Parasitoid host location: using volatiles on different spatial scales and in context of distorting elements

点击翻译按钮获取中文摘要

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.As a model system I will use the parasitoid wasp Cotesia glomerata, which attacks caterpillars of the Cabbage white (Pieris rapae and P. brassicae). To assess the distance, at which HIPVs emitted by the brassicaceous host plants of caterpillars are active in the field, I will perform mark-and-capture studies with parasitoids released in different distances from caterpillar infested plants. Comparing behavior of parasitoids that leave the release site and the directedness of movement of recaptured parasitoids with and without HIPVs will yield information about parasitoid behavior in the presence and absence of attractive plant volatiles. This will help to interpret foraging behavior of parasitoids that are released at different distances from the odor source.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. To test the influence of signal strength, identity and composition on parasitoid attraction, the field experiment will be repeated with different numbers of infested and non-infested plants as well as non-host plants. Additionally, controlled olfactometer and wind-tunnel experiments with different plant volatiles will be performed in the laboratory.Knowing the spatial scale over which HIPVs are attractive under field conditions and how this distance is influenced by non-host volatiles will drastically improve our understanding of insect foraging and distribution and will increase the efficiency of volatile-based pest control strategies.