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. The induced maize odors are useful cues for the parasitoids and indicate the presence of a potential host. This odor is mainly composed of terpenoid compounds. We have studied different abiotic and biotic factors that determine the specificity and variation of the signal emitted by maize plants in response to caterpillar damage. Light intensity is the most important factor, but odor emissions were also affected by the soil and air humidity, temperature and the degree of fertilization. We found enormous quantitative and qualitative differences among maize genotypes. The absolute amount of volatiles emitted was negatively correlated with the plant age, while larval instar appeared to have little or no effect. We discuss these results in the context of reliability of plant-induced signals as cues that allow parasitic wasps to find a suitable host.

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