Abstract
Indirect plant defences act by offering natural enemies of herbivores shelter, food or chemical information on herbivore presence. Induced indirect defence (lID) is triggered in response to damage by the herbivore and leads to the release of greater quantities and changed ratios of constitutively produced volatiles and in several cases to emission of volatiles not released by intact plants. These volatiles attract natural enemies such as predators and parasitoids. The costs and benefits of lID are under de bate especially for parasitoids, as (I) parasitoid attack does not always result in a reduced consumption by the herbivores and (2) no rigorous tests under field conditions have been performed. The main objective of the proposed project is to establish the effect of parasitization of herbivores on the fitness (reproductive output of viabIe seed) of plants compared to the reproductive output of plants damaged by unparasitized herbivores and that of undamaged plants, under greenhouse and field conditions. The project win address four aspects of direct relevance to the central hypothesis: (1) parasitoid responses to plants damaged by herbivores; (2) determination of herbivore load leading to decreased reproductive output; (3) fitness of mutants and transgenes modified in defensive signal transduction pathways leading to parasitoid attraction; (4) ecological costs of lID. The project win examine plant species in the Brassicaceae. As herbivores two Pieris species, specialized feeders of the Brassicaceae, win be studied. Pieris rapae is cryptic and solitary, whereas P. brassicae is aposematic and gregarious. As natural enemies two closely related parasitic wasp species win be investigated, C. glomerata as a generalist and gregarious species, C. rubecula as a solitary specialist on P. rapae. In studying these tritrophic interactions we expect to gain insight in the evolutionary significance of lID in plant evolution and the existence of benefits of information transfer between the first and third trophic levels.
Netherlands