Ichneumonidae - Reproduction and Oviposition

Reproduction and Oviposition

Some species of ichneumon wasps lay their eggs in the ground, but most inject them directly into a host's body, typically into a larva or pupa. Host information has been notably summed up by J.F. Aubert, J.F. Perkins, and H.T. Townes and coworkers.

In some of the largest species, namely from the genera Megarhyssa and Rhyssa, both sexes will wander over the surface of logs, and tree trunks, tapping with their antennae. Each sex does so for a different reason; females are searching for the scent of wood boring larvae of the horntail wasps (hymenopteran family Siricidae) upon which to lay eggs, males are searching for emerging females with which to mate.

Upon sensing the vibrations emitted by a wood-boring host, the female wasp will drill her ovipositor into the substrate until it reaches the cavity wherein lies the host. She then injects an egg through the hollow tube into the body cavity. There the egg will hatch and the resulting larva will devour its host before emergence. How a female is able to drill with her ovipositor into solid wood is still somewhat of a mystery to science, though it has been found that there is metal (ionized manganese or zinc) in the extreme tip of some species' ovipositors. The adult insect, following pupation is faced with the problem of extricating itself from tunnels of its host. Fortunately, the high metal concentrations are not limited to the female's ovipositor as the mandibles of the adult are also hardened with metals and it uses these to chew itself out of the wood.