Component of the Host Haemolymph that induces Oviposition in a Parasitic Insect

Abstract

To select a host and to oviposit in it, parasitic Hymenoptera may require visual, olfactory and/or chemotactile stimuli^1–3. Some species can recognize a host by piercing it with the ovipositor^4–6, but nothing is known of the stimuli (supposedly chemical) that elicit such recognition. In the wild the North American ichneumonid, Itoplectis conquisitor (Say), attacks host pupae in cocoons, hollow stems or rolled leaves. In the laboratory, females are attracted to artificial host shelters, such as paper tubes examining them with the antennae and probing them with the ovipositor. If pupae of various Lepidoptera are placed in such tubes eggs are deposited in them. In similar conditions, we have found that eggs are laid in pupal haemolymph of the greater wax moth, Galleria mellonella L., but not in distilled water, saline solution, egg albumin, chicken blood or a mixture of amino-acids. Apparently females can recognize the contents of tubes (for the purpose of oviposition) by probing with the ovipositor. Here we report the isolation of a physiologically active component of G. mellonella haemolymph that induces oviposition by I. conquisitor. To our knowledge this is the first demonstration of a chemical that induces oviposition by a parasitic insect.