Hymenoptera | |
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Hymenopterans from different families; Clockwise from top-left: Red imported fire ant (Formicidae), Vespula vulgaris (Vespidae), Tenthredopsis sordida (Tenthredinidae), and Western honey bee (Apidae) | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Class: | Insecta |
(unranked): | Holometabola |
Superorder: | Hymenopterida |
Order: | Hymenoptera Linnaeus, 1758 |
Suborders | |
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Hymenoptera is a large order of insects, comprising the sawflies, wasps, bees, and ants. 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 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 (complete metamorphosis)—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 the Ancient Greek πτερόν (pteron) for wing. [6] The Ancient Greek ὑμήν (hymen) for membrane provides a plausible etymology for the term because species in this order have membranous wings. [6] 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, a nymph with a prominent role at the wedding of Zeus.[ citation needed ]
Molecular analysis finds that Hymenoptera is the earliest branching group of Holometabola. [7]
Holometabola |
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Hymenoptera originated in the Triassic, with the oldest fossils belonging to the family Xyelidae. Social hymenopterans appeared during the Cretaceous. [8] The evolution of this group has been intensively studied by Alex 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 of ultra-conserved elements confirmed many previous findings and produced a relatively robust phylogeny of the whole Order. Basal superfamilies are shown in the cladogram below.
Hymenoptera | |||||||||||||||||||||||||||||||||||
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Symphyta (red bar) are paraphyletic as Apocrita are excluded. |
Hymenopterans range in size from very small to large insects, and usually have two pairs of wings. Their mouthparts are adapted for chewing, with well-developed mandibles (ectognathous mouthparts). Many species have further developed the mouthparts into a lengthy proboscis, 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", 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. 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 suborder Symphyta, the eruciform larvae resemble caterpillars 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 maggotlike 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 is determined by the number of chromosomes an individual possesses. [12] Fertilized eggs get two sets of chromosomes (one from each parent's respective gametes) and develop into diploid females, while unfertilized eggs only contain one set (from the mother) and develop into haploid 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 called haplodiploidy.
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 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. [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 of eusociality 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 as worker policing. [15]
Another consequence is that hymenopterans may be more resistant to the deleterious effects of inbreeding. 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. [16]
Some hymenopterans take advantage of parthenogenesis, the creation of embryos without fertilization. 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 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 , [17] the clonal raider ant Cerapachys biroi , [18] the predaceous ant Platythyrea punctata , [19] and the electric ant (little fire ant) Wasmannia auropunctata . [20] It also occurs in the Cape honey bee Apis mellifera capensis . [21]
Oocytes that undergo automixis with central fusion often have a reduced rate of crossover recombination, which helps to maintain heterozygosity and avoid inbreeding depression. Species that display central fusion with reduced recombination include the ants Platythyrea punctata [19] and Wasmannia auropunctata [20] and the Cape honey bee Apis mellifera capensis. [21] In A. m. capensis, the recombination rate during meiosis is reduced more than tenfold. [21] In W. auropunctata the reduction is 45 fold. [20]
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. [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 and pollen.
A huge number of species are parasitoids 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. [23] 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. [8]
The Hymenoptera are divided into two groups; the Symphyta which have no waist, and the Apocrita which have a narrow waist. [4]
The suborder Symphyta includes the sawflies, horntails, and parasitic wood wasps. The group may be paraphyletic, as it has been suggested that the family Orussidae 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, usually with three pairs of true legs, prolegs (on every segment, unlike Lepidoptera) and ocelli. The prolegs do not have crochet 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 of Pamphiliidae. [24]
The wasps, bees, 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. 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]
Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the full set of genes of their single parent and thus the newly created individual is genetically and physically similar to the parent or an exact clone of the parent. Asexual reproduction is the primary form of reproduction for single-celled organisms such as archaea and bacteria. Many eukaryotic organisms including plants, animals, and fungi can also reproduce asexually. In vertebrates, the most common form of asexual reproduction is parthenogenesis, which is typically used as an alternative to sexual reproduction in times when reproductive opportunities are limited. Some monitor lizards, including Komodo dragons, can reproduce asexually.
Sawflies are wasp-like insects that are in the suborder Symphyta within the order Hymenoptera, alongside ants, bees, and wasps. The common name comes from the saw-like appearance of the ovipositor, which the females use to cut into the plants where they lay their eggs. The name is associated especially with the Tenthredinoidea, by far the largest superfamily in the suborder, with about 7,000 known species; in the entire suborder, there are 8,000 described species in more than 800 genera. Symphyta is paraphyletic, consisting of several basal groups within the order Hymenoptera, each one rooted inside the previous group, ending with the Apocrita which are not sawflies.
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. Therefore, it is general practice, when discussing the body of an apocritan in a technical sense, to refer to the mesosoma and metasoma rather than the "thorax" and "abdomen", respectively. 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. 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 or in a nest cell provisioned by their mothers.
The superfamily Ichneumonoidea contains one extinct and three extant families, including the two largest families within Hymenoptera: Ichneumonidae and Braconidae. The group is thought to contain as many as 100,000 species, many of which have not yet been described. Like other parasitoid wasps, they were long placed in the "Parasitica", variously considered as an infraorder or an unranked clade, now known to be paraphyletic.
Gall wasps, also traditionally calledgallflies, are hymenopterans of the family Cynipidae in the wasp superfamily Cynipoidea. Their common name comes from the galls they induce on plants for larval development. About 1,300 species of this generally very small creature are known worldwide, with about 360 species of 36 different genera in Europe and some 800 species in North America.
Thelytoky is a type of parthenogenesis and is the absence of mating and subsequent production of all female diploid offspring as for example in aphids. Thelytokous parthenogenesis is rare among animals and reported in about 1,500 species, about 1 in 1000 of described animal species, according to a 1984 study. It is more common in invertebrates, like arthropods, but it can occur in vertebrates, including salamanders, fish, and reptiles such as some whiptail lizards.
Arrhenotoky, also known as arrhenotokous parthenogenesis, is a form of parthenogenesis in which unfertilized eggs develop into males. In most cases, parthenogenesis produces exclusively female offspring, hence the distinction.
Haplodiploidy is a sex-determination system in which males develop from unfertilized eggs and are haploid, and females develop from fertilized eggs and are diploid. Haplodiploidy is sometimes called arrhenotoky.
Parasitoid wasps are a large group of hymenopteran superfamilies, with all but the wood wasps (Orussoidea) being in the wasp-waisted Apocrita. As parasitoids, they lay their eggs on or in the bodies of other arthropods, sooner or later causing the death of these hosts. Different species specialise in hosts from different insect orders, most often Lepidoptera, though some select beetles, flies, or bugs; the spider wasps (Pompilidae) exclusively attack spiders.
Bombus ternarius, commonly known as the orange-belted bumblebee or tricolored bumblebee, is a yellow, orange and black bumblebee. It is a ground-nesting social insect whose colony cycle lasts only one season, common throughout the northeastern United States and much of Canada. The orange-belted bumblebee forages on Rubus, goldenrods, Vaccinium, and milkweeds found throughout the colony's range. Like many other members of the genus, Bombus ternarius exhibits complex social structure with a reproductive queen caste and a multitude of sister workers with labor such as foraging, nursing, and nest maintenance divided among the subordinates.
Parthenogenesis is a natural form of asexual reproduction in which the embryo develops directly from an egg without need for fertilization. In animals, parthenogenesis means development of an embryo from an unfertilized egg cell. In plants, parthenogenesis is a component process of apomixis. In algae, parthenogenesis can mean the development of an embryo from either an individual sperm or an individual egg.
Nasonia vitripennis is one of four known species under the genus Nasonia - small parasitoid wasps that afflict the larvae of parasitic carrion flies such as blowflies and flesh flies, which themselves are parasitic toward nestling birds. It is the best known and most widely studied of the parasitoid wasps, and their study forms a vital part of the information used to describe the order Hymenoptera, along with information from bees and ants. This parasitoid behaviour makes the wasps an interest for the development of biopesticide and biological systems for controlling unwanted insects.
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. The wasps do not constitute a clade, a complete natural group with a single ancestor, as bees and ants are deeply nested within the wasps, having evolved from wasp ancestors. Wasps that are members of the clade Aculeata can sting their prey.
Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete with a single set of chromosomes combines with another gamete to produce a zygote that develops into an organism composed of cells with two sets of chromosomes (diploid). This is typical in animals, though the number of chromosome sets and how that number changes in sexual reproduction varies, especially among plants, fungi, and other eukaryotes.
The little fire ant, also known as the electric ant, is a small, light to golden brown (ginger) social ant native to Central and South America, now spread to parts of Africa, Taiwan, North America, Puerto Rico, Israel, Cuba, St. Croix and six Pacific Island groups plus north-eastern Australia (Cairns). It is a very harmful invasive species.
Eusociality evolved repeatedly in different orders of animals, notably termites and the Hymenoptera. This 'true sociality' in animals, in which sterile individuals work to further the reproductive success of others, is found in termites, ambrosia beetles, gall-dwelling aphids, thrips, marine sponge-dwelling shrimp, naked mole-rats, and many genera in the insect order Hymenoptera. The fact that eusociality has evolved so often in the Hymenoptera, but remains rare throughout the rest of the animal kingdom, has made its evolution a topic of debate among evolutionary biologists. Eusocial organisms at first appear to behave in stark contrast with simple interpretations of Darwinian evolution: passing on one's genes to the next generation, or fitness, is a central idea in evolutionary biology.
Dufour's gland is an abdominal gland of certain insects, part of the anatomy of the ovipositor or sting apparatus in female members of Apocrita. The diversification of Hymenoptera took place in the Cretaceous and the gland may have developed at about this time as it is present in all three groups of Apocrita, the wasps, bees and ants.
Lysiphlebus is a genus of parasitoid wasps belonging to the family Braconidae.
Androgenesis is a system of asexual reproduction that requires the presence of eggs and occurs when a zygote is produced with only paternal nuclear genes. During standard sexual reproduction, one female and one male parent each produce haploid gametes, which recombine to create offspring with genetic material from both parents. However, in androgenesis, there is no recombination of maternal and paternal chromosomes, and only the paternal chromosomes are passed down to the offspring. The offspring produced in androgenesis will still have maternally inherited mitochondria, as is the case with most sexually reproducing species.
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