Hymenoptera is one of the larger orders of Insects, comprising the sawflies, wasps, bees, and ants. The name comes from the membranous wings (Greek hymen, a membrane), of which most forms have two pairs, the front wings larger than the back.
Females typically have a special ovipositor for inserting into hosts or otherwise inaccessible places, often modified into a stinger. The young develop through complete metamorphosis - that is, they have a worm-like larval stage and an inactive pupal stage before they mature.
Among the hymenopterans, sex is determined by the number of chromosomes the individual receives. Fertilized eggs get two sets of chromosomes, and so develop into diploid females; unfertilized eggs only receive one set, and so develop into haploid males. This phenomenon is called haplodiploidy. Note, however, that the actual genetic mechanisms of haplodiploid sex determination are 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.
The 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 is unusually advantageous, and varying degrees of sociality have appeared several times among the different subgroups. The most extreme form is eusociality.
The wasps, bees, and ants together make up a suborder of the Hymenoptera called the Apocrita, characterized by a constriction between the first and second abdominal segments called a wasp-waist. The remaining forms (sawflies) were once classified as a second suborder, the Symphyta, but this appears to be paraphyletic. A classification of the Apocrita is as follows:
Hymenopterans classified in the suborder Symphyta include the following superfamilies:
- Xyeloidea
- Megalodontoidea
- Siricoidea
- Orussoidea
- Cephoidea
- Tenthredinoidea
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