University of Neuchâtel, Institute of Zoology, Lab. of Animal Ecology and Entomology, Case Postale 2, 2007 Neuchâtel, Switzerland.
Many parasitoids that attack phytophageous insects make use of plant odors to locate the habitat of their host. In maize large amount of these odors are specifically emitted by a plant after it has been damaged by a herbivore, but not after mechanical damage. The odor emissions occur systematically throughout the plant. Factors in the oral secretion of the herbivores are the main elicitors of the plants' reaction. One such elicitor, volicitin, was recently isolated and identified. The induced maize odors are useful cues for the parasitoids and indicate the presence of a potential host. We have studied different factors that determine the specificity and variation of the signal emitted by maize plants and found that there can be considerable variation amoung different genotypes of maize plant. This variation is also observed in the emission of wild relatives of maize. Abiotic factors, like light and soil humidity, seem to also play an important role in the emission of volatiles by maize plants. We discuss these results in the context of reliability of plant-induced signals as cues that allow parasitic wasps to find a suitable host.