Host Discrimination: Isolation of Hydrocarbons from Dufour's Gland of a Braconid Parasitoid1

Many hymenopteran parasitoids are able to recognize hosts that are parasitized and, consequently, reject them as unsuitable sites for oviposition. For some of these parasitoids this discriminatory ability results from the detection of a marking material, or spoor factor, left on the host (Rabb and Bradley 1970, Salt 1937) or in its immediate vicinity during a previous ovipositional attack by a female (Greany and Oatman 1972, Price 1970).