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A brackish wasp ( Trioxys complanatus ) providing in its ovipositor their eggs in one aphid
Aphid parasitized by a brackish wasp ( Praon sp.)
From the toads Goldfliege ( Lucilia bufonivora parasitized) Common Toad . The larvae protrude from the greatly enlarged nostrils

A parasitoid is an organism, usually an insect , that lives parasitically in its development , but kills the host at the end of the parasitization. Another name for this behavior is predatory parasite . It is estimated that around 10% of all Metazoa species are parasitoids.


The term parasitoid is usually only used for insects. In other groups there are organisms with a comparable way of life. Examples can be found under some fungi (e.g. insect parasitic core lobes such as the Chinese caterpillar fungus and Ophiocordyceps unilateralis , or Entomophthorales such as the fly killer ), under nematodes (genera Heterorhabditis and Steinernema ) and a few protozoa ( Ciliophora ). Despite this comparable way of life, it is usually not common in these groups to speak of parasitoids. Some biologists criticize this use of language and call for standardization, which has not yet been implemented.

Within the insects, about 75% of the parasitoids belong to the insect order of the hymenoptera ( Hymenoptera ). The most important parasitoid representatives within this large group are the ichneumon wasps (Ichneumonidae), the Braconidae and the Chalcidoidea . The second largest group of parasitoids occurs among the two-winged birds (Diptera), with around 16,000 described parasitoids species, these comprise around 20% of parasitoids. In contrast to the hymenoptera, in which the parasitoid way of life probably developed only once (with the common ancestor of the Waist Wasps and the Orussidae ), this way of life developed independently of one another in 24 families. The Tachinidae family is particularly noticeable here, as it almost exclusively contains parasitoids. Two-winged birds are also more diverse in their way of life. While the hosts of hymenoptera parasitoid are always arthropods , the two-winged species also include strudelworms , snails , earthworms and amphibians . A parasitoid way of life can also be observed in a few other insect orders such as beetles (Coleoptera) and reticulated winged birds (Neuroptera), even if fewer examples are known. The small insect order of the fan-winged (Strepsiptera) consists exclusively of parasitoids. Some authors do not rate these as parasitoids because the host is “only” sterilized and the fan-winged adults can survive hatching for a period of time (a few days). However, this only shows that our more or less artificial categories and sorting systems do not perfectly map nature, where there are many flowing transitions. Today it is assumed that around 10% of the approximately one million insect species described lead a parasitoid way of life.

Ways of life

The life stage of the parasitoid living in the host is its larva. The adults are usually free living and have a different diet. In some cases they take no food at all, others are flower visitors. In numerous cases they also feed, at least in part, on the haemolymph of the host species that they occupy with eggs. The mostly winged insect females normally lay their eggs on or in the future host. As an exception, a few groups ( Trigonalidae , some Tachinidae ) scatter their eggs on plants, where they are unintentionally eaten by the future host. The Legimmen among the Hymenoptera drill her egg usually one with the ovipositor into the skin of their host. Two-winged birds such as the Tachinidae do not have an ovipositor; they usually lay their eggs on the host or in its immediate vicinity (as an exception, species of the subfamily Phasiinae have developed pointed, modified sternites that serve as oviposers). Other legimes, the Aculeata parasitoids, and most two-winged birds from other families also do not bore their eggs directly into the host. In these groups, the hatched larva bores through the intestine, the tracheal walls or simply through the body wall. All stages of development are infested with arthropods as hosts: eggs, larvae, pupae, adults, but especially larvae and eggs. In many groups a parasite larva lives in the host, in others numerous parasitoids can develop from the same host organism; so-called gregarous parasitoids. In the other case, parasitoid larvae of the same or different species often eliminate each other when they meet in a host, many have developed a specialized larval stage with dagger-like jaws for this purpose. Gregar parasitoids of insect eggs are often particularly small; the smallest insects belong to this group. Parasitoid larvae are very often attacked again by parasitoids themselves; one speaks of hyperparasitism (the names no longer differentiate between parasites and parasitoids).

Other common distinctions:

according to the whereabouts:

  • Ectoparasitoids feed on their host from the outside. Often the head or the mouthparts are anchored in the surface of the body.
  • Endoparasitoids feed inside their host.

According to the influence on the host:

  • Idiobiont parasitoids are those in which the egg-laying female paralyzes or immobilizes the host through a poison sting (more rarely through applied pathogens). This form is considered to be evolutionarily more original. The host of an idiobiont parasitoid no longer grows and is easy prey for predators due to the inability to move. Most species with this way of life therefore occupy hosts who live protected and hidden, z. B. in drill holes in wood. Idiobionts can be endo- or ectoparasitoids.
  • Koinobionte parasitoids do not paralyze their host when they lay eggs (or only temporarily). The host remains active, it can eat, grow and shed its skin several times. In the meantime, the parasitoid eats parts of its body, but initially spares vital organs. Shortly before pupation or hatching of the parasitoid, the host is usually killed after all (very rarely does it remain alive). Often this occurs when the host stops growing, e.g. B. if he wants to molt from the larval stage to the pupa. Coinobionts are usually always endoparasitoids.

As a rule, each type of insect is attacked by one or more types of parasitoid. These can be generalists with a wide range of hosts, or specialists who often only accept a single host species. Herbivorous (phytophagous) insects are usually particularly heavily infested. Phytophagus examined more closely had an average of two to eight, but in quite a few cases also a hundred or more parasitoids. A particularly large number of parasitoids specialize in species that live in plant galls or mines (but these are well protected from predators).


In some hymenoptera species with a parasitoid lifestyle (from the families Platygasteridae , Braconidae , Encyrtidae and Dryinidae ) the embryos divide obligatorily and develop into numerous larvae, which would be analogous to identical twins in humans. This development process is called "polyembryony". Polyembryonia is also often associated with a morphological differentiation of the (genetically identical) larvae, which occur in two morphs or boxes : A larval form develops normally into winged sex animals (imagines). The other form is used exclusively for defense against other parasitoid larvae in the same host, especially unrelated conspecifics. Polyembryonia also occurs in the parasitoid fan-winged birds (Strepsiptera). The behavior is remarkable because some morphologically and ethologically (in behavior) distinguishable relatives form a non-self-reproducing caste: This fulfills the common definition of eusociality , which is otherwise associated with non-parasitoid hymenoptera.


The best known example is the aforementioned parasitic wasps (Ichneumonidae) whose larvae among others in caterpillars grow. To do this, the wasp's egg is placed next to the caterpillar, and the hatching wasp larva bores itself into the caterpillar, or the wasp lays its egg directly into the caterpillar using the laying spike. After the wasp larvae hatch, the caterpillar is eaten from the inside out. First, the vital organs are spared so that the host organism lives as long as possible. Ultimately, the host dies at the beginning of the pupation phase , the parasitic wasp larvae pupate and the parasitic wasp leaves the dead host. The adults of the parasitoid insects live as nectar suckers, herbivores or predators.

Applied ecology of parasitoids

Parasitoids are playing an increasing role in biological pest control .


The monster from the movie Alien by director Ridley Scott is a parasitoid. It nests in a foreign organism, only to leave it in larval status, which kills the host.

See also


  • Nicholas F. Britton: Essential Mathematical Biology. Springer, London a. a. Springer, 2003, ISBN 1-85233-536-X ( Springer Undergraduate Mathematics Series ).
  • SB Vinson: The behavior of parasitoids. In: GA Kerkut, LI Gilbert (Ed.): Comprehensive insect physiology, biochemistry and pharmacology. Volume 9: Behavior. Pergamon Press, Oxford 1985, ISBN 0-08-030810-4 , pp. 417-469.
  • Jeff Waage, D. Greathead (Ed.): Insect parasitoids. Academic Press, London 1986, ISBN 0-12-728900-3 ( Symposia of the Royal Entomological Society of London 13 ).

Individual evidence

  1. ^ HE Roy, DC Steinkraus, J. Eilenberg, AE Hajek, JK Pell (2006): Bizarre interactions and endgames: entomopathogenic fungi and their arthropod hosts. Annual Review of Entomology 51: pp. 331-357. doi : 10.1146 / annurev.ento.51.110104.150941
  2. ^ GC Smart, Jr. (1995): Entomopathogenic Nematodes for the Biological Control of Insects. Journal of Nematology (Supplement) 27 (4S): pp. 529-534.
  3. For example Jaime Gómez-Gutiérrez, William T. Peterson, J. Frank Morado (2006): Discovery of a ciliate parasitoid of euphausiids off Oregon, USA: Collinia oregonensis n. Sp. (Apostomatida: Colliniidae). Diseases of aquatic organisms 71: pp. 33-49.
  4. ^ Paul Eggleton, Kevin J. Gaston (1990): “Parasitoid” Species and Assemblages: Convenient Definitions or Misleading Compromises? In: Oikos 59 (3): pp. 417-421.
  5. Donald H. Feener Jr., Brian V. Brown (19979): Diptera as parasitoids. Annual Review of Entomology 42: 73-97. doi : 10.1146 / annurev.ento.42.1.73
  6. Jeffrey H. Skevington: Intimate neighbors: Parasitoids and parasites. In: Jeffrey H. Skevington, PT Dang (2002): Exploring the diversity of flies (Diptera). In: Biodiversity 3 (4): 8–12.
  7. Jeyaraney Kathirithamby (2009): Host-Parasitoid Associations in Strepsiptera. Annual Revue of Entomology 54: 227-249. doi : 10.1146 / annurev.ento.54.110807.090525
  8. MA Jervis & NAC Kidd (1986): Host feeding strategies in Hymenopteran parasitoids. Biological Reviews 61: 395-434. doi : 10.1111 / j.1469-185X.1986.tb00660.x
  9. D. Giron, A. Rivero, N. Mandon, E. Darrouzet, J. Casas (2002): The physiology of host feeding in parasitic wasps: implications for survival. Functional Ecology 16: 750-757.
  10. Michael R. Strand & Miodrag Grbic (1997): The life history and development of polyembryonic parasitoids. In: Nancy E. Beckage (editor): Parasites and pathogens: effects on host hormones and behavior. New York (Chapman & Hall): 37-56.
  11. YP Cruz (1981): A sterile defender morph in a polyembryonic hymenopterous parasite. Nature 294: 446-447.