Analysis of Host Discrimination in the Parasite Orgilus lepidus (Hymenoptera: Braconidae)

Host discrimination by Orgilus lepidus Muesebeck, a solitary endoparasite of the potato tuberworm, Phthorimaea operculella (Zeller), was found to be based upon the perception of a pheromone left in the locale of the host by earlier females and upon the detection of an oviposition deterrent within parasitized hosts. The pheromone was extractable from O. lepidus females, but not males, and was localized within the abdomen of the females. Contact with hosts parasitized 1 hour earlier and transferred to sites free from the pheromone resulted in withdrawal of the ovipositor moments after insertion. Rinsing parasitized hosts in distilled water failed to reinstate their acceptability. A ligation experiment indicated that the oviposition deterrent was a humoral factor. The possible sources of the pheromone and of the internal deterrent are considered.