculeata Aculeata is a subclade of Hymenoptera containing ants, bees, and stinging wasps. The name is a reference to the defining feature of the group, which is the modification of the ovipositor into a stinger. However, many members of the group cannot ...
) generally have 10 pairs of spiracles, or breathing pores, whereas parasitic forms usually have nine pairs present.


Reproduction


Sex determination

Among most or all hymenopterans, sex is determined by the number of
chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins ar ...
s an individual possesses. Fertilized eggs get two sets of chromosomes (one from each parent's respective
gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce ...
s) and develop into
diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectiv ...
females, while unfertilized eggs only contain one set (from the mother) and develop into
haploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respective ...
males. The act of fertilization is under the voluntary control of the egg-laying female, giving her control of the sex of her offspring. This phenomenon is called haplodiploidy. However, the actual genetic mechanisms of haplodiploid sex determination may be more complex than simple chromosome number. In many Hymenoptera, sex is actually determined by a single gene locus with many alleles. 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 were siblings 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. One consequence of haplodiploidy is that females on average actually have more genes in common with their sisters than they do with their own daughters. Because of this, cooperation among kindred females may be unusually advantageous, and has been hypothesized to contribute to the multiple origins of eusociality within this order. 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 as worker policing. Another consequence is that hymenopterans may be more resistant to the deleterious effects of
inbreeding Inbreeding is the production of offspring from the mating or breeding of individuals or organisms that are closely related genetically. By analogy, the term is used in human reproduction, but more commonly refers to the genetic disorders a ...
. As males are haploid, any recessive genes will automatically be expressed, exposing them to natural selection. Thus, the genetic load of deleterious genes is purged relatively quickly.


Thelytoky

Some hymenopterans take advantage of
parthenogenesis Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and developmen ...
, the creation of
embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...
s without
fertilization Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Pro ...
. 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 same
meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately ...
fuse to form a diploid zygote. This process tends to maintain heterozygosity in the passage of the genome from mother to daughter. It is found in several ant species including the desert ant ''
Cataglyphis cursor ''Cataglyphis cursor'' is a species of ant in the genus '' Cataglyphis''. Described in 1846, it is known only from the Mediterranean parts of France. Reproduction Parthenogenesis is a natural form of reproduction in which growth and developmen ...
'', the clonal raider ant '' Cerapachys biroi'', the predaceous ant ''
Platythyrea punctata ''Platythyrea punctata'' is a species of ant in the family Formicidae. References Further reading * Ponerinae Articles created by Qbugbot Insects described in 1858 {{ponerinae-stub ...
'', and the electric ant (little fire ant) '' Wasmannia auropunctata''. It also occurs in the Cape honey bee ''
Apis mellifera capensis The Cape honey bee or Cape bee (''Apis mellifera capensis'') is a southern South African subspecies of the western honey bee. They play a major role in South African agriculture and the economy of the Western Cape by pollinating crops and produc ...
''.
Oocyte An oocyte (, ), oöcyte, or ovocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The female ...
s that undergo automixis with central fusion often have a reduced rate of crossover recombination, which helps to maintain heterozygosity and avoid
inbreeding depression Inbreeding depression is the reduced biological fitness which has the potential to result from inbreeding (the breeding of related individuals). Biological fitness refers to an organism's ability to survive and perpetuate its genetic material. ...
. Species that display central fusion with reduced recombination include the ants ''
Platythyrea punctata ''Platythyrea punctata'' is a species of ant in the family Formicidae. References Further reading * Ponerinae Articles created by Qbugbot Insects described in 1858 {{ponerinae-stub ...
'' and '' Wasmannia auropunctata'' and the Cape honey bee ''Apis mellifera capensis''. In ''A. m. capensis'', the recombination rate during meiosis is reduced more than tenfold. In ''W. auropunctata'' the reduction is 45 fold. Single queen colonies of the narrow headed ant '' Formica 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.


Diet

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 and pollen. A huge number of species are
parasitoid In evolutionary ecology, a parasitoid is an organism that lives in close association with its host (biology), host at the host's expense, eventually resulting in the death of the host. Parasitoidism is one of six major evolutionarily stable str ...
s as larvae. The adults inject the eggs into a host, which they begin to consume after hatching. For example, the eggs of the endangered '' Papilio homerus'' are parasitized at a rate of 77%, mainly by Hymenoptera species. Some species are even hyperparasitoid, 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.


Classification

The Hymenoptera are divided into two groups; the Symphyta which have no waist, and the Apocrita which have a narrow waist.


Symphyta

The suborder Symphyta includes the sawflies, horntails, and parasitic wood wasps. The group may be
paraphyletic In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic ''with respect to'' the excluded subgroups. In ...
, as it has been suggested that the family
Orussidae The Orussidae or the parasitic wood wasps represent a small family of sawflies ("Symphyta"). Currently, about 93 extant and four fossil species are known. They take a key position in phylogenetic analyses of Hymenoptera, because they form the sis ...
may be the group from which the Apocrita arose. They have an unconstricted junction between the thorax and abdomen. The larvae are herbivorous, free-living, and eruciform, with three pairs of true legs, prolegs (on every segment, unlike
Lepidoptera Lepidoptera ( ) is an order of insects that includes butterflies and moths (both are called lepidopterans). About 180,000 species of the Lepidoptera are described, in 126 families and 46 superfamilies, 10 percent of the total described speci ...
) and ocelli. The prolegs do not have crochet hooks at the ends unlike the larvae of the Lepidoptera.


Apocrita

The
wasp A wasp is any insect of the narrow-waisted suborder Apocrita of the order Hymenoptera which is neither a bee nor an ant; this excludes the broad-waisted sawflies (Symphyta), which look somewhat like wasps, but are in a separate suborder ...
s,
bee Bees are winged insects closely related to wasps and ants, known for their roles in pollination and, in the case of the best-known bee species, the western honey bee, for producing honey. Bees are a monophyletic lineage within the superfami ...
s, and ants 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 the
thorax The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the c ...
. 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. In general, the anus only opens at the completion of larval growth.


Threats

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.


See also

* Hymenoptera Genome Database * Insects in literature (ant, bee, wasp) * Worker policing


References


External links

;General
Hymenoptera Anatomy Ontology project

Hymenoptera Anatomy Glossary

Hymenoptera Forum
German and International

* ttp://www.hymenopterists.org/ International Society of Hymenopterists
Bees, Wasps and Ants Recording Society
(UK)
Ants Photo Gallery
(RU)


Hymenoptera images on MorphBank, a biological image database

Order Hymenoptera
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Afrotropical The Afrotropical realm is one of Earth's eight biogeographic realms. It includes Africa south of the Sahara Desert, the majority of the Arabian Peninsula, the island of Madagascar, southern Iran and extreme southwestern Pakistan, and the island ...
Hymenoptera Excellent images
checklist of Australian Hymenoptera
{{Authority control Cenozoic insects Extant Triassic first appearances Insect orders Mesozoic insects Taxa named by Carl Linnaeus Triassic insects Hymenopterida