Parasitoid wasp

The term parasitoid wasp refers to a large evolutionary grade of hymenopteran superfamilies, mainly in the Apocrita. The parasitic or parasitoidal Apocrita are divided into some dozens of families. They are parasitoids of various animals, mainly other arthropods. Many of them are considered beneficial to humans because they control populations of agricultural pests. Others are unwelcome because they are hyperparasitoids, attacking beneficial parasitoids.

Parasitoidal wasps range from some of the smallest species of insects, to wasps about an inch long. Some are parasitoids that complete their metamorphosis in a single small egg of a small insect, and such a wasp is necessarily less than 1 mm long. Most females have a 'spine-like' ovipositor at the tip of the abdomen (Drees and Jackman), therefore lacking venom glands and sting. The egg and larval stage are usually not observed unless dissected from the host in which the adult female parasitized, except in species that practically fill the skin of the host with parasitoid larvae.

Caterpillars provide major examples of larval Lepidoptera as a class of host, but various species of parasitoid wasps in several Hymenopteran families parasitize their own favoured life stages [egg, larva, adult] of species in many other orders of insects, including Coleoptera, Diptera, Hemiptera and other Hymenoptera. Some attack other Arthropoda, such as spiders. Adult female wasps of most species oviposit into their hosts' bodies or eggs. The females of some parasitoid species also insert secretory products that protect the egg from the immune system of the host. These are produced in combinations that may include polydnaviruses, ovarian proteins, and venom. Once a host of a parasitoid that expresses polydnavirus particles has been parasitised, the virus that accompanied the egg during oviposition infects the cells of the host in ways that benefit the parasitoid.

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