Parasitoid host location: using volatiles on different spatial scales and in context of distorting elements
Parasitoid wasps attack a wide range of insects, including economically important pest species. They can drastically reduce herbivore density and are thus important biocontrol agents, but their effectiveness in controlling insect populations depends strongly on their foraging efficiency. It is well known that parasitoids use chemical cues to locate their host insects and that herbivore-induced plant volatiles (HIPVs) which are emitted after an herbivore attack are of special importance for foraging parasitoids. Even though HIPVs are often considered to act as long-range cues, the distance at which HIPVs attract parasitoids under field conditions has never been measured and may range from less than 1 m to more than 100 m. Therefore, the main aim of my project is to determine the actual distance over which HIPVs are attractive in the field.
The distance over which HIPVs are active may further be influenced by the strength of the signal and by the surrounding background odor. Volatiles from surrounding non-infested host plants of the herbivore or from plant species that cannot be used as host plants may enhance host location by parasitoids, because these volatiles may be easy to locate and provide additional information about the host habitat. Similarly, these cues may interfere with parasitoid host location by providing contrasting information.