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Hymenoptera

2007 Schools Wikipedia Selection. Related subjects: Insects, Reptiles and
Fish

                iHymenoptera
          Scientific classification

   Kingdom:    Animalia
   Phylum:     Arthropoda
   Class:      Insecta
   Subclass:   Pterygota
   Infraclass: Neoptera
   Superorder: Endopterygota
   Order:      Hymenoptera
               Linnaeus, 1758

                                  Suborders

     * Apocrita
     * Symphyta
     * Many families

   Hymenoptera is one of the larger orders of insects, comprising the
   sawflies, wasps, bees, and ants. The name refers to the membranous
   wings of the insects, and is derived from the Ancient Greek ὑμήν
   (humaen): membrane and πτερόν (pteron): wing. The hindwings are
   connected to the forewings by a series of hooks called hamuli.

   Females typically have a special ovipositor for inserting eggs 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.
   (See holometabolism.)

   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. (See
   Haplo-diploid sex-determination system.)

   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 may be
   unusually advantageous, and has been hypothesized to account for the
   high incidence of eusociality in this order.

Suborder Symphyta

   Hymenopterans classified in the suborder Symphyta include the sawflies,
   horntails, and parasitic wood wasps. The group appears to be
   paraphyletic, as it is often believed that the family Orussidae may be
   the group from which the Apocrita arose. They have an unconstricted
   junction between the thorax and abdomen, and the larvae of free-living
   forms are herbivorous, have legs, prolegs (on every segment, unlike
   Lepidoptera), and ocelli.

Suborder Apocrita

   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 (
   petiole), also involving the fusion of the first abdominal segment to
   the thorax. Also, the larvae of all Apocrita do not have legs, prolegs,
   or ocelli.

Evolution

   Hymenoptera originated in the Triassic, the oldest fossils belonging to
   the family Xyelidae. Social hymenopterans appeared during the
   Cretaceous. The evolution of this group has been intensively studied by
   A. Rasnitsyn, M. Engel, G. Dlussky, and others.
   Retrieved from " http://en.wikipedia.org/wiki/Hymenoptera"
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   with only minor checks and changes (see www.wikipedia.org for details
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