Die Wirkung arbuskulärer Mykorrhizasymbiose auf die Raubmilbe Phytoseiulus persimilis

Recent studies have shown that the arbuscular mycorrhizal fungus Glomus mosseae positively influences the reproduction of the herbivorous two spotted spider mite, Tetranychus urticae (Acari: Tetranychidae), on bean plants. This is puzzling because at first glance it seems that the mycorrhizal symbiosis leads to a fitness decrease of the bean plant and the fungus via promoting the herbivore. For symbiosis to evolve and be evolutionary stable it is however a principle that neither “partner” experiences a net fitness cost. In the proposed research I therefore hypothesize that the beneficial effects of arbuscular mycorrhiza (AM) on T. urticae are compensated for by positively influencing the predatory mite Phytoseiulus persimilis (Acari: Phytoseiidae) resulting in a net benefit for the plant. The influence of AM on P. persimilis may be mediated by the plant and the prey and may be grouped into three categories: (1) enhanced long distance predator recruitment by the plant via a change in the quantity and quality of the emitted herbivore induced volatiles (HIPV), (2) increased attractiveness of T. urticae and its colony components affecting the local foraging efficiency of P. persimilis, and (3) improved prey quality of spider mites feeding on mycorrhizal plants. My proposal consists of five separate but interrelated experiments, all of which compare the effects of mycorrhizal vs. non-mycorrhizal bean plants on (1) the life history of T. urticae, (2) long range prey detection by P. persimilis, (3) short range prey detection and within patch foraging behaviour of P. persimilis, (4) life history of P. persimilis and (5) fitness of the plant. The latter experiment is carried out with whole bean plants and compares plant growth, fungus colonization, mite population dynamics and finally the fitness of the plant (i.e. the fruits) of mycorrhizal and non-mycorrhizal plants.