The hemimetabolic insects, known as the taxon Hemimetabola Burmeister, 1835, synonymously also Exopterygota Sharp , 1899, or Heterometabola Packard , 1898, are a group within the insects that is delimited according to the form of individual development ( ontogenesis ), from the youth stage to the sexually mature animal .
The hemimetabolic insects develop gradually so that each of the youthful stages, which are terminated by a molt , gradually becomes more and more similar to the adult animal, called imago . This used to be called "imperfect metamorphosis" ( metamorphosis is a technical term for the form of development). The hemimetabolic insects also differ from those insects in which the stages of youth and sexually mature adults can only be distinguished by the presence of the functional sexual organs, called ametabolic insects , by the development of the wings . Only the imaginal stage has functional wings (the only exceptions are the mayflies with two winged stages). The youth stages of the hemimetabolic insects have outgrowths called wing sheaths in their place, inside which the wings grow. The expression Exopterygota (after ancient Greek, literally outside-winged) is derived from these wing sheaths. The group of hemimetabolic insects was first introduced by the entomologist Hermann Burmeister in 1835.
The youth stage of the hemimetabolic nymph is named correctly in terms of nomenclature if it has no independent formations that the imago lacks (e.g. gills). If, on the other hand, it has such “larval organs”, it should be called a larva , just like the juvenile stages of holometabolic insects. In actual language usage, this difference is hardly ever observed so strictly. B. spoken of "locust larvae".
In the hemimetabolic insects, in contrast to the other main group of insects, the holometabolic insects (holometabola), there is no transformation via a pupal stage , formerly called “complete metamorphosis”.
Hemimetabola as a taxon
The hemimetabolic insects were earlier, as hemimetabola, as a taxon in the rank of a superordinate or subclass . As far as we know today, it is a so-called paraphyletic taxon. This means that the holometabolic insects are not the sister group of the hemimetabolic insects, but have emerged from them. According to the current system, the so-called Paraneoptera (this is a family group that includes the Schnabelkerfe and the Fringewing ) are more closely related to the holometabols than they would be with the other hemimetabolics (see phylogenetic systematics of insects ).
Paraphyletic taxa were not uncommon in classical taxonomy, as other examples such as "reptiles" show. According to the method of phylogenetic systematics (or cladistics ) that predominates in taxonomy and systematics today , which goes back to the entomologist Willi Hennig , paraphyletic taxa are to be avoided because they disguise the actual relationships. As with the term “reptiles”, research continues to use the term “hemimetabolic”, although users are well aware of the circumstances. It is a practical, abbreviated term that is helpful when sorting.
Insect orders with hemimetabolic development
With the exception of the holometabola and the ametabolic fish and rock jumpers , all insects belong to the hemimetabolic insects. These are as Palaeoptera summarized mayflies (Ephemeroptera) and vials (Odonata), the group of Polyneoptera , inter alia, with the cockroaches (Blattodea), Mantis (Mantodea), termites (Isoptera), stone flies (Plecoptera) Tarsenspinnern (Embioptera) Locusts (Orthoptera), ghosts (Phasmatodea) and gladiators (Mantophasmatodea) and the group of Paraneoptera with the dust lice ( Psocoptera) and animal lice (Phthiraptera) as well as the beaked peas ( Hemiptera) and the fringed winged or thrips (Thysanoptera).
- Michael E. Adams: Development, Hormonal Control of. In: VH Resh and RT Cardé (editors), Encyclopedia of Insects. Academic Press. Amsterdam, 2003. ISBN 978-0-08-092090-0
- PJ Gullan, PS Cranston: The Insects: An Outline of Entomology. John Wiley & Sons, Hoboken, 2009. ISBN 978-1-40-514457-5 .
- "First main group: Kerfe with imperfect metamorphosis, Insecta Hemimetabola" in Hermann Burmeister: Handbuch der Entomologie. Berlin: G. Reimer; from vol. 2: Theod. Chr. Friedr. Enslin, 1832-1855.
- http://www.naturspektrum.de/text/text_hemimetabolie.php Info (comparison of hemimetabolism ↔ holometabolism)
- Hemimetabola , entry in the lexicon of biology, www.spektrum.de.