ICHNEUMON PARASITIC WASP

Ichneumon is a genus of the parasitic wasp family Ichneumonidae, also known as the ichneumon wasps, Darwin wasps, or ichneumonids. This genus include about 270 species.

The Ichneumonoidea are insects classified in the hymenopteran suborder Apocrita. The superfamily is made up of the ichneumon wasps (sometimes inaccurately called "ichneumon flies"); family Ichneumonidae and the braconids (family Braconidae). Like other parasitoid wasps, they were long placed in the "Parasitica", variously considered as an infraorder or an unranked clade, but actually not a monophyletic group.

The superfamily Ichneumonoidea has been estimated to contain well over 80,000 different species. The ichneumon wasps are more familiar to non-entomologists, being larger and about three times as diverse as the braconids.

They are solitary insects, and most are parasitoids; the larvae feed on or in another insect which finally dies. Being in the same order, ichneumons are closely related to other hymenopterans, such as ants and bees.

Members of the family Ichneumonidae are usually larger than members of the Braconidae, and are distinguished primarily by details of wing venation. Many species in both families use polydnaviruses to suppress the immune systems of their host insects.

Ichneumon wasp species are highly diverse, ranging from 3 to 130 mm (0.12 to 5.12 in) long. Most are slender, with the females of many species (particularly in the genus Megarhyssa) having extremely long ovipositors for laying eggs.

The female finds a host and lays an egg on, near, or inside the host's body. Upon hatching, the larval ichneumon feeds either externally or internally, killing the host when it is ready to pupate. Despite looking formidable, the ovipositor does not deliver a sting like many wasps or bees. It can be used by the wasps to bore into and lay eggs inside rotten wood.

Some members use many different insects as hosts; others are very specific in host choice. Various ichneumons are used commercially as biological control agents in controlling horticultural pests such as flies or beetles.

An example is the parasitic wasp Ichneumon eumerus, which parasitizes the butterfly Phengaris rebeli. The adult wasp locates the P. rebeli by searching for Myrmica ants' nests, the nests that the P. rebeli parasitize as larvae in order to get nutrition. They only enter the Myrmica ants' nests which contain the P. rebeli caterpillar.

A very few ichneumonid species lay their eggs in the ground, but the vast majority inject eggs either directly into their host's body or onto its surface, and this may require penetration of substrate around the host, as in wood-boring host larvae that live deep inside of tree trunks, requiring the ichneumon to drill its ovipositor through several centimeters of solid wood (e.g., Megarhyssa species). After hatching, the ichneumonid larva consumes its still living host. The most common hosts are larvae or pupae of Lepidoptera, Coleoptera and Hymenoptera. Some species in the subfamily Pimplinae also parasitise spiders. Hyperparasitoids such as Mesochorinae oviposit inside the larvae of other ichneumonoids.